Surface signatures of surge dynamics over six decades at Tweedsmuir Glacier, Saint Elias Mountains, Canada

The dynamically driven advance and retreat of surge-type glaciers shapes surrounding ecosystems and landscapes differently from non-surging glaciers; however, the diversity in surge behaviour, even among neighbouring glaciers, makes them challenging to predict. Here, we reconstruct the six-decade surge history of Tweedsmuir Glacier in the Saint Elias Mountains, capturing two surge cycles. We use historical and satellite images to document rates of ice-thickness change, surface slope, cycle length, dynamic balance line position, and terminus advance and retreat between 1950 and 2010. Additionally, spectral analysis of the reconstructed glacier surfaces confirms that surface topography is amplified during and immediately following surges. Collectively, these proxies indicate that either the surge cycle lengthened over the study period, or the most recent surge (2007--2009) initiated with a lower driving stress than the preceding one (1973). While the glacier historically contacted the river during surges, terminus retreat has likely reduced the hazard of ice-damming. This study extends the known surge record of Tweedsmuir Glacier by two-and-a-half decades and provides a new proxy for distinguishing surge and quiescent phases from historical DEMs, multidecadal validation data to test theories of glacier surging, and a potential test site for improved bed-topography inversions that leverage high-slip regimes.