Possible Cause of Plumes from Bennett Island, Soviet Far Arctic
James W. Clarke, Pierre St. Amand, Michael Matson
Since 1974, NOAA satellites have shown more than 150 plumes coming from the vicinity of Bennett Island in the Soviet far Arctic (long. 149°3^primeE, lat. 76°7^primeN). These plumes, which may be hundreds of kilometers long and as much as 30 km wide at the origin, start and end abruptly. Multiple sources occur. Infrared imagery indicates that the plumes are as cold as -45°C.
The geologic section on Bennett Island suggests that the region is gas prone. Lower Cretaceous sedimentary and volcanic rocks lie unconformably on Cambrian-Ordovician sedimentary rocks. At the base of the Cretaceous is a 20-m thick section of sandstone, dark shale, and coal beds.
Bennett Island is now 500 km from mainland Siberia; however, during most of the last 5 m.y., it was part of the mainland, and the nearest sea was 350 km north. Permafrost would have developed throughout this entire area. Within this permafrost zone, methane derived from the Cretaceous coal beds would have gone into the hydrate form.
With the relatively recent melting of the great continental ice sheets and accompanying rise in sea level, the region around Bennett Island has been covered by tens of meters of water. Permafrost and associated hydrates are unstable under such conditions and have begun to break up.
We propose that methane, released by breakup of the permafrost and accompanying hydrate, escapes periodically into the atmosphere, expands adiabatically, and in the process entrains particles of hydrate, water, and clay. These particles cause condensation of atmospheric moisture, forming the plumes that are observed by the satellites.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.