Mud volcanoes appear when sediments like silt and clay become pressurized by hot gas trapped underground. A subduction zone beneath Pakistan supplies the tectonic activity that heats and holds the gas. The Arabian and Eurasian tectonic plates collide offshore of Pakistan, forming a subduction zone, but today's earthquake was onshore and mostly strike-slip — each side of the fault moved horizontally.
Mud volcanoes burble up during earthquakes because the shaking releases mud and water that are trapped beneath barriers in seafloor sediments.
"For example, a clay or shale layer can be impermeable, but if fractured during an earthquake, could release mud and water that was under pressure below the layer. Or a water-rich clay layer could undergo liquefaction that would be released along fractures in the sediments," explained James Hein, a senior scientist with the U.S. Geological Survey in Santa Cruz, Calif. "Some think the island was there before the earthquake, and that would be very easy to check by looking at satellite photos of that area taken the week prior," he said.
But Geologist Dave Petley, a landslide expert, thinks the island's low, arcuate (or bow) shape — as seen in the few pictures released so far — suggests a rotational landslide, rather than a conical mud volcano. A rotational landslide moves along a rupture surface that is curved or concave, like the inside of a spoon.
At this point it is still too early. "It is really very strange, and the pictures are just too indistinct to be able to tell," said Petley, a professor at Durham University in the United Kingdom.
The Arabian Sea isn't the only spot on Earth to spout mud and gas when jiggled by earthquakes. In Japan, the town of Niikappu on the island of Hokkaido sports mud volcanoes that erupt after earthquakes, reports a study published in 1997 in the Journal of the Geological Society of Japan.
The world's most notorious mud volcano, Indonesia's Lusi, destroyed a town in 2006. It may have been caused by an earthquake or by drilling operations nearby.
Earthquakes also rattle geysers and real volcanoes. The 2002 Denali earthquake in Alaska changed the spurting schedule of Yellowstone National Park's famous geysers for several months. And seismic shaking can sometimes cause a surge in eruptions at nearby volcanoes after an earthquake.
Email Becky Oskin or follow her @beckyoskin. Follow us @OAPlanet, Facebook & Google+. Original article on LiveScience's OurAmazingPlanet.
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