Rhyolite tuyas at Torfajökull, Iceland. The ridge in the foreground is composed of lava lobes, dykes and hyaloclastite, and was formed in a fissure eruption. The flat-capped mountains in the background are tuyas emplaced during the last two glacial periods. Tuya bases are at ~600 m elevation, and their summits reach 920-1200 m elevation.

This image was provided by Hugh Tuffen, Lancaster University.

Reference

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 Unpublished PhD thesis, Open University, UK.