Global Volcanism Program | Image GVP-11195
An ash plume rises from a new crater near the southern margin of Grímsvötn caldera in November 2004. Grímsvötn, Iceland's most frequently active volcano in historical time, lies largely beneath the vast Vatnajökull icecap. The 6 x 8 km wide caldera is the source of frequent jökulhlaups (glacier outburst floods) produced when melting raises the water level high enough to lift its ice dam. Long NE-SW-trending fissure systems extend from the central volcano, including the noted Laki (Skaftar) fissure, which erupted in 1783.
Photo by Freysteinn Sigmundsson, 2004 (Nordic Volcanological Center).