J. Volc. Geotherm. Res. http://dx.doi.org/10.1016/j.jvolgeores.2011.12.008 (2012)
Volcanic eruptions beneath glaciers should rapidly melt the overlying ice, allowing lava to spew out unconfined. However, field observations from the Askja Volcano, Iceland, suggest an alternative: ice can rapidly chill intruding magma, preventing extensive ice melting.
Alison Graettinger at the University of Pittsburgh and colleagues studied the character of ancient basaltic dykes — intrusions of magma into overlying ice and sediments — that are exposed on the flanks of the once ice-covered Askja Volcano. Many of the dykes have sharply defined, glassy margins, yet their interiors are composed of mixed sediment, ash and magmatic rocks. The researchers suggest that the edges of the dykes were quickly chilled, forming the glassy margins and limiting further melting of ice or mixing with the surrounding sediment. In contrast, ice and sediments within the intruded region rapidly melted and mixed with the magma to form the diverse interior of the dyke.
Detection of similar dykes could be used to identify previously glaciated areas on Earth and Mars.
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Whitchurch, A. Magma on ice. Nature Geosci 5, 91 (2012). https://doi.org/10.1038/ngeo1397