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Noon seminar - Volcanic rocks and subglacial volcanism beneath the West Antarctic Ice Sheet

Monday, March 05, 2012, 12:00PM - 1:00PM


John Behrendt



ARC room 620

Radar ice sounding and aeromagnetic surveys reported over the West Antarctic Ice Sheet (WAIS) have been interpreted as evidence of subglacial volcanic eruptions. Several active volcanoes have shown evidence of eruption through the WAIS and several other active volcanoes are present beneath the WAIS reported from radar and aeromagnetic data. Aeromagnetic profiles (>10,000 km) acquired in the early 1960s over the West Antarctic Ice Sheet (WAIS) combined with coincident aeromagnetic and radar ice sounding in 1978-79 and the 1990s indicated numerous high-amplitude, shallow-source, magnetic anomalies over a very extensive area (>500,000 km2) of the volcanically active West Antarctic rift system interpreted as caused by subglacial volcanic rocks. Five-kilometer spaced coincident aeromagnetic and radar ice sounding surveys since 1990 provide three-dimensional characterization of the magnetic field and bed topography beneath the ice sheet. These 5-50-km width, semicircular magnetic anomalies range from 100->1000 nT as observed ~1 km over the 2-3 km thick ice have been interpreted as evidence of subglacial eruptions. Behrendt et al, (2005, 2008) interpreted these anomalies as indicating >1000 "volcanic centers." More than 80% of these anomaly sources at the bed of the WAIS have been modified by the moving ice into which they were injected, requiring a younger age than the WAIS (about 25 Ma).

Although exposed volcanoes surrounding the WAIS extend in age to ~34 m.y., Mt Erebus, (<1 Ma) Mt. Melbourne, (<0.26 Ma), and Mt. Takahae (<0.1 Ma) are examples of exposed active volcanoes in the WAIS area. However, the great volume of volcanic centers is buried beneath the WAIS. If only a very small percentage of these >1000 volcanic, magnetic-anomaly sources are active today, or in the recent past, in the drainage area of the WAIS, subglacial volcanism may still have a significant effect on the dynamics of the WAIS. Interpreted active subglacial volcanism is revealed by aerogeophysical data reported by Blankenship et al., (1993, Mt. Casertz), and Corr and Vaughan, (2008, near Hudson Mts.), who raised the question of possible volcanic effects on the regime of the WAIS.

Magnetic data indicate a caldera and a surrounding broad low in the WAISCORE vicinity. High heat flow inferred from temperature logging in the WAISCORE (Clow 2012, personnel communication; Conway, 2011) and a prominent volcanic ash layer in the core (Dunbar, 2011, personal communication) are consistent with the magnetic data. A prominent subaerially erupted subglacial volcano, here named Mt Thiel, about 100 km distant, may be the source of the ash layer.

Even if there is a low probability, future effects on the stability of the WAIS and associated sea-level rise should not be ignored, as changes observed in the past 20 years resulting from global warming, could be accelerated by subglacial volcanism.