Ice cauldron

Their surface areas reach from some meters (as indentations or holes in the ice) to up to 1 or more kilometers (as bowl shaped depressions).

When an eruption takes place under a bigger glacier, e.g. an ice cap, it normally begins with an effusive stage.

"At this stage, the surface ice begins to act brittle and creates concentric fractures that cave in towards the meltwater reservoir.

"(…) hydrothermal systems are created that bring heat up from a magma body, continuously melting ice into water that may be stored at the glacier bed until it breaks out in jökulhlaups".

Katla is an important caldera and central volcano situated under the Mýrdalsjökull glacier cap in the southern part of Iceland's East Volcanic Zone.

[8] Within the caldera 12–17 ice cauldrons are supra- and inglacial manifestations of a near-surface magmatic storage system.

[8] K. Scharrer explains that "twenty permanent and 4 semi-permanent ice cauldrons could be identified on the surface of Mýrdalsjökull indicating geothermally active areas in the underlying caldera".

It is still subject of discussion if they were eruption caused or initiated by heating up of the geothermal areas under these cauldrons.