Global Volcanism Program | Image GVP-05771
The most prominent of a series of fissures extending NE and SW from Grímsvötn central volcano is the noted Laki (Skaftár) fissure, which trends vertically across the photo SW of Grímsvötn. Laki produced the world's largest known historical lava flow during an eruption in 1783. However, most of Grímsvötn, Iceland's most frequently active volcano during historical time, lies beneath the vast Vatnajökull icecap. The caldera lake is covered by a 200-m-thick ice shelf, and only the southern rim of the 6 x 8 km caldera is exposed.
Photo by Sigurdur Thorarinsson (courtesy of Richard Williams, U.S. Geological Survey).