The Puget Sound Glaciation

Robyn Brown

November 2011

ES 767 Quaternary Geology
Emporia State University

Image taken from the Washington State Department of Ecology
Puget Sound Under Ice


Table of Contents

Introduction
Glacial History
Drainage
Evidence of Glaciation
References
Illustrations


Introduction

The Puget Sound is a large body of water that is located on the western side of Washington state in the Pacific Northwest. It lies in the middle of the Olympic and Cascade Mountains. This area was affected by glaciation in the Pleistocene Age around 20,000 to 25,000 years B.P. (before present). The glaciers blanketed the valleys in the middle of the Olympic and Cascade mountains. The glaciation was named the Fraser Glaciation and it consisted of two phases, the Evans Creek Stade and the Vashon Stade. The maximum extent of the glaciation was nearly 15,000 years B.P. The altitude of the ice sheet ranged from nearly 1,000 meters at the Canada/U.S. border to 0 to 300 meters in the southern Puget lowland (Waitt, 1983). Evidence of glaciation is easily seen today all along the Puget Sound area. The glaciation persisted for roughly 10,000 years.

Left: GIS map of the Puget Sound glaciation. Right: GIS map of present day. Image taken from The Puget Lobe (Used by permission).


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Glacial History

The Cordilleran ice sheet advanced southward during the Fraser Glaciation. It was called the Fraser Glaciation as it affected the Fraser lowland as well as the Puget lowland (Waitt, 1983). This glaciation was associated with two phases. The first phase was the Evans Creek Stade, in which alpine glaciers developed on the Cascade and Olympic mountains. This stage did not directly affect the Puget Sound area (Tubbs, 1977). The maximum extent of this stage occurred approximately 20,000 years B.P (Ogden, 2001). The second phase or the main phase was the Vashon Stade, in which the Cordilleran ice sheet advanced farther into the valleys in between both mountain ranges. The maximum extent of this stage was nearly 15,000 years B.P (Waitt, 1983). As the Cordilleran ice sheet moved southward into the Puget lowland, the Puget lobe was born (Tubbs, 1977). During this phase, a series of seven ice stagnation events took place. Three of the seven main stages are represented; The Tokul Delta Stage, the Inglewood Stage, and the Redmond Channel Stage. All three episodes had depositional features that were formed by the retreating glacier in the present day lower Issaquah Valley (GWAC).

Tokul Delta Stage
Image taken from Glaciation Stages (Used by permission)


Inglewood Stage
Image taken from Glaciation Stages (Used by permission)


Redmond Channel Stage
Image taken from Glaciation Stages (Used by permission)


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Drainage

The Strait of Juan de Fuca was blocked by the advancement of the Puget lobe in which a pro-glacial lake formed. This lake flowed south into Grays Harbor through meltwater streams in the lower Chehalis Valley. Sediment and water infiltrated the lake which marked the northern boundary. The finer sediments sank to the bottom of the calmer water further downstream while the coarser sediment was transported and deposited along the stream beds (Tubbs, 1977). Drainage flowed south in the Cascade and Olympic Mountains from the alpine valley glaciers and merged with meltwater streams that formed wide outwash plains south and west toward the Pacific Ocean. The Cordilleran ice sheet engulfed major drainage basins in the northern portion of the Cascade mountains. In this region, the altitude of the ice sheet ranged from 2,600 meters at the Canada/U.S. boundary to 270 meters in the Columbia River Valley. Expansion of pro-glacial lakes and ice-marginal streams to the north was a result of the recession of the Puget lobe. During the initial recession of the ice sheet, glacial Lake Russell flowed toward the south and glacial Lake Bretz flowed north (Waitt, 1983). During the Vashon stade, the ice sheet formed in British Columbia and flowed south to southeast through the Issaquah area. A pro-glacial lake was created at the head of this glacier. The drainage took a south route through passages located east and west of Squak Mountain (GWAC).

Valley that was carved out by the glaciers.
Image taken in 7/05 by R. Brown


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Evidence of Glaciation

During the episodes of ice stagnation, streams and depositional features formed in the lower Issaquah Valley. The five stages are represented from oldest to youngest.

Stage 1: The glacier was located at what is now Lake Sammamish. As the ice melted, it deposited sediments and the meltwater drainage flowed south through Issaquah Creek and Tibbetts Creek Valley (GWAC).

Stage 2: The glacier retreated north and Glacial Lake Sammamish was created in the lower Issaquah Valley. Drainage from the glacier ran east through Issaquah Creek. Large deltas were formed and the meltwater drained south through Tibbets Creek (GWAC).

Stage 3: The drainage from Glacial Lake Sammamish turned northwest along what is present day I-90. A large delta was created in the North Fork of Issaquah Creek. Deltas kept forming on the eastern shore of Lake Sammamish (Ogden, 2001).

Stage 4: Today, Lake Sammamish is smaller than its original size as it filled the lower Issaquah Valley area (Ogden, 2001).

Stage 5: South of Issaquah, a delta with an elevation of 100 to 150 feet above sea level was built (Ogden, 2001).

Pro-glacial fluvial and lacustrine sediment was dropped as the Puget lobe pushed toward the south. Cobbles, clay, silt, sand, pebbles, and boulders are till known as Vashon till. Vashon till is layered all through the Puget Sound area. A large portion of the till was derived from the Canadian Mountains where the glacier process began (Dawes, 2001) For more information on the Puget Sound glacial stratigraphy, check out Glacial Stratigraphy of the Puget Sound Region. The landscape was transformed with features such as deltas, uplands, valleys, channels, outwash plains, and glacial lakes as the Puget lobe retreated quickly. The present day features was persistently altered by weathering and erosion over the past several thousand years.

Present Day Puget Sound. Glacial deposits are along the bank of the Sound.
Image taken in 7/05 by R. Brown


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References

Dawes, Ralph L., PH.D. and Dawes, Cheryl D., 2001. Focus Page #5--Continental Ice Sheet in the Pacific Northwest http://www.wenval.cc/rdawes/focuspages/icesheet.html#strt Retrieved Nov 12, 2011.

GWAC. Glaical History. Groundwater Advocates Coalition. http://www.issaquah.org/COMORG/gwac/Glac.htm Retrieved Nov. 8, 2011

Ogden, Amanda. 2001. The Fraser Glaciation. http://www.atmos.washington.edu/2001Q2/211/groupD/page4.html Retrieved Nov. 9, 2011.

Tubbs, Donald W. and Dunne, Thomas. 1977. Geologic Hazards in Seattle. http://www.tubbs.com/geohaz77/geohaz77.htm Retrieved Nov. 8, 2011.

Waitt, Jr. and Thorson. 1983. The Cordilleran Ice Sheet in Washington, Idaho, and Montana: Late-Quaternary Environments of the United States, Volume 1: The Late Pleistocene: University of Minnesota Press, 407 p. Retrieved Nov. 9, 2011.


Figures and Illustrations

D.E. The Puget Sound Under Ice. The Department of Ecology Puget Sound Shorelines. http://www.ecy.wa.gov/programs/sea/pugetsound/tour/geology.html Retrieved Nov. 15, 2011.

Greenberg, Harvey. Glacial History of Puget Sound. http://rocky.ess.washington.edu/areas/Puget_Lobe/ Retrieved Nov. 15, 2011.

GWAC. Glaciation Stages. Groundwater Advocates Coalition. a href="http://www.issaquah.org/COMORG/gwac/Glac.htm Retrieved Nov. 9, 2011.


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