shilston LUSI

On 29 May 2006, a new mud volcano erupted in the Sidoarjo regency of East Java, Indonesia, eventually burying villages and farmland in an area of nearly six square kilometres. Fourteen people were killed and around 40,000 people lost their homes in the immediate aftermath.

The volcano quickly became known as ‘LUSI’, taking its name from the Indonesian word for mud (lumpur) and its location (Sidoarjo). At its peak it was spewing 180,000 cubic metres of mud a day, equivalent to 50 Olympic-sized swimming pools.

Following the eruption, Atkins was approached by a client concerned about mud reaching nearby industrial facilities and the potential for ground subsidence. As a result, Atkins’ UK-based ground engineering team has been monitoring and assessing these risks since early 2007, using innovative satellite interpretation techniques and site visits.

David Shilston, Atkins’ technical director for engineering geology, commented: “The opportunity to study a new, active mud volcano is rare and LUSI’s eruption is an example of the hazards and risks that such features present to the general public and to industry.”

LUSI is unlike other mud volcanoes in that it erupts with a continuous high flow of mud, expelled at high temperatures. The discharged mud now covers an area of 5.6km² and is being confined by man-made earth embankments that surround the volcano on all sides. To the south of LUSI, some of the mud is also being pumped into the adjacent Porong River.

The cause of the mud volcano’s eruption has been hotly debated in the Indonesian media and international technical literature, as well as at conferences and on internet forums. The majority view is that LUSI erupted as a result of a blow-out of a gas exploration well that was being drilled at the time. The contrasting opinion is that it was due to an earthquake that occurred a few days before the eruption started. What is clear, however, is that almost seven years after the initial eruption, LUSI continues to emit a mixture of steam, water, mud and gas, and remains an ever present risk to communities in the surrounding area. Until May 2011, LUSI was erupting between 100,000m³ and 180,000m³ of mud per day, however this has now dropped to between 10,000m³ and 26,000 m³ per day.

With the client’s agreement, Atkins adopted a remote sensing approach to assess the effects of the ongoing eruption, including the lateral extent of the mud flows from the volcano and movements of the ground surface. Our innovative approach has combined:

• • Optical satellite imagery to map and monitor the extent of the mud flows and how they are being retained by the surrounding earth embankments;

  • Satellite radar data to monitor ground movements around the mud volcano area, using Differential Interferometric Synthetic Aperture Radar (‘DifSAR’) analysis;

  • Desk study reviews, and occasional site visits to verify actual ground conditions against the image data.

This approach has meant that our work can be done quickly and cost-effectively (whilst maintaining suitable discretion) and can be repeated at regular intervals over an extended period of time. To date, the results from repeated DifSAR monitoring have shown no detectable ground surface deformation in the area of the client’s facilities and have confirmed that ground movements are limited to the area within, and a little beyond, the mud flow extent, which is now contained by the earth embankments surrounding the eruption centre.

The evolution of LUSI in the long term remains uncertain. Geologists estimate that the volcano could continue to erupt for a further 20 to 100 years – possibly more. Questions also remain about whether present levels of activity are likely to continue at the current rate into the future.

The eruption rate could influence the amount of ground surface movement that might occur, the size of the area affected, and the likely impact on facilities and the densely populated area around LUSI. These are all issues and questions that Atkins, the client and other organisations involved with LUSI have to consider.