Cause

Mudflow, photo taken on July 21 2006

There is controversy as to what triggered the eruption and whether the event was a natural disaster or not. According to one side, mainly PT Lapindo Brantas, it was the May 2006 earthquake that triggered the mud flow eruption, and not their drilling activities. Two days before the mud eruption, an earthquake of moment magnitude 6.3 hit the south coast of Central Java and Yogyakarta provinces killing 6,234 people and leaving 1.5 million homeless. At a hearing before the parliamentary members, senior executives of PT Lapindo Brantas argued that the earthquake was so powerful that it had created deep underground faults, allowing the mud to flow thousands of meters away, and that their company presence was coincidental, which should exempt them from paying compensation damage to the victims. If the cause of the incident is natural, then the government of Indonesia has the responsibility to cover the damage instead. This argument was also recurrently echoed by Aburizal Bakrie, the Indonesian Minister of Welfare at that time, whose family firm controls the operator company PT Lapindo Brantas.

Geologists disregarded the natural cause and mentioned that the earthquake is merely coincidental. The earthquake could have generated a new fracture system and weakened strata surrounding the Banjar-Panji 1 well, but it does not support the formation of a hydraulic fracture to create the main eruption vent 200 m away from the borehole. Apart from that, there was no other mud volcano reported on Java after the earthquake and the main drilling site is 300 km (186.5 miles) away from the earthquake's epicenter. The intensity of the earthquake at the drilling site was estimated to have been only magnitude 2 on Richter scale, the same effect as of a heavy truck passing over the area