Glacial II - Started Tuesday November 8th, 2011 Earth/Envir...

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Unformatted text preview: Started Tuesday November 8th, 2011 Earth/Envir Sc 1G03 Earth & the Environment THE FROZEN WORLD Glacier erosion and deposition Things you have to do! Read Chapter 16: Glaciers, Glaciation and Permafrost Answer these questions: What information regarding global climate change can be obtained from ice cores? Where is Lake Vostok? Outline 1. Glacial erosion abrasion, plucking 2. Landforms of glacial erosion 3. Glacial deposition subglacial, supraglacial, glaciolacustrine athabasca glacier moulin 1. Glacier erosion Where does erosion take place? the base tunnel under the ice - At the base; clean ice does not erode -- need abrasive debris! How does debris get into ice? - entrained by freezing (stuck by freezing) - forms thin basal debris zones glacier base bedrock basal debris zone sediment How does ice erode? Abrasion - debris in ice dragged across substrate - forms STRIATIONS (scratches), smoothes rock What landforms are created by abrasion? - smoothed & streamlined landforms e.g. roche moutonee, whalebacks (sheep rock) What does abrasion do to debris carried in the ice? - shapes stones (faceting) - bullet-shaped boulders with pointed end & 'blunt' end ice flow blunt Reduces grain sizes, produces lots of SILT How else do glaciers erode? - debris released by fracturing of bedrock - frozen into glacier chopped o flow Fig. 16.12 Produces 'chopped o' ends of roche moutonee 2. Landforms of glacial erosion - STRIATIONS STRIATIONS grooves, gouges groove whitefish falls, near sudbury roches mountonee Corries, cirques Semi-circular erosional 'hollows' Horns, aretes - HORN - remnant peak of a mountain ARETE - narrow erosional ridge Glacial troughs, fiords - U-shaped valley carved out by glacier e.g. Yosemite, CA FIORDS - flooded valleys 3. Glacial deposition Glaciers carry unsorted debris - variety of shapes, sizes Deposit debris in a range of settings - subglacial - supraglacial - glaciolacustrine Subglacial deposits Debris in base of ice smeared onto substrate - forms lodgement till Hard, compact, no bedding Often sits on striated bedrock Subglacial landforms ice flow flutes - lodgement till plain drumlins Streamlined forms (parallel to ice flow) -drumlins -flutes Flutes Saskatchewan Glacier Ice marginal landforms - Transverse to ice flow push ridges - created by advance of the ice front in winter in winter the ice front freezes and bulldozes sediment forward, making ridges, then melts backwards in summer and repeats Supraglacial deposits How does debris get onto glacial ice? - Rockfall debris from valley walls Forms lateral and medial moraines on glaciers Supraglacial landforms - Ice melts slowly from under debris - Forms kettle holes hummocks ice is melting out below these holes Produces irregular, hummocky topography; Dundas Valley Glaciolacustrine deposits - Lakes common on the margins of glaciers - fed by meltwater (meltwater carries sediment with it) What kinds of sediment are deposited in glacial lakes? - Sands and gravels deposited on deltas Silts and clays carried into lake - slowly settle out from suspension What else can carry sediment into glacial lakes? ICEBERGS - carry coarse debris - debris melts out from ice - forms dropstones Things you have to do! Read Chapter 15: Groundwater Answer these questions: What are the main sources of groundwater contamination in southern Ontario? What caused the Walkerton tragedy? ...
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This note was uploaded on 11/28/2011 for the course ENV SCI 1G03 taught by Professor Padden during the Fall '11 term at McMaster University.

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