Over on Jon Frimann's Iceland Volcano and Earthquake Blog, there has been a lot of talk about the activity under Vatnajökull (see map below), the largest glacier on Iceland and specifically near Grímsfjall/Grímsvötn. I thought I'd take a closer look at the great glacier of the island nation and specifically, the volcanic activity that occurs around and under the icecap (and then take my speculative stab at what might be going on near Grímsvötn).
Map of the Vatnajökull glacier, Iceland.
First things first: Vatnajökull is big (see below). Real big, at least as modern glaciers go. It covers 8100 km^2 of the landmass of Iceland with a maximum thickness around 1000 m (1 km) thick, but the average thickness is closer to 400-500 m, leading to a rough estimate of the total volume of ~3300 km^3 glacial ice. The glacier is still actively accumulating snow that will become glacial ice ...
