Erosional unloading, hillslope geometry, and the height of the Cascade Range, Washington State, USA

2009 ◽  
Vol 34 (8) ◽  
pp. 1108-1120 ◽  
Author(s):  
Sara Mitchell ◽  
David Montgomery ◽  
Harvey Greenberg
Keyword(s):  
Washington State ◽  
Cascade Range ◽  
Erosional Unloading

Influence of a glacial buzzsaw on the height and morphology of the Cascade Range in central Washington State, USA

2006 ◽  
Vol 65 (1) ◽  
pp. 96-107 ◽  
Author(s):  
Sara Gran Mitchell ◽  
David R. Montgomery
Keyword(s):  
Washington State ◽  
Cascade Range ◽  
Stream Power ◽  
Glacial Erosion ◽  
Spatial Gradients ◽  
Hypsometric Analysis ◽  
Erosion Models ◽  
Exhumation Rates ◽  
High Precipitation ◽  
Hillslope Processes

AbstractAnalysis of climatic and topographic evidence from the Cascade Range of Washington State indicates that glacial erosion limits the height and controls the morphology of this range. Glacial erosion linked to long-term spatial gradients in the ELA created a tilted, planar zone of 373 cirques across the central part of the range; peaks and ridges now rise ≤600 m above this zone. Hypsometric analysis of the region shows that the proportion of land area above the cirques drops sharply, and mean slopes >30° indicate that the areas above the cirques may be at or near threshold steepness. The mean plus 1σ relief of individual cirque basins (570 m) corresponds to the ∼600-m envelope above which peaks rarely rise. The summit altitudes are set by a combination of higher rates of glacial and paraglacial erosion above the ELA and enhanced hillslope processes due to the creation of steep topography. On the high-precipitation western flank of the Cascades, the dominance of glacial and hillslope erosion at altitudes at and above the ELA may explain the lack of a correspondence between stream-power erosion models and measured exhumation rates from apatite (U-Th/He) thermochronometry.

Timing and extent of early marine oxygen isotope stage 2 alpine glaciation in Skagit Valley, Washington

2010 ◽  
Vol 73 (2) ◽  
pp. 313-323 ◽  
Author(s):  
Jon L. Riedel ◽  
John J. Clague ◽  
Brent C. Ward
Keyword(s):  
Oxygen Isotope ◽  
Washington State ◽  
Cascade Range ◽  
Glacial Lake ◽  
Oxygen Isotope Stage ◽  
Glacier Recession ◽  
Alpine Glaciers ◽  
Valley Glacier ◽  
Skagit Valley ◽  
Sand And Gravel

Twenty-two new radiocarbon ages from Skagit valley provide a detailed chronology of alpine glaciation during the Evans Creek stade of the Fraser Glaciation (early marine oxygen isotope stage (MIS) 2) in the Cascade Range, Washington State. Sediments at sites near Concrete, Washington, record two advances of the Baker valley glacier between ca. 30.3 and 19.5 cal ka BP, with an intervening period of glacier recession about 24.9 cal ka BP. The Baker valley glacier dammed lower Skagit valley, creating glacial Lake Concrete, which discharged around the ice dam along Finney Creek, or south into the Sauk valley. Sediments along the shores of Ross Lake in upper Skagit valley accumulated in glacial Lake Skymo after ca. 28.7 cal ka BP behind a glacier flowing out of Big Beaver valley. Horizontally laminated silt and bedded sand and gravel up to 20 m thick record as much as 8000 yr of deposition in these glacially dammed lakes. The data indicate that alpine glaciers in Skagit valley were far less extensive than previously thought. Alpine glaciers remained in advanced positions for much of the Evans Creek stade, which may have ended as early as 20.8 cal ka BP.

scholarly journals Glacier Outburst Floods at Mount Rainier, Washington State, U.S.A.

1989 ◽  
Vol 13 ◽  
pp. 51-55 ◽  
Author(s):  
Carolyn L. Driedger ◽  
Andrew G. Fountain
Keyword(s):  
Debris Flows ◽  
Monitoring Program ◽  
Washington State ◽  
Cascade Range ◽  
Hydraulic Pressure ◽  
Flood Water ◽  
Outburst Floods ◽  
Mount Rainier ◽  
Volcanic Debris ◽  
Southern Flank

During the twentieth century, glacial outburst floods have been the most destructive natural events on Mount Rainier, a stratovolcano in the Cascade Range in Washington State, U.S.A. In the period between 1930 and 1980 numerous floods were reported from five glaciers on the mountain, most of which flowed from Nisqually, Kautz, or South Tahoma Glaciers on its southern flank. Such floods threaten lives and property because they occur without warning and quickly mobilize the loose volcanic debris into debris flows. A monitoring program was begun in 1987 which was designed to measure the dimensions and timing of outburst floods, but this has been unsuccessful because no floods have yet occurred on the monitored streams. Four floods did burst from South Tahoma Glacier that was unmonitored, but in spite of this they have been useful in providing evidence of flood storage and release mechanisms. All flood volumes were found to be of approximately similar orders of magnitude, of 1 × 105 m3 of water, indicating that all floods probably had similar mechanisms for storage and release of water. Hydraulic pressure considerations indicate that such a large volume of flood water would be stored at the bed of the glacier rather than in isolated englacial cavities. The stepped bedrock terrain provides an ideal setting for the formation of subglacial cavities capable of storing the volumes of flood water noted.

scholarly journals Polygenetic topography of the Cascade Range, Washington State, USA

2006 ◽  
Vol 306 (9) ◽  
pp. 736-768 ◽  
Author(s):  
S. G. Mitchell ◽  
D. R. Montgomery
Keyword(s):  
Washington State ◽  
Cascade Range

Aggregations of Sharptail Snakes (Contia tenuis) on the East Slope of the Cascade Range in Washington State

1996 ◽  
Vol 77 (2) ◽  
pp. 47 ◽  
Author(s):  
William P. Leonard ◽  
David M. Darda ◽  
Kelly R. McAllister
Keyword(s):  
Washington State ◽  
Cascade Range

scholarly journals Glacier Outburst Floods at Mount Rainier, Washington State, U.S.A.

1989 ◽  
Vol 13 ◽  
pp. 51-55 ◽  
Author(s):  
Carolyn L. Driedger ◽  
Andrew G. Fountain
Keyword(s):  
Debris Flows ◽  
Monitoring Program ◽  
Washington State ◽  
Cascade Range ◽  
Hydraulic Pressure ◽  
Flood Water ◽  
Outburst Floods ◽  
Mount Rainier ◽  
Volcanic Debris ◽  
Southern Flank

During the twentieth century, glacial outburst floods have been the most destructive natural events on Mount Rainier, a stratovolcano in the Cascade Range in Washington State, U.S.A. In the period between 1930 and 1980 numerous floods were reported from five glaciers on the mountain, most of which flowed from Nisqually, Kautz, or South Tahoma Glaciers on its southern flank. Such floods threaten lives and property because they occur without warning and quickly mobilize the loose volcanic debris into debris flows.A monitoring program was begun in 1987 which was designed to measure the dimensions and timing of outburst floods, but this has been unsuccessful because no floods have yet occurred on the monitored streams. Four floods did burst from South Tahoma Glacier that was unmonitored, but in spite of this they have been useful in providing evidence of flood storage and release mechanisms. All flood volumes were found to be of approximately similar orders of magnitude, of 1 × 105 m3 of water, indicating that all floods probably had similar mechanisms for storage and release of water. Hydraulic pressure considerations indicate that such a large volume of flood water would be stored at the bed of the glacier rather than in isolated englacial cavities. The stepped bedrock terrain provides an ideal setting for the formation of subglacial cavities capable of storing the volumes of flood water noted.

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