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Monday Noon Seminar - Evidence for subglacial volcanic activity beneath the West Antarctic Ice Sheet

Monday, March 02, 2015, 12:00PM - 1:00PM


John Behrendt



ARC room 620

Full title

Modeled aeromagnetic anomalies, controlled by radar ice sounding as evidence for subglacial volcanic activity in the West Antarctic Rift System (WR) beneath the West Antarctic Ice Sheet (WAIS)


The Amundsen Sea ice shelves (e.g. Pine Island and Thwaites), buttressing the WAIS, have passed a turning point as they are thermally eroded by warm deep ocean waters (Joghin et al., 2014; Rignot et al., 2014). These authors concluded WAIS disintegration is inevitable in ~200-900 years from this process. A comprehensive, 21-year analysis of this fastest-melting region of Antarctica has found that the melt rate of glaciers there has tripled during the last decade (Sutterly et al., 2014).

Also, there is increasing geophysical and glaciological evidence for subglacial volcanic activity that could speed up the process of disintegration of the WAIS flowing through the WR. Aeromagnetic, radar ice–sounding, high heat flow, and seismicity are used here to provide evidence for volcanic rocks beneath the WAIS. Late Cenozoic alkaline volcanic rocks are exposed throughout the area. Some volcanoes are active.

The 5-km, orthogonally line-spaced, central West Antarctica (CWA) aeromagnetic and radar ice sounding 1990s survey defined >400 high amplitude volcanic magnetic anomalies correlated with glacial bed topography. Modeled anomalies defined magnetic properties. Interpreted volcanic edifices were mostly removed by the moving ice into which they erupted. Very high apparent susceptibility contrasts (.001->.3 SI) are required to fit the anomalies. About 18 high relief, (~600-2000 m) “volcanic centers” beneath the WAIS surface, probably were erupted subaerially when the WAIS was absent; nine of these are in the general area beneath the divide of the WAIS. A 70-km wide, ring of interpreted subglacial volcanic rocks may define a volcanic caldera underlying the WAIS divide (Behrendt et al., 1998). Powell et al. (2014) interpret CWA aerogravity data as consistent with the caldera inference. A 2-km high subaerially erupted volcano (subglacial Mt Thiel) ~ 100 km north of the WAISCORE, could be the source an ash layer observed in the core (Dunbar et al., 2012). Fisher et al. (2014) reported directly measured geothermal heat flux of 285+/- 85 W/m2 from beneath subglacial Lake Whillans. They suggested a melt rate of a few cm/yr, which is higher than the value of 230 W/m2 reported by Clow, (2013), for the WAIS Core. Lough et al. (2014) used observations of hundreds of small seismic events in the crust beneath the West Antarctic Ice Sheet to infer current magma movement in a volcanic system beneath the ice, which may bring heat up to the rock–ice interface and thus affect ice flow. Tulaczyk and Hossainzadeh, 2011, modeled 4-5 mm/yr melting beneath a large area of the WAIS.

These various lines of evidence lead to the general interpretation that the ice divide area and other areas of the WAIS overlie present to recent subglacial volcanic activity that may have an influence on the past and future behavior of the WAIS.



Free and open to the public.