At first snow collects in a natural hollow on a mountain (at a high altitude/above the firn line). Over time this snow is compressed by the pile up of more snow on top of it. This extra weight forces air partials out, and thus more denser, compacted, recrystallised ‘firn’ snow is created (this snow eventually turns into ice, which will form part of the glacier.
Although the ice is trapped inside a hollow, the gravitational potential energy created by it, forces erosion to occur. This erosion (at first) comes in the form of ‘plucking’ (where dense ice picks at the wall behind it). This wall, known later as the headwall/backwall, forms the main basis of the corrie. Plucking induces abrasion (process where rock gained from plucking erodes away at bedrock) to occur also. These collectively widen and increase the volume of the cirque. These two processes are often given ‘zones’ (i.e. The ‘zone of plucking/abrasion). Weathering, further down the corrie (away from the plucking ice) happens as well. This is freeze-thaw weathering – where water seeps into porous rock formations and sets as ice; this expansion of ice, forces the rock to break.
A bergschrund is normally formed when the natural rotation of the glacier causes the The circular erosion inactive /stationary ice (ice not moving as fast patterns of the forming as ice nearer the tip of the glacier) to break glacier can cause a from the ‘bulk’. bergschrund to appear.Aburgschrundcan reach upto 100 metersin depth.
Over quantities of time, the corrie becomes arm chair-shaped. The cirque (which is actually French for ‘Arena’) normally gains three obvious sides as well. One is the noticeable Backwall and the other two (in this analogy – the ‘arms’) are steep cliffs. Nonetheless these can become knife-edged ridges known as arêtes (if two corries erode towards it) However there is a fourth; this is called the rock lip. The rock lip (easier to see when the glacier has retreated/melted) is formed when debris/moraine collects at the basin of the hollow. The glacier flows through here when it is finally forced out with the aid of gravity. Lastly a pyramidal peak can be created if three or more corries erode towards one another (this occurs when backwalls are forced to meet, by erosion).
When the ice within a corrie melts a lake, called a tarn lake is often left behind. This is seasonal and freezes in deep winter. Finally the reason why it is able to form is because of the rock lip (which was created by moraine and collected debris at the bottom of the cirque).
I showed you this image earlier, now name the parts! You have 1 minute! 1 2 3 4 7 5 6
1. Steep back wall.2. Burgschrund.3. Moraine.4. Rotation of glacial erosion.5. Corrie/Cirque lip or Rock lip.6. Abrasion of bedrock.7. Plucking of the backwall/ headwall(as ice forms around rock fragments). Thank you.