Anatomy of the ?Lusi? Mud Eruption, East Java

Abstract

Early in the morning of the 29th of May 2006, hot mud started erupting from the ground in the densely populated Porong District of Sidoarjo, East Java. With initial flow rates of ~5000 cubic meters per day, the mud quickly inundated neighbouring villages. After almost four years, the ?Lusi? eruption has expelled over 73 million cubic meters of mud at an average rate of approximately 64000 cubic meters per day and at maximum rates of 170000m3/day. The mud flow has now covered over 700 hectares of land to depths of over 25 meters, engulfing a dozen villages and displacing approximately 40000 people. In addition to the inundated areas, other areas are also at risk from subsidence and distant eruptions of gas. However, efforts to stem the mud flow or monitor its evolution are hampered by an overall lack of knowledge and consensus on the subsurface anatomy of the Lusi mud volcanic system. In particular, the largest and most significant uncertainties are the source of the erupted water (shales versus deep carbonates), the fluid flow pathways (purely fractures versus mixed fracture and wellbore) and disputes over the subsurface geology (nature of deep carbonates, lithology of lithological unit between shales and carbonates). This study will present the first balanced overview of the anatomy of the Lusi mud volcanic system with particular emphasis on these critical uncertainties and their influence on the disaster.