Autonomous detection of calving-related seismicity at Kronebreen, Svalbard

Abstract

Abstract. We detect and cluster waveforms of seismic signals recorded close to the calving front of Kronebreen, Svalbard, to identify glacier-related seismic events and to investigate their relation to calving processes. Single-channel geophone data recorded over several months in 2009 and 2010 are combined with eleven days of direct visual observations of the glacier front. We apply a processing scheme which combines conventional seismic event detection using a sensitive trigger algorithm and unsupervised clustering of all detected signals based on their waveform characteristics by means of Self-Organizing Maps (SOMs). About 10 % of the directly observed calving events close to the geophone (<1 km) can be correlated with seismic detections. We are able to distinguish between false detections, instrumental artifacts, and three classes of signals which are, with different degrees of uncertainty, emitted by calving or glacier activity in general. By extrapolating the interpretation of seismic event classes beyond the time period of visual observations, the temporal distribution of glacier-related events shows an increase in event rate in autumn, particularly for the class which is related to iceberg calving. Using the seismic event distribution in this class as a proxy for the calving rate and measurements of glacier velocity and glacier front position, we discuss the possible relationship between glacier dynamics and calving processes at Kronebreen.

Surface speed and frontal ablation of Kronebreen and Kongsbreen, NW Svalbard, from SAR offset tracking

“…Advances regularly occur in spring and summer when the velocity is especially high due to enhanced lubrication and calving rates are low (Köhler et al, 2012). The timely occurrence of the retreat in autumn is in line with observations from Köhler et al (2012), who found that in 2009 and 2010 calving-related seismicity at Kronebreen predominantly occurred in autumn, after the peak in velocity. In late summer and autumn decreased velocity and warm ocean water entering the fjord, hence increased melt, undercutting and calving, lead to retreat (Luckman et al, 2015).…”

“…Note that this thinning rate refers to fixed positions upstream of the front but not to the retreating front, the height of which above sea remained roughly constant. Kääb et al, 2005, Rolstad and Norland, 2009, Köhler et al, 2012, and Luckman et al, 2015.…”

Rapidly changing subglacial hydrological pathways at a tidewater glacier revealed through simultaneous observations of water pressure, supraglacial lakes, meltwater plumes and surface velocities

“…Kronebreen is currently in a period of rapid retreat, having receded ∼ 1 km between 2011 and 2016. Strong correlation between bulk calving rates and fjord water temperature indicates that this retreat primarily reflects melting of the glacier front beneath the waterline (Köhler et al, 2012;Luckman et al, 2015;.…”

Tidal and seasonal variations in calving flux observed with passive seismology

“…This study builds on existing calving icequake research that has focused on the identification and location of calving events [ O'Neel et al , , ; Köhler et al , ]. Although iceberg sizes are potentially recoverable from glacial earthquake signals [ Tsai and Ekström , ; Veitch and Nettles , ], few other studies have systematically demonstrated an ability to capture iceberg size, and therefore calving flux, using properties of calving icequakes.…”