ARSF project IPY07/02: Lava penetrating water; led by Dr. Neil Mitchell (SEAES, University of Manchester); Site: Nesjahraun, Thingvallavatn, Iceland

We requested LiDAR data to record the surface morphology of lava that entered a lake on Iceland 2,000 years ago. Surface relief and flow-wise gradients was-- quantified from these data to compare with similar measurements from geophysical data collected within the lake in 1997 and previously. On entering water, lava becomes effectively less dense because of buoyancy and cools more rapidly because of water's greater heat capacity than air. Volcanic islands, where water-entering flows have been located previously, are typically strongly eroded by sea-swell around coasts so they usually provide poor information on morphological effects of buoyancy and cooling in shallow regions, but lavas emplaced into lakes are less affected. This target Thingvallavatn lava indeed shows evidence for an abrupt steepening 0-20 m below water level that could be caused by inflation of the lava as it lost effective density immediately on entering water. Combined with further fieldwork and analysis of sample physical properties, this project therefore sought to address the behaviour of lava in a site only 30 km from Reykjavik.