Seismic Observations of Glacier Calving and Surging on Spitsbergen, Svalbard
Friday, 19 December 2014
Seismic waveform observations can be used to monitor and better understand glacier dynamics such as basal sliding, crevassing, ice faulting, and calving. We use seismic data recorded on permanent broadband stations on Spitsbergen, the main island of the Svalbard Archipelago, as well as data from a local, temporary seismic network in northwestern Spitsbergen to detect, locate and analyze glacier seismicity. We observe a high number of icequakes related to glacier calving with characteristic seasonality and signal frequency spectrum. We calibrate regionally observed calving events by using the local records and direct visual observations of calving at Kongsfjord, northwestern Spitsbergen. We analyze the temporal distribution of calving seismicity within the past decade with special focus on Kronebreen, a fast-flowing tidewater glacier at Kongsfjord that shows a recent accelerating retreat.
We also observe a cluster of seismic events emitted by a catastrophic glacier surge in southern Spitsbergen. The Nathorstbreen glacier system went through a surge phase between 2008 and 2013. In early 2009, a high number of seismic events are observed during the initial surge phase of Zawadskibreen, one of the branches of the system. Observable seismicity is absent during the progression of the surge after May 2009. We discuss different source mechanisms for these events, i.e. bed-failure at the glacier tongue and ice faulting. Remote sensing observations show fault-like structures within the ice along the margin of Zawadskibreen, where the ice is ripped apart on the margins. These structures have a much larger extent than normal glacier crevasses and their generation during the initial phase of the surge may be the source of seismic evens. We also observe another, but indirect indicator for glacier surging in Svalbard: there is a dramatic increase in number of seismic calving events during surges of Tunabreen (2003) and Wahlenbergbreen (2011) compared to melt seasons in other years.