Earth Science: 7.1 Glaciers
Terms in this set (24)
Understand the reasons why it is important to study glaciers.
LOCALLY: They are major agent of erosion and deposition: they played a major part in shaping the landscape of our area . WORLD:Glaciers are melting as global temperatures warm and will be a major contributor to seal level rese. Also Scientists can study the atmosphere of the past by looking at tiny gas bubbles trapped in glacial ice on Greenland and Antarctica. Helps us to understand natural climate cycles.
What is an ice age? Are we in an ice age (glacial or interglacial period)?
Ice age is any period of time during which glaciers covered a large part of the earth's surface. Today we are in an interglacial period within an ice age because glaciers are melting (retreating or losing mass) but are still here. (Glaciations = glacial advances or more ices).
Understand how North America has been changed by the action of glaciers.
Downcutting of the grand canyon, Colorado Plateau, Laurentide ice sheet in the north east, Cordilleran ice sheet in the Canadian Rockies, Large lakes in the Great Basin.
Provide examples of landforms in Acton and Boxborough that were formed by glacial processes.
Boxborough Eskers, Oak HIll/Tophet Chasm, Acton Arboretum Esker and Quaker Bog, Walden Pond.
Understand the connection between glaciers and Climate Change.
Global warming-the warmer the temp the more the glaciers will melt and sea levels will rise.
How much is sea level likely to rise by the end of this century from the predicted melting of glaciers?
If melted-it is 80% of world's ice the Antarctic Ice Sheet alone- sea levels would rise 60-70 meters.
Understand the definition of a glacier. Is a glacier the same thing as an iceberg?
Glaciers are a thick mass of ice that originates on land from the accumulation, compaction, and re-crystallization of snow (into ice) that moves under the influence of gravity. An Iceberg ???? (originates in the sea)???
Describe where and how glaciers form.
Where: In areas where more snow falls in winter more than melts during the summer. High latitudes (close to sea level and up) and high altitudes.
1). Snowflakes become smaller, thicker, and rounder, air is forced out=granular snow. 2).Snow is recrystallized into a much denser mass of small ice grains called FIRN. 3). Once the ice is 50 m thick, firn fuses into a solid mass of interlocking ice crystals-GLACIAL ICE.
Compare and contrast the two main types of glaciers.
1). Valley Glaciers (alpine)
- In mountainous areas
- Flows down a valley from a zone of accumulation at its head
- Long and narrow
2).Continental Glaciers (ice Sheets)
- Cover large areas (whole continents or islands)
-Only 2 today: Greenland, Antarctica
-Flows outward from an accumulation center.
Explain the two processes by which glaciers move.
1). Internal Plastic Flow:
- Some parts of the ice move farther than others.
-Under pressure, ice behaves as a plastic material-it can flow or deform without breaking (Plasticity).
-Weight of overlaying ice puts pressure on the ice below-causing it to flow.
-like squeezing toothpaste.
2). Basil Slip
-Entire ice mass slipping along the ground due to gravity
-Lubricated by thin layer of water at base melted under pressure
-The upper layer of a glacier is not under enough pressure to have plastic flow-upper zone of glacier=very brittle-ZONE OF FRACTURE. It piggybacks a ride on the flowing ice below.
-Like pushing a box across the floor
What is a crevasse?
Cracks caused by tension in brittle ice.
Understand the "work" of glaciers on earth's surface. (what roles do glaciers play in the rock cycle?)
Rock Cycle-they are an agent of erosion.
- Erode, transport and deposit sediment
-Erode by: Polishing bedrock (abrasion); Plucking- ice wedging
Plucking=as a glacier flows over the fractured bedrock surface it losens and lifts blocks of rock and incorporates them into the ice.
Abrasion-As the glacial ice and its load of rock fragment slide over bedrock-it works like sandpaper to smooth and polish the surface below.
Be able to calculate the speed of glacial ice flow from a map.
Be able to calculate the rate (toe) of glacier is advancing or retreating from a map.
Understand the concept of a glacial budget and how it determines if the end of a glacier is advancing, retreating or stationary.
The balance or lack of balance between accumulation at the upper end of a glacier and loss or wastage at the lower end. If more ice accumulates at the glacier head than melts or calves at the glacier foot, then the glacier advances. The glacier retreats when it loses ice faster than it gains it.
What is the zone of accumulation, zone of wastage, and snowline.
1). Zone of accumulation: More snowfall than melting in upper 1/3 of glacier.
2). Zone of wastage: More melting than snowfall in lower 2/3 of glacier
3). Snoline: snowfall=melting, divides zones.
What controls the rate of erosion?
1) rate of glacial movement.
2).Thickness of the ice
3).Shape, abundance, hardness of rock fragments.
4).Type of surface below the glacier.
Describe the landscape features that are produced by glacial erosion (mainly valley glacier features) and be able to identify them on a map or figure.
Unlike rivers that produce V-shaped valleys by cutting into their beds glaciers carve (erode) deeper wider U-shaped valley or glacial troughs.
Erosional Features in Valley Glaciers:
1). Cirque: Bowl shaped depression at head of valley
- TARN-Lake in a cirque
2). Arete: Sharp ridge separating cirques
3).Horn: steep peak where arêtes meet.
(Matterhorn in the swiss Alps).
Be able to name and describe features of glacial deposition (mainly associated with continental glaciers) and be able to identify them on a map or figure.
2 Main types of glacial sediment: Glacial Till and stratified drift.
- no layers (unstratified) and:
- unsorted (clay,silt, sand and gravel mixed)
Continental (Ice Sheet) Glaciers:
1). Drumlins: Made of till;smooth,tear-shaped hills; steep side faces the direction from which the ice advanced.
2). Moraine-a general term for deposits of till along the edges of a glacier
a) Terminal end moraine-at foot of glacier marks the farthest extent of a glacier. b). Recessional Morraine- marks the location of the end of a glacier as it retreated. c). Ground moraine-till deposited underneath a glacier.
3). Outwash plains: Layered sand and gravel deposited by meltwater leaving a glacier, not directly by the glacial ilce. Water sorts the sediments (all same size deposited together. 4). Kame-small cone shaped hills formed at the edge of the glacier by melt water pouring sediment off the surface. Deposits are layered. Mined for sand and gravel 5). Esker-long, winding ridges of gravel and coarse sand. Layered sediment -also mined for sand and gravel. 6). Kettle Lake Formation: A portion of glacial ice is buried in glacial sediment-as it melts it leaves a hole0sediment collapses into the hole and leaves a depression. Some have lakes in them like Walden Pond.
Distinguish between stratified drift and glacial till and identify features made of till or stratified drift.
- no layers (unstratified) and:
- unsorted (clay,silt, sand and gravel mixed)
4). Kettle Lake
Name and describe two features that could be used to tell the direction from which a glacier flowed.
Drumlin-The steeper side indicates where the glacier came from
The steeper side indicates where the glacier came from
How doe Whatleback (Roche Moutonnees) form?
Glaciers advance over bedrock and polishes the leading edge and top. May also leave striations (scratches) and grooves. The trailing edge is plucked leaving a steep face.
What is a glacial erratic?
Isolated rocks (boulders) Deposited by glaciers. They were once imbedded in the ice and may have moved very long distances. Not the same rock type as bedrock in the area.
Explain 2 ways glaciers can create lakes.
Kettle Lakes: Portion of glacial ice is buried in glacial sediment. As the piece of ice melts it leaves a hole. The sediment collapses into the hole and leaves a depression. Some have lakes in the (Walden Pond)>