Seasonal fluctuations in the advance of a tidewater glacier and potential causes: Hubbard Glacier, Alaska, USA

Abstract

Satellite imagery has been used to acquire seasonal terminus positions of tidewater Hubbard Glacier, Alaska, from 1992 to 2006. During this 15 year time period the width-averaged advance of the entire terminus has been ~620 m at a mean rate of 35 m a⁻¹. Seasonal fluctuation of the terminus ranges 150 - 200 m and varies spatially. The section of the terminus near Gilbert Point exhibited little to no mean advance during this time period but displayed seasonal fluctuations of 300 - 500 m. Seasonal variability in surface ice speeds and surface seawater temperatures were also observed; both are potential forcing mechanisms for terminus fluctuations. Seasonal changes in seawater temperature of 10 to 12 °C, as well as seasonal changes in subglacial freshwater discharge are inferred to influence calving and submarine melting at the terminus, driving seasonal variations. Displacements of the medial moraine separating Hubbard Glacier and Valerie Glacier at the terminus suggest surge-like pulses of the latter with a periodicity of several years. The timing of these pulses suggests they may influence the Hubbard terminus near Gilbert Point and have implications for future closures of Russell Fjord.