Iceberg calving from a Canadian Arctic tidewater glacier

Abstract

Time lapse imagery, an audio recorder and geophones were used to detect iceberg calving events on the Belcher Glacier, Devon Island, in the Canadian High Arctic, in order to identify the major controls on the rate and style of calving. Eleven calving events were identified between June 4th and August 14th 2009 which accounted for 44% of the annual calving flux. Several of the events recorded in the audio data were associated with debris avalanching and disintegration of large tabular bergs. The geophones did not identify calving events but did record hydro-fracturing when terminus water-filled crevasses drained into the glacier. None of the calving events were a direct response to an increase in ice velocity in the terminus region, break-up of the sea ice/mélange, tidal flexure of the terminus, or propagation of water-filled crevasses. The Belcher Glacier maintains a lightly grounded stable terminus position but develops a protrusion at the glacier centreline every few years. When this occurs, as it did in 2009, the meltwater plume is active in eroding the lateral stability of the protrusion by locally enhancing the calving rate. Further investigation is required to examine whether basal melt also undercuts the protrusion, eventually leading to its flotation. In 2009 the protrusion calved off as a series of tabular icebergs which strongly suggests it was floating, as do calculations of height-above-buoyancy and subglacial effective pressure. In general, calving was not driven by a single identifiable cause and its stochastic timing may reflect the progressive accumulation of damage to the ice as it is transported to the terminus. The interactions of ice flow with the ice and bed geometry, as well as ponding and hydro-fracturing of supraglacial meltwater, seemed to be the main contributors to this damage.