Exit and Paradise Creek Drainage Area Boundaries, Alaska, 2012

Definition of upper elevation boundaries for Exit Glacier and small areas of Paradise Glacier, where these glaciers merge at their flow divides with other glaciers of the Harding Icefield, relied upon patterns of ice movement determined from flow vectors computed using offset techniques between December 31, 2006-February 15, 2007 and January 25, 2010-March 12, 2010 satellite image pairs (Burgess et al., 2013), and also upon crevasse orientations in the 2007 Kenai Fjords orthophoto. Non-ice covered areas outside the valley floor were delineated using traditional topographic techniques along topographic divides determined from 2008 Harding Icefield lidar data, where available, or from topographic maps. Within the valley floor, ambiguous topography resulting from historically transbasin flow required arbitrary distinctions between the Exit and Paradise basins. The margin of the Paradise Creek to Exit Creek transbasin flow path above the Little Ice Age moraine (about halfway up the valley floor) and the 2012 extent of Paradise Creek near the stream mouth were adopted as the divide between Exit and Paradise Creek. Near the mouths of Exit and Paradise Creeks, where frequent channel migration made the location of discharge to the Resurrection River ambiguous or time-dependent, the envelope of channels apparent from 1950-2012 in aerial imagery defined the origin of the drainage area. Drainage area was computed from the delineated drainage area boundaries in ArcGIS.