Giant sea-bed pockmarks; evidence for gas escape from Belfast Bay, Maine

Circular depressions, or pockmarks, cover the sea floor in many estuarine regions of the western Gulf of Maine. In Belfast Bay, Maine, they are found in densities up to 160/km2, are up to 350 m in diameter and 35 m in relief, and are among the largest and deepest known. The pockmarks appear to form...

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Bibliographic Details
Published in:Geology (Boulder) 1994-01, Vol.22 (1), p.59-62
Main Authors: Kelley, Joseph T, Dickson, Stephen M, Belknap, Daniel F, Barnhardt, Walter A, Henderson, Mark
Format: Article
Language:English
Subjects:
acoustical methods
aliphatic hydrocarbons
alkanes
Atlantic Ocean
Belfast Bay
Brackish
cores
density
estuarine environment
gases
Geology
geophysical methods
geophysical profiles
geophysical surveys
Gulf of Maine
hydrocarbons
Maine
Marine
methane
Natural gas
North Atlantic
ocean floors
Oceanography
organic compounds
organic materials
pockmarks
pore water
reflection
sediment transport
seismic profiles
surveys
United States
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Summary:Circular depressions, or pockmarks, cover the sea floor in many estuarine regions of the western Gulf of Maine. In Belfast Bay, Maine, they are found in densities up to 160/km2, are up to 350 m in diameter and 35 m in relief, and are among the largest and deepest known. The pockmarks appear to form from the escape of biogenic natural gas and pore water and are far larger than features associated with thermogenic gas elsewhere. These pockmarks are thought to have formed (1) catastrophically during an earthquake, tsunami, or storm, or (2) slowly over thousands of years. Recent observations of bubble releases suggest continuing activity and a potential geologic hazard. The pockmarks involve a poorly documented coastal process of sediment redistribution and methane release, largely unrecognized in the rock record but widespread in middle- to high-latitude embayments.
ISSN:0091-7613
1943-2682
DOI:10.1130/0091-7613(1994)022<0059:GSBPEF>2.3.CO;2