Abstract
Terminus fluctuations of five glaciers and the correspondence of these fluctuations to temperature and precipitation patterns were assessed at Oregon’s Mount Hood over the period 1901–2001. Historical photographs, descriptions, and climate data, combined with contemporary GPS measurements and GIS analysis, revealed that each glacier experienced overall retreat, ranging from −62 m at the Newton Clark Glacier to −1102 m at the Ladd Glacier. Within this overall trend, Mount Hood’s glaciers experienced two periods each of retreat and advance. Glaciers retreated between 1901 and 1946 in response to rising temperatures and declining precipitation. A mid-century cool, wet period led to glacier advances. Glaciers retreated from the late 1970s to the mid-1990s as a result of rising temperatures and generally declining precipitation. High precipitation in the late 1990s caused slight advances in 2000 and 2001. The general correspondence of Mount Hood’s glacier terminus fluctuations with glaciers in Washington and Oregon suggests that regional, decadal-scale weather and climate events, driven by the Pacific Decadal Oscillation, play a key role in shaping atmosphere-cryosphere interactions in Pacific Northwest mountains. Deviations from the general glacier fluctuation pattern may arise from local differences in glacier aspect, altitude, size, and steepness as well as volcanic and geothermal activity, topography, and debris cover.
Highlights
Glaciers thicken and advance when accumulation exceeds ablation; glaciers thin and retreat under negative mass balance conditions
Statistical analysis shows that Coe, Eliot, and Ladd glaciers displayed generally synchronous patterns of advance and retreat within this overall period of retreat
Supporting evidence for glacier-climate linkages comes from other mountainous areas around the Pacific Northwest (PNW)
Summary
Glaciers thicken and advance when accumulation (e.g., snowfall and avalanches) exceeds ablation (e.g., snowmelt and calving); glaciers thin and retreat under negative mass balance conditions. North America’s Pacific Northwest glaciers have generally receded during the past century, a period characterized by a regionwide temperature rise of ;0.88C and precipitation increase of approximately 7 cm (JISAO/SMA Climate Impacts Group, 1999) Most such glacier change has been attributed to climate fluctuations; glacier aspect, altitude, size, and steepness as well as volcanic and geothermal activity, accumulation area, topography, and debris cover can complicate a direct response to climate forcing. Reid (1905, 1906) described the Coe, Eliot, Ladd, Newton Clark, and White River glacier termini in 1901 His termini photographs are a remarkable baseline for 20th century glacier studies at Mount Hood. This paper addresses two questions: (1) how did Coe, Eliot, Ladd, Newton Clark, and White River glacier termini fluctuate between 1901 and 2001; and (2) how did these fluctuations correspond to Mount Hood’s temperature and precipitation patterns?. With a total glacier surface area of 13.5 km and a volume of 0.4 km, Mount Hood ranked fifth in glacier cover in the Cascade Range (Driedger and Kennard, 1986; Kennard and Driedger, 1987; Carolyn Driedger, written communication, 16 December 2003)
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