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REVIEW. What is a Glacier? = An accumulation of compacted snow & ice that moves slowly under the force of gravity 2 types of glaciers: Valley glacier = wedge-shaped stream of ice in a valley Continental glacier = sheet of ice over all/part of a continent
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REVIEW • What is a Glacier? • = An accumulation of compacted snow & ice • that moves slowly under the force of gravity • 2 types of glaciers: • Valley glacier = wedge-shaped stream of ice in a valley • Continental glacier = sheet of ice over all/part of a continent • (Ice caps are small ice sheets)
Firn/ Neve • = snow compressed from being buried, which has taken on a rough, granular ice form. It is in a state between snow and ice. • It is snow “on the way” to becoming glacial ice.
Snow line • = the lowest level that permanent snow reaches in the summer • Lowest snow line near poles • Highest snow line near equator Banff Snowline
Glacial Movement & Erosion • Movement of glaciers: • Glaciers move due to their great weight under the force of gravity • fastest movement at the surface and • in the centre • glaciers melt at lower elevations where it’s • warmer • The melting end of a glacier is called the ice front or terminus
Glacier movement can cause crevasses to form • crevasse = large fissure/crack in ice
Calving= when the ice front meets a sea, and chunks of glaciers break off into the water • icebergs = chunks of glacier broken off into water
2) Weathering and Erosion from glaciers: • As glaciers move, they pick up and move rock • Rock of all sizes is moved, from powder to house-sized boulders • Glaciers move rock in different ways: • rock drops on top of a glacier • rock is incorporated into a glacier • rock is dragged at the bottom of a glacier • Plucking = a glacier “freezes around” a large rock, picking it out of the ground and carrying it away
Glaciers can leave striations ( = parallel scratches on bedrock) because the rock material being dragged at the bottom of the glacier scratches the rock beneath it • Striations show the direction a glacier moved
Rock flour = fine sediment formed by the crushing of rock beneath a glacier
3) Landforms caused by glacial erosion: • U-shaped Valley = a valley with a U-shape • Hanging Valley = where a shallow U-shaped valley (caused by a small glacier) is intersected by a deep U-shaped valley (caused by a large glacier) • Cirque = a semicircular basin formed at the head of a glacial valley • Arete = a sharp divide between 2 cirques • Horn = a peak formed from 3 or more cirques
3) Landforms caused by glacial erosion: • U-shaped Valley = a valley with a U-shape • Hanging Valley = where a shallow U-shaped valley (caused by a small glaceir) is intersected by a deep U-shaped valley (caused by a large glacier) • Cirque = a semicircular basin formed at the head of a glacial valley • Arete = a sharp divide between 2 cirques • Horn = a peak formed from 3 or more cirques
3) Landforms caused by glacial erosion: • Cirque = a semicircular basin formed at the head of a glacier
3) Landforms caused by glacial erosion: • Arete = a sharp divide between 2 cirques
3) Landforms caused by glacial erosion: • Horn= a peak formed from 3 or more cirques
*Assignment 1: Draw a “before glacier erosion” and “after glacier erosion” picture of mountains, using the diagrams on p.325 to help you. • *Assignment 2: Do 1 – 5 (Pg 325)
3) Deposition by glaciers: • When glacial ice melts (e.g., at the bottom or sides of a glacier), the rock it carries gets deposited • Glacial deposits are called till • Till is unsorted (rock of all sizes is jumbled together) • Moraine = a long pile of glacial till, formed at the end or sides of a glacier • End moraine (end) • Lateral moraine (sides) • Cirque = a semicircular basin formed at the head of a glacial valley • Arete = a divide between 2 cirques • Horn = a peak formed from 3 or more cirques • Task 1 : Do 1 – 5 (Pg 325)
15.3 : Glacial Deposits • Glaciers carry & deposit drift ( = foreign rock material – eg: boulders, bedrock) • There are 2 types of drift: • Till = unsorted, unstratified rock deposited directly by ice • Ex: Moraines are rock deposits of till when the glacier retreats • Ex: Drumlins are canoe-shaped hills made of till found in swarms when advancing glaciers ran over a moraine • Outwash = sorted, stratified rock deposited by streams of glacial melt-water • Ex: Eskers are winding ridges formed when sand & gravel fill melt-water tunnels beneath a glacier.
Moraines = accumulations of glacial till • Rock flour = mixture of sand & silt formed by crushing rock under a glacier • Glacial milk = milky, white melt-water due to suspended rock flour. • Kames = cone-shaped hills of stratified sand/gravel • Kettles = circular hollows formed on moraines & outwash plains • There are 3 types of lake formed from glaciation: • Cirque lakes • Kettle lakes • Moraine dammed lakes • Task : Do 1 – 5 (Pg 328)
15.4 : Ice Ages • Evidence of ice ages: • It began 2 million years ago + 4 advances of ice • Interglacial periods between advances • Many ice ages in the past • Advances + retreats occurred at the same time in both hemisphere • Hypothesis of causes of ice ages: • Change in the sun energy • Volcanic dust in the atmosphere • Continents blocking ocean mixing • Changes in earth axis & orbits • Task : Do 1 – 5 (Pg 333)
