Continuous deflation at Askja, Iceland, as seen in InSAR and precise levelling

The Askja Volcanic center, in the Northern Volcanic Zone in Iceland, hosts 3 calderas. The main, Askja caldera has been deflating at least since 1983 and probably even since 1973. The last eruption at Askja took place in 1961 when an 800 m long fissure opened along the northern part of the caldera. Here, we present a comparison of precise levelling measurements with interferometric data, from 2010. We have separated LOS changes into mostly vertical and mostly horizontal components to facilitate comparison to precise levelling data. Our aim is to use this detailed information to help resolve different models for the source of deformation.Time series of interferograms were created from RADARSAT radar images, supplied by the Canadian Space Agency, using the StaMPS software. The complete InSAR data set covers the Askja caldera and its surroundings during the 2000-2010 period. Precise levelling has been conducted at Askja intermittently since 1966. The levelling profile is located within the Askja caldera itself, on the 1961 lava flow. The data suggest an exponential decay of the observed subsidence. If we compare a one year interferogram from the beginning of this period to a one year interferogram from the end of the period, a clear decline in deflation is visible. Both data sets show that the Askja caldera continues to deflate at a smooth rate, eventually with small superimposed undulations. In 2007-2008, a large lower crustal intrusion took place in Upptyppingar , just 20 km to the East of Askja (Soosalu, 2009). Rymer et al. (2010), interpreted their 2008-2009 micro-gravity data in terms of a mass increase beneath Askja caldera. So why did neither of these two processes significantly effect the main subsidence pattern? The 2010 data, InSAR as well as levelling, suggest the independence of the lower crustal intrusion under Uptyppingar and pressure changes at the Askja volcanic system. Soosalu H, Key J, White RS, Knox C, Einarsson P, and Jakobsdóttir SS (2009) Lower-crustal earthquakes caused by magma movement beneath Askja volcano on the north Iceland rift. Bull of Volcanol. doi:10.1007/s00445-009-0297-3. New mass increase beneath Askja volcano, Iceland - a precursor to renewed activity? Rymer, H et al. Terra Nova, 22, 309-313, 2010.