Seismic Studies of Giant Pockmark-like Features in Southern Chatham Rise, New Zealand

Methane is one of the most aggressive greenhouse gases driving climate change. Occurrence of marine gas hydrates depends on temperature, pressure, available gas and fresh water. Therefore changes in pressure and bottom water temperature will influence the formation or dissolution of gas hydrates. In general both parameters vary slowly and hence changes do not result in large Methane contribution to the atmosphere. An exception could be a sudden dissolution of larger quantities of gas hydrate with a related expulsion of Methane. Such focused fluid flow appears as funnel-shaped depressions at the seafloor, so called “pockmarks”. Typical dimensions are within a few hundreds of meters. However, five to twelve kilometre wide “giant pockmarks” (GP) are known as well. The mechanism of formation of GPs is not fully understood. New 2D and 3D multichannel seismic data have been acquired across two fields of giant pockmark-like features to better understand the formation of these depressions and potential for catastrophic methane release in the past.