• col: A saddle or depression in a divide (arete)

• Typically found in alpine landscapes
• Horns and arete were nunataks during glaciation

• Fjords: submerged coastal trough ( Hardangerfjord, Norway)
• Hanging Valleys: A tributary glacial trough entering a larger trough at a higher elevation.

• simple cirque: a single isolated feature
• compound cirque and cirque complexes: composed of two or more cirque basins
• cirque trough: The cirque at the head of a glacial trough
• related features
  • Tarn: a modern lake or pond occupying a cirque basin
  • bergshrund/radclift: the crevass at separating the glacier from the cirque headwall. This is the region of quarrying and headward erosion.

Positive feedback mechanisms perpetuating the formation of a rock basin

• the basin form enhances extending and compressive flow
• crevassing over reigels increases local quarrying and overdeepening down-ice (Hook, 1991) -pater noster lakes

Excavation of basins beneath ice sheets associated with

• Alpine--carved by a valley glacier in mountainous terrain
• Icelandic--trough terminated at one end by a trough head (nick point)
  • formed beneath an ice cap or ice sheet by headward erosion of a nick point as ice flows over the margin of a plateau.
    • nick point location is most likely controlled by one or more of the following
      • a local concentrated discharge
      • preglacial topography
      • lithologic or structural weakness
• Through-valley trough--Large trough open at both ends and generally cut through a divide-formed beneath an ice cap or ice sheet
• Inverse troughs - valley floors slope upward in the down-ice direction (e.g. Finger Lakes)

• Cross sectional profile is U-shaped (or more typically parabolic) with steep valley walls and a flat valley floor
  • See Harbor, 1992
• Longitudinal profile rapidly deepens at the head (overdeepened)
  • Why are alpine troughs over deepened? Possible explanations:
    • intense quarrying beneath the bergschrund
    • extending flow in the accumulation area increases abrasion
    • higher regions are subject to glacial processes for longer periods of time
    • the region of greatest discharge and velocity (equilibrium line) is located up ice from the snout
    • ELA migrates up valley during retreat
  • Why are continental troughs over deepened?
    • streaming flow, greater Q and V, and basal melting all result in increased erosion
• the longitudinal profile is commonly irregular with local basins and benches called riegels. A string of lakes occupying the basins are called pater noster lakes.

1. Preglacial topography (i.e. river or stream valley): Alpine glaciers and outlet glaciers typically occupy and modify preexisting valleys
2. Bedrock composition, structure and jointing and orientation relative to flow: Weaker rocks are preferentially scoured. Beneath ice sheets elongate basins and troughs are more easily scoured where structures parallel glacial flow.
3. Regions of streaming flow beneath an ice sheet: Secondary inflence most likely related to 1 and 2.