Pockmarks are craters in the seabed

Seabed

The seabed is the bottom of the ocean.- Ocean structure :Most of the oceans have a common structure, created by common physical phenomena, mainly from tectonic movement, and sediment from various sources...

 caused by fluids (gas and liquids) erupting and streaming through the sediments. Pockmarks were discovered off the coasts of Nova Scotia

Nova Scotia

Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...

, Canada in the late 1960s by Lew King and Brian McLean of the Bedford Institute of Oceanography

Bedford Institute of Oceanography

The Bedford Institute of Oceanography is a major Canadian government ocean research facility located in Dartmouth in the Halifax Regional Municipality in Nova Scotia. The Bedford Institute of Oceanography is the largest ocean research station in Canada...

. As pockmarks are uncommon on the land surface, they were not expected in the ocean. They were discovered off Nova Scotia, using a new side scan sonar developed in the late 1960s by Kelvin Hughes.

The craters off Nova Scotia are up to 150 m in diameter and 10 m deep. Pockmarks have been found worldwide. Discovery was aided by the use of high-resolution multibeam acoustic systems for bathymetric mapping. In these cases, pockmarks have been interpreted as the morphological expression of gas or oil leakage from active hydrocarbon

Hydrocarbon

In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

 system or a deep overpressured petroleum reservoir.