Pockmarks are concave, crater-like depressions on seabeds that are caused by fluids (liquids and gasses) escaping and erupting through the seafloor. They can vary in size and have been found worldwide. Pockmarks were discovered off the coasts of

Nova Scotia Nova Scotia ( ; ; ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. Nova Scotia is Latin for "New Scotland". Most of the population are native Eng ...

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

Bedford Institute of Oceanography The Bedford Institute of Oceanography (BIO) is a major Government of Canada ocean research facility located in Dartmouth, Nova Scotia. BIO is the largest ocean research station in Canada. Established in 1962 as Canada's first, and currently la ...

, using a new

side scan sonar Side-scan sonar (also sometimes called side scan sonar, sidescan sonar, side imaging sonar, side-imaging sonar and bottom classification sonar) is a category of sonar system that is used to efficiently create an image of large areas of the sea ...

developed in the late 1960s by

Kelvin Hughes Hensoldt UK, formerly Kelvin Hughes, is a British company specialising in the design and manufacture of navigation and surveillance systems and a supplier of navigational data to both the commercial marine and government marketplace. The company ...

. Before the two researchers King and McLean used the side scan sonar, they had noticed 'notches' on echo sounder and shallow seismic records in the seafloor off Nova Scotia. They believed these notches to represent gullies and curvilinear troughs in the muddy seafloor. However, they could never work out how to join these notches from one survey line to the next. It was, therefore, not before they surveyed with the area-coverage system, Side scan sonar, that they realized the notches were in fact closed depressions (craters) and not curvilinear features. This was a great surprise, because there are very few craters on the Earth's surface. Although pockmarks were first documented and published 50 years ago, they are currently still being discovered on the ocean floor and in many lakes, the world over. Spatial delineation and morphometric characterisation of pockmarks in the central North Sea seabed have been achieved by semi-automatic methods. The craters off Nova Scotia are up to in diameter and 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 In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...

system or a deep overpressured

petroleum reservoir A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations. Such reservoirs form when kerogen (ancient plant matter) is created in surrounding rock by the presence ...

. Specifically, long term deep fluid flow resulting in pockmarks is linked to undersea methane gas escape under pressure.Chand et al (2017) Long-term fluid expulsion revealed by carbonate crusts and pockmarks connected to subsurface gas anomalies and palaeo-channels in the central North Sea Geo-Mar Lett (2017) 37:215–227 DOI 10.1007/s00367-016-0487-x

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Sedimentology Oceanography Lakes {{geology-stub

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