Unit 7 - Ice Is Nice

• 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.

Ice Is Nice:

Yosemite, Glacier, Rocky Mountain, Bear Meadows, and NE Greenland

Ice Is Nice:

Yosemite, Glacier, Rocky Mountain, Bear Meadows, and NE Greenland

Unit 7 - Ice Is Nice

Slip Sliding Away: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.

Unit 7 - Ice Is Nice

Ages of Ice: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.

Unit 7 - Ice Is Nice

Ice-Age Records:Ice-Age Records:

• 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.

Unit 7 - Ice Is Nice

Bear Meadows:Bear Meadows:

• Ice sheets today 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.

Unit 7 - Ice Is Nice

Glacier Tracks:Glacier Tracks:

• 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.