Grímsvötn the water flooded volcano, located in Iceland, northwest side below Vatanjökull iceberg.
Grímsvötn eruptions are interesting in that way under the ice. Heat eruptions melted enough ice, which causes pressure and the subsequent outpouring of the enormous quantity of water from the lake. In 1996, floods destroyed part of the journey Hringvegur (circular road around Iceland). It is regularly monitored by the state of Volcanology volcano.
The lake is also interesting that in 2004 it discovered the bacterium, the first in a lake under the ice with very little oxygen.
(° source Wikipedia)