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Pakistan earthquake and mud volcano, 24-Sep-2013
At 4:30 in the afternoon (local time) on 24-Sep-2013, a magnitude 7.7 earthquake struck western Pakistan. The death toll is at least 350, most of which are in the Arawan district in the province of Baluchistan, though the quake was felt as far away as New Delhi. It also triggered eruption of a small mud volcano, forming a small new island of the south coast of Pakistan.
This is an area where the Indian plate is sliding past the Eurasian plate, which makes up much of western Pakistan. The rocks on either side of this boundary are stuck by friction most of the time, but eventually the stress builds up to the point where the rocks slip, causing an earthquake. In 1935, there was a large earthquake (magnitude 7.5) on this same fault, just to the north. That earthquake occurred closer to more densely populated areas and killed tens of thousands of people.
There are many steps that we can take to prepare for earthquakes. One of the most important is to build our homes, schools, and other buildings to be earthquake-resistant. It is the collapse of poorly built buildings that gives rise to a disaster, not the earthquake alone.
There are other earthquake faults in this region. The Arabian plate is sliding under western Pakistan. In 1945, there was a magnitude 8.2 earthquake along this plate boundary that produced a tsunami many metres tall. Earlier this year (16-Apr-2013), a magnitude 7.8 earthquake in a neighboring region of Iran is also associated with this plate motion, but was much deeper. Exactly how these different kinds of plate motion, different earthquake faults, and different individual eathquakes interact with one another is an important topic of ongoing research.
Although we cannot predict earthquakes, we do know that this area has many active earthquake faults. We therefore know that there will be future earthquakes and that some of them will be large and damaging, even if we cannot say exactly when and where the next large earthquake will happen.
A mud volcano, triggered by the earthquake, creates a new island
After the 24-Sep-2013 earthquake, people living at the coastal city of Gwadar found a new island emerging from the sea about 400 km away from the epicenter. The local news claims that this tiny baby island is about 100 m wide and nearly 10 m high above sea level, where the flammable gas is bubbling out from its muddy surface.
The shape and the composition of this island, as well as the gas bubbling phenomena, suggest this island is created by the action of a mud volcano beneath the ocean. The current eruption was very likely triggered by the seismic wave from the earthquake nearly 400 km away.
A mud volcano is not related to molten rock, as the word ‘volcano’ might suggest. Instead, underground mud and fluids that are under pressure can periodically erupt. Eruptions can be triggered by earthquakes but can also occur on their own in sudden response to slower changes underground.
The paired images below are the satellite images before and after the magnitude 7.7 Pakistan earthquake taken by NASA’s Landsat-7 satellite at the western Gwadar area. This may be the first public satellite image that captured the shape of the new island from space. This tiny round island southwest of the coastline is visible on September 25, 2013 (right), but was absent in an earlier image on September 16, 2013, about a week before the earthquake (left).
The close look of the image (below) shows the diameter of the island is about 150 m, similar to the dimension reported from the local news.
Islands such as this one have appeared, then disappeared, in the past. Erupting mud adds new material, growing the island. But over time, wave action erodes the material away. Once the eruption stops, over time, wave erosion will cause the island to shrink and eventually disappear.
Just a few years ago, another offshore mud volcano island emerged about 340 km east of Gwadar. On November 26, 2010, Pakistani fishermen reported that a new island emerged about 3 km from the coast (below). NASA’s Earth Observing-1 (EO-1) satellite captured its image on January 11, 2011 and showing the mud was flowing out from the island (left image). This island did not last for long. In fact, the satellite image taken in July 9, 2011 by DigitalGlobal shows the island had been eroded away by wave action, with just a tiny trace remaining above sea level (image from Google Earth, on right).
The dimension of 2011 mud volcano is very similar to the mud volcano in 2013 offshore the Gwadar coast, about 160 meters in diameter.
For more information about the 2011 mud volcano, you can visit the NASA Earth Observatory webpage.