Abstract

If we want to understand how volcanoes behave we need to know what happens in the magma chambers that feed the eruptions. We can’t directly access the magma stored under active volcanoes but we can take a look at the deeply-eroded roots of ancient volcanoes. The east coast of Greenland is scattered with the remains of a vast outpouring of magma associated with the opening of the North Atlantic some 60 million years ago. The excellent exposure of the Skaergaard intrusion reveals a complex story of basalt magma trapped underground, with progressive solidification on the walls, roof and floor forming crystal mushy layers and a gradual change in the composition of the remaining magma. Detailed examination, both in the field and back in the lab, show how the process of fractionation actually works.