Report on Grimsvotn (Iceland) — 7 September-13 September 2016
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 7 September-13 September 2016
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2016. Report on Grimsvotn (Iceland). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 7 September-13 September 2016. Smithsonian Institution and US Geological Survey.
64.416°N, 17.316°W; summit elev. 1719 m
All times are local (unless otherwise noted)
On 8 September the Icelandic Meteorological Office (IMO) stated that the water level of the Skaftá river at Sveinstindur (the closest gauging station at 28 km downstream from the ice margin) rose significantly in the previous 24 hours, suggesting the beginning of a glacial outburst flood (jökulhlaup), originating from Grímsvötn's Western Skaftá ice cauldron. The discharge rate of Skaftá at Sveinstindur was 270 m³/s. IMO warned that hydrogen sulfide released from the floodwater as it drains is particularly potent at the river outlet from the ice margin, where concentrations may reach poisonous levels.
Geologic Background. Grímsvötn, Iceland's most frequently active volcano in historical time, lies largely beneath the vast Vatnajökull icecap. The caldera lake is covered by a 200-m-thick ice shelf, and only the southern rim of the 6 x 8 km caldera is exposed. The geothermal area in the caldera causes frequent jökulhlaups (glacier outburst floods) when melting raises the water level high enough to lift its ice dam. Long NE-SW-trending fissure systems extend from the central volcano. The most prominent of these is the noted Laki (Skaftar) fissure, which extends to the SW and produced the world's largest known historical lava flow during an eruption in 1783. The 15-cu-km basaltic Laki lavas were erupted over a 7-month period from a 27-km-long fissure system. Extensive crop damage and livestock losses caused a severe famine that resulted in the loss of one-fifth of the population of Iceland.