On Tuesday, a 7.7-magnitude earthquake struck a remote part of western Pakistan, killing more than 260 people and displacing hundreds of thousands. It also triggered formation of a new island off the coast, which has quickly become a global curiosity.
But scientists say the island won’t last long.
“It’s a transient feature,” said Bill Barnhart, a research geophysicist with the U.S. Geological Survey. “It will probably be gone within a couple of months. It’s just a big pile of mud that was on the seafloor that got pushed up.”
Indeed, such islands are formed by so-called mud volcanoes, which occur around the world, and Barnhart and other scientists suspect that’s what we’re seeing off the Pakistani coast.
News organizations have reported that the Pakistani island suddenly appeared near the port of Gwadar after the quake. The island is about 60 to 70 feet (18 to 21 meters) high, up to 300 feet (91 meters) wide, and up to 120 feet (37 meters) long, reports the AFP.
Media reports have located the new island at just a few paces to up to two kilometers off the coast of Pakistan. It is about 250 miles (400 kilometers) from the epicenter of the earthquake.
Map by National Geographic maps.
The island appears to be primarily made out of mud from the seafloor, although photos show rocks as well, Barnhart told National Geographic. He has has been studying images and media accounts of the new island from his lab in Golden, Colorado.
“It brought up a dead octopus, and people have been picking up fish on [the island],” he said.
A similar mud island appeared off Pakistan after a 2011 earthquake there, Barnhart said: “It lasted a month or two and then washed away.”
Though mud volcanoes have been seen elsewhere, they don’t always produce islands.
Such volcanoes were seen in California after a 2010 earthquake, Barnhart noted, when the tremors caused carbon dioxide to bubble up through the ground, but the result was “vigorous boiling,” not new islands.
Barnhart said Pakistani scientists will soon be measuring the new landmass to better understand how it formed.
People walk along the island that emerged after a 7.7 magnitude earthquake struck a remote part of Pakistan.
Photograph from Gwadar Government/AP
“We don’t know much about it so far,” he added. “We haven’t had a satellite pass over it yet to really identify it.”
Seismic waves from the quake likely caused some fluid material under the seafloor to expand, Barnhart said. The crust holding that pressurized fluid ruptured, and mud spewed up.
The whole process is similar to liquefaction, Barnhart said, which is when seismic waves turn normally solid layers of soil into a flowing fluid, often with disastrous results for the buildings and people above.
He was skeptical of media reports that the underlying fluid was methane hydrates.
“We don’t know exactly what this was, whether it was free methane, carbon dioxide, water, or some other kind of fluid,” he said. But methane hydrates are offshore in much deeper water, he said.
Although earthquakes have been known to radically reshape coastlines, the mud volcano off Pakistan is highly localized, Barnhart said. The epicenter was too far from the coast to cause any widespread changes, and the earthquake was the wrong type to cause big uplifts.
A 9.5-magnitude earthquake off Chile in 1960 pushed whole villages several feet up in the air. But that was from a dip-slip earthquake, when tectonic plates are colliding vertically.
This week’s Pakistan earthquake was a strike-slip type, meaning there was only movement horizontally.