Right now there is a large outpouring of lava taking place at the Holuhraun lava field in Iceland, just to the north of the Vatnajökull ice sheet (http://tinyurl.com/k8xsdg5).
When lava pours out from beneath the ground, there is often a space problem. Large amounts of lava can’t easily pour out on the surface without leaving some space underground that is open, and the Earth doesn’t like open spaces. In Hawaii, this type of scenario created the huge Kilauea Caldera centuries ago. In Iceland today, we’re seeing collapse of the ground beneath the ice sheet.
This is a photo of Dyngjujökull, one of the outlet glaciers of the large ice cap. This photo was taken by the Iceland department of Civil Protection and Emergency Management on an overflight of this glacier, which sits just to the southwest of the eruption site. Here you see a large circular pit formed by subsidence; the ground beneath the glacier is literally moving down due to evacuation of the lava belowground. This type of subsidence is being observed at several craters including Bárðarbunga, where the seismic activity that preceded this eruption started. This crater is currently showing over 30 meters of subsidence.
From The Eruptions of Iceland’s Bardarbunga Volcano, one of 14 photos. An aerial picture taken on September 14, 2014 shows a small plane flying over the Bardarbunga volcano as it spews lava in southeast Iceland. The Bardarbunga volcano system has been rocked by hundreds of tremors daily since mid-August, prompting fears the volcano could explode. Bardarbunga, at 2,000 meters (6,500 feet), is Iceland’s second-highest peak and is located under Europe’s largest glacier, Vatnajoekull. (Bernard Meric/AFP/Getty Images)