Glacial Erosional Features

Glacial Erosional Features

1. Abrasion

   • Rock fragments embedded in glacial ice act like sandpaper on underlying rock
     • Ice flow picks up rocks and sediment (rock fragments)
   • Striations
     • Larger rocks at bottom of ice gouge lines in bedrock
     • Can't occur with too little debris. Too much would slow speed of glacier
       • Needs to be middle balance of debris concentration for striation to occur
   • Plucking
     • Glacial ice picks up rock fragments and incorporates them into the internal flow
     • Fracturing/crushing of bedrock
     • Break down bedrock - crack - water in crack - block breaks off
     • Create loose material and weaknesses in rock
   • Polishing
     • Ice abrades and polishes substrates - produce fine pulverised 'rock flour'
     • Makes water look, very blue bc rock flour moves into water containing materials from rocks surface
     • The smoothest surfaces are youngest

2. Meltwater

   • Water moving through glaciers
   • Supra glacial: channels on glaciers surface
   • Englacial: channels within the ice
   • Subglacially:under ice
     • (Temperate glaciers)
   • Main processes:
     • Mechanical
       • Abrasion: sediment carried in water erode surfaces
       • Attrition: stones in transport are thrown into one another
       • Hydraulic action: sheer force of water erodes
     • Chemical
       • Corrosion: where weak acids within water react with rocks, bed and bank of river
       • Temperate glaciers
       • High flushing rates - lots of water passing through

3. Microscale (<1m)

   • Striations
   • Concentric fractures
   • Glacial groove
   • Mini crag and tail
     • Rocky outcrop with tapering ridge of glacial deposits extending to one side
   • Small landforms - less than <1m

4. Mesoscale (10m-10km)

   • Streamlined bedrock features
   • Meltwater channels
     • Form in direction that ice flows
   • Stoss (upstream) and lee (downstream) forms
     • Whaleback
       • Ice-smoothed bedrock bumps which lack the steep, plucked lee side faces
     • Roche moutonee
       • Asymmetric bedrock hills shaped by ice
     • Crag and tail
     • Pod (school) of whalebacks

5. Macroscale (>10km)

   • U-shaped valley
   • Fjords
     • U-shaped glacial troughs that have become flooded by the sea
   • Hanging Valley
     • Larger intersection of tributary glacier with a larger valley glacier
   • Arete
     • Sharp-crested serrate ridge separating the heads of opposing valleys
   • Horn
     • A pointed mountain peak formed by there or more cirques that collapse
   • Nunatak
     • Exposed, often rocky element of ridge, mountain or peak not covered with ice/snow within an ice field

6. Depositional Features

   • Ice surge: material pushed forward - deposited material at the front
   • Ice-marginal moraines: accumulation of unconsolidated material in glacier - ceases ridges - different names depending on where ridge is
   • Terminal marraines: furthest point of any ice surge. Glacier eventually retreats from moraine - leaves sediment there
   • Erratic boulders: massive boulders which have been moved by ice, often hundreds of km
   • Drumlins: under ice - smooth, oval shaped composed of glacial sediment
   • Flutes: long ridges on ground parallel to movement of a glacier around a boulder