Unusually, the LUSI mud volcano in the Sidoarjo area in East Java, Indonesia has been erupting hot fluidized mud for over a year since its genesis on 29 May 2006, causing the displacement of tens of thousands of people. A recent study suggests that it was triggered by an earthquake that occurred in southern Java on 27 May 2006, and not by the penetration of an exploration well, as had been previously hypothesized.

Credit: © 2007 Elsevier

From the eruption rate, the nature of the underlying sediments, and the compositional characteristics of mud and fluids erupted by the mud volcano, Adriano Mazzini of the University of Oslo and colleagues1 (including Bambang Istadi from EMP Brantas, the local oil company) conclude that the erupted products come from a clay-rich layer between ∼1615 to 1828 metres below the surface, which was depressurized by the earthquake. The ∼15 million cubic metres of water erupted by the volcano to date show isotopic characteristics that suggest it was released by the transformation of clay minerals from hydrated smectite into dehydrated illite — a process that would have increased pressure in the sediment layer.

Since its birth, the water content of the material erupted at LUSI mud volcano has halved, and the pulses of more powerful eruptions are becoming less frequent. Perhaps the mud volcano is gradually switching off.