A spectacular 20 m-thick columnar-jointed rhyolite lava flow at Bláhnúkur, Torfajökull. Columnar joints indicate that the lava flowed within a steep-walled tunnel melted into the glacier base during the late stages of the subglacial eruption.

This image was provided by Hugh Tuffen, Lancaster University.

References

Tuffen H, Gilbert JS, McGarvie DW (2001) Products of an effusive subglacial rhyolite eruption: Bláhnúkur, Torfajökull, Iceland. Bulletin of Volcanology, 63,179-190.

Tuffen H (2001) Subglacial rhyolite volcanism at Torfajökull, Iceland. Unpublished PhD thesis, Open University, UK.