the sidoarjo mud volcano case study

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The sidoarjo mudflow and the muddiness of an environmental disaster.

The Sidoarjo mudflow, also known as “Lusi,” a contraction of its Indonesian name Lumpur Sidoarjo, is one of the longest ongoing disasters in recent memory. A mud volcano in the Sidoarjo district, East Java, Indonesia, has been spewing hot mud and gases since 29 May 2006. Its muck is inundating an ever-increasing area in the region.

Aerial view of the affected area in August 2006

Ikonos Satellite Image © Centre for Remote Imaging, Sensing and Processing, National University of Singapore (2006).

This work is used by permission of the copyright holder.

Aerial view of the affected area in May 2007

Ikonos Satellite Image © Centre for Remote Imaging, Sensing and Processing, National University of Singapore (2007).

Aerial view of the affected area in June 2008

Ikonos Satellite Image © Centre for Remote Imaging, Sensing and Processing, National University of Singapore (2008).

Aerial view of the affected area in June 2010

Ikonos Satellite Image © Centre for Remote Imaging, Sensing and Processing, National University of Singapore (2010).

Aerial view of the affected area in August 2013

Ikonos Satellite Image © Centre for Remote Imaging, Sensing and Processing, National University of Singapore (2013).

This disaster has attracted the attention of many scholars, including natural scientists (mainly geologists, but also petroleum engineers and earth scientists), humanities scholars, and social scientists, who have been examining the disaster using the analytical tools of their respective disciplines as well as drawing on multidisciplinary perspectives.

Popular accounts of the disaster have also filled the pages of Indonesia’s well-known national print and digital media as well as of those abroad. In one such article, the Sidoarjo mudflow was labeled by journalist Erin Wayman as “the world’s muddiest disaster.” This label draws attention not just to the salient physical feature of the catastrophe, but also to the unclear circumstances that led to the disaster, the ongoing debate about the cause of the disaster, and the murkiness of the government’s treatment of the disaster victims. In other words, Lusi is a disaster that is muddy literally and figuratively.

The Lusi disaster is muddy in the literal sense of the word because hot mud and gases have been continually erupting from underground for over 10 years now. The mud has drowned 15 villages, several paddy fields, dozens of factories and schools, countless houses, and a long segment of a toll road. This catastrophe, according to a July 2015 Nature Geoscience article by Mark Tingay et al. , has internally displaced 39,700 people and cost more than USD 2.7 billion in damages. According to a 2016 Environmental Communication article by Phillip Drake , the earthen levees constructed to contain the mudflow cover an estimated area of “10 square kilometers and depth of 30 meters.” It took me and my motorcycle driver about one hour to circumnavigate the perimeter of the dikes when I visited the site on 13 December 2016.

Figuratively speaking, the debate about the cause of the disaster among scientists who have investigated it has merely served to muddy the waters. On the one hand, there are those who support the “drilling hypothesis,” which contends that PT Lapindo Brantas’s reckless drilling activities caused the disaster. Many academic scientists such as Richard Davies of Newcastle University, Michael Manga of UC Berkeley’s Department of Earth and Planetary Sciences, and Mark Tingay of the University of Adelaide support this hypothesis. On the other hand, there are other scientists who ascribe to the “earthquake hypothesis,” arguing that the eruption of the mudflow was triggered by an earthquake in the nearby city of Yogyakarta that had occurred two days earlier. Those who fall into this camp are scientists who are affiliated with Energi Mega Persada (the parent company of PT Lapindo Brantas) such as Nurrochamat Sawolo and his colleagues, as well as Adriano Mazzini of the University of Oslo and his co-authors on a 2007 Earth and Planetary Science Letters paper that proposed this hypothesis.

Furthermore, there is much that is unclear about the circumstances that led to PT Lapindo Brantas’s exploratory drilling activities. In their book Kronik Lumpur Lapindo Skandal Bencana Industri Pengeboran Migas di Sidoarjo , Batubara and Utomo claim that PT Lapindo Brantas tricked some residents into selling their lands using an intermediary by promising to build a chicken farm. Moreover, sociologist Anton Novenanto also claims in his three-part article published on the activist website Korbanlumpur.info that, contrary to what many think, some government agencies were actually complicit in allowing the company to set up an exploratory well in a heavily populated area in the first place, in violation of Indonesia’s Mining Law.

Finally, the Indonesian government scheme to help the disaster victims was murky. The policies were ambivalent, haphazard, and unclear. In the disaster’s aftermath, the government issued a regulation and drew up a “map of the affected areas” ( peta area terdampak ) in an attempt to enclose the disaster geographically, financially, and politically. The map instead produced tensions, anxieties, anger, and frustration among residents since the compensation received was unequal. Subsequent amendments to the regulation did little to assuage the angst of many victims until late 2014, when a new government decided to settle the compensations once and for all. Even so, some environmental, health, and social problems persist. These issues afflict both residents who have lost their properties and those who were not directly affected by the disaster.

How to cite

Mohsin, Anto. “The Sidoarjo Mudflow and the Muddiness of an Environmental Disaster.” Environment & Society Portal, Arcadia (Spring 2017), no. 5. Rachel Carson Center for Environment and Society. https://doi.org/10.5282/rcc/7767 .

ISSN 2199-3408 Environment & Society Portal, Arcadia

2017 Anto Mohsin This refers only to the text and does not include any image rights. Please click on an image to view its individual rights status.

• Batubara, Bosman, and Paring Waluyo Utomo. Kronik Lumpur Lapindo Skandal Bencana Industri Pengeboran Migas di Sidoarjo. Yogyakarta: INSISTPress, 2012.
• Davies, Richard, Michael Manga, Mark Tingay, Susila Lusianga, and Richard Swarbrick. “Sawolo et al. (2009) the Lusi Mud Volcano Controversy: Was it Caused by Drilling?” Marine and Petroleum Geology 27 (2010): 1651–57.
• Drake, Phillip. Indonesia and the Politics of Disaster: Power and Representation in Indonesia’s Mud Volcano. London and New York: Routledge, 2017.
• Drake, Phillip. "Indonesia’s Accidental Island: Composing the Environment in the Echo of Disaster." Environmental Communication 2016: 1–13.
• Novenanto, Anton, et al. Membingkai Lapindo Pendekatan Konstruksi Sosial Atas Kasus Lapindo (Sebuah Bunga Rampai). Jakarta: Penerbit Kanisius, 2013.
• Sawolo, Nurrochmat, et al. “Was LUSI Caused by Drilling?—Authors Reply to Discussion.” Marine and Petroleum Geology 27 (2010): 1658–75.
• Schiller, Jim, Anton Lucas, and Priyambudi Sulistiyanto. “Learning from the East Java Mudflow: Disaster Politics in Indonesia.” Indonesia 85 (2008): 51–77.
• A website created by activists to give a voice to the disaster victims (in Indonesian).
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A mud volcano has been erupting for ten years – and scientists are still undecided what caused it

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Michael Manga receives funding from US National Science Foundation.

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The world’s most destructive mud volcano was born near the town of Sidoarjo, on the island of Java, Indonesia, just over 11 years ago – and to this day it has not stopped erupting. The mud volcano known as Lusi started on May 29, 2006, and at its peak disgorged a staggering 180,000 cubic metres of mud every day, burying villages in mud up to 40 metres thick. The worst event of its kind in recorded history, the eruption took 13 lives and destroyed the homes of 60,000 people . But although the mud is still flowing more than a decade later, scientists are not yet agreed on its cause.

The debate is whether the eruption of Lusi was due to an earthquake several days previously , or down to a catastrophic failure of the Banjar Panji 1 gas exploration well that was being drilled nearby at the time. Given the huge impact of the volcano on the communities nearby and the fields that were their livelihoods, why are we still unsure of the cause?

Mud volcanoes are extremely common on Earth, with thousands of examples known worldwide. They come in many shapes and sizes and behave a little like their molten-rock counterparts, going through long periods of inactivity with periodic violent eruptions. Mud volcanoes, however, spew out not molten hot lava from the Earth’s mantle, but usually a cold mixture of gas, water and solids.

Some of the most spectacular examples of mud volcanoes are in Azerbaijan where they can range from a few metres across to the size of a small mountain. They are commonly found at tectonic plate boundaries, and also underwater at river deltas where sediment is buried rapidly, causing unusually high pressures to build up underground. The muddy mix is also pushed to the surface by the buoyant gas it contains. Usually mud volcanoes grow slowly, through layer upon layer of mud. What happened in Sidoarjo in 2006 is unique, with Lusi by far the fastest growing mud volcano we know of, having drowned surrounding houses, factories, places of worship and schools in a foul-smelling, emulsion-like mud.

Drilling or earthquake?

The journal Marine and Petroleum Geology is publishing a special issue that examines the ways this amazing phenomena is developing. It includes one paper by geoscientists Stephen Miller and Adriano Mazzini (“[More than ten years of Lusi: A review of facts, coincidences, and past and future studies”) that exhumes the debate of what caused the eruption, offering strong support for the earthquake as the trigger and dismissing the idea the borehole was responsible.

The explanation implicating the drilling is that water from surrounding bedrock entered the 2,834 metre-deep Banjar Panji 1 well, which for its lowest 1,743 metres was unprotected by steel and cement casing. The pressure the water exerted was enough to fracture surrounding rock or pre-existing faults. Mixing with underground mud from the Kalibeng Formation , which makes up part of Java’s geology, this pressurised water and mud rushed to the surface through a fault, forming the Lusi mud volcano just 200 metres from the drilling site.

The alternative explanation is that despite its proximity the drilling well was coincidental, and that the 6.3 magnitude Yogyakarta earthquake on May 27, 260km away had sent vibrations into the Kalibeng Formation’s mud layer, causing it to liquefy and rise to the surface under pressure.

That earthquakes can trigger eruptions has been documented as far back as Pliny’s Encyclopedia in the first century . It’s also the case that the eruption started as a series of small eruptions, all aligned along a geological fault, so the role of the earthquake certainly deserves full consideration. But in comparison with other eruptions triggered by earthquakes such as in Azerbaijan, Pakistan and California , the Yogyakarta earthquake was very far away given its size. More compelling still is that there have been bigger and closer earthquakes that have not triggered eruptions , while other earthquakes have caused greater shaking and vibrations right at the site of Lusi , yet nothing happened on those occasions. If the earthquake caused liquefaction we would expect to see the widespread release of gas from the liquefied layer – but a study by Mark Tingay and colleagues in 2015 showed this did not happen .

The well was drilled by the Indonesian company PT Lapindo Brantas , which blamed the earthquake. Information on the borehole was passed to us at the time, which showed there was an influx of water that we estimated was sufficient to cause the rocks around the uncased borehole to crack . So the new paper by Miller and Mazzini doesn’t bring any new information or reasoning to the debate, which will now probably remained mired unless new data from the borehole or from the critical period at the end of May 2006 comes to light, and this is unlikely.

Distinguishing between two hypotheses for a unique event can be a challenge. We cannot go back in time and collect the ideal set of data and samples to test the hypotheses, nor can we make direct comparisons with other similar phenomena for which we know the cause. There are other major disasters that we still cannot be certain had a man-made cause, such as earthquakes potentially triggered by filling dams with water .

In the case of Lusi, we very strongly favour the argument that the drilling was responsible, but neither of us were at the site of the incident almost two kilometres underground at the time to witness it, and more than ten years on it’s clear the data and reasoning behind our argument have yet to convince everyone.

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Follow our news, recent searches, 15 years on, mud continues to gush in east java villages as residents reel from odour and heat, advertisement.

The mud flow in Sidoarjo first started to emerge on May 29, 2006. (Photo: Boy Slamet)

Kiki Siregar

SIDOARJO, East Java: Indonesian Muanisah, who goes by one name, recalled the day when she held her 40-day-old baby in despair as he had trouble breathing.

She was just about to have her breakfast on May 29, 2006 when she smelled a pungent odour, which she believed caused her baby to cry while gasping for air. 

“He was yawning ... unable to breathe. I was afraid something wrong had happened to my child,” said Mdm Muanisah.

Unaware of what the smell was, she got out of her house but the odour was there too.

She decided to take public transport and seek refuge at her family’s house a few kilometres away where the air was clean. There, her baby could finally breathe normally again, she said.

“They (authorities) just said there was a gas leak,” said Mdm Muanisah, who was 22-year-old at the time.

Within a few days, it became clear that the cause of the odour was a mud flow bursting in the middle of a paddy field in Sidoarjo, East Java, just 200m away from Mdm Muanisah’s house.

Now, 15 years later, the mud flow has buried thousands of homes, factories and shops. It is believed to be covering an area of more than 650ha currently and is showing no signs of stopping.

The Sidoarjo mud flow has disrupted the lives of about 60,000 people, forcing them to flee or adapt to the unpleasant conditions. 

The mud flow also produces methane, a powerful greenhouse gas that causes global warming and leads to climate change. 

A February study by senior researcher Adriano Mazzini et al showed that the mud flow releases 100,000 tonnes of methane yearly into the atmosphere. This is said to be the site with the highest methane emission ever recorded for a single natural gas manifestation.

PEOPLE SUFFER FROM THE MUD FLOW

The cause of the mud flow is still a topic of debate until today.

Some argue that the eruption was triggered by a 6.3 magnitude quake two days earlier in Yogyakarta, some 260km away.

There are also people who believe that drilling by oil and gas company Lapindo Brantas nearby was the culprit. Others think that the combination of both events may have contributed to the mud flow.

READ: IN FOCUS: The fight against Jakarta’s devastating yearly floods

Mr Khudori, whose house was buried by the mud flow six months after it first emerged, is frustrated by the inconveniences.  

“The smell was too strong … and it also affected the water, (I got) itchy, it was polluted, we can’t drink it. Previously, we could drink it before mud flow existed.

"After the emergence of the mud flow, sometimes if I take a shower, I’ll feel itchy. And the smell made me short of breath,” said Mr Khudori, who goes by one name.

The 54-year-old was forced to find a new home about 1.5km away.

“I can still smell it. Never mind 1.5km, even at the distance of 5km it can still be smelled during the rainy season. 

“If it’s the rainy season, the smell of methane is very strong. Though when it is the dry season, it is not so obvious,” said Mr Khudori.

He also observed that since the mud flow emerged, Sidoarjo has become hotter. “The mud flow releases heat,” the father of six said, adding that floods seemed to occur more now. 

He said there is nothing he can do about the condition, apart from turning to bottled mineral water for consumption.

A 2017 study showed that the mud temperature, which was previously 100 degree Celsius, was 60 degree Celsius. Meteorological agency data showed that the average temperature in Sidoarjo has seen an increase of less than 1 degrees Celsius in the last 15 years. 

READ: 'Everything dies' - Mining, climate change threaten livelihoods of Bintan's fishing communities

Mr Khudori, who used to work at a factory near the mud flow, now works as a motorcycle taxi rider with no fixed income as the mud had also buried his workplace.

Mdm Muanisah, whose house was buried by the mud in November 2006, has since rented a house about 5km away from the mud flow.

She said there is also nothing she can do about the complaints they have, apart from using a mask at home to repel the odour she occasionally smells.

“Even before COVID-19, I have gotten used to wearing a mask,” she said.

EMBANKMENT AND PIPES TO CONTAIN THE BURST

At its peak, the mud discharged was equivalent to about 25 Olympic-sized swimming pools daily, said authorities.

To ensure that the mud flow does not continue to bury the surroundings, an embankment and pipes have been built to divert the mud to a nearby river. 

The mud comprises 80 per cent water, said Mr Pattiasina Jefry Recky, head of Sidoarjo Mud Control Center (PPLS) which is the agency overseeing the mud flow.

“The mud from the burst is about 60,000 to 90,000 cubic metres per day. And we can flow about 30 million cubic metres per year into the Porong river, but that is not enough because we are dealing with quite a lot of problems. 

“The ships which (pump the mud) are old ships, so we can't work more effectively,” he said.

In addition, the agency needs to ensure that the embankment is strong.

Mr Pattiasina said some geological experts predicted that the mud flow will ooze for at least 40 years.

"It has only been 15 years. If the drainage and embankment protection is safe, then it is safe. 

"We're only afraid of the rainy season because our embankment is an earthen-filled dam. It was built in a rush back then. For us technical people, a technical embankment should not be like that."

READ: Death threats, intimidation not a deterrence to scientist's mission to save Indonesia forests

He said that the embankment is 11m high. "And most likely it can’t be more than that. We are afraid that if it is higher, it will collapse because the carrying capacity is not strong," he added.

PROPOSALS TO MAKE USE OF THE MUD FLOW

Mr Mazzini, who is a senior researcher at the Centre of Earth Evolution and Dynamics (CEED) of the University of Oslo, said the Sidoarjo mud flow is something between a magmatic volcano and a mud volcano. 

Mr Mazzini, who has studied the mud flow since 2006 and has visited the site numerous times, concluded that the mud flow is connected to the active Arjuno-Welirang volcanoes about 20km away.  

The conclusion was made because the gas and water from the mud flow and the volcanoes are the same.

His latest study, which was conducted with his colleagues using a combined method of ground-based and satellite observations, showed that the methane concentration in Sidoarjo is very high compared to other parts of East Java. Most of the methane originates from the mud flow, according to the study.

Government agencies told CNA they do not know how much gas methane has been released by the mud flow.

Mr Pattiasina of PPLS said there have been plans to make lithium batteries out of the mud, but as of now it is still being discussed.

Head of Sidoarjo’s environment and sanitation agency Sigit Setyawan said the agency had planned to work with an energy company to produce biomass from the mud as an alternative source of renewable energy since 2019. 

“However, the plan was constrained by the COVID-19 pandemic,” he told CNA.

He added that the agency also proposed to plant productive crops on the land buried by the mud, which the government has bought from locals as the area was too dangerous to live in. 

GOVERNMENT HAS TO DO MORE: ENVIRONMENT NGO 

Mr Anung Suprayitno, head of the meteorological, climatological and geophysical agency (BMKG) Malang, said that even though the mud flow has existed for 15 years, more data is needed to conclude its impact on the climate. 

The agency, which oversees the management of meteorological and climatological data throughout East Java, said it does not know the full extent of Sidoarjo mud flow's contribution to greenhouse gas emission.

While meteorological data in the last 15 years shows that the temperature at Sidoarjo has increased by less than 1 degree Celsius and rainfall has increased in a small amount, Mr Suprayitno said the agency does not know if the mud flow is an reinforcing factor that accelerates the local scale of climate change. 

Mr Rere Christanto, who is the director executive of environmental non-governmental organisation Walhi East Java, said that there has been an increase in disasters over the past few years in East Java especially floods and landslides.

The Sidoarjo mud flow is part of a site that accounts for the largest emission of methane gas, and hence it has a big role to play in the build-up of greenhouse gas emissions in the atmosphere, he said. 

READ: Planting crops, building wells - Local volunteers take the lead to prevent yearly peatland fires in Indonesia's Riau

He said it is important that the government acknowledges this and does more than discharging the water sludge into the Porong river. 

The government has to analyse the mud and look into the possible extent and danger of its content, he said. 

"Now, if we have a threat map, we can imagine what actions the government can take and then take precautions. How large the area is and where. For example, the community can be given masks to wear.

"But it won't happen if the government doesn't want to admit (that the site releases huge amounts of methane)."

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The evolution of Sidoarjo hot mudflow (Lusi), Indonesia

H T Wibowo 1 , B Prastisho 1 , C Prasetyadi 1 and D F Yudiantoro 1

Published under licence by IOP Publishing Ltd IOP Conference Series: Earth and Environmental Science , Volume 212 , International Conference on Earth Science, Mineral, and Energy 11–12 October 2018, Yogyakarta, Indonesia Citation H T Wibowo et al 2018 IOP Conf. Ser.: Earth Environ. Sci. 212 012050 DOI 10.1088/1755-1315/212/1/012050

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1 Geological Engineering Department, UPN Veteran Yogyakarta Jl. SWK 104 Condong Catur, Sleman, Yogyakarta

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A spectacular hot mudflow in Sidoarjo on May 29, 2006 seized the attention of many people ranging from the general public, government, to experts related from within the local and abroad. Sidoarjo hot mudflow until now still flowing and this geological evidence has not shown any signs of stopping in the near future and causing a great impact on the surrounding environment and socio-economic life of the community as well as raising other speculation against to this geological evidence.

The regional geology of hot mud discharge areas in between the edge of a volcanic arc and back arc basin. This event shows the discharge of material from subsurface layer containing a higher pressure clay from hydrostatic pressure (over pressure shale), very plastic and possibly even in mobile (hydrodynamic) conditions. It is very common in the ellisional basin called mud volcano, although there are differences in the characteristics of LUSI with other mud volcanoes, which are temperature about 100 °C on the surface with a discharge of 150,000 m3 / day. For nearly 12 (twelve) years of flowing, observation activities and measurement of characteristics and behavior continue to be convergence with geological, geochemical, geophysical and geodetic approaches.

The results of the fluid geochemical analysis show that LUSI has already related to geothermal phenomena [16,18]. The result of geological structure analysis shows the existence of piercement structure crossing through the center of eruption while the geodesy analysis using InSAR indicates there are some areas that subsidence and some are uplifted [1] . Based on the results of various approaches and a comprehensive analysis shows that the hot mudflow Sidoarjo has evolved for characteristics, the ratio of the enlarged water, the constant temperature around 100 °C that show to the of volcano signature or it is making of the Neovolcanism.

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Rare earth element contents of the Lusi mud: An attempt to identify the environmental origin of the hot mudflow in East Java – Indonesia

The Sidoarjo mudflow in East Java, Indonesia, has been erupting since May 29 th , 2006. The eruption has been known as the Lusi (lumpur Sidoarjo), which was previously considered as a remote seismic event consequence, but current geyser-like activities show an association with a geothermal phenomenon. A method of characterizing rare earth elements (REE) is commonly an effective tool for recognizing a geothermal system, and here it is adapted to particularly indicate the environmental origin of the Lusi mud. Results show that the Lusi hot mud is made of a porous smectite structure of a shale rock type, which becomes an ideal tank for trapping the REE, especially the light REE. Volcanic activities seem to be an important influence in the eruption; however, since there is a lack of significant isotopic evidences in the mobilization of the REE during the eruption, the chloride neutral pH water of the Lusi may hardly contain the REE. The moderate Ce and Eu anomalies found in the REE patterns of the mud strongly indicate a sea-floor basin as the most probable environment for the REE fractionation during the sedimentary rock formation, in which the weathering processes of volcanic rock origin enriched the Lusi shale with the REE.

1 Introduction

A hot mud eruption has been occurring in the Porong area of Sidoarjo, East Java, Indonesia since May 29 th , 2006. The eruption is well known as the Lusi (lumpur Sidoarjo) mud volcano. In the early stage of the eruption, scientists disputed over the initiation of the eruption whether it was caused by seismic events [ 1 , 2 , 3 , 4 ], or by underground blowouts [ 5 , 6 , 7 ].

The domination of steam in the current eruption shows, however, a geothermal phenomenon, as the most significantly visible characteristic of the eruption is constant high temperature ( Figure 1 ). The previous temperature was about 100°C measured on mud around the crater [ 1 ], and it is still over 60°C in the current eruption. The changes in temperature could be due to the changes in the mud proportion of clay–water from 60:40% [ 1 , 8 ] to the current proportion of 30-70% [ 9 ]. This could be the case of changing the eruption behavior from sticky hot mudflow to steam eruption.

The history of the Lusi mud eruption in Sidoarjo, East Java, Indonesia. May 2006, it was just a steam eruption at 200 m distance from the exploration rig of the Banjarpanji-1 [ 3 , 4 ]. July 2006, the surrounding area was covered with hot mud. May 2007 – September 2009, the inner embankment dam was built to keep hot mud within the crater area. But, since the end of 2009 hot mud has already covered the area of 642 hectares. Since March 2014 up to date, a phreatic steam eruption has dominated the Lusi eruption.

In geological terms, mud volcano is usually considered as a geothermal manifestation caused by geothermal driving forces [ 10 ]. In characterizing a geothermal system, a method to use rare earth elements (REE) mobilized within waters is commonly applied as a reliable tool [ 11 ]. This is the reason that the method may, therefore, have a merit to be adapted here in characterizing the REE of the Lusi mud.

Rare earth elements are fourteen metals of atomic numbers from 57 (La) to 71 (Lu). Two of these elements, Ce and Eu, often have anomalous behavior indicating the environment of the element sources. The Ce element occurs in oxidation, and the Eu element occurs in a stable chemical form [ 11 ]. In general, the REE provide information regarding thermodynamic conditions, which govern the water-rock interaction process. Rare earth elements are commonly immobile during this process, but when the condition changes into hydrothermal and metasomatic processes, the elements become mobile [ 12 ].

In the case of the Lusi eruption, water may come from a very deep source, possibly >3,000 m [ 5 ], and it may also pass through the nearness of the volcanic arc [ 1 ], or a hot igneous rock [ 13 ]. The heated water is then adsorbed within pressurized mud materials at the depths of 900-1,871 m, which results in hot solution gel to erupt at the surface [ 1 ].

The mud is composed of shales of the Pleistocene Upper Kalibeng Formation deposited within a very deep volcano-sedimentary environment [ 3 , 4 ]. This type of rock is ideally enriched with rare earth elements that fractionate during weathering of sedimentary rocks [ 14 ]. This is the scenario explored in this paper in conjunction with the geothermal eruption scenario [ 10 ].

2 Geological setting

The geology of the Porong area, where the Lusi located, is made of three rock types: sandstone, mudstone and siltstone. These volcanic marine materials were deposited within the period of Plio-Pleistocene to Pleistocene [ 4 ]. According to the Banjarpanji-1 drilling hole [ 1 , 4 ], the rocks form a very thick stratigraphy of over 2800 m. Then, Mazzini et al . [ 1 ] divided the stratigraphy into three intervals. The first interval (<900 m) comprises Pleistocene siltstone of littoral to inner shelf sediments; the second interval (900-1871 m) comprises Pleistocene mudstone of inner to outer shelf sediments; the third interval (1871-2833 m) comprises Pleistocene coarse sandstone of turbidity sediments.

In connection with the geological setting of the Java Island, particularly Central and East Java, the Lusi is not the solely mud volcano, since a number of paleo-mud volcanoes located in the region [ 3 , 4 ]. Along the region, there is a depression zone called the Kendeng zone, located from Sangiran in Central Java to Probolinggo in East Java ( Figure 2 ). Within the zone, the geological structures of fault and fold are commonplace, and one of these structures is the Ngelam-Watudakon fold that cuts through the Lusi mud volcano in Sidoarjo [ 15 ]. This could be understandable that such structures may result in the formation of mud volcanoes, as the case of the Lusi [ 3 , 16 ].

A number mud volcanoes are located in the Kendeng Depression Zone, setting up from Sangiran in Central java to Probollnggo in East Java. Paleo-mud volcanoes typically formed domes in Sangiran and Bludug Kuwu in Central java; while Gunung Anyar, Kalang Anyar, Gunung Gangsir, Gunung Grati, and Gunung Bentar in East Java. As well as, the currently active mudflow in Sidoarjo (Lusi) has already been constructing a dome of a height of 11 m and an area of 642 Ha.

Interestingly, the Kendeng depression zone is located at the back of the volcanic zone, where a chain of volcanoes from the Mt. Sindoro in Central Java to the Mt. Raung in East Java can be found. The Lusi mud volcano is just located at the back of the Mt. Arjuno and Mt. Welirang volcanoes. With only 20 km distance from the Arjuno-Welirang geothermal complex, the Lusi mud volcano can have a correlation with the complex [ 10 ], although, it may not necessarily be a direct correlation.

Since occupying the same Kendeng Zone, the Lusi mud volcano may share similar rock characteristics with other mud volcanoes. The Bludug Kuwu ancient mud volcano in Purwodadi, Central Java, is still erupting hot mud mixed with rock grains. The mud temperature is about 50°C. Besides mud temperature, the Lusi may also share typical pyroclastic and fine rocks materials, including mudstone, siltstone, and sandstone.

Mudstone and sandstone found within the rocks at the Gunung Bentar paleo-mud volcano dome in Situbondo show sedimentary structures, possibly incorporated into turbidity structures [ 1 ], indicating paleo-sedimentation activities in deep marine environment. Foraminifera index plankton ( e . g . Globorotalia miocenica ) found within the rocks indicated Early Pliocene in age, similar with that of the Upper Kalibeng Formation of the Lusi [ 4 ]. Based on benthonic foraminifera ( e . g . Virgulina rotundata ), the sedimentary rock should be deposited at the probable depths of 819–1128 m. Basaltic breccia of pyroclastic rocks at Gunung Grati in Probolinggo and Gunung Gansir in Bangil, contains dominant olivine and plagioclase minerals. This breccia rock is related to that of the upper Lusi stratigraphy [ 1 , 4 ], or similar with that the Pleistocene Kabuh Formation in Central Java.

It seems that the similarity of the combination between volcanic and argillaceous sedimentary materials typically forms the rocks of mud volcanoes in Central and East Java. Interestingly, since the Kendeng depression zone is located at the back of volcano complexes, thus to some extent, these may contribute consequences to the zone, as the Lusi mud volcano case [ 10 ]. Accordingly, as they show similar geological features, rocks of all mud volcanoes are most probably to develop within the same depression zone and similar activity of marine volcanism in during the Plio-Pleistocene period.

3 Samples and methods

Four sets of mud samples were taken from the Lusi mudflow site at the east of the crater. The location was considered as the most undisturbed part around the site at the time, as a large amount of mudflow has already been dredged from the site to the Porong River since 2010 [ 9 ].

Mud samples were manually drilled from two drilling points: R1 (E 07°3l′ 51.6″, S 112° 42′ 59.0″) and R2 (E 07° 31′ 50.1″, S 112° 43′ 01.5″) ( Figure 3 ). Each sample was retrieved from every 0.2 m depth down to the drilling holes of 2.0 m. Fresh mud samples were also taken from mud channels near the drilling points, FMR1 and FMR2, in which fresh mud was flowing from the crater into the east pond.

Locations of mud samples at the east side of the crater. Mud samples for REE tests were drilled from two holes, R1 and R2. Fresh mud was taken from two mud channels, FMR1 and FMR2, flowing from the crater to the east pond, closed to the drilling holes R1 and R2, respectively.

A series of laboratory tests were conducted including major oxide and rare earth element geochemistry and clay structure studies for the mud samples and isotope analysis for the water samples. Mud samples for clay structure observations were taken from the pond using a bucket, then they were airy dried for several days prior to cutting for the preparation for scanning. A scanning electron microscope (SEM) was used for the observation with a series of magnifications from 600 x to 20,000 x.

For geochemical analyses, airy-dried mud bulks were powdered using a rubber hammer; then the mud powder was sieved through no. 200 sieve, or the ASTM E-11 standard mesh size of 75 microns. The atomic absorption spectrometry (AAS) method was applied for major oxide analyses and the Neutron Activation Analysis (NAA) method was used to measure rare earth elements contents of the mud samples. Both analyses were carried out at the laboratories of the Indonesian Atomic Agency (BATAN).

Isotopic VSMOW analyses were conducted on water samples taken from the Lusi site and its surrounding. For the analysis, a mass spectrometry was used to measure the isotopes of oxygen-18 ( δ 18 O) and hydrogen-2 ( δ 2 H). The goal of the test was to investigate the environmental origin of the water.

4 Results and discussions

4.1 the lusi mud.

Grey mud materials were mostly retrieved from the drilling holes of Rl and R2 ( Figure 4 ). The drilling holes were divided into four layers. The first layer (surface to 0.2 m) contained dry brown clay mixed with basaltic igneous rock grains and white broken shells. Then, the second layer (0.2–0.4 m) contained sticky dark grey mud materials. The third layer (0.4-1.6 m) contained wet dark grey mud materials. The bottom layer contained slurry dark grey materials.

Drilling logs of R1 and R2. The drilling hole of R2 was closer to the crater, so it might have a shallower depth of slurry mud from the surface than the R1. Grey clay is dominated by the mud of both drilling holes. Mud on the surface was already dry. But, down into the holes, mud was still wet and slurry at the time of drilling. The bottom part was deposited before October 2010.

Igneous rock grains found within the mud might come from coarse sandstone and breccia formations. According to the Lusi stratigraphy [ 1 ], these materials could possibly be from the first interval. These typical coarse grain materials are also found within the rocks of three paleo-mud volcanoes in East Java. As discussed earlier, andesitic and basaltic igneous rock materials formed fragments within pyroclastic breccia, such that might be part of mud breccia consequences in mud volcanism [ 17 ].

The geochemistry of clay fraction of this grey mud is dominated by SiO 2 and Al 2 O 3 with an average of 50% and 17% in weight, respectively. Some other major oxides are also relatively high, including Na 2 O and K 2 O, with a ratio of Na 2 O/K 2 O of greater than 1.2. As shown in Table l , the oxide contents of the Lusi mud indicate smectite-rich clay. As suggested by Mazzini et al . [ 1 ], the mud could be coming from either a volcano-clastic source layer or mixing with material from the smectite-rich interval (1341–1432 m) on the way to the surface.

A series of mud sampling for geochemical measurement was conducted during the period of 2007-2014. Hot mud samples were taken from the main crater of the Lusi at the same location for each date.

4.2 Water geochemistry and isotope

4.2.1 water geochemistry.

The geochemistry of the Lusi water is dominated by Na and Cl elements of up to 9,465 and 17,288 mg/L, respectively; while the concentration of Ca is higher than that of Mg, which is over 1,200 mg/L. Such a high concentration may suggest that the water is not from the surface or seawater intrusion, but it is possibly from a paleo-water deposit formation of marine environment [ 3 ].

The Na and Cl concentrations, however, reduced for about 25 and 32%, respectively, in the period of 2007–2013 ( Table 2 ). The reduction might occur after the peak eruption reached in the period of June–September in 2009, since then the viscosity of the mud changes, and more fluids are erupting to the surface than solids [ 9 ]. Water geochemical results are consistent with data provided by Mazzini et al . [ 1 ], who suggested that the Lusi water might be a mixture of deep and shallow fluids.

The chemical composition of Lusi water. Samples were taken from around the crater, during the period of 2007–2013.

The pH values of the Lusi water are in neutral conditions, although, the water has already been heated. The pH values of the Lusi water are similar with that of fresh waters around the Lusi site ( Tables 3 and 4 ), which fall in the range of 6.08–7.95. The highest pH value for the Lusi water is 7.95, close to that of Carat located at the Arjuno-Welirang Complex.

The pH values of waters taken from the Lusi crater, sampled during the period of 2007–2013. The average pH value is 7.52.

The pH values of waters taken from the surrounding area of the Lusi site, sampled during the period of 2008–2013. The average pH value is 7.12.

The lowest pH value is, however, shown by waters taken from Siring Barat, which is 6.08. This slight acid water might be influenced by the heat condition of the location. Siring Barat is located at the west of the Lusi site, which was the hottest location outside the Lusi, as a lot of hot bubbles were found at the location at the time [ 13 ]. The isotopic contents of waters may support the argument, (SB-1 and SB-2 in Table 6 ).

However, in general, the neutral water of the Lusi was consistent during the period of 2007-2013. Waters taken from Kalang Anyar also revealed this condition, but those at Gunung Anyar showed a different pH value. The pH values of both paleo-mud volcanoes in Surabaya were 7.50 and 8.62, respectively, [ 13 ].

4.2.2 Water isotope

The isotopic compositions of δ 18 O and δ 2 H for the Lusi water are from +2.75%ffl to +10.11%ffl, and from –2.7%ffl to –20.5%ffl, respectively ( Table 5 ); and those for fresh waters collected from the surrounding area are from –13.05%ffl to +2.9%ffl, and from –81.2%ffl to –3.4%ffl, respectively, ( Table 6 ). The differences in the isotopic values could be due to the differences in water sources. The Lusi water may be issuing from deeper sources, and it is possible from a limestone rock formation at the depths of more than 3000 m [ 3 ]; whereas, the fresh water is coming from shallow sources. At depths of more than 1700 m the Lusi water was formed by the diagenetic modification and dilution of seawater, enriched in the isotopic contents of δ 18 O and depleted in the isotopic contents of δ 2 H; then at shallower formations (<900 m) the Lusi water was possibly added with meteoric water [ 1 ].

Isotopic contents of the Lusi water.

Isotopic contents of surrounding area waters.

In Figure 5 , a meteoric water line is drawn to differentiate between meteoric and formation waters. The δ 18 O values of the Lusi waters are far away from the meteoric water line, and they are concentrated on the area of formation water; whereas those of the fresh waters are concentrated along the meteoric water line. Due to the anomalies in the isotopic contents, the Lusi water should be heated at a very deep source [ 13 ], although it may not be necessary a direct volcanic source [ 1 ]. The Lusi water is enriched with neutral pH chlorides ( Table 3 ), and depleted in K and Mg ( Table 2 ). Thus, it seems that the depletion of K and Mg reveals the influence of heat in the water adsorbed within the Lusi smectite clay, since the K/Na geothermometer is usually used as a heat tracker [ 13 ].

Correlation between the isotope oxygen-18 ( δ 18 O) and the isotope hydrogen-2 ( δ 2 H) of waters. A meteoric water line is drawn to differentiate between waters from the Lusi and fresh waters from the surrounding area. Water criteria are due to Hoefs [ 19 ], and the Lusi waters are included into formation water criteria.

4.3 REE content and clay structure

Rare earth element analyses were conducted on 24 mud samples taken from the Lusi site. The concentrations of fourteen rare earth elements can be seen in Tables 7 and 8 . The REE concentrations of the Lusi mud are substantially high. Commonly, the light REE (LREE) concentrations, (La, Ce, Pr, Nd, Sm, Eu, and Gd), are higher than that of the heavy rare earth elements (HREE), (Tb, Dy, Ho, Er, Tm, Yb, and Lu). The highest concentration is for La with 78.18 mg/kg, while the lowest concentration is for Lu with 0.18 mg/kg ( Table 8 ). High concentrations of the REE are consistent with previous results [ 18 ].

REE contents of the Lusi mud of the R1 and FMR1 locations. The fresh mud of FMR1 was taken from the channel flowing from the crater to the east pond closed to the R1 drilling point. FMR1 is put on the depth of 0.00 m in the table.

REE contents of the Lusi mud of the R2 and FMR2 locations. The fresh mud of FMR2 was taken from the channel flowing from the crater to the east pond closed to the R2 drilling point. FMR2 is put on the depth of 0.00 m in the table.

High REE concentrations may be influenced by two factors: temperature and clay structure [ 12 , 20 ]. The initial temperature of the Lusi mud was 100°C measured directly on the surface. Mazzini et al . [ 1 ] used this temperature and assumed a geothermal gradient of 42°C/km to calculate the mud source temperature, which resulted in a temperature of 100-140°C at the depths of 1700-2667. While, Zaennudin et al . [ 13 ] used the isotope δ 13 C of CO 2 and CH 4 gasses released to the surface to calculate a temperature of 125°C at the depth of 2800 m. Some data of the isotope δ 13 C can be seen in Table 9 , and detailed data can be found in Mazzini et al . [ 10 ]. Since the current surface temperature of the mud is still consistently high, of about 60°C, the temperature seems to some extent to play an important role in the REE abundances.

Analysis results of gas isotopes of CH 4 and CO 2 released to the surface.

The clay structure seems, however, to be the most important factor in the Lusi REE concentration, in which the porous smectite structure of the Lusi mud is ideal for trapping rare earth elements. The XRD analysis conducted by the USGS [ 17 ] shows that the clay fraction of the Lusi mud was dominated by smectile, illite and mixed smectite and illite over kaolinite and chlorite minerals ( Table 10 ). The REE is commonly adsorbed within this type of clay structure [ 14 ]. This could mean that the Lusi mud could develop a tank for the REE abundances within its structure.

Results of semi-quantitative XRD analysis of the Lusi mud [ 18 ].

Commonly, the structure has a combination of one sheet of octahedral alumina and two sheets of tetrahedral silica weakly bonded by potassium ions [ 21 ]. The SEM photograph of the enlargement of 20000 x shows that the Lusi mud structure has the gap among sheets of 2 μm, the thickness and width of each sheet of 0.05 μm and 5 µm, respectively ( Figure 6 ). This structure results in porosity of about 30%, previous suggestion was 25% [ 8 ]. The proportion of clay fraction and grain of 81.5 and 18.5% may contribute to this porosity. Such porosity may correspond to the sedimentation process of the mud that had a depositional rate of about 2.48 m/ka [ 1 ]. This rapid process may consequence in a combination of fine and coarse grain materials, forming a typical bookhouse assemblage [ 21 ], so that structure is suitable for the mud to adsorb the REE.

SEM photographs show silica and alumina sheets of the smectite structure of the Lusi mud. The structure is reasonably porous, as the gap between a pair of combined sheets is up to 2 μm.

Having two factors controlling the REE concentration of the Lusi mud, however, the REE abundance may also depend on rock type [ 11 ]. The Lusi mud is part of the Upper Kalibeng Formation that comprises volcano-clastic argillaceous rock types [ 3 ]. The Lusi mud is a shale rock type that contains highly SiO 2 , Al 2 O 3 and K 2 O. This type of rocks is usually more enriched in the REE [ 22 , 23 ] compared to arenaceous rock types [ 24 , 25 ]. So, this may be the case that the LREE is found to be abundant within the Lusi mud [ 26 , 27 , 28 ].

4.4 REE and eruption sequences

In chondrite [ 29 ] normalized diagrams, the REE concentrations of the Lusi mud are far above the chondrite ( Figure 7 ). Being enriched in the LREE, the mud of a shale rock type commonly has a slight HREE enrichment and negative Eu anomaly [ 26 , 30 ]. The REE enrichment may be dependent on the minor mineral assemblages and the sedimentological factor controlling the assemblages [ 26 ].

(a-d) Distribution of the chondrite-normalized REE in the Lusi mud from the surface to the depths of 2.0 m of the R1 and R2, where the FMR1 and FMR2 samples of fresh mud flowing on the surface channels are put at the depth of 0.0 m on the graphs.

When the REE concentrations of the Lusi mud are correlated to those of the drilling log in Figure 4 , the REE concentrations slightly change with respect to depth. The REE concentration at the depths below 1.2 m is higher than that at the lower depths ( Figure 7 ). The changes in the LREE concentrations seem to be more significant compared to that of the HREE. Moreover, the Lusi mud within the ponds may correlate to the eruption sequences [ 9 ], so does the REE concentration. The mud of the initial eruption, below the depths of 1.2 m deposited before October 2010 [ 9 ], has relatively higher REE concentrations compared to that of the current eruption.

The changes in the REE concentration due to the eruption sequences might be slight, however, there is a general decrease trend in the REE concentration from the initial to the current sequence. Being the highest reduction of the Lu elements of up to 50%, the reduction seems to reflect the decreasing clay mineral abundance within the mud, since the current mud has more granular contents compared to that of the early stage mud. The granular mud is presumably coming from the shallower depths, probably from the depths of less than 900 m, since the rocks at these depths comprise sandy materials [ 1 , 3 ]. So, increasing sandy material contents within the Lusi mud toward the surface of the ponds may be to some extent responsible in the reduction of the REE concentration. The more grainy the mud, the less the REE enrichment [ 14 , 26 ], as the reduction may be associated with quartz contents [ 14 ].

4.5 REE environment

As expected, the alumina-silicate mudrock of the Lusi has characteristically similar REE concentrations of shales [ 14 , 26 , 31 , 32 ]. For comparison, the North American composite shale (NACS) is commonly considered as typical REE abundances, particularly enriched in the LREE [ 14 , 26 , 31 ]. The other typical shale of the post-Archean average Australian sedimentary rocks (PAAS) also shows a similar enrichment [ 30 , 31 ].

Shales are generally taken to indicate that fine-grained sedimentary material is efficiently mixed during weathering, erosion and transport, so the REE abundances of shales may represent the REE contents of the upper continental crust [ 14 , 26 ]. The lower HREE concentration compared to the LREE may represent the difficulty of the HREE to form soluble complexes [ 14 ], so the concentration may depend on the localized input of volcanic materials, perhaps on K-enrichment [ 31 ].

The REE contents of shales are usually normalized with the NASC [ 26 ], or PAAS [ 31 ] to show the patterns, and Figure 8 shows the comparison. Both graphs show a similar pattern that the general pattern of the normalized REE by the NASC and PAAS exhibits the depletion in the LREE, and a slightly negative slope shown from La to Lu for all samples. The depletion in the LREE is commonly dependent on the rock type, and the anomaly behavior of the Ce and Eu elements could indicate the environment of the REE abundances [ 11 ].

Patterns of normalized REE: (a) NASC-normalized REE [ 26 ]; (b) PAAS-normalized REE [ 30 ].

The analysis of the Ce and Eu anomalies follows the linear interpolation of the shale-normalized Ce and Eu, Ce N /Ce N * and Eu N /Eu N * [ 33 ]; rather than the chondrite-normalized REE [ 31 ]. In Figure 8 , the graphs show moderate Ce anomalies that are between 0.48 and 0.67, 0.37 and 0.50; which result in the average Ce anomalies of 0.59 and 0.43 for the R1 and R2, respectively. As the Ce anomaly represents oxidation conditions [ 14 , 22 ], the less negative Ce anomaly, the more oxiding condition [ 32 ]. These moderate Ce anomalies suggest that the Lusi mud might develop in a deep ocean basin that had less oxidation conditions, which could be an ocean-basin floor environment [ 33 ].

Similarly, the Eu abundances show less negative anomalies, compared to the Ce, which are 0.53-0.97. Commonly, the Eu element occurs in a stable chemical form [ 11 ], and the Eu anomaly reflects the deficiency of the element in the upper crust [ 22 ]. The Eu anomaly may correlate to the feldspar mineral enrichment within the earth crust, and it becomes increase in more felsic-feldspar, then decrease in mafic mineral enrichment [ 34 , 35 ].

The Eu anomaly may also be influenced by complexing agents [ 11 ]; but, as the Lusi mud is rich in chlorides, the Eu anomaly may indicate stable chemical fractionation in rock formation rather than in water-rock interaction. The negative Eu pattern of the Lusi mud does not really show a typical “gull wing” as shown by the geothermal hot waters from the Taupo volcanic zone in New Zealand [ 20 ]. The slight negative anomaly of Eu might be correlated to the second phase of heat activity, which could mean that the host rock is hot igneous rocks [ 13 ], but it is not necessary a magmatic rock. This case has been investigated for metamorphic rocks and shales near a geothermal field in Turkey, in which the temperature controls over the REE abundances in liquid and vapor phases of heated fluids, as at a temperature of over 145°C the REE becomes volatile and emission associated with geothermal activity [ 36 ].

However, such a case seems not to occur in the Lusi, the hot mud might have a temperature of over 175°C at the depth of 900 m [ 1 ], the neutral-chloride hot water hardly to contain the REE. One of many factors controlling the REE mobility, pH is the major factor, that under acidic conditions, the REE is easily removed from clays but under neutral or alkaline conditions the REE becomes fixed [ 14 , 20 ]. Thus, considering the Lusi case, the REE mobilization may occur during weathering but is unlikely to be significant during transport [ 14 , 27 ].

Seemingly, the negative Eu anomaly shows a typical Eu pattern of shales ( Figure 8 ), that weathering processes of such rocks may contribute in the REE abundances [ 14 ]. The REE was mobilized during alteration processes, such that caused the argillaceous shales become enriched in the REE concentration [ 27 , 28 ]. The processes might take place within the ocean-basin floor [ 33 , 36 , 37 ], which is consequently ideal environment for the Lusi shale to form the REE.

The current results are, although, of a preliminary investigation into REE contents, they have shown a further step in understanding the Lusi mud environment. The investigation certainly requires a continuous time series research to ensure that the availability of rare earth elements within the Lusi mud is consistent. Geological data show rock type relevancies of being typical marine shale rock types of mud volcanoes in Central and East Java.

5 Conclusions

Erupted hot mud in Sidoarjo, East Java, contains coarse igneous rock grains and fine rock materials. Particularly, clay fraction of the mud is made of the smectite clay mineral dominated by silica and alumina oxides to form a bookhouse assemblage. The porous structure of a typical shale rock is ideal for trapping mobilized rare earth elements, mostly the light rare earth element (LREE). Besides clay structure, temperature to some extent plays an important role in the REE abundances of the Lusi mud. The moderate Ce and Eu anomalies of the REE patterns strongly indicate a deep sea-floor environment. So, the most probable scenario of the REE fractionation is during the shale rock formation that weathering processes enriched the Lusi mud with the REE, rather than that of the hot water–rock interaction of a geothermal system. This is due to the isotopic contents of the Lusi hot water that the neutral chloride water may hardly contain the REE.

Correlation between the Lusi and paleo-mud volcanoes in Central and East Java supports the scenario that the Lusi mud volcano is part of deep rapid depositional marine activities. Rocks of the combination between volcano-clastic and marine fine materials form characteristically rock materials of mud volcanoes located in the Tertiary Kendeng depression zone. Such combination may typically be part of mud breccia significances in mud volcanism.

Acknowledgement

The authors express gratitude to two Indonesian Ministries: The Ministry of Education and Culture who provided funds for research through the HIKOM program; and the Indonesian Ministry of Research and Technology who provided funds through the Sinas incentive program. The authors also acknowledge the Sidoarjo Mud Agency (BPLS) for data and photographs. Soffian Hadi, Dodie Irmawan, Alwi Husein, Moch. Charis, Dwinata Irawan, and Arief Wijaya are thanked for help during field survey. Akhmad Zaennudin of Indonesian Geological Survey is specially thanked for valuable data and discussions. The Indonesian Atomic Agency (BATAN) is thanked for laboratory analyses. Also, the authors acknowledge geological laboratory supports from University of UPN “Veteran” Yogyakarta. Finally, anonymous reviewers are thanked for constructive reviews.

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Abdul Hakim , Arif Gunawan; Evaluation of Sidoarjo mud volcano embankment. AIP Conf. Proc. 18 August 2020; 2251 (1): 040018. https://doi.org/10.1063/5.0016225

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Since 2006, Sidoarjo Mud Volcano Levee has been gradually elevated by The Sidoarjo Mud Flow Mitigation Center (PPLS). It was constructed to prevent hot mud volcano, which was unpredictably erupted and debatable among researchers, whereas it is flowing into surrounding areas. Analysis of embankment stability was conducted by Agustawijaya et al. (2012) and Widjaja et al. (2017) at point 10 D and point 21, respectively. However, the eruption on it is insufficiently stopped, although the quantity has decreased significantly. In this case, PPLS, as an authority of LUSI, performed some increased levee as an additional embankment. Nevertheless, the high embankment causes instability. They, moreover, built on the soft soil foundation that has made a significant awareness to analyze the embankment stability, particularly on the point of 10 D. A limit equilibrium method was used for evaluation of embankment stability, and the result shows that factor of safety (FoS) of the embankment is 1.7.

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The World’s Muddiest Disaster

Earth’s most violent mud volcano is wreaking havoc in Indonesia. Was drilling to blame? And when will it end?

Erin Wayman

The newest landmark in Indonesia is a spectacular disaster. On May 29, 2006, mud and steaming hot water squirted up in a rice field in Sidoarjo, East Java, marking the birth of the world’s most destructive mud volcano. Since then, the volcano, nicknamed Lusi (a contraction of the Indonesian word lumpur , meaning mud, and Sidoarjo), has erupted almost nonstop, engulfing an area more than twice the size of New York City’s Central Park and belching as much as six million cubic feet of muck—enough to fill 800 railroad boxcars—in a single day.

The ongoing disaster has displaced 13,000 families and closed 30 factories and hundreds of small businesses. Dozens of schools and mosques are buried in muck. Rice paddies and sugar cane plantations have been replaced by a brown expanse of cracked mud. A major toll road was inundated, and a gas pipeline exploded after it broke under the weight of Lusi’s outpouring, killing a dozen people.

The land surrounding the volcano’s main vent has started to sink because so much water and mud from beneath the ground have erupted and now weigh it down. New mud bubbles—smaller fissures where mud and gas escape to the surface—continue to pop up across the landscape. The price tag to contain the mess and compensate victims is more than half a billion dollars—and that number is rising.

But now, after more than five years, the mud volcano’s behavior appears to be changing; the nonstop eruptions have given way to more episodic spewing. Geologists are working to determine what that means for the future and how long Lusi will continue to ravage East Java.

“I think it’s good news,” says Richard Davies, a geologist at Durham University in England. “I think the worst is over in terms of the volume of mud coming up.”

Mud volcanoes are common in Indonesia. The humid climate provides an abundance of rain that washes sediments down the country’s numerous volcanic peaks, says Michael Manga, a geologist at the University of California at Berkeley. The wet sediments collect in low-lying areas and are rapidly buried by more and more debris eroding down from the mountains. The overlying sediments compress the lower layers, and pressure builds as the upper layers get thicker and heavier, and the squeezed water has nowhere to go. If a path to the surface opens, the highly pressurized water will shoot up like water from a fire hydrant and bring subsurface sediments with it.

Lusi is an unusual mud volcano for several reasons, including its long eruption period—most mud volcanoes erupt for only a few days at a time. It’s also unique because it’s the first mud volcano that scientists have observed from day one. Oil and natural gas exploration is common in East Java, and researchers have used subsurface data collected from a nearby exploration well to learn more about Lusi’s origins and behavior. It’s “the first time ever you know exactly what the subsurface was like prior to an eruption,” says Manga. “That’s kind of cool.”

But that same well may be to blame for the disaster. The day before the eruption began, the Indonesian company PT Lapindo Brantas removed a drill from the exploration well and experienced a “kick,” or influx of water into the well’s borehole, which cracked the surrounding rock. The next day, just 650 feet away, Lusi erupted.

Many geologists, including Manga and Davies, say drilling unleashed Lusi. Others, including geologist Adriano Mazzini of the University of Oslo, think a magnitude-6.3 earthquake centered 155 miles southwest of Sidoarjo that struck two days before Lusi began reactivated a fault, allowing water and mud to spurt to the surface. In 2008, the issue was put to a vote at an international conference of petroleum geologists; 55 out of 74 attendees agreed drilling played some role in the birth of the mud volcano. Lapindo has paid hundreds of millions of dollars to the displaced and to mitigate further damage, according to the non-governmental organization Humanitus, despite its claim of no wrongdoing.

Geologists are now moving on from the debate over what caused the disaster. “The most important question isn’t who’s responsible but when is the eruption going to end,” Manga says. “It’s a billion-dollar question.”

This year, two research teams considered the question—and came to different conclusions. Manga and his colleagues reported in the journal  Earth and Planetary Science Letters  that there is a 50 percent chance Lusi will last more than 41 years and a 33 percent chance it will last more than 84 years. A team led by Davies had a slightly more optimistic outlook: It suggested in the  Journal of the Geological Society of London  that the mud volcano’s most likely total life span is 26 years.

In either case, more territory will be swallowed by mud. Further geological analyses might help Indonesian officials better manage the disaster and explain how the recent slowdown in Lusi’s eruptions fits in with the predictions.

The different results emerge from the way the teams modeled Lusi’s plumbing and driving forces. Davies’ team says the water propelling the eruption comes from a 15-million-year-old layer of rock that sits at least 2,000 feet beneath the erupting mud. Twenty-six years, Davies says, is an estimate of how long it will take for the water pressure to return to normal.

Manga’s team says water within the mud layer itself is fueling the eruption. “If we’re right, it’s not typical of most mud volcanoes,” Manga says. Lusi is acting like a can of fizzy soda, he says, with bubbles of carbon dioxide and methane helping bring mud to the surface.

The mud volcano’s recent changes in activity may signal that the mechanism driving the eruption has changed, Davies says, but it’s not yet clear what they mean for the long-term outlook.

This year, scientists who study the eruption met in Indonesia for a conference and to observe the volcano. Instead of belching continuously, Lusi seemed to be “pulsing” every few minutes, Davies says. “It’s a bit like Old Faithful.” It’s also spewing less mud, adds Max Rudolph, a graduate student at UC-Berkeley. At a rate of about 530,000 cubic feet per day, he says, “the current eruption rate is [down by] a factor of 10 or more from its peak in 2006.”

Does this mean Lusi is quieting down for good, or just taking a break before ramping up again? Nobody knows for sure. It “made me realize we need to constantly re-evaluate the longevity estimates,” Davies says.

Getting a good estimate of Lusi’s life span is one reason why Humanitus, an education and community development organization based in Australia, organized the conference. After watching a documentary about the mud volcano, Humanitus Executive Director Jeffrey Richards says, he realized that “no one seemed to be looking at the future.” The controversy over the eruption’s cause was overshadowing the disaster, he says. “It has made it difficult for the government to get any sort of international assistance, which is normally the case for any disaster on that scale.”

Ironically, Lusi may offer ways to fix the area’s damaged economy. Businesses could use the heap of mud to make bricks and other construction materials, Richards says, and the mud volcano could even become a tourist destination. After years of coping with the hardships created by the disaster, the people of Sidoarjo “need some good positives to start coming out of this,” Richards says. As he and other scientists at the conference suggest, “It’s time to look at Lusi as a positive for this region.”

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Erin Wayman | | READ MORE

Erin Wayman is a science and human evolution blogger for Hominid Hunting. She has M.As in biological anthropology and science writing.

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Sidoarjo Mud Flow, Indonesia

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On May 29, 2006, a scalding mud volcano began erupting in a densely populated area in eastern Java, Indonesia. In the months that followed, the Sidoarjo mud flow (also known as the Lapindo mud flow, or Lusi) showed no signs of slowing, and mitigation efforts such as dropping chains of concrete balls down the crater proved ineffective. By September 2006, the mud had breached some early containment walls and sprawled across a nearby toll road. The mud’s footprint continued growing in February 2007. By June 2008, the massive mud lake spawned by this eruption had smothered a dozen villages and displaced some 30,000 residents.

Despite its destructive history, however, the Sidoarjo mud flow appeared contained by levees in November 2008. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite acquired these images on November 11, 2008, (top) and August 24, 2004 (bottom). In these false-color images, red indicates vegetation, pale blue and green indicate bare ground and/or fallow fields, and black indicates water. The mud from the volcano appears charcoal gray.

In the image acquired in August 2004, almost two years before the eruption started, crops appear as a patchwork of red and pale blue or pale green. Between the agricultural fields, settlements resemble multicolored grains of sand. In the east, shrimp farms vaguely mimic the patterns of the agricultural fields, but water colors them black.

In the image acquired in November 2008, more than two years after the eruption began, the mud volcano dominates the scene. A network of levees around the volcano contains most of the mud. On the eastern side of the levee network, the contained material appears deep blue or green, suggesting that these sections hold water that partially separated from the mud. A channel on the southern end of the containment structure funnels volcanic mud into the Kali Porong. (Indonesia’ president authorized pumping the volcanic mud into this river to carry the mud to the sea.) The tiny white puff near the center of the containment network results from volcanic steam at the mud’s primary eruption center. This patch of vapor testifies to the volcano’s continued activity. Although it was contained at the time this image was acquired, the mud still had the potential to breach its new containment structure.

From the time the eruption occurred, geologists debated the cause of the eruption. Some geologists pointed to a minor earthquake in the region. In June 2008, however, a report released by British, American, Indonesian, and Australian scientists concluded that the volcano was not a natural disaster, but the result of oil and gas drilling. At the time the report was released, the volcano was producing roughly 100,000 cubic meters (3.5 million cubic feet) of mud per day— enough to fill 53 Olympic swimming pools.

• Plumlee, G.S., Casadevall, T.J., Wibowo, H.T., Rosenbauer, R.J., Johnson, C.A., Breit, G.N., Lowers, H.A., Wolf, R.E., Hageman, P.L., Goldstein, H., Anthony, M.W., Berry, C.J., Fey, D.L.,, Meeker, G.P., and Morman, S.A. (2008). Preliminary analytical results for a mud sample collected from the LUSI mud volcano, Sidoarjo, East Java, Indonesia. U.S. Geological Survey Open-File Report 2008-1019.

NASA image created by Jesse Allen, using data from NASA/GSFC/METI/ERSDAC/JAROS, and the U.S./Japan ASTER Science Team. Caption by Michon Scott, based on interpretation by Geoffrey S. Plumlee, U.S. Geological Survey Crustal Imaging and Characterization Team.

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Despite its destructive history, the Sidoarjo mud flow in eastern Java, Indonesia, appeared contained by levees in November 2008.

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References & Resources

• Whitelaw, C., Sanders, R. (2008, June 9). Javan mud volcano triggered by drilling, not quake. UC Berkeley News. Accessed December 9, 2008.
• Wikipedia. (2008, November 17). Sidoarjo mud flow. Accessed December 9, 2008.

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Java mud volcano continues to grow.

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Lusi Mud Volcano, Indonesia

Lusi, the world’s largest and fastest growing mud volcano, had developed the mound-like shape of a volcano when this false-color image was acquired in October 2009, two and a half years after its birth.

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A Muddy Mess in Indonesia

More than a decade after boiling mud began spurting from the ground in East Java, the Lusi mud flow is still going strong.

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No end in sight: Sidoarjo mudflow continues to drown hopes, 15 years on

Mud has continued to flow over the past 15 years in Gempol Sari village, sinking hopes and homes along with it, in the unresolved aftermath of the mud volcano that erupted in Sidoarjo, East Java.

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ot wind and the sharp odor of methane is what Sukardi has experienced every day for the past 15 years in Polo Gunting hamlet of Gempol Sari village in Tanggulangin district, Sidoarjo regency, East Java.

Life has been full of hardship for the 52-year-old resident since a mud volcano erupted in 2006 in the adjacent district of Porong, about 5 kilometers from his house. The resulting mudflow slowly submerged the villages, rice fields and other places of his childhood, now immortalized only in Sukardi's memories. The mud also drowned his hopes for a better life and sank him deep into pessimism.

“I'm tired already. Even worse, I don't know in whom we should place our hopes. The government? I don't think depending on them is a good idea,” he told The Jakarta Post on May 29, the anniversary of the disaster.

“[Community] solidarity is the only thing that has kept me here until today. It helps me to accept all the conditions I've been through. Even if we feel broken and defeated, as long as we're together, we'll be alright," he said .

Sukardi's house is located just 50 meters or so from the embankment that was built to hold back the mudflow. His daily view is just mounds of earth, the gritty soil scattering into his yard whenever the wind blows hard. He has also been condemned to live an old age with the respiratory problems he developed after inhaling the polluted air every day.

“This village used to be beautiful. Every morning over there,” he said, pointing to the south, “Mount Arjuna-Welirang used to be such a sight.”

“Now look at the embankment and the wall. There is nothing beautiful about it,” Sukardi said, laughing.

Sukardi's house is slowly subsiding because of the embankment and as a result, he is constantly repairing and renovating his house. Sometimes, small mounds of earth appear suddenly, and he says not a day passes without the anxiety that his house will collapse due to the land shifting.

"Especially when it rains. Wow, I feel like I'm going have a heart attack all the time. The embankment cracked several times, [and] a heavy flow of mud seeped through. As a result, our house was flooded. It was pretty deep, up to the waist,” Sukardi said, covering his face with his hand. He then looked out beyond the vast embankment, which currently resembles a lake of mud.

Sukardi said he had received a one-time payment of around Rp 1.5 million (US$105) as compensation in the 15 years that had passed since the disaster. Otherwise, he had been left to fend for himself in maintaining his house as well as his health.

“What's more, in the past, my livelihood was also affected. I was a farmer and owned a rice field. [...] I was prosperous. My field is not exactly sinking, but it's no longer clean and cannot be planted because it is often exposed to waste seeping from the embankment. Water mixed with mud has spread over the field several times. Now, I’ve ended up becoming a hawker like this. The income is miniscule, but what else can I do?" he said.

Contaminated water

The shortage of clean water is a critical issue for people who live near the Lapindo embankment. The 2006 disaster contaminated the water that supplies the villages in southern Sidoarjo with toxic substances. The water is a cloudy reddish-brown and tastes salty, and the residents must bear the costs of accessing a clean water supply.

One resident who has experienced this is Warsita, or “Grandmother Sita”, an elderly woman who lives with her grandson in Gempol Sari.

Sita said she had to pay Rp 10,000 every day for clean water, because the water that supplies her house can’t be used for anything other than washing the dishes. It cannot be used for washing clothes, which come out dirtier.

It is even worse for her family’s daily drinking needs, and there is no doubt that their health is at stake.

"Rather than catching disease, we have to buy our own water supply whether we want it or not,” said Sita.

“The [house’s] water is so sticky, it's not fresh at all. If you mix the water with soap, no foam appears. We don't know about toxic substances or what [the water] contains. But just looking at it, something just doesn't seem right, don't you think?” she said .

Helping on threat of death

On the 15th anniversary of the Sidoarjo mudflow disaster, more commonly referred to as the “Lapindo mudflow disaster” in Indonesian media, nonprofit Komunitas Kecil Bergerak Indonesia (KKBI) delivered five 700-liter tanks to hold the village’s clean water supply.

The tanks have been placed around the village perimeter and are filled to the top every weekend. The villagers are not charged a single rupiah for either the water or the service, which are entirely funded by the KKBI.

The initiative has not been appreciated in some quarters, however, and Ardi Kurniaji of the four-member KKBI says he receives frequent calls threatening his life if he did not immediately stop helping the villagers. But he has no intention to do so, and rather intends to share the joys and sorrows of his fellow human beings, he says, as is his calling.

"I'm not afraid at all. Such threats are common, and also an understandable risk for me. After all, we don't ask for money from [the government], it's all from our own pockets. If my life ends here, I'm not afraid,” said Ardi.

The residents of Gempol Sari have been promised one year of clean water via the KKBI, which is self-funded. The community’s four young members, all creative workers, have set aside a portion of their income to help meet the needs of the people who live along the embankment.

Bitter irony

A thin man sits idly on a motorcycle, slowly smoking a cigarette. This is Puji Waluyo, better known locally as Mr. Keple (using the English term), who has been busy for the past decade guiding visitors on a tour to his submerged village. Occasionally, he offers them a DVD containing early amateur footage of how the mudflow occurred.

"This is ironic, actually. It is as if I am inviting strangers to visit our family's grave. The problem is, it's not just the land. There are history and memories that have been buried deep down beneath the mud,” he said with a small smile and turned away.

"But it is even more ironic if my family at home can't eat at all," Keple said, his eyes holding back tears.

Keple’s village, Jati Rejo, was submerged at the beginning of the long tragedy spawned by the disaster. He had to move from one rented house to another, he said, because he only received 20 percent of the compensation. While he declined to say how much, he said it led to a fight with one of his brothers who was also struggling with financial difficulties.

Since COVID-19 broke out in Indonesia, Keple said he could count the tourists who visited the embankment on one hand. In the 2010s, he could bring home hundreds of thousands of rupiah each day, but over the past year, he sometimes didn’t make enough to cover the gasoline for his motorcycle. He endured hunger all day long just so he could bring home a meager income for his family.

"Now, earning just Rp 50,000 is a struggle. Even on weekends, I don't make that much. Just today, an important day, I only had one customer,” he said, referring to the anniversary of the disaster. “But this is not so bad, [it’s] better than nothing."

Keple took the Post to tour the 7.5-square-kilometer area the embankment contains and stopped at a place where dredgers were anchored. He threw away the cigarette he was smoking and with a trembling finger, pointed to the expanse of mud, saying in a hoarse voice that this was where his house once stood.

"Now you can imagine it, right? Just imagine how deep was the mud that inundated our village. Fifteen years and nothing is settled. Even by them, the culprit of all this tragedy. Masya Allah ['dear God'],” he said, wiping at the slow tears falling from his eyes.

Keple was referring to oil and gas company PT Lapindo Brantas that was drilling for gas in the area at the time of the disaster, which has been widely determined to be a manmade disaster and not a natural one.

The mud has continued to flow over the years, inexorably sinking the people’s hopes for a solution or settlement, let alone any improvements to their lives or living conditions. Sukardi, Keple and Granny Sita seem to believe that eventually, their village will become a giant mud lake.

"If [the mudflow] is not resolved, it will be as though the other villages are just waiting for their turn. Yesterday, you could see that my village was drowning. But tomorrow, it could be your village, nobody knows,” Keple said.

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Life After the Mud

In indonesia, the world’s largest mud volcano has been erupting continuously for 10 years. a wealthy family's gas company may be to blame. but it’s the poor who’ve paid the price..

By Aria Danaparamita

SIDOARJO, Indonesia — At 6 a.m., Muslimah, 45, steams rice and fries tempeh for her husband and children. After they eat, she dons a baseball cap and heads to work. Like many others in East Java who were displaced by the mud volcano, she drives an ojek, or motorcycle taxi. Her passengers are tourists, who flock to look upon the blighted landscape she once called home.

The mud now covers over 1,600 uninhabitable acres. It’s cracked dry in places, wet sludge in others. In the expanse’s distant center, white smoke rises from the crater.

It’s been ten years, but Muslimah still remembers vividly the quiet morning in May of 2006, when scalding mud and gas burst violently from the ground here in Sidoarjo, a small regency in East Java, Indonesia. “I was shocked,” she says. “It was terrifying: The mud soared like a black tower to the sky.” As the day wore on, the watery sludge, emanating from a single point, flooded homes, rice paddies, and factories, as villagers scrambled to collect their belongings and flee. The flow hasn’t stopped since. Within a month, Muslimah’s house was submerged entirely.

The Sidoarjo mudflow is the longest continuous disaster Indonesia has faced. Every year on May 29, those who lost their homes mark the anniversary of the day the eruption began.

For the first few months, the crater on average spewed  26 million gallons of boiling mud a day, according to the Sidoarjo Mudflow Mitigation Agency (BPLS), a government body formed in 2007 to oversee the disaster recovery. The rate has since slowed to 7-15 million gallons. Over the past decade, the mud has swallowed 12 villages, and displaced over 39,000 people, according to the government. At various sites around the mudflow, methane leaks are prone to combust at the careless flick of a lighter — although this problem has subsided with time.

For the victims, the nightmare has become a new normal.

Muslimah points to the spot where her home once stood.

A former factory, all but the utmost peak of its roof submerged in mud.

A Sidoarjo mud formation.

Mud from the Sidoarjo disaster drains into the Porong River.

Kick-starting her motorbike, Muslimah snakes past rice fields before joining the road that connects Sidoarjo to Surabaya and Malang, the nearest major cities. Along the way, hand-painted signs announce: “Mud Tourism.” Atop the levee that holds back the heavy muck, ojek drivers lounge in the shade of bamboo shelters as visitors take photos of the surreal scenery.

“I don’t really understand why the tourists come, but I don’t mind,” Muslimah says. “I’m happy to meet visitors from all over Indonesia, from Malaysia, from America, from the Netherlands. Sometimes they give me foreign currency to keep as souvenirs. I ask myself, what am I supposed to do with 20 ringgits? So I exchange them.”

And then there are the scientists, who come to take measurements and collect samples. To this day, experts debate the origin of the event. Indonesia is known for its high volcanic and seismic activity. Some say a 6.3-magnitude earthquake, which struck the city of Jogjakarta 160 miles away just two days before the eruption, triggered the disaster.

Another culprit seems likely: Lapindo Brantas, an oil and gas company that was drilling for natural gas about 800 feet from the rupture. “We’re now 99 percent confident that the drilling hypothesis is valid,” Mark Tingay — an earth scientist at the University of Adelaide and lead author of a report on the mudflow, published by the journal Nature Geoscience — told the New York Times last year.

The family of the well-known former cabinet minister, tycoon, and failed presidential candidate Aburizal Bakrie controls Lapindo. In 2007, a year after the eruption commenced, the Bakrie family topped the Forbes list of richest Indonesians, with a net worth of $5.4 billion.

Over the past decade, victims like Muslimah and her family have waged a protracted battle to demand compensation from Lapindo. In the face of public outrage, a month after the eruption, the company apologized and announced its commitment to fully compensate for all losses. At first, it promised to hand out cash and/or resettlement packages within two years of receiving any given claim.

Then the 2008 financial crisis hit, and payments began to slow. “Sometimes it would stop for a month, sometimes three months. It was a very difficult time,” says Muslimah’s husband, Sadli. The 46-year-old had lost his job at a concrete factory when it, too, was buried under the mud. Many faced similar fates. Unable to afford new houses, the evacuees were forced to rent grimy apartments or take shelter in the homes of relatives. By the thousands, they staged marches and mass prayers.

Muslimah prepares breakfast in her kitchen.

In December 2014, the national government finally stepped in. Newly elected President Joko Widodo loaned Lapindo $45.5 million to finance the outstanding compensations — fulfilling the campaign promise that won him Sidoarjo in the 2014 presidential election . Under the arrangement, the land that was once villages has been bought and paid for by Lapindo. The company will need to repay the government within four years — or forfeit those assets to the state.

Over the course of 2015, most displaced villagers finally received full compensation, although dozens are still waiting for their papers to be verified by authorities.

But earlier this year, outrage swept the community anew. Lapindo announced a plan to drill two new wells, just over two miles from the eruption site. Drilling was slated to begin this past March. Local protests halted the project.

“How can we not protest? We’re still traumatized,” Muslimah says.

Before the mudflow, she had lived in a house in Siring village for her entire life. She had sold fried snacks and iced drinks. She has two children from a past marriage, and two more with Sadli. Their youngest was six years old when the mud came.

Once the sludge reached knee level, the family abandoned their home, and, alongside Muslimah’s elderly father, took refuge in the new market in Porong, a neighboring district. Lapindo reported that 2,590 people sought shelter in the market’s vacant stalls.

“We piled into a small stall with three, sometimes four families,” says Sadli. “We slept on mats, and when help started pouring in, we were given blankets and some food — rice, with fish or eggs on the side. It wasn’t much, but we lived.”

Life was rough. “We couldn’t shower, we couldn’t wash our clothes,” Sadli says. “For every toilet, there were dozens of people constantly in line.”

After nine months, the first compensation payment came. The family rented a two-bedroom apartment. Muslimah thought it would be temporary, just until the rest of the payments arrived. But they didn’t. “It was too much for my father,” she says. He passed away in 2008.

Muslimah holds a portrait of her father.

Ojek drivers hang out atop the levee that contains the Sidoarjo mudflow.

A papaya stall at Pasar Baru Porong, the New Porong Market, which served as an evacuation site after the eruption.

A mosque and graveyard stand abandoned. The surrounding villages were evacuated as the mud rose.

The family eventually lucked out and found a house for just over $3,000 in Kedung Kampil village. “But it was just the walls, there were no tiles or anything,” Muslimah says. They painted the interiors bright pink, purple, and yellow.

After the government stepped in, the family received almost $30,000 in compensation. For the first time in a decade, they can focus on moving forward. They bought a cart to sell banana pastries — manned by their second son — while their eldest raises fighting cocks in bamboo cages behind the house. Muslimah and Sadli both go to the mud field each day as ojek drivers, and Sadli picks up odd jobs in construction.

Across the gray expanse where Muslimah parks her motorbike to wait for customers, the mud is wet and gleaming. A rough, steady motor roars. A dredger sucks up sludge, channeling it toward a spillway that drains into the Porong River.

“Our understanding now is that the mud cannot be stopped. At the beginning, many tried. Researchers and technicians wrote proposals, but none of it worked,” says Riko Aditya, head of the operations supervision subgroup at the BPLS. “Now, our aim is just to stop the mud from outflowing.”

The disaster zone is ringed by levees made from packed soil that run for almost ten miles. Funded by Lapindo and the government, these barriers were built, then rebuilt and raised, as the muck continued to rise. In July 2015, the BPLS estimated that the area contained over 1.26 billion cubic feet of mud, compared to 1.1 billion in 2010. “The only current solution is draining the mud,” Riko says.

A dredging camp at the Sidoarjo mudflow disaster site. Draining mud into the Porong River remains the only viable mitigation method.

The effect on the waterway has been drastic. Dewi Hidayati, a professor of biology at the Tenth of September Technological Institute in nearby Surabaya, has analyzed fish survival rates in the Porong River between 2010 and 2013. “Downriver from the effluent, the dominant fish are those who can adapt to the mud. The rest die,” she says. “The mud also alters their habitat. Now the riverbed is covered with mud, so for example, it’s not conducive for fish to lay eggs. They are stressed.”

A number of studies have tracked changes to the environment around the mudflow, from biodiversity to land subsidence. Despite fears, the mud has shown no urgent effects on human health, though it still needs to be studied thoroughly, Dewi says.

“For now, what’s evident is that the effect is indirect,” she says. “The mud contains a high level of aluminum, which in a normal pH, is perfectly safe.” But if the pH levels drop, due to household or industrial waste, for example, she says the aluminum will begin to pose a hazard.

“There needs to be awareness, that although the ecosystem can adapt to a certain extent, if the conditions become extreme, then it could be catastrophic,” she warns. “People have begun to forget about the mud. Now they think of it as normal. But it’s not normal.”

Muslimah and Sadli haven’t forgotten what they lost.

Sitting on a wooden bench at home, Sadli notes that this year’s anniversary of the eruption falls a week short of Ramadan, the Muslim holy month that ends with Idul Fitri, a festive celebration during which Indonesians traditionally return to visit their hometowns. “And us?” Sadli asks. “Where do we go?”

Photos by Aria Danaparamita for Foreign Policy

Aria Danaparamita is a journalist based in Jakarta, Indonesia. She covers social transitions in Southeast Asia. ( @mitatweets )