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Date Permissions Signed
Date of Award
Master of Science (MS)
Clark, Douglas H., 1961-
Easterbrook, Don J., 1935-
Bach, Andrew J.
Hansen, Thor A.
Moraines of at least two ages occur in alpine cirques near the Mt. Baker volcano in the North Cascades Range, WA. The south Swift Creek cirque preserves a distinct sequence of moraines representing the two primary age groups. In south Swift Creek cirque, the upper group of moraines (1450-1550 m) has little soil development and vegetation. Increment borings of the oldest trees growing on the upper moraines suggest that they were formed between the late 1800s and early 1900s. This age range correlates with numerous late Little Ice Age (LIA) moraines elsewhere in the Cascade Range. The south Swift Creek cirque Little Ice Age moraines have a reconstructed equilibrium line altitude (ELA) of 1550 m.
The lower moraines in south Swift Creek cirque are overlain by and older than Mazama ash (6800 14C yrs B.P.). In addition, a date of 9560±50 14C yrs B.P. on charcoal from the base of a bog just outside the lowermost moraine provides a closer minimum limiting age. A date of 9350±180 14C yrs B.P. from a branch near the base of a bog behind the uppermost pre-Mazama moraine indicates that trees were growing at the edge of the cirque by that time. Other cirque moraines in Swift Creek and Shuksan Creek, which are similar in extent to the older group of south Swift Creek cirque moraines, are constrained only as older than Mazama ash.
Moraines several kilometers distant and similar in altitude and geomorphic position to the pre-Mazama moraines of south Swift Creek cirque occupy the mouth of Bagley Creek cirque and dam Highwood Lake. A basal radiocarbon date from a Highwood Lake sediment core demonstrates that deglaciation occurred before 9410±50 14C yrs B.P.
The similar limiting radiocarbon dates and similar reconstructed equilibrium line altitudes (ELAs) of ~ 1400 m for pre-Mazama moraines in both Bagley Creek cirque and south Swift Creek cirque indicates that they are correlative. Two dates with a mean of ~10,700 14C yrs B.P. from charcoal layers in outwash associated with moraines 40 km down the North Fork Nooksack valley provide a maximum limiting age, constraining the Swift Creek and Bagley Creek moraines to the early Holocene or late Pleistocene (Kovanen and Easterbrook, 2001).
The minimum ages indicate that Bagley Creek cirque and south Swift Creek cirque moraines predate most of the early Holocene moraines on the south flank of Mt. Baker and probably correlate to the similar-scale McNeely II moraines near Mt. Rainier (Heine, 1998). However, the range of limiting dates (10,700 - 9600 14C yrs B.P.) allows an alternative correlation with the youngest Sumas moraines (younger than 10,250 14C yrs B.P.) from the remnant of the Cordilleran Ice Sheet on the Fraser Lowland (Kovanen and Easterbrook, in review-a).
The modern local ELA is estimated at 1640 m from small existing glaciers at the heads of south Swift Creek cirque and Bagley Creek cirque and a regional ELA of 1890 m based on northeast-to-northwest facing, modern glaciers near the study area. The difference (ΔELA) between the modern local and the south Swift Creek Little Ice Age ELAs is 75 m. The local ELA is used because local topographic effects that strongly influence mass balance and the FT .A today probably also influenced the LIA glacier. The ΔELA between the regional ELA and the late-Pleistocene/early Holocene ELA in Swift Creek and Bagley Creek is ~ 490 m. The mean regional ELA is a more appropriate comparison for the earlier glacier positions because the glaciers were large enough at that time to have substantially reduced local topographic effects on mass balance and ELA.
Simple comparisons of modem climate at reconstructed ELAs with modern glacier ELA climate conditions suggest that in order to build the oldest moraines in south Swift Creek cirque and Bagley Creek cirque, ablation season temperature would have to decrease by 1.6- degrees C or winter precipitation would have to increase by 870 mm. Similarly, building the oldest LIA moraine in south Swift Creek cirque would require a 0.85-degree C decrease in ablation season temperature or a 440-mm accumulation season precipitation increase.
Alpine cirques, Moraines, South Swift Creek cirque, Glacial chronology
Western Washington University
Subject – LCSH
Glacial epoch--Washington (State)--Baker, Mount, Region; Paleoclimatology--Washington (State)--Baker, Mount, Region; Cirques (Glacial landforms)--Washington (State)--Baker, Mount, Region; Moraines--Washington (State)--Baker, Mount, Region; Geology, Stratigraphic--Holocene
Baker, Mount, Region (Wash.)
Copying of this thesis 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.
Burrows, Robert A. (Robert Allen), "Glacial Chronology and Paleoclimatic Significance of Cirque Moraines near Mts Baker and Shuksan, North Cascade Range, WA" (2000). WWU Graduate School Collection. 826.