Corrie = Corries, also known as cirques, are often the starting point of a glacier. Snowflakes collect in a hollow. As more snow falls, the snow is compressed and the air is squeezed out to become firm. With the pressure of more layers of snow, the firm will, over thousands of years, become glacier ice. Erosion and weathering by abrasion, plucking and freeze-thaw action will gradually make the hollow bigger.
Corries will decrease because of climate change due to human activity such as burning fossil fuels. These were used as a source of fresh water.
Tarn = Tarns are formed when more erosion occurs at the base of a cirque then the front. When glacial melt occurs, these depressions fill up with water. One example is Crypt Lake. Other lakes are created when the melt water is damned by glacial deposits called moraines. Alderson Lake and Cameron Lake are examples of this.
Tarns may decrease because of the increase in temperature due to the increase of climate change because of human activity. When it melts it is also used as a fresh water source.
Pyramidal peak = When three or more Corries erode backwards and meet they cannot form an arete; it has steep sides but doesn't have the length to make a ridge. Imagine three Corries at the corners of a triangle, eventually all eroding back and meeting in the middle. A sharp pointed pyramid shape is created. This is called a Pyramidal Peak.
The peak isn't really used for anything, and the peaks will decrease and cause flooding in local areas due to human activity.
Arête = When a Corrie is formed, its back and side walls tend to be steep and jagged, perhaps almost vertical. When two Corries form next to each other, and their adjacent walls are eroded backwards until they meet, a narrow and pointed rock ridge is formed. This is often likened to a knife edge, with near vertical sides and a sharp top edge. This feature is called an arete.