Date of Award

Summer 5-20-2021

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Aaron Putnam

Second Committee Member

Brenda Hall

Third Committee Member

Kirk Maasch

Additional Committee Members

Karl Kreutz

Abstract

Understanding the global pattern of glaciation can aid interpretation of what caused late-Pleistocene glacial cycles. Here I investigate the glacial history of the Khumbu Glacier of the Mount Everest region of Nepal. Prominent hypotheses for Himalayan glaciation suggest important roles for orbitally modulated insolation change and the Asian summer monsoon. Here I test these hypotheses by developing a 10Be surface-exposure chronology of moraines constructed by the Khumbu Glacier during the last glacial period. My chronology is underpinned by detailed glacial-geomorphic mapping constructed by use of drone and satellite imagery. The ages presented in this study indicate that the Khumbu glacier stood at maximum positions within the Dingboche moraine complex at ~67.1 ka, 38.1 ka, 36.7 ka, 29.7 ka, ~22.6 ka, 17.8 ka. The data indicate ice-surface lowering of ~100 m from the top of the Pheriche moraine to the Pheriche recessional landforms between 17.8 ka and 15.8 ka. These data suggest that moraine construction occurred throughout an entire orbital insolation cycle. Therefore, insolation intensity cannot explain the signature of Khumbu glacier fluctuations during the last glaciation. Likewise, peak glaciation occurred during a period of relatively weak monsoon intensity, suggesting that monsoonal forcing mechanisms (i.e., precipitation and/or cloudiness) are insufficient for explaining the pattern of glaciation indicated by the chronology presented here. The Khumbu Glacier chronology therefore raises a key question: If insolation and local monsoonal forcing did not drive the last glacial cycle in the high Himalaya, then what climatic factor(s) did? In this regard, I pose a preliminary suggestion that tropical heat fluxes inferred from Indian Ocean sea-surface temperatures, perhaps coupled with relatively low atmospheric CO2 concentrations, may have played an important role in driving Himalayan glaciation. Further evaluation of Himalayan glacier chronology could yield greater insights into the dominant drivers of Earth’s ice-age climate cycles.

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