Mud volcanoes are formed when a combination of mud, fluid, and gas erupts on the Earth’s surface.
On May 29, 2006, rice farmers living in Sidoarjo Regency, Indonesia, woke up to a bizarre sight. The ground where they lived had cracked open overnight and was spewing steam.
In the following weeks, water, hot mud, and natural gas were added to the mix erupting onto the surface. As the eruption intensified, the mud began to spread across the fields. Alarmed residents evacuated, hoping the eruption would quickly come to an end.
But it did not stop. Weeks passed, and the mud spread, engulfing entire villages. In a frantic race against time, the Indonesian government began constructing levees to contain the mud and prevent its spread. As the mud overflowed these levees, they built new ones behind the first line. The government ultimately succeeded in halting the advance of the mud, but not before the flows had swept away dozens of villages and forced 60,000 people to relocate.
Why did the Earth suddenly “vomit” such a massive amount of mud?
Mud, fluid, and gas erupting on the Earth’s surface.
Overview of Mud Volcanoes
The Lusi structure – a shorthand for Lumpur Sidoarjo – is an example of a geological feature known as a mud volcano. They form when a combination of mud, fluid, and gas erupts on the Earth’s surface. The term “volcano” is borrowed from the traditional concept of volcanoes, where molten rock layers rise to the surface.
In the case of mud volcanoes, the mud is often pushed to the surface quite quietly. However, sometimes the eruptions can be quite violent. Furthermore, most gases emitted from mud volcanoes are methane, which is highly flammable. This type of gas can ignite, leading to dramatic and intense eruptions.
Mud volcanoes are not common in Europe and North America but are prevalent in many other regions, not only Indonesia but also Azerbaijan, Trinidad, Italy, and Japan.
They form when fluids and gases accumulate under pressure within the Earth’s core and find a way to escape to the surface through a network of fractures. The fluids move up these fractures, carrying mud with them, creating a mud volcano as they erupt.
You can think of this similarly to a tire filled with compressed air. As long as the tire remains intact, the air stays safely inside. However, when the air finds an escape route, it begins to leak out. Sometimes the air escapes as a slow leak, and in other cases, we witness a strong hiss.
The impact of the mud volcano in Sidoarjo has spread to 7 square kilometers.
When fluids flow underground within the Earth, they often cannot escape under the weight of the overlying sediment. Some of these fluids may have been trapped in the sediments as they were deposited. Other fluids can migrate in from deeper sediments, while others may be generated in place by chemical reactions within the sediments. Some important chemical reactions produce oil and natural gas. Ultimately, fluids can become over-pressurized if they are squeezed by tectonic forces during mountain formation.
Over-pressurization is also commonly encountered during oil and gas drilling, but these are usually planned in advance. A primary way to manage this excessive pressure is to fill the drill hole with dense drilling mud, heavy enough to suppress the excess pressure.
However, if wells are drilled with insufficient drilling mud, any fluid under excessive pressure can surge up the wellhead and erupt onto the surface. Famous examples include the Spindletop geyser incident in Texas (USA) in 1901 and the Deepwater Horizon disaster in 2010 in the Gulf of Mexico. In those cases, oil, not mud, erupted from the well causing explosions.
Scientifically speaking, mud volcanoes are seen as windows into fascinating information about everything deep within the Earth. Mud volcanoes can bring up materials from depths of 10 km below the Earth’s surface. Thus, their chemical composition and temperature can provide valuable insights into processes occurring deep inside the Earth, information that we cannot obtain in any other way.
For instance, analyzing the erupted mud from Lusi revealed that the water was heated by a magma chamber underground associated with the Arjuno-Welirang volcanic complex nearby.
The Lusi Mud Eruption Continues
Homes submerged by the flow of mud, forcing 60,000 people to evacuate.
Today, over 16 years after the eruption began, the Lusi structure in Indonesia continues to erupt, though at a much slower rate. Its mud has covered a total area of approximately 7 square kilometers, which is larger than 1,300 football fields, and is contained behind a series of levees built to a height of 30 meters. Nearly 180,000 cubic meters of mud have been erupted, and this process is expected to continue for the next 30 years.
Interestingly, alongside this natural phenomenon, there have been legal battles to assign blame for the disaster. The initial eruption occurred near a gas exploration well being drilled at a depth of 200 meters, leading to accusations that the oil company was responsible for the incident. The well operator, oil exploration company Lapindo Brantas, argued that the eruption was natural, caused by an earthquake that occurred a few days earlier.
Those who believe the gas well caused the eruption argue that the drilling operation led to an eruption due to insufficient mud weight to control pressure, but then the eruption did not travel directly to the surface. Instead, the fluid only rose partway up the well before being pumped into one of the geological fractures and erupting on the surface several hundred meters away. Furthermore, they argue that the earthquake was too far from the well to have any effect.
An employee in Sidoarjo testing the water temperature near the Lusi mud volcano in 2011.
Conversely, proponents of the earthquake cause believe that the Lusi eruption was due to an active hydrothermal system beneath the surface. They argue that such systems have a long history, influenced by earthquakes that occurred far away, thus claiming that Lusi being too far from the earthquake is invalid.
Moreover, they suggest that a pressure test in the well conducted after the eruption began showed that the drilling well remained intact, not broken due to fractures or fluid leaks. At the same time, there was no evidence that any drilling mud had escaped from subsequent eruptions.
In 2009, the Indonesian Supreme Court dismissed a lawsuit alleging the company acted negligently. That same year, police dropped criminal investigations into Lapindo Brantas and some of their staff, citing a lack of evidence. Although the lawsuits have been resolved, the debate among researchers continues.
