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Introduction to glaciers. Chapter 13 Pages 44 - 50. What are “glaciers”?. H uge masses of ice flowing slowly over land They form in any area that is permanently cold and has a year-to-year surplus of snow. Location, location, location. Glacial ice forms because of:
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Chapter 13 Pages 44 - 50
What are “glaciers”? • Huge masses of ice flowing slowly over land • They form in any area that is permanently cold and has a year-to-year surplus of snow
Location, location, location • Glacial ice forms because of: • 1) accumulation* in winter > ablation* in summer • 2) latitude* • 3) altitude* • 4) colour- white
Formation of a glacier (45) • Must be cold enough, but with enough moisture in the air • As these layers pile up, their weight increases and causes the snow crystals below the surface to compact, or compress together, to form grains • Year after year, new layers of snow bury and compress the previous layers.
Firns • During compaction, freezing and thawing creates crystallized slush called a firn* • Compacted firn creates solid glacial ice • Eventually, the glacier increases in size and weight
Zone of Accumulation Zone of Ablation • Zone of Accumulation*: • The area above the firn line, where snowfall accumulation > the losses from ablation (melting) • Zone of Ablation*: • Loss of snow and ice through ablation > gain of snow and ice
Blue glaciers?! • It appears blue, but is not really blue • Ice is so concentrated that all colours except blue are absorbed • Low oxygen content • Melts s…l…o…w…l…y
Did you know? Duringthe last Ice Age, 32 % of Earth's land area was covered with glaciers. At present, glaciers cover roughly 10 % of the land area.
Erosional action of glaciers (46) Plucking* Abrasion*
1) Plucking * • Glacial ice can melt and infiltrate cracks present in the bedrock • Once this water has seeped through the bedrock and it can refreeze • This frost actionleads to the dislodging of rock fragments from the bed as the glacier moves rocks ripped away and carried off
http://www.homepage.montana.edu/~geol445/hyperglac/eroproc1/animated~plucking.gifhttp://www.homepage.montana.edu/~geol445/hyperglac/eroproc1/animated~plucking.gif
Abrasion* • Plucked and frozen debris in ice scrapes and grinds into the bedrock • This grinding leaves long grooves or scratches in the bedrock called striations* • This scratching and abrasive action can produce rock flour*
Did you know? Glacier ice crystals can grow to be as large as baseballs.
Glacial Deposition (47) Drift* till* outwash*
Drift* • Drift: Any material deposited by a glacier • The result of ice melting and leaving behind the material it was carrying
Drift type #1: Till* • Till: material directly deposited and left behind when glacial ice melts • Unsorted debris • Sand, gravel, boulders, rock flour
Drift type #2: Outwash* • Outwash: sediments and materials deposited by running glacial water • Well sorted and stratified (e.g. boulders' are separated from finer particles)
Did you know? • The Kutiah Glacier in Pakistan holds the record for the fastest glacial surge. In 1953, it raced more than 12 kilometres in three months, averaging about 112 meters per day.
Types of glaciers • There are two types of glaciers and each has different features: Alpine/ Valley Glaciers* Continental Glaciers*
1) Alpine/ Valley Glaciers* (45) • Long, narrow mountain glaciers that occupy a former river valley • Occur in mountainous regions • These “rivers of ice” greatly modify the land form as they slowly erode and transport rock debris
Alpine/ Valley Glacier movement • Main force: Gravity • Movement due to slope • Glaciers advance when accumulation of snow and ice > ablation (melting) • Top and middle move the fastest, creating a curved shape (glacial snout*) at the front
2) Continental Glaciers* (46) • Known as Ice sheets that spread outwards over surrounding lowlands • Cover flat, lowland regions • Move slowly • Continental glaciers are presently found only in Greenland and Antarctica (polar regions)
Continental glacier movement • Continental glaciers covered a large portion of North America during the last ice age • The weight of the ice sheets pushed the continent down (isostatic sinking*) • After the ice sheets retreated, the continent began readjusting or (isostatic rebounding*)
Did you know? • Antarctic ice is over 4,200 meters thick in some areas and has been in existence for at least 40 million years
Evidence of glacial action • Very powerful and sometimes rapid agent of erosion, transport, and deposition • Rearranged soil in North America • Valleys can be eroded into U-shaped valleys • Evidence of glacial deposition is everywhere! (We will learn more about this tomorrow)
Did you know? If all land ice melted, sea level would rise approximately 70 meters worldwide.
Benefits of glaciation • Left behind an abundance of fresh water and lakes • Small lakes (tarns*) used for hydroelectricity in Norway • Provides water for Streams (Alpine Glaciers) • Tourist attractions
Did you know? • Glaciers store about 75% of the world's freshwater. • In Washington state alone, glaciers provide 470 billion gallons of water each summer.
Memory aids • Crazy visual associations • Drawings/ diagrams • Situations where the word may be used • Word associations (“tender”… “tinder is tender”) • Acronym (ROYGBIV)
Group 1) cirque, tarn, arête, col, horn • Group 2) ground moraine, lateral moraine, medial moraine, terminal moraine, recessional moraine • Group 3) esker, truncated spur, hanging valley, crevasse, icefall • Group 4) pro-glacial lake, ribbon/ finger lake, kettle lake • Group 5) drumlin, outwash plains, erratics • Group 6) roche mountonnee, crag and tail, U-shaped valleys, Hanging valleys, waterfalls
