Editing Glacier (section)

=== {{anchor|Glacial valleys}}Glacial valleys, cirques, arêtes, and pyramidal peaks ===
[[File:Glacial landscape.svg|thumb|Features of a glacial landscape|left]]

Before glaciation, mountain valleys have a characteristic [[V-shaped valley|"V" shape]], produced by eroding water. During glaciation, these valleys are often widened, deepened and smoothed to form a [[U-shaped valley|U-shaped]] glacial valley or glacial trough, as it is sometimes called.<ref>{{cite web |url=https://nsidc.org/cryosphere/glaciers/gallery/troughs.html |title=Glacial Landforms: Trough |publisher=[[National Snow and Ice Data Center]] |website=nsidc.org}}</ref> The erosion that creates glacial valleys truncates any spurs of rock or earth that may have earlier extended across the valley, creating broadly triangular-shaped cliffs called [[truncated spurs]]. Within glacial valleys, depressions created by plucking and abrasion can be filled by lakes, called [[paternoster lake]]s. If a glacial valley runs into a large body of water, it forms a [[fjord]].

Typically glaciers deepen their valleys more than their smaller [[tributary|tributaries]]. Therefore, when glaciers recede, the valleys of the tributary glaciers remain above the main glacier's depression and are called [[hanging valley]]s.<ref name=dkp/>

At the start of a classic valley glacier is a bowl-shaped cirque, which have escarped walls on three sides but is open on the side that descends into the valley called the "lip". Cirques are where ice begins to accumulate in a glacier. Two glacial cirques may form back to back and erode their backwalls until only a narrow ridge, called an [[arête]] is left. This structure may result in a [[mountain pass]]. If multiple cirques encircle a single mountain, they create pointed [[pyramidal peak]]s; particularly steep examples are called [[Glacial horn|horns]].<ref name=dkp/>