An Actively Evolving Glacier Forefield, Mt. Baker, WashingtonDouglas Clark
Western Washington University
Continent: North America
Country: United States of America
UTM coordinates and datum: none
Climate Setting: Boreal
Tectonic setting: Continental Arc
Type: Process, Stratigraphy
Click the images for a full-sized view.
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.