HR: 1340h
AN: C43B-0228    [Abstracts]
TI: Late Pleistocene Glaciation and Paleoclimate in the Rocky Mountains: Insights From GIS Analysis
AU: * Leonard, E M
EM: eleonard@coloradocollege.edu
AF: Department of Geology, Colorado College, Colorado Springs, CO 80903 United States
AB: Reconstruction of glaciological characteristics of Pleistocene glaciers is an important source of information on paleoclimate. Depression of equilibrium line altitudes (ELAs) and mass balance modeling have be used to assess the magnitude and character of late Pleistocene-to-present climate change, particularly for alpine glaciers, which respond rapidly to climate. Application of GIS methods to such data facilitates analysis of regional patterns of climate change. GIS studies may also reveal spatial patterns in glaciological response to climate forcing. This presentation considers two applications of GIS to the study of the paleoglaciology and paleoclimate of the southern Rocky Mountains, looking first at late Pleistocene equilibrium-line depression in Colorado and second at magnitudes of climatic change necessary for glacier inception and growth in different ranges throughout the region. The few modern glaciers in Colorado are in topographically favored locations, out of equilibrium with regional climate. Theoretical modern ELAs, more closely related to regional climate, were determined using summer temperature and snow accumulation data from 74 SNOWTEL sites, modern altitudinal gradients of accumulation and temperature, and an empirical equation relating summer temperature to accumulation at equilibrium lines of modern glaciers. A theoretical modern ELA surface was constructed across the state. Late Pleistocene ELAs were determined by accumulation area ratio methods for 149 well-mapped late Pleistocene glaciers, and a paleo ELA surface was constructed. Comparison of the surfaces indicates that the magnitude of ELA depression varied significantly across the state, with a mean of ca 900m. The greatest depression (1000-1250m) occurred in the southern portion of the San Juan Mountains, likely reflecting increased Pleistocene southwesterly moisture flow. Greater than average ELA depression (900-1150m) also occurred in the northern mountains. Central ranges of the state experienced the least ELA depression (600-900m) In most areas there was a pattern of decreasing magnitude of ELA depression away from primary moisture sources, suggesting that the central ranges of the state were buffered from the effects of climate change by the topographic barriers of the marginal ranges. Modern climate data spanning the Rockies from Wyoming to New Mexico were utilized along with the empirical relationship between summer temperature and winter accumulation at the ELA to examine the location and scale of glaciation that would develop in response to different magnitudes of climate change. The results show non-linear relationships between magnitude of climate change and pattern of glaciation, reflecting primarily the topography of areas of potential glaciation. High linear ranges initiate glaciation with small amounts of climate change, but the ultimate extent of glaciers may be limited. Broader areas of high topography, notably the Yellowstone Plateau and San Juan Mountains, do not develop significant glaciers with small amounts of climate change, but with increasing magnitudes of climate change develop extensive glaciation.
DE: 3344 Paleoclimatology
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting