Dataset: Accelerated Retreat of Coastal Glaciers in the Western Prince William Sound, Alaska
Description
Analysis of historical maps and Landsat imagery suggests coastal glaciers in the western Prince William Sound have retreated since the end of the Little Ice Age, with a period of accelerated retreat after 2004/06. I develop a multi-temporal inventory of 43 glaciers based on historical field observations, topographic maps, and Landsat imagery. Area and length measurements are derived from digitized outlines, and center lines calculated using a semi-automatic, geographic information system-based algorithm. Land-based glaciers retreated at a rate of 22 m a-1 from ~1950 to 2004/06 and peaked to 48 m a-1 after 2004/06. From ~1950 to 2018, the total area of land-based glaciers decreased by 228 km2, with 36% of the glacier loss occurring after 2004/06. Tidewater glaciers reacted asynchronously compared to land-based glaciers, with differing rates of area and length loss. Evaluation of climate trends indicates increasing temperatures and decreasing winter precipitation in the study area. Historical topographic maps of the study area provide the spatial data needed to extend glacier length change and area chronologies to the 1950s. The 21 maps I obtained for this study are available for download in a georeferenced format from the USGS (https://ngmdb.usgs.gov/topoview/viewer/#4/40.00/-100.00), allowing for use in geographical information systems (GIS) without further processing. The maps span 1951-1960 and are produced at the 1:63,360 scale from aerial photographs acquired from 1948-1957. I access Landsat images from an online service portal (ESRI, 2019). The images are georeferenced and orthorectified by USGS, allowing for direct integration into GIS. The images, at 30-60 m resolution, provide the spatial data for the repeat measurement of glacier outlines spanning 1973-2018. Previous studies provided Little Ice Age maximums for eight of the land-based glaciers analyzed in this study (Barclay et al., 2003; Wiles et al., 1999). I manually digitize outlines from historical maps, topographic maps, and Landsat images for glaciers 10 km2 or larger. Each study glacier is identified by a project identification number; Global Land Ice Measurements (GLIMS) and Randolph Glacier Inventory (RGI) identification numbers; and glacier name, if available. I manually digitize and adjust glacier boundaries based on the interpretation of 1950/57 topographic maps and Landsat images acquired in 1973/75, 1986, 1994, 2004/06, and 2018. Glacier length changes are measured from the intersection of the center line with each glacier terminus. I repeat measurements for 1950/57 topographic maps and the Landsat images acquired in 1973/75, 1986, 1994, 2004/06, and 2018, resulting in a glacier length change chronology for each glacier. For a subset of eight glaciers, I measure length changes to the digitized LIA maximum terminus positions identified in previous studies.