World of Glaciers: Erosional and Depositional Features

Cirques

A Cirque is a bowl shaped depression in a mountain. It is formed due to the expansion of neve, seasonal snow, to Firn, thick multi-year ice. This landscape means that it was the formation point for a glacier as one can say a Cirque is the cradle of an alpine glacier.

Arete

An Arete is essentially a wall between two cirques, it can tell us that the area it was in is highly glaciated, forming almost like a large ridge.

Horn

If an Arete is a ridge between two cirques, a horn is between three or more. These horns are kinda like nunataks though not all nunataks have to be around cirques. One of the more famous horns is the Matterhorn in Zermatt Switzerland.

Tarns

Tarns are essentially a lake inside a Cirque. They typically form as a result of the death of a glacier. Now the reason that they are lakes or ponds and not rivers is because they are dammed by glacial moraines on one side. We'll get more into moraines later in this blog.

U Shaped Valley

When a Valley glacier comes down a valley, it erodes the side of the valley turning it from its typically, v shaped set up to more of a wider U shape. This shows us the exact path an Alpine glacier has took.

Hanging Valley

A Hanging Valley is essentially a U shaped valley of a small alpine Glacier which gets cut off by a larger alpine glacier . This forms a land form in which one valley is essentially hanging above the larger one. These Valleys are known for having huge waterfalls come down.

Fjord

A Fjord is essentially a sunken U shaped valley. The big difference pertaining to their formation however, is that they are made primarily from outlet glaciers rather than from valley glaciers.

Paternoster Lakes

Technically both Depositional and Erosional, Paternoster lakes are like a staircase manner of lakes as a glacier recedes upward.

Roche Moutonnees

Roche Moutonnees, also known as sheepbacks are humps formed through two processes those being glacial abrasion and plucking. To better understand this feature lets split it into two parts. The stoss side or the gentle incline and the lee side or the steeper incline. The stoss side was formed by abrasion, the process in which the rocks and sand attached to the bottom of the glacier act like sand paper smoothing out the hill. The lee side was formed by plucking where there was a crack in the rock in which water seeps through it, expanding, leaving a steep drop off. It is important to note that the ice flow goes from stoss to lee.

Moraines

Moraines are essentially ridges of till formed by primarily Alpine glaciers. There are five types we will be talking about, Terminal, Lateral, Medial, Recessional and ground.

Terminal Moraines are a deposit of till at the furthest extent of a glacier. They mark the point when a glacial starts melting and shrinking.

These are essentially historical Terminal Moraines where glaciers have approached and then slightly retreated before expanding again.

These are solely for Alpine Glaciers and form at the glacial sides. These Moraines can tell you the maximum higher of a glacier.

When two glaciers merge in a valley, they create a ridge in the middle of them from the adjacent Lateral moraines coming together.

These Moraines are not actually a ridge but rather a deposited plain of till from the bottom of the glacier.

Drumlin

Drumlins are the depositional version of Roche Moutonnees. They are essentially hills made out of Till. One important thing to note is that the sides of the Drumlin can also be referred to as Stoss and Lee though the Stoss is the blunt steep side while the Lee is the tail. Rather than being made from abrasion the formation of Drumlins are mostly unknown. The two leading theories are sediment is deposited from subglacial waterways or erosion causes an influx of till which gathers to form a Drumlin.

Erratics

An Erratic is essentially deposits of glacial rocks whose composition differs from the local bedrock. Their size ranges from tiny pebbles to boulders as large as a house. Thats it for Direct deposition for the rest of the features they are indirect deposition

Kames

A Kame is an irregularly shaped mound which is formed when till accumulates in a depression on the glacier and when that glacier melts the meltwater forms and shapes it into a hill.

Eskers

The best way to describe these features is by using the term "upside down riverbeds". They are formed through subglacial streams depositing stratified sediment in long windy ridges.

Outwash Plain

An outwash plain is a large plain formed by the stratification of sediment by glacial outwash. It consists of braided streams and the soil lacks much nutrition. Boulders and heavier rocks drop closer to the terminal moraine while fine silt is carried farther.