Glaciers Erosive forces

Glacier persistent body of dense ice that is constantly moving under its own weight. It forms where the accumulation of snow exceeds its ablation (melting and sublimation) over many years.

Glacier formation Snowfall Glaciers form where the accumulation of snow and ice exceeds ablation. o This snow collects and is compacted by the weight of the snow falling above it, crushing the individual snowflakes and squeezing the air from the snow Firn left over from past seasons and has been recrystallized into a denser substance snow repeatedly freezes and thaws, changing into granular ice Glacial Ice Once all air has been squeezed from it, the snow is turned into extremely dense glacial ice When the mass of snow and ice is sufficiently thick, it begins to move due to a combination of surface slope, gravity and pressure.

Clicker What is ablation? a)Melting and sublimation b)Melting and evaporation c)Freezing and evaporating d)Melting and precipitation Timer Times up!

Explain what the growth of a glacier depends on The balance between snow fall received and the amount of ice lost be melting and sublimation(evaporation)

Advance v. Retreat Advance o Snow accumulation is greater than ablation Retreat o Ablation is greater than snow accumulation

Glacier Types Alpine (Valley)Continental Long, narrow wedge shaped form on the crests and slopes of mountains. o Ex. Alaska, Himalayas, Alps, Andes Wide, very large millions of km 2 Polar regions o Only found in two places Greenland and Antarctica

Clicker Today a continental ice sheet is located in? a)Eastern Europe b)New Zealand c)Alaska d)Greenland Timer Times up!

Glacial Movement Basal SlipInternal Plastic Flow glacier slides over the terrain on which it sits, lubricated by the presence of liquid water. o Refreezes as pressure removed Solid ice crystals slip over each other, causing slow forward motion. o Slope o Thickness o Temperature (of Ice) Surface faster o Friction

Erosion Plucking/ Ice wedging : Plucking: “pluck” material from V sides makes a U shaped valley Ice wedging: water seeps into cracks and expands leaving larger cracks.

Erosion Abrasion: o Mechanical erosion of rocks (think sand paper) as glacier scrapes over the landscape/ bedrock below

Features caused by Erosion Cirques: o start of a classic valley glacier is a bowl-shaped Horns: o 3 or more cirques or Arêtes that encircle a single mountain (looks like a pyramid) Arêtes: o Two glacial cirques may form back to back and erode their back walls until only a narrow ridge or “spine” is formed U-shaped valley: o widened, deepened, and smoothed, by a glacier forming a "U"- shaped glacial valley

Features caused by Erosion Hanging valleys: o when glaciers recede, the valleys of the tributary glaciers remain above the main glacier's depression ( water falls often) Striations: o Grooves from plucking/ and abrasion Kettle lake o shallow, sediment-filled body of water formed by retreating glaciers or draining floodwaters.

Clicker Cirques are best described as a)rounded knobs of rock. b)bowl-shaped depressions. c)sharp, curved peaks. d)sharp and jagged ridges. Timer Times up!

Deposition Drumlins: o elongated hill in the shape of an inverted spoon or half-buried egg formed by glacial ice acting on underlying unconsolidated till or ground moraine.

Deposition Eskers: o An esker is a long, winding ridge of stratified sand and gravel.

Deposition Kames: o an irregularly shaped hill composed of sand, gravel and till that accumulates in a depression on a retreating glacier.

Deposition Moraines: o are accumulations of dirt and rocks that have fallen onto the glacier surface or have been pushed along by the glacier as it moves. o End/recessional: between glacier and last moraine o Terminal= farthest forward motion o Lateral: side (parallel)

Glacial sediment Erratics: o are stones and rocks that were transported by a glacier, and then left behind after the glacier melted.

Glacial sediment till: o Glacial till is unsorted sediment deposited directly by glacial ice.

Glacial sediment Outwash: o Glacial outwash is sand and gravel deposited by running water from the melting ice of a glacier.

Michigan’s Glacial History

Big idea Great lakes Each of the Great Lakes began as a river.

As the climate cooled… The rivers froze. Glaciers moved through them – widening and deepening them to form today’s “U” shaped lake bottoms.

Why do scientists believe that glaciers once covered Michigan? The unsorted moraine deposits follow the outline of Great Lakes. Other depositional features such as drumlins and kettle lakes are found throughout Michigan. Erosional features like striations are found in Michigan as well.

Explain what happens to Earth’s crust when a glacier is removed. Isostatic Rebound –The upward movement of the Earth’s crust