A new island emerged from the ocean offshore of the city of Gwadar, Pakistan, after a strong magnitude-7.7 earthquake shook the country Sept. 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.
On September 26, 2013, NASA’s Earth Observing-1 (EO-1) satellite captured this image of a new island off the coast of Pakistan. The “mud island” rose from the seafloor near Gwadar on September 24, shortly after a magnitude 7.8 earthquake rattled the Balochistan province of northwestern Pakistan.
This image shows the same area on April 17, 2013.
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.
In this photo released by the Gwadar local government office on Wednesday, Sept 25, 2013, people walk on an island that reportedly emerged off the Gwadar coastline in the Arabian Sea.
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.
The highest intensity shaking is marked in orange, near the epicenter of the Sept. 24 Pakistan earthquake.
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.
"We will need to wait until the morning to know. 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.