Media playback is unsupported on your device Media caption Footage shows people flocking to see the new island, which oceanographer Dr Simon Boxhall describes as "quite extraordinary, but not unique"

Barely half an hour after they were jolted by a major earthquake on Tuesday, people of the Pakistani coastal town of Gwadar had another shock when they saw a new island emerge in the sea, just over a kilometre from the shore.

A local journalist, Bahram Baloch, received the news via a text message from a friend.

"It said a hill has appeared outside my house," Mr Baloch said.

"I stepped out, and was flabbergasted. I could see this grey, dome-shaped body in the distance, like a giant whale swimming near the surface. Hundreds of people had gathered to watch it in disbelief."

We could hear the hissing sound of the escaping gas Bahram Baloch, Local journalist

Mr Baloch and some friends landed on the island on Wednesday morning to check it out and to take pictures.

"It's an oval shaped island which is about 250ft to 300ft (76-91m) in length, and about 60 to 70ft above the water," he said

It has a rough surface, much of which is muddy and some parts are mostly made up of fine- to coarse-grained sand. One part of it is solid rock, and that is where Mr Baloch and his friends landed.

Image caption Observers embrace a rare opportunity to tread on land recently risen from the seabed

Image caption Some parts are composed of fine- to coarse-grained sand; whereas other sections appear to be solid rock

Image caption Seismic activity appears to have sparked the unusual land formation

Image caption Much of the new piece of land is muddy

Image caption Subsidence may erase the island again

"There were dead fish on the surface. And on one side we could hear the hissing sound of the escaping gas," Mr Baloch said.

Although they couldn't smell gas, they did put a match to the fissures from where it was oozing, and set it on fire.

"We put the fire out in the end, but it was quite a hassle. Not even the water could kill it, unless one poured buckets over it."

The story now doing the rounds in Gwadar is that a similar hill had jutted out of the sea 60 or 70 years ago, and that the elders had then named it the Zalzala Koh, or the quake hill.

They say Tuesday's earthquake has brought it back.

New island seen from space

Their story is not entirely incorrect. However the quake hill that appeared in 1945 was not near Gwadar, but over 100km to the east, although it was along the same coastline, which is called the Makran coast.

The island that popped up is the fourth in this region since 1945 Rashid Tabrez, Institute of Oceanography

About 700km from east to west, the Makran coast is characterised by high seismic activity, and is home to several hills called mud volcanoes, having craters at the top from which methane gas seeps.

These volcanoes are located inland, and have been there for a long time. But similar formations that emerge offshore are usually washed away by the sea.

Geologists say it is part of the continuing process of continental drift, or the drift of land mass across the oceans that brought the Indian sub-continent to collide with Eurasia and created the fault-lines, some of which run through the Makran coast.

Gas activation

Image caption Tuesday's earthquake shook Balochistan

Rashid Tabrez, the director-general of the Karachi-based National Institute of Oceanography, says the energy released by the seismic movements of these fault-lines activates inflammable gases in the seabed.

"The seabed near the Makran coast has vast deposits of gas hydrates, or frozen gas having a large methane content," he explained.

"These deposits lay compressed under a sediment bed that is 300m-800m thick."

"When the plates along the fault-lines move, they create heat and the expanding gas blasts through the fissures in the earth's crust, propelling the entire sea floor to the surface."

The island that popped up near Gwadar is the fourth in this region since 1945, and the third during the last 15 years, he said.

Image caption Mud volcanoes like Chandragup are formed as a result of gases from seismic activity on the coastal seabed

In 1999, and again in 2010, islands appeared within 1km of the coast of Ormara, just below the delta of the Hingol river.

One of the best known mud volcanoes of the region, the Chandragup, is located just inland from this location, a little way off the Hingol river.

Image caption Pilgrims give offerings to Chandragup's crater

The volcano serves as a holy site for Hindu pilgrims who make their offerings here in April each year before proceeding to the nearby cave temple of Hinglaj.

Mr Tabrez says the seismic activity in the coastal seabed has caused the gases to make conduits inland, leading to the formation of Chandragup and other mud volcanoes.

But while these inland volcanoes have sat along the Makran coast for centuries, the islands appearing in the sea hardly last more than a few months.

"One reason is that over a period of time, the pressure that propelled the sea floor to the surface eases up, causing the islands to subside," he says.

"Another reason is that the fine-grained muddy material of the sedimentary seabed soon starts to erode due to sea action. In seven or eight months, the island is gone, and only its signature remains on the seabed."