Alan Judd

Gas Emissions from Mud Volcanoes

There are about 1,000 mud volcanoes on land and 5,500 offshore — mostly in deep water. Activity varies between gentle emissions and violent eruptions accompanied by the release of enormous volumes of gas — mainly (85%+) methane and carbon dioxide. Global gas emissions are provisionally estimated to exceed 27 billion cubic metres per year, of which more than 23 billion (15.8 Tg) is methane. More than 70% of this is from short-lived eruptions, about 30% of which ignite to produce flames tens or hundreds of metres high. The majority of the methane is emitted by submarine mud volcanoes, most in deep water. About 11.4 Tg per year is lost to the hydrosphere, but a tentatively estimated 3.6 Tg per year escapes to the atmosphere. So, mud volcanoes are significant sources of atmospheric methane, much of it ‘fossil’. Contributions are thought to increase when sea level is low (in glaciations), providing negative feedback to global warming and working to limit climatic extremes.

Evaluating the Hazard Potential of Pockmarks

Shallow crater-like depressions called pockmarks are known to occur in many parts of the world. Interest in pockmarks has been aroused by uncertainty of their exact mode and rate of formation, and the possibility that they might pose a threat to offshore installations. The current understanding of pockmarks is reviewed and the apparent correlation between pockmark formation and sediment type is discussed, as are the problems involved in the accurate mapping of these features.