A New Bed Topography Map for Columbia Glacier

Tidewater glaciers are an important, yet poorly understood component of future sea level rise. The processes controlling calving, and therefore tidewater glacier retreat, are a complicated interplay between surface and bed topography of the glacier and fjord, ice dynamics, sedimentary conditions, and water temperature/heat flux. Columbia Glacier, Alaska, is a large tidewater glacier that began a rapid retreat ca. 1980, which continues today. It is one of the best-studied glaciers in the world, with an extensive dataset that predates the retreat and continues through the present day. Little is known, however, about the bed topography of Columbia Glacier upstream of the 2004 terminus. Knowledge of the bed topography informs knowledge of ice volume and thickness distribution, the latter of which is a critical iceflow parameter. In addition, knowledge of the total ice volume constrains future sea level rise projections. The existing topography map is limited to 15% of the current and formerly glacierized area, and is not without substantial errors. Using a method based on continuity of mass and constrained by surface velocity fields, surface DEMs, bathymetry, and surface mass balance rates, a new full-coverage bed topography map of Columbia Glacier is presented, along with an estimate of the current ice volume.