An Actively Evolving Glacier Forefield, Mt. Baker, Washington

Location

Continent: North America
Country: United States of America
State/Province: Washington
City/Town: Bellingham
UTM coordinates and datum: none

Setting

Climate Setting: Boreal
Tectonic setting: Continental Arc
Type: Process, Stratigraphy

Click the images for a full-sized view.

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This is a shaded topographic map showing the location of the Easton Glacier on the southwest side of Mt. Baker. The Little Ice Age glacier forefield is directly downslope of the modern glacier terminus. DeLorme XMap.

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Oblique aerial view of the Easton Glacier, Mt. Baker. This view provides a detailed overview of the Easton Glacier (as of 2007) and the glacier trough below it (the forefield) that was occupied during the height of the Little Ice Age (about 150-200 years ago). Note the bedrock outcrops near the glacier terminus, the streamlined, fluted till plain further downvalley, and the well formed lateral moraines on either side of the trough. A modest hike up the center of the trough to the glacier terminus takes a few hours from the trailhead. View to the northeast. photo by John Scurlock (http://www.pbase.com/nolock).

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Dr. Bob Mitchell, WWU Hydrologist, surfs a glacially smoothed "bullet boulder" imbedded in ground moraine below the Easton Glacier terminus. Note the striae indicating glacial sliding over the boulder after it was emplaced in the till. View upglacier. Created by Douglas Clark.

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Oblique aerial view down valley of the terminus of the Easton Glacier. Note well formed lateral moraines (Metcalf moraine on the left, Railroad Grade moraine on the right), and the expression of fluted ground moraine and sculpted bedrock in the trough below the modern terminus. photo by John Scurlock (http://www.pbase.com/nolock).

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Tait Chirenje poster for intro workshop 2008. Tait Chirenje et al., Richard Stockton College of New Jersey.

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Stelling poster intro workshop 2008. Pete Stelling, Western Washington University.

Description

Most of the people living in northern North America live in relict landscapes that owe much of their form to the massive glaciers that repeatedly flowed across the region as recently as 20,000 years ago. But in most places, those glaciers are long gone and it's hard for most people to conceive of them other than in the abstract. We're fortunate in northwestern Washington; Mt. Baker Volcano, in Bellingham's backyard, has the most extensive glacier cover of any of the Cascade volcanoes other than Mt. Rainier. It has a contiguous ice apron spreading outward and downward from its summit at 10,880', which eventually splits into individual tongues of ice as the glaciers drop below their equilibrium line. One of these tongues, the Easton Glacier, provides an excellent opportunity to study the interactions between flowing ice and landscape modification: it has a relatively simple geometry, several kilometers of retreat during the last 100 years has exposed some spectacular moraines, ground till, and other glacial features, and it is readily accessible with a modest hike.

The Easton Glacier, like most alpine glaciers in the American West, reached its Holocene maximum extent only ~150 years ago, during the height of what is called the "Little Ice Age" (in contrast to the much larger Pleistocene ice ages), and since then has retreated substantially. What it has left behind is a beautifully preserved set of very young glacial landforms that can be clearly linked to the flow of the glacier itself, and the processes associated with its retreat.

The trail from Schriebers Meadow crosses bouldery outwash stream deposits several times before crossing over the lateral moraines from the Little Ice Age advance. As with many alpine glaciers, the terminal moraine is not well preserved because the outwash stream has eroded most of it away. However, once inside the terminal moraine, there is a broad surface in the Easton trough that is above the outwash stream that has beautifully formed ground moraine, shaped and molded into streamlined "drumlinoid" forms. These forms are best viewed from the air (see attached photo), but it is only on the ground that you can see how they formed. In most cases, they are a "rat tail" stretching out behind a till stone or resistant outcrop that poked into the ice, creating a void down-glacier into which basal till was pushed or plastered.

These streamlined hills also provide direct evidence for basal glacial sliding (like the grooves your tongue leaves behind in ice cream when you lick it), and flow direction.

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