Arete: A sharp ridge of erosion resistant rock, an arete is formed when two cirque glaciers converge but do not meet, allowing a spine of rock to remain between them.

Cirque: Deep horseshoe-shaped basins formed as a result of glacial erosion, cirques are the ‘headwaters’ of a glacier. Cirque formation is initiated when the climate is cool enough in the area to allow snow to remain year-round in small hollows above the snowline. Meltwater from these small snowfields seeps into cracks in the surrounding rocks during times of partial melt, then re-freezes as the temperature falls in the winter, fracturing and loosening the bedrock. Subsequent meltwater and ice-flow remove the loose debris and the process begins anew. Over a period of thousands of years, the cycle of fracturing, erosion, and removal transform the small hollows into spectacular cirques. As the glacier retreats and, eventually, completely disappears a lake will often remain in the cirque. Such lakes are known as tarn lakes.

Col: As two cirque glaciers converge, they form an arete. If they should continue to converge and overtop the ridge separating them, they will erode the ridge in the center. The result is a low pass (col) in the middle of what was formerly an arete.

Drift: Generic term for any glacial deposit

Drumlin: A streamlined, spoon shaped hill created by glacial deposition. The steep side of a drumlin faces in the direction from which the glacier came. The process that forms drift drumlins is still debated by glaciologists. The most popular explanation is that the pressure of the ice overriding existing moraines, drift, and till is sufficient to deform them and mold them into elongate ridges. They are steeper on the upslope side because that is where the greatest pressure is exerted by the flowing ice.

Esker: An esker is a sinuous ridge of stratified fluvial sediments deposited underneath a glacier in meltwater channels. These channels are initially eroded both into the underlying bedrock, but as the channel fills it begins to erode into the overlying ice while continuing to deposit sediments. When the ice retreats these channel deposits are left behind as topographic highs. Eskers vary greatly in size and extent, but can be 100 feet high and 100 miles long.

Gyttja: A dark, pulpy, freshwater mud characterized by abundant organic matter that is more or less determinable and deposited or precipitated in a lake whose waters are rich in nutrients and oxygen, or in a marsh. It is an anaerobic sediment laid down under conditions varying from aerobic to anaerobic and is capable of supporting aerobic life.

Horn: As three or more cirque glaciers erode headward into the same mountain, they will form a steep peak with three or more distinct sides, called a horn. The most famous horn in the world is, of course, the Matterhorn in the Swiss Alps.

Kettle: A depression formed in drift or till (commonly found in moraines) as a result of large blocks of ice trapped in the drift melting after the glacier has retreated, allowing the overlying drift to settle and form a depression.

Moraine: A moraine is an elongate ridge of unconsolidated drift deposited along the margins of a glacier. There are several different types of moraines including end, terminal, recessional, lateral, and medial moraines. An end moraine is the general term describing a moraine deposited at the toe of the glacier during times of glacial stability (when the glacier stays in one place long enough for a significant amount of drift to accumulate). A terminal moraine is an end moraine that marks the greatest advance of the glacier before its retreat (i.e. it is farthest from the cirque). A recessional moraine is an end moraine deposited during periods of stability while the glacier is retreating. A lateral moraine is deposited along the margins of a glacier (often found on the walls of U-shaped valleys). A medial moraine is formed when two glaciers advance beyond their valleys and merge, at which point their lateral moraines combine to form a medial moraine between the two glaciers. Lateral and medial moraines only form in mountain glaciers, while the other moraines form in both mountain and continental glaciations.

Outwash: Sediment transported by meltwater from a glacier and deposited in front of (down slope from) the terminus of the melting glacier.

Plucking: Process which allows glaciers to erode bedrock surfaces via a three stage progression. In the first stage (a.), meltwater at the base of the glacier seeps into cracks in the bedrock. Once collected in these fractures the water freezes and expands, further fracturing the rocks and making bedrock debris available to the glacier (b). This debris is then removed either by freezing to the bottom of the glacier or by being dislodged by rocks projecting from the bottom of the ice (c).

Roche Mountonee: Roche Mountonees (also called rock drumlins)are asymmetric knolls or hills made of bedrock. They are an erosional feature of glaciation. The steep side of a roche mountenJ e is the down glacier, or lee side. The more gently sloped side points in the direction from which the glacier came. The steep edge is formed by a type of glacial erosion known as ‘plucking’. Meltwater at the base of the glacier seeps into cracks in the bedrock and then freezes, resulting in more fracturing of the rock. As the glacier moves over this area, it ‘plucks’ the fractured pieces of rock and transports them away, exposing a new surface in the rock on which the process is repeated.

Striated bedrock: As glaciers move over the ground surface they pick up abundant rock debris by plucking and simply incorporating pre-existing debris. Much of this debris is concentrated at the base of the glacier. The pressure of the overlying ice is transmitted through these stones to the underlying bedrock, causing the stones to dig elongate striations into the bedrock showing the direction of glacial transport. Another result of this process is the formation of striated and faceted stones often found in glacial deposits. These form as the bedrock grinds away at the stones at the base of the glacier.

Tarn: Lake which forms in the basin of a cirque .

Till: Glacial sediment deposited directly by glacial ice (i.e. not meltwater). Till is characteristically, unsorted and unstratified, consisting of sand, silt, pebbles, cobbles, boulders, and other debris.

U-shaped valleys: Most valleys formed by stream erosion will have essentially a V-shaped profile. Valley modified by glaciers, however, have U-shaped profiles. This is a result of the mechanics of glacial flow. Without getting into great detail, what happens in a glacier is that the ice at the top and bottom of the glacier tend to flow slower than the ice in the middle. As a result, the faster moving ice in the middle has a greater ability to erode the valley walls than the ice at the top or the bottom. This removes the valley wall material as you approach the apex of the ‘V’ and transforms it into a ‘U’.