DRAMATIC CHANGES TO GLACIAL VOLUME AND EXTENT SINCE THE LATE 19TH CENTURY AT MOUNT RAINIER NATIONAL PARK, WASHINGTON, USA

Surface area extents and estimates of total volume of glacial ice and perennial snow within Mount Rainier National Park (MORA) were inventoried in 2015 to study glacier changes over a century. Surface extents in 2015 were compared with inventories from 1896, 1913, 1971, 1994, and 2009, while volume estimates were compared with inventories completed in 1913, 1971, 1981, 1994, 2003, 2008, and 2009.

In 2015, MORA contained a total of 29 named glaciers which covered a total of 78.76 km² (30.41 mi²). Including perennial snowfields, the total perennial snow and glacier cover at MORA in 2015 was 80.82 km² (31.21 mi²). The change in glacial and perennial ice surface area from 1896 to 2015 was -52.08 km² (-20.11 mi²), a total reduction of 39.1%; a corresponding average rate of -0.44 km² per year (-0.17 mi² × yr^-1) during the 119 year period. Recent changes (between 2009 and 2015) revealed a reduction of -1.46 km² (-0.56 mi²) of glacial surface area, or a 1.8% reduction in glacial area and a rate that corresponded to -0.24 km² per year (-0.09 mi² × yr^-1).

The preliminary results for the volume of glacial ice and snow at MORA in 2015 are estimated at 2.86 km³ (0.69 mi³).The overall data shows a slight increase in glacial volume from 1971 to 1981 (4.34 to 4.42 km³ [1.04 to 1.06 mi³]). However, the overall average rate of volume loss during the entire period is equal to -0.027 km³ per year (-0.0065 mi³ × yr^-1) since 1913. The rate of volume loss has dramatically increased in the 7-year period between 2008 and 2015 with a corresponding loss rate of -0.14 km³ per year (-0.033 mi³ × yr^-1). This rate is approximately five times higher than the overall average rate of volume loss since 1913.

Our data shows an overall loss of ice extent and volume at MORA. Despite a relatively gradual decrease in glacial area, glacial volume loss is accelerating as glaciers thin. This loss is significant since glaciers at MORA represent a major source of fresh water for the region. The loss of these ice stores can have severe implications to aquatic organisms, regional freshwater usage, dam operations, and geologic hazards to the region. If the regional climate continues to change in ways that shrink glacial extent, further volume loss park-wide is anticipated, as well as the complete loss of small, lower-elevation glaciers in the next few decades.