Since 29 May 2006, a mud volcano has been spewing out a hot, viscous and foul-smelling slurry in the district of Sidoarjo, on the eastern side of the island of Java, Indonesia. 12,000 people have been evacuated from the area.

Between 5,000 m3 and 150,000 m3 of mud is erupting from the volcano every day. The mud is coming from a pocket of pressurized hot water 2,700 metres below the surface. As it rises, the water mixes with sediments to form a viscous slurry of mud.

The cause of the eruption has not yet been established, but it could be linked to borehole drilling operations by an Indonesian company exploring for gas.

Initial attempts to plug the volcano vent failed and work began on holding dams to contain the mud flow.

Rainy season precipitation is running off the mud toward agricultural irrigation channels.

Many experts believe it is impossible to tell how long the eruption will last. The volcano could continue spewing mud for years or decades to come.

The volcano, called Lusi for LUmpur SIdoarjo, claimed its first victims on 6 November 2006 when an underground gas pipeline exploded a few hundred metres to the north of the crater.

The explosion breached a dam, causing mud to flood land north of the crater and the main road connecting the city of Surabaya to the rest of the island.

The mud volcano erupted over farmlands near small-scale industrial facilities.

There are many villages in the area and a large, recent housing estate to the north of the crater.

Situated at a hub of the road and rail network, the mudflow threatens important communication links as well as three bridges and a dam on the Porong river.

On the basis of the first measurements, we can estimate the lake’s extent one year on and project its impact (orange circle).

29 May 2006: start of eruption

7 August 2006
- The mud lake (outlined in red) covers an area of 230 hectares (2.3 km²)
- Its average rate of expansion is 3.3 hectares a day

Projection on 29 May 2007
The extent of the mud lake (orange circle) could reach 1,200 hectares (12 km²).

Comparison of the estimated extent with a new image acquired 9 months later (18 March 2007) shows that:

The mud lake has reached the north and south bounds of the circle.

Its expansion has been contained by holding dams and basins (light orange outlines).

The level of the continuing mudflow has therefore risen.

Looking at the site closer up, gullies descending from the crater confirm that the volcano is rising.

The shadow to the north-west of the crater encircled by dams highlights its elevation and shows that a volcanic peak is forming.