dökkrautt

dökkrautt is a geological term used primarily in Icelandic geology to describe a collapsed cave or void within basaltic lava fields. The word derives from the Icelandic "dökk" meaning cave, combined with the suffix "-rautt," which denotes a result or derivative. In practice, a dökkrautt refers to a sudden collapse of a lava tube roof, often leaving a pit or cinder cone aboveground. The feature is most commonly found in regions that experienced continuous fluid lava flows, such as the dark lava fields surrounding Fagradalsfjall and the Oxararfjall area.

Formation of a dökkrautt begins when hydrothermal alteration weakens the structural integrity of a pre-existing lava tube. As surface water infiltrates the tube, it accelerates weathering of the surrounding rock, creating a thin, unstable roof. If the roof can no longer support its own weight, it collapses, resulting in a circular or irregular pit. The size of the collapse ranges from a few meters to over a hundred meters in diameter, and rockfall from the roof may create a secondary crater or ring.

Dökkrautt features are of interest to volcanologists because they preserve evidence of past volcanic activity and fluid dynamics of lava flows. They serve as natural laboratories for studying hydrothermal alteration, fracture patterns, and post-collapse erosion. Recent surveys conducted by the Icelandic Meteorological Office have mapped more than 120 documented dökkrautt sites, providing valuable data on the frequency and distribution of such features across the country.