Glaciers are such immensely powerful rivers of ice that they shape landscapes in their path. They have done this to such a degree that new words needed to be created to describe their aftermath. This essay introduces the language of glaciers through their three greatest landscape-shaping powers: erosion, transport, and deposition.

To shape a landscape, erosion must happen and glaciers do this in multiple ways. First, they can pluck (or quarry) rocks. Bedrock has gaps and cracks that are filled with air and water. When that water freezes, chunks of bedrock separate from the parent material. These loosened rocks are then available to passing glaciers to pick up and sweep into the ice matrix. Sediment of all sizes gets picked up along the way.

These hitchhiker rocks and passing ice then gather more stones from surrounding bedrock and rock faces through abrasion – the simple act of scraping. Abrasion acts like sandpaper, wearing away the landscape. Some sediment is so finely ground that it is called rock flour. Rock flour is what causes glacial-fed streams to be a milky color. Fluting happens when glaciers flow over jagged ridges and smooth them into teardrop shapes. Fluted ridges parallel the direction of a glacier’s movement. Subglacial streams can also cause erosion, especially where a glacier is plowing through sediment. The heavy ice sheet causes very high pressure and erosive power in these streams. They are thought to have been an important factor in carving out Salish Sea channels.The fjord landscape of the Salish Sea, characterized by steep walls and a basin filled with a mix of ocean water and freshwater runoff, is the historic footprint of the latest glacier’s erosion.

Glacial drift is the material, in a wide spectrum of types and sizes, transported by a glacier. Glaciers move in fits and starts, sometimes advancing, sometimes retreating, and sometimes at rest. Meltwater is the water released by melting snow and ice. The water can collect in lakes in front of a glacier, and very fine silt and clay particles are deposited there, creating ancient lacustrine deposits, or lake beds. Lacustrine deposits are very poor at water infiltration given the teeny tiny spaces between the teeny tiny particles – hard for water to move through.

Ice chunks can be abandoned by glaciers, much like a train leaving a boxcar behind on the tracks. Over time, abandoned ice chunks are buried by sediment from the parent glacier’s meltwater. When the ice finally melts, which can take quite some time, the ground collapses, creating depressions called kettles.

And now the language of glaciers goes into overdrive. There are many different types of glacial deposits left on the landscape long after the glacier has retreated. Some of those deposits have been sifted or stratified by meltwater passing through them and others have not. Till is the general term that refers to the unsifted, heterogenous glacial drift deposited directly by glaciers. Moraines are unsifted glacial deposits that form arched hills, sometimes hundreds of feet high, along the edges or base of a glacier indicating a time of glacial rest. The US Geologic Survey includes eight types of moraines in their online dictionary of glacial terms.

There are a number of sifted or stratified glacial deposits. Preceding the glacier’s advancing edge is an outwash plain – a wide, low-gradient deposit of sediments washed from the glacier. Outwash plains may extend for miles, with sediment sizes decreasing with increasing distance from the glacier’s edge.

Rivers of meltwater can flow beneath glaciers. Stratified sand to cobble-sized gravel deposits form along the edges of meltwater streams, creating sinuous deposits called eskers. Kames are another form of stratified glacial deposit in the shape of hills, mounds, knobs, hummocks or ridges .

Because glacially-created landscape features are often a product of a combination of their erosive, transport, and deposition actions, it only seems fitting to end with two terms that are understood only by looking at all of these processes. Erratics, those rocks standing alone and unique in the landscape, are the plucked or abraded rocks that get transported some distance by glaciers and are then abandoned in a new landscape with completely different rock types. Drumlins are long hills shaped like inverted spoons. They were formed as glacial drift deposits that are then smoothed out and shaped by subsequent surges of their parent glaciers or glaciers that came afterwards.

And, I believe, this is just the tip of the iceberg (not to be confused with glaciers). If you would like to learn more, see FIND OUT MORE below.

Gonzalez, Mark, “What a Long, Strange (S)Trip(E) It’s Been!”, NCDS Newsletter, Vol. 30, No. 1, pg. 1

Puget Lowland Geology — a great illustrated overview of the geology of the Puget Lowlands by Washington Department of Natural Resources

Native Soils of Western Washington

A glossary of technical terms related to the ice age floods by Ice Age Floods Institute

A glossary of glacial terminology by USGS

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Thanks so much for your interest and your support.