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Date Permissions Signed
6-7-2016
Date of Award
Summer 2016
Document Type
Masters Thesis
Degree Name
Master of Science (MS)
Department
Geology
First Advisor
Clark, Douglas H., 1961-
Second Advisor
Mitchell, Robert J. (Geologist)
Third Advisor
Linneman, Scott
Abstract
The Holocene glacial history of the North Cascades is poorly understood, in part because most existing records rely on moraine remnants and are therefore discontinuous. To develop a more complete record of Holocene fluctuations of North Cascades glaciers, we collected and analyzed glaciolacustrine sediments (i.e., rock flour) deposited over the past ~7800 years in Lyman Lake by the upstream Lyman Glacier. We combined these results with equilibrium-line altitude (ELA) reconstructions and glacier-climate modeling to quantify the climatic conditions that drove these fluctuations. Finally, we compared the Lyman Glacier’s continuous fluctuation record to existing glacier and climate records of the North Cascades.
Our results indicate that the Lyman Glacier was absent in the early Holocene, from before 7.8 ka until ~4.9 ka, when it experienced an early Neoglacial advance that persisted until at least ~3.8 ka. Following an extended non-glacial interval, the glacier experienced significant advances between ~2.6 – 2.25 ka, ~1.8 – 1.3 ka and ~1.1 – 0.9 ka. An advance starting ~ 0.8 ka (1150 CE) culminated at the glacier’s maximum Holocene extent between ~0.6-0.5 ka (~1350 – 1450 CE), from which it retreated and disappeared entirely by ~0.35 ka (~1600 CE). After ~200 years with no significant glacier presence in the cirque, the glacier reformed and rapidly advanced to its maximum Holocene extent (~1800 – 1900 CE). Following this event, the glacier retreated steadily throughout the 20th and early 21st centuries and as of 2014, has approached its minimum viable extent. Paleo-ELA reconstructions of the glacier’s maximum Holocene extents suggest that summers were ~2.6 °C cooler than modern (l981 – 2010 CE); alternatively, glacier-climate modeling indicates that annual temperatures ~1.5 °C cooler than modern would result in maximum glacier extents.
Combining these new results with existing North Cascades glacial records indicates that: 1) the earliest Neoglacial advances in the region (starting ~6 ka) occurred asynchronously, with higher latitude and more maritime sites experiencing earlier advances; 2) Neoglacial advances remained small, infrequent and asynchronous until the last millennium; 3) Beginning at ~1.0 ka, glaciers throughout the North Cascades advanced synchronously, signaling the onset of the Little Ice Age (LIA); 4) North Cascades glaciers reached their maximum Holocene extents during the 15th and early 16th centuries (~0.55 – 0.45 ka), followed by apparent regional retreat and a final smaller 19th century (~0.15 – 0.05 ka) re-advance. The asynchronous early-to-mid Neoglacial fluctuations followed by synchronous LIA behavior suggests that local climate factors drove glacier fluctuations until the regional climate signal became strong enough to induce synchrony ca. 1.0 ka. Although the inferred regional retreat remains uncertain, the disappearance of the Lyman Glacier in the mid-LIA (~0.45 – 0.15 ka) is consistent with the precipitation record at Castor Lake (~100 km to the east), which indicates unusually dry winter conditions between ~1450 – 1850 CE (~0.5 – 0.1 ka).
Type
Text
DOI
https://doi.org/10.25710/ry1m-py37
Publisher
Western Washington University
OCLC Number
951812898
Subject – LCSH
Glaciers--Washington (State)--Lyman Lake (Chelan County); Sediments (Geology)--Washington (State)--Lyman Lake (Chelan County); Glaciology--North Cascades (B.C. and Wash.); Geology, Stratigraphic--Holocene
Geographic Coverage
Lyman Lake (Chelan County, Wash.); North Cascades (B.C. and Wash.), Washington (State)
Format
application/pdf
Genre/Form
masters theses
Language
English
Rights
Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this thesis for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.
Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.
Recommended Citation
Wershow, Harold N., "A Holocene Glaciolacustrine Record of the Lyman Glacier and Implications for Glacier Fluctuations in the North Cascades, Washington" (2016). WWU Graduate School Collection. 513.
https://cedar.wwu.edu/wwuet/513