Review the Unit 7 Introduction
You have reached the end of Unit 7! Double-check the list of requirements on the Unit 7 Introduction page and the Course Calendar to make sure you have completed all of the activities listed there.
Unit 7 Overview
Review of the main topics and ideas you encountered in Unit 7.
Ice Is Nice: Yosemite, Glacier, Rocky Mountain, Bear Meadows, and NE Greenland
- Glacier = pile of ice and snow that flows
- Forms if snow exceeds melt enough to make a pile
- Takes water (as ice) and sediment from accumulation zone (snow exceeds melt) to ablation zone (melt exceeds snow) or to calve icebergs
- Flows in downhill direction of the upper surface (where ice meets air), even if that means the bottom flows uphill
- Think of pancake batter flowing on a waffle iron
Slip Sliding Away
- Glacier moves by deformation within ice, and if bed warmed to freezing point, by sliding over substrate or deforming sediment there
- Most deformation deep, but top fastest because rides along on deeper layers
- Ice deforms because almost hot enough to melt
- Glaciers erode by plucking rocks loose, sand-papering bed, and by subglacial streams
- Thawed-bed glaciers, especially those with surface meltwater reaching the bed, change landscape more rapidly than streams, etc.
Ages of Ice
- Recent (about 20,000-year-old), unique glacier tracks across broad areas now far from ice suggest past ice age(s)
- Ice-age hypothesis predicts land rising where ice was, sinking around, and that is indeed observed
- Ice-age hypothesis predicts sea level was lower when ice big, and indeed observe dead shallow-water corals of that age in growth position deep, flooded river valleys, etc.
- Isotopically lighter water evaporates more easily
- Bigger ice-->isotopically heavier ocean and shells
- Shell-isotopic history from ocean-mud cores shows biggest ice every 100,000 years, smaller wiggles about 41,000 and 19,000 years apart
- Predicted by Milankovitch before observed--these are wiggle-spacings in Earth’s orbit
- Ice grows globally when little northern sunshine
- Orbitally changing sun controls northern ice, which affects CO2, which controls southern ice
- Ice sheets today cover about 10% of land area; at height of ice age covered about 30% of modern land; central PA just beyond edge of Canadian ice
- Rocky Mountain, coastal NE Greenland National Parks have permafrost--soil at some depth frozen year-round
- Permafrost freeze-thaw and enhanced creep (summer melt can’t drain down, so soil soggy and creep easy) make distinctive features
- Those features exist but are not forming in central PA
- So, we were really cold in the ice age
- Abrasion (sandpapering) under ice makes striae (scratches) and polishes rock
- Smooths upglacier, plucks downglacier sides of bumps
- Glaciers make valleys with “U”-shaped cross-sections, often with side-valley floors hanging above main-valley floor; streams make “V” shape without hanging valleys
- Glaciers gnaw bowls called cirques into mountains
- Glaciers deposit all-different-size-pieces till and washed-by-meltwater outwash, often in outlining ridges called moraines
Reminder - Exercise #3 is due and Exercise #4 opens this week. See Course Calendar for specific dates and times.
Following are some supplementary materials for Unit 7. While you are not required to review these, you may find them interesting and possibly even helpful in preparing for the quiz!
Comments or Questions?
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