Late Pleistocene and Holocene Aged Glacial and Climatic Reconstructions in the Goat Rocks Wilderness, Washington, United States

Abstract

Eight glaciers, covering an area of 1.63 km 2 , reside on the northern and northeastern slopes of the Goat Rocks tallest peaks in the Cascades of central Washington.At least three glacial stands occurred downstream from these glaciers. Closest to modern glacier termini are Little Ice Age (LIA) moraines that were deposited between 1870 and 1899 AD, according to the lichenometric analysis. They are characterized by sharp, minimally eroded crests, little to no soil cover, and minimal vegetation cover. Glacier reconstructions indicate that LIA glaciers covered 8.29 km 2 , 76% more area than modern ice coverage. The average LIA equilibrium line altitude (ELA) of 1995 ± 70 m is ~150 m below the average modern ELA of 2149 ± 76 m. To satisfy climate conditions at the LIA ELA, the winter snow accumulation must have been 8 to 43 cm greater and mean summer temperatures 0.2 to 1.3 ºC cooler than they are now. Late Pleistocene to early Holocene (LPEH) aged moraines are located between 100 and 400 m below the LIA deposits. They have degraded moraine crests, few surface boulders, and considerable vegetation and soil cover. Volcanic ashes indicate LPEH moraines were deposited before 1480 AD while morphometric data suggest deposition during the late Pleistocene or early Holocene. The average LPEH ELA of 1904 ± 110 m is ~ 240 m and ~90 m below the modern and LIA ELAs, respectively. The climate change necessary to maintain a glacier with an ELA at that elevation for LPEH conditions requires the winter accumulation to increase by 47 to 48 cm weq and the mean summer temperature to cool by 1.4 to 1.5 ºC.Last glacial maximum (LGM) moraines are located more than 30 km downstream from ii modern glacial termini. They are characterized by hummocky topography, rounded moraine crests, complete vegetation cover, and well developed soil cover. Moraine morphometry, soil characteristics, and distance from modern glacial termini indicate that deposition occurred at least 15 ka BP during an expansive cooling event, the last being the LGM. The LGM ELA of 1230 m is ~920 m below the modern ELA. The climate change necessary to maintain a glacier with an ELA at that elevation for LGM conditions requires the mean summer temperature to cool by 5.6 ºC with no change in precipitation.iii DedicationThis thesis is dedicated to two women who have taught and continue to teach me how to give to the world through my heart: my fiancée and my mother.Thank you for all your love.iv Acknowledgments I would like to thank my advisor, Andrew G. Fountain, for making this thesis opportunity possible, for his continued effort and outpouring of knowledge submitted from a broad range of latitudes, and for his guidance and patience that helped make my graduate school experience very enjoyable. I am grateful to Scott Burns for taking time in the field to educate me on alpine soil characteristics and for his ubiquitous enthusiasm and positivity in every discussion I've ever had with him. I thank Jim O'Connor for sharing his understanding and insight of alpine environments and h...

Inventory of glaciers and perennial snowfields of the coterminous USA

“…Used 2009 NAIP imagery to help define the headwalls at the Conrad, McCall, and Packwood glaciers. Heard (2000) previously mapped the glacier perimeters. The maximum extent of the seasonal snow covering the terminal regions was not digitized.…”