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Askja Volcano, Iceland
Askja is a large central volcano that forms the Dyngjufjoll massif.
It is truncated by three calderas, the largest of which is 8 km wide.
This view from the SE looks across Oskjuvatn lake, which fills the youngest caldera.
It formed in 1875 during Askja's largest historical eruption and truncates a larger caldera, whose wall is seen in the distance above the lava-covered caldera floor.
The 100-km-long Askja fissure swarm, which includes the Sveinagja graben, is also related to the Askja volcanic system.
Askja is a large basaltic central volcano that forms the Dyngjufjoll massif.
It is truncated by three overlapping calderas, the largest of which is 8 km wide and may have been produced primarily from subglacial ring-fracture eruptions rather than by subsidence.
A major rhyolitic explosive eruption from Dyngjufjoll about 10,000 years ago was in part associated with the formation of Askja caldera.
Many postglacial eruptions also occurred along the ring-fracture.
A major explosive eruption on the SE caldera margin in 1875 was one of Iceland's largest during historical time.
It resulted in the formation of a smaller 4.5-km-wide caldera, now filled by Oskjuvatn lake, that truncates the rim of the larger central caldera.
The 100-km-long Askja fissure swarm, which includes the Sveinagja graben, is also related to the Askja volcanic system, as are several small shield volcanoes such as Kollatadyngja.
Twentieth-century eruptions at Askja have produced lava flows from vents located mostly near Oskjuvatn lake.
PHOTO SOURCE: Michael Ryan, 1984 (U.S. Geological Survey), courtesy of the Global Volcanism Program, Smithsonian National Museum of Natural History, used with permission.
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