A new island emerged from the ocean offshore of the city of Gwadar, Pakistan, after a strong magnitude-7.7 earthquake shook the country on the morning of September 24.
The mound appears to be 20 to 40 feet (6 to 12 meters) high and 100 feet (30 m) wide, DIG Gwadar Moazzam Jah, a district police officer, told Pakistan's Geo News. It rose out of the sea at a spot located about 350 feet (100 m) from the coast, he said.
The news sparked lively chatter among geologists, who debated whether the hill was a landslide, a fault scarp or even a hoax. A fault scarp marks vertical displacement along a fault, anything from a small step to a huge, steep cliff.
Scientists are still far from consensus, but many think that Pakistan's newest piece of land may be a mud volcano.
Geologist Bob Yeats, an expert on Pakistan's earthquake hazards, said he's waiting until he hears from his colleagues in Pakistan (it's currently night there) before judging the case. The two most likely possibilities are a landslide or a mud volcano, Yeats told LiveScience's OurAmazingPlanet.
Yeats said Gwadar is several hundred kilometers southwest of the earthquake's epicenter, making it highly unlikely that the new island is a fault scarp.
"[The island] is a long way from where they reported the earthquake. We're looking at two different things," said Yeats, an emeritus professor at Oregon State University.
A mud volcano is a likely possibility because Gwadar's coastline already has several of the gurgling, steamy cones, both onshore and at sea. One suddenly popped up where sea level was 30 to 60 meters (100 to 200 feet) deep on Nov. 26, 2010, creating an island. NASA satellites snapped a photo of the birth. [7 Ways the Earth Changes in the Blink of an Eye]
And in 1945, the magnitude-8.1 Makran temblor triggered the formation of mud volcanoes offshore of Gwadar, according to a study on mud volcanoes in Pakistan published in 2005. A recent study in the journal Nature Geoscience also suggests the 1945 earthquake released tons of methane from the seafloor.
Get ready to rumble
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.