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EROSION PROCESSES & LANDFORMS

A. Introduction

Learning outcomes - You should be able to:

Readings


photo: rock embedded in ice B. Erosion Processes

Glacial Abrasion

Glacial Plucking

Patterns of erosion


C. Micro-Scale Features

Striae

photo: Striations, Valders Quarry, Wisconsin
Image credit: K.A. Lemke
photo: striations & grooves
Image credit: ©Michael Collier. Image source: Earth Science World Image Bank http://www.earthscienceworld.org/images

Chatter marks & crescentic gouges

photo: chatter marks
Image credit: ©Bruce Molnia, Terra Photographics. Image source: Earth Science World Image Bank http://www.earthscienceworld.org/images
photo: crescentic gouges
Image credit: Natural Resources Canada http://gsc.nrcan.gc.ca/surf/kivalliq/photo1_e.php

Micro crag & tails

  • abrasion

  • form in lee of resistant material (crag)

  • indicate both orientation & direction of ice flow

photo: crag & tail
Image credit: Natural Resources Canada http://gsc.nrcan.gc.ca/surf/kivalliq/photo1_e.php

Potholes

photo: potholes
Porcupine Mountain State Park, MI
photo: pothole

C. Meso-Scale Features

Streamlined features

  • Crag & tail: resistant rock with tail forming downstream


    Image credit: Natural Resources Canada, Canadian Landscapes Photo Collection. http://gsc.nrcan.gc.ca/landscapes/details_e.php?photoID=171

  • Roches moutonnees

    • stoss side: high effective normal pressure & abrasion

    • lee side: cavity formation & plucking

    • most likely to form in areas of thin, fast moving ice

    • idealized morphology: smoothed, gently sloping stoss side and jagged steep lee side

    • acutal morphology function of preexisting joint and fracture patterns in rock; not always a reliable indicator of ice flow direction


      Image credit: Natural Resources Canada, Canadian Landscapes Photo Collection. http://gsc.nrcan.gc.ca/landscapes/details_e.php?photoID=472
photo: roches moutonneesphoto: crag & tail

Rock grooves & rock basins

photo: rock grooves
Glacier National Park, MT
photo: rock basin
  • Finger Lakes, New York

    • combination of glacial abrasion and high pressure subglacial meltwater flow

photo: Finger Lakes, NY
Image credit: NASA Visible Earth . New York's Finger Lakes. Courtesy of ISS Crew Earth Observations experiment and the Image Science & Analysis Group, at NASA’s Johnson Space Center. http://visibleearth.nasa.gov/view_rec.php?id=17036


D. Macro-Scale Features

Cirques, aretes and horns

  • Cirques

    • cirque headwall: arcuate & much steeper than cirque floor

      • formed primarily by plucking and freeze-thaw weathering

    • cirque floor may contain a rock basin (tarn)

      • combination of abrasion and plucking

    • underlying geologic structure affects actual shape

    • grow in clusters; cirques within cirques

    • elevation indicative of regional snow line

    • orientation affected by local & regional climatic factors

  • Aretes: ridges separating cirques

  • Horns: pyramid shaped peaks formed when multiple glaciers erode back into the same peak

Picture (300x450, 54.9Kb)
Image credit: Steve Hillebrand, US Fish & Wildlife Service Digital Library System http://images.fws.gov/default.cfm?CFID=3302570&CFTOKEN=37370443
photo: cirques, aretes, horns
Image credit: ©Bruce Molnia, Terra Photographics. Image source: Earth Science World Image Bank http://www.earthscienceworld.org/images
photo: cirques, aretes, horns
Image credit: ©Bruce Molnia, Terra Photographics. Image source: Earth Science World Image Bank http://www.earthscienceworld.org/images

Glacial troughs

photo: glacial trough
Image credit: K.A. Lemke
photo: glacial trough
Image credit: ©Bruce Molnia, Terra Photographics. Image source: Earth Science World Image Bank http://www.earthscienceworld.org/images

photo: hanging valley

Areal scouring

photo: areal scouring
Image credit: Natural Resources Canada, Canadian Landscapes Photo Collection. http://gsc.nrcan.gc.ca/landscapes/details_e.php?photoID=108
photo: areal scouring
Image credit: Natural Resources Canada, Canadian Landscapes Photo Collection. http://gsc.nrcan.gc.ca/landscapes/details_e.php?photoID=106

E. Summary

Erosion Processes

Erosional Landforms


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©Karen A. Lemke: klemke@uwsp.edu
Last revised March 24, 2014