"A reconnaissance flight over Bárðarbunga, the volcano where the first earthquakes were detected last month, shows that the ice over the caldera has fallen nearly 20 meters across an area about 7 kilometers long and 5 kilometers wide. This is a change in volume of 250 million cubic meters. The scientists at the University of Iceland attribute this shift to a movement of the base of the glacier rather than to melting. Magma has drained from a chamber under the glacier as it moves to the northeast and erupts onto the surface. As the chamber has emptied, the rock above it has shifted downward, carrying the glacier ice downward as well. This is the largest subsidence that has been observed in Iceland since measurements of the surface were begun over fifty years ago. This movement does not seem to be associated with geothermal activity at Bárðarbunga, or of a higher likelihood of an eruption there. A recent photo from a helicopter flight shows the large extent and relative shallowness of this cauldron (the technical term for these craters)."