pockmarks - gas emission structures at the seafloor
TRANSCRIPT
Large pockmarks on the Angola passive continental margin (Sahling, 2008)
Pockmarks are morphological features on the seafloor that have a bowl-like
shape, i.e. a shallow depression in the seafloor. They can be circular to oval and
span a wide range of sizes, from only several meters in diameter to over one
kilometer and from only few centimeters in depth to over 100 m. Having first been
discovered in the 1970s on the Scotian Shelf they have since been found on large
parts of the continental margins worldwide. This is due to improvements in
hydroacoustic methods such as the swath bathymetry echosouder allowing for
efficient high resolution mapping of the seafloor along with ever increasing
research and exploration activity in the world's oceans.
Pockmarks have been linked to gas escape from the seafloor since their
discovery. Theories about their formation include the sudden escape of a large
volume of gas (methane formed in organic-rich sediments), gas hydrate
dissociation leading to collapse structures as well as a constant bubble stream
escaping from the seafloor and preventing local sedimentation.
My PhD project deals with seepage features and their tectonic as well as
sedimentological setting on the West African passive continental margin. Gas
seepage there is linked to salt tectonic activity providing pathways like faults for
gas from depth to the seafloor, supplying seepage features including large scale
pockmarks. I apply a variety of geophysical methods in my study including
multichannel seismic data, high-frequency echosounder and swath bathymetry
echosounder systems.
Stefan Wenau, GLOMAR PhD-student
Pockmarks - gas emission structuresat the seafloor