Synopsis of the June 13, 2014, Friday night lecture given by Dr. Maxwell Rudolph, assistant professor, PSU Geology Department
Ever since the mud started spewing from the Lumpur Sidoarjo (aka “Lusi”) mud volcano in the subdistrict of Porong, Sidoarjo on East Java Island, Indonesia, on May 29, 2006, an opportunity to study the feature and, fortunately or unfortunately, become embroiled in the political controversy over it opened in the geological community. Newly appointed Assistant Professor Maxwell Rudolph of Portland State University was involved in studies related to this phenomenon during his doctoral years at UC Berkeley ending in 2012, and spoke to GSOC at the June Friday night lecture describing his work.
Lusi is the world’s largest mud volcano, and at its peak it discharged 180,000 cubic meters of mud per day, and the current discharge is 10,000 cubic meters per day. The Lusi volcano inundated an area of several square kilometers within a mixed use suburban area, and the mud has destroyed the homes and livelihood of thousands of people, with damage and cleanup costs estimated to exceed $1 billion.
Two incidents occurred immediately prior to the eruption which ignited the controversy over its origin. On May 27, 2006. a MM6.3 Yogyakarta earthquake occurred more than 250 km away to the southwest of the eruption site. Also, on May 28, 2006, a PT Lapindo Brantas gas exploration well being drilled at a distance of 200 meters from the eruption site produced a “kick” or blowout. It is significant that the well was nearly 3 kilometers deep with only the top 1100 meters of the well having steel casing.
The drilling company subsequently blamed the mud volcano on the earthquake and claimed that their drilling activity was coincidental to the eruption of the nearby mud. Rudolph’s research group, advised by Michael Manga of UC Berkeley and in collaboration with a team of American and international geologists, got involved to work out the mechanics of naturally produced mud volcanoes and ascertain what sort of earthquake event might produce mud volcano activity.
The studies done by the research team focused upon a group of mud volcanoes produced by seismic and geothermal activity associated with the terminus of the San Andreas fault beyond the southeastern margin of the Salton Sea in California. Here lacustrine and deltaic deposits are underlain by relatively shallow heat sources, so that hot mud and gaseous emissions create a group of mud eruptions. Shortly after the study began, a major earthquake, the April 4, 2010 El Mayor-Cucapah MM7.2 Earthquake, produced strong shaking in the area. Several smaller quakes hit the area during the study as well, and enabled the research group to measure the heightened activity of the mud eruptions immediately following the earthquakes and compare it with normal eruptive activity.
In the Salton Sea mud volcanoes, a definite relationship was found between earthquake shaking and mud eruptions. The researchers measured gaseous output from the mud eruptions as well as counting the number of fresh eruptions in the field. These output results were plotted on a seismic energy density contour map, this being a function which combines the magnitude of the quake and the distance from the quake. They found that there is a seismic energy density threshold below which the earthquake shaking did not result in eruptive activity for the study site. Several smaller earthquake events during the study did not have a noticeable effect on the mud volcanoes. They also noted that duration of shaking and frequency response of the earthquake affected the mud volcanic output. The researchers also compiled a database of earthquake triggered mud volcano eruptions worldwide which were plotted on the graphs.
And how can these results be used to compare the mud volcanoes at the Salton Sea to the Lusi volcano? The ground shaking relationships with mud volcano output suggested that the Yogyakarta earthquake did not produce enough shaking at the site of the Lusi eruption to be a causal factor. No other mud volcanoes erupted as a result of this earthquake, either.
In addition to the field measurements the research team analyzed the gaseous discharge and studied the mud’s mechanical responses to stress (i.e., its rheological properties). They looked at the mechanisms that the conduits of the mud volcano had for conveying the mud to the surface. They believe that the main mechanism leading to a mud eruption is an increase in the permeability of the overburden, effectively “unclamping” the conduits to the surface, as well as bubble propagation which is stimulated by ground shaking.
The geology of the Lusi mud volcano is somewhat different than that of the Salton Sea mud volcanoes as the mud source is a bit deeper. Marine carbonates and muds are folded into an anticline that has been over-pressured since the Miocene. Scientists who support the idea that the drilling produced the mud volcano believe that the pressure at the drilling depth exceeded the ability of the uncased well sides to withstand it, causing the observed “kick” and a chain reaction of fracturing in the mud strata resulted, which propagated to the surface. Several studies, which both support and refute this idea, have been put forth and analyzed by the scientific community.
What will happen to the Lusi mud volcano in the future? Currently the mud is being contained by levees constructed around an area of several square kilometers and excess mud is being drained off into a manmade river nearby and sent out to the coast, with the associated environmental degradation implied by that scheme. The discharge has been decaying so that by 2017 it is expected to drop below 1000 cubic meters per day. There has been measurable ground subsidence in the area surrounding the mud volcano and gas well which reflects the evacuation of the mud from the source chamber below. Some reparations have been paid to the victims but they only have amounted to a fraction of the damages.
Other studies are being conducted to better understand the eruption of mud volcanoes. They are found at plate boundaries throughout the world, usually underwater. Rudolph cited studies at the most violent of mud volcanoes in Azerbaijan and a newly formed mud island off the coast of Pakistan. Hopefully the knowledge gained in the study of these eruptions will be put to responsible use in preventing events like those that created Lusi.
References and Additional Reading
Wikipedia: Sidoarjo_mud_flow web page has good background on the Lusi mud volcano.
Cyranoski, D. (2007). Indonesian eruption: Muddy waters. Nature, 445(7130), 812–815. doi:10.1038/445812a
Davies, R., Swarbrick, R., & Evans, R. (2007). Birth of a mud volcano: East Java, 29 May 2006. GSA Today, 17(2), 4–9.
Maxwell Rudolph publication page includes links to many of his articles.
Rudolph, M.L., Tingay, M., Manga, M., Davies, R.J., Wang, C.-Y. The Lusi mud eruption was not triggered by an earthquake. Comment submitted to Nature Geoscience.