Glaciers
Objectives
1) Describe three causes of ice ages
2) Describe the two types of glaciers and identify the two land areas that have most of the glacial ice of the earth
3) Describe the two main methods by which glaciers erode debris
4) Describe how glaciers affected North America during the ice ages, affect it today, and in the future
5) Describe how glacial landforms provide both problems and opportunities for humans
6) Examine glacial landforms and state whether they are produced by an alpine glacier, continental glacier, or both
7) Recognize glacial landforms on topographic maps and air photos.

Glaciers act as agents of erosion and deposition to help to create unique landforms which you will study in this unit.

Introduction

ice : an agent of erosion

- as permanent snow cover increases in thickness, the underlying layers of snow are transformed into ice by tremendous pressure exerted by snow on top

- large volumes of ice behave like plastic and under great pressure they begin to flow out in tongues

- the weight and abrasive power of these glaciers changes the landscape

- during last 1 000 000 years (i.e. the Pleistocene epoch), scientists estimate that there have been four glacial advances with the last one ending approximately 10 000 years ago

I) Why Do Ice Ages Occur?

Theories

a) Volcanic eruptions send a layer of ash and dust around the earth in the atmosphere.
Solar radiation from the sun is partially blocked resulting in cooling.

b) A reduction in the amount of carbon dioxide in the atmosphere reduces the earth's ability to
absorb longwave radiation being emitted by the surface. Therefore, not as much heat is trapped by the atmosphere.

c) The amount of energy emitted by the sun has cyclic variations. Glaciation coincides
with periods of reduced solar activity.

d) Changes in the tilt of the earth's axis as well as changes in its orbit.

Further Information and Theories

Note: Once snow and ice begin to accumulate in large quantities, they provide positive feedback towards advancing the onset of the ice age. This occurs as a result of snow and ice having a high albedo effect. Albedo is the ability of a surface to reflect solar radiation.

II) How Do Glaciers Move?

Glacial flow is caused by glacial creep and basal sliding.

Glacial Creep

- due to the tremendous weight and pressure of the glacier, the ice becomes pliable and flows
- it flows fastest in the middle of the glacier where it is thickest (i.e. internal flow)

Basal Sliding

- movement along the bottom of the glacier due to the warmth of the earth and internal streams

The key to whether a glacier advances or retreats depends on the two opposing forces of
accumulation and ablation . Ablation is the wasting or loss of material from a glacier.

If accumulation > ablation, the tip of the glacier advances
If accumulation = ablation, the tip of the glacier is stationary
If accumulation < ablation, the tip of the glacier retreats

Keep in mind that even when the tip of the glacier is retreating or stationary, the internal flow of the ice still goes on throughout the glacier. The flow continues to move the ice forward, but the forward movement is offset by the loss of ice from ablation.

III) How Do Glaciers Erode?

1) quarrying or plucking: aided by freeze thaw action

- an example of a feature produced by this action is a roche moutonnée which occurs when an outcrop of hard rock is smoothed on the side facing the ice and plucked by freeze thaw action on the side facing away

eg A Roche Moutonnée, Melville Peninsula, Nunavut. The ice flowed to the right and plucked rock from the end of the outcrop.

Courtesy: Geological Survey of Canada

eg Crag-and-tail, Interior, British Columbia
Formed when an outcrop of rock (near the trees in the middle of photo) acted as an anchor for a streamlined mass of till to be dragged out as the ice moved from right to left in the photo. Therefore, in contrast to a roche moutonnée which is an erosional feature, a crag-and-tail is a depositional feature.
.

Courtesy: P. Mleziva

2) abrasion: scraping or gouging by an ice sheet and the debris it moves

- an example of a feature produced by this action is striations

eg
Two sets of striations are preserved on a flat bedrock island along the emerging Hudson Bay coast near Whale Cove. Deep striae and crescentic fractures indicating ice flow towards the ESE (1) are preserved on the gentle lee-sides (west) surfaces striated to the SE (2). The SE flow dominates on the island and the older ESE flow is found only on the west sides of outcrops.

Courtesy: Geological Survey of Canada

IV) Forms of Glaciation

alpine : glaciation which originates at high altitudes
continental : glaciation which occurs over a broad land mass

 

A) Alpine Glaciation

- snow line: at the equator: 4800 metres
in southern BC: 2700 metres

- occurs largely where fold mountains lie close to a coastline and are exposed to considerable precipitation from onshore winds

- better chance of glaciation in the northern continents because they extend into high latitudes

- best known snow capped peak in the tropics: Mt. Kilimanjaro in Tanzania

Features Produce by Alpine Glaciation

- because of constant freezing and thawing, the head of the glacier plucks out the side of the mountain and a circular amphitheater is cut into the peak. This huge, armchair-like depression with its vertical sides and basin-like floor is known as a cirque.

eg Cirque Mountain, Labrador


Courtesy: Geological Survey of Canada

Below are several cirques still partially covered by ice and snow in Antarctica.


Courtesy: Thomas Lowell, Department of Geology, University of Cincinnati

- after the ice in the cirque is gone, the depression may be occupied by a mountain lake called a tarn.

"Lake Ellen Wilson is an example of a tarn. The back wall of the cirque containing Lake Ellen Wilson is marked on the topographic map [below] in red. The photo was taken part-way down the cirque headwall where the camera is located, looking towards the southwest" (Karen A. Lemke - University of Wisconsin).

Courtesy: Karen A. Lemke, University of Wisconsin-Stevens Point,
and The Virtual Geography Department Project



Courtesy: Karen A. Lemke, University of Wisconsin-Stevens Point,
and The Virtual Geography Department Project

- if cirques connect around a peak, only a pinnacle of rock may remain called a horn.

eg Matterhorn peak in the Swiss Alps

Courtesy: SAWF

eg Mount Caubvick, Labrador

Courtesy: Geological Survey of Canada

- sharp knife-edged ridges of rock between cirques are called aretes

eg Mt. Oberlin

Courtesy: Karen A. Lemke, University of Wisconsin-Stevens Point,
and The Virtual Geography Department Project


Courtesy: Karen A. Lemke, University of Wisconsin-Stevens Point,
and The Virtual Geography Department Project


- a cirque which breaks a space in a continuous ridge forms a col


Courtesy: Karen A. Lemke, University of Wisconsin-Stevens Point,
and The Virtual Geography Department Project


Courtesy: Karen A. Lemke, University of Wisconsin-Stevens Point,
and The Virtual Geography Department Project

- V-shaped river valleys after being occupied by a glacier become U-shaped due to erosion.

eg Rocky River Valley in Jasper National Park, Alberta.

Courtesy: Geological Survey of Canada


- tongues of ice carve their own U-shaped troughs, but because the volume of ice in the main glacier is much larger, after the ice melts, the smaller troughs join the main valley at an altitude above the valley floor. These smaller troughs that join the main valley at right angles are known as hanging valleys.

- a stream that occupies a hanging valley will enter the main valley as a waterfall

"This hanging valley in Glacier National Park [below] contains a waterfall called Bird Woman Falls. A small glacier flowed out of this valley and joined a larger valley glacier that flowed where Logan Creek is located today. Since this glacier was small, it was unable to erode down into the landscape very far, and a hanging valley is what we see today. We are looking towards the south in this photo. On the map [below], north is towards the top. The photo was taken from the camera location on the map. The floor of the hanging valley is relatively flat, and thus the contour lines on the topographic map are more widely spaced than those contours representing the sides of the valley. The close spacing of the contour lines at the edge of the hanging valley indicates a steep drop-off, which is where the waterfall is located" (Karen A. Lemke - University of Wisconsin).

Courtesy: Karen A. Lemke, University of Wisconsin-Stevens Point,
and The Virtual Geography Department Project


Courtesy: Karen A. Lemke, University of Wisconsin-Stevens Point,
and The Virtual Geography Department Project

- truncated spurs are triangular faces on the vertical walls of the U-shaped valley. They have been formed as a result of the glacier truncating the interlocking spurs of the former V-shaped river valley

eg upper Kananaskis River, Alberta

Courtesy: Geological Survey of Canada

- lateral moraine is the erosional debris left at the side of the valley

- medial moraine occurs when the lateral moraine of two glaciers combines to form a single line

"[The] photo [below] shows two medial moraines (blue arrows) as seen from the air. The black arrows point to lateral moraines that have formed along the sides of the valley wall. Where the two main glaciers shown in the photo flow together, their lateral moraines join to form a medial moraine. The medial moraine on the right formed in the same way, however we can't see where the glaciers flow together to form the moraine" (Karen A. Lemke - University of Wisconsin).

Courtesy: Karen A. Lemke, University of Wisconsin-Stevens Point,
and The Virtual Geography Department Project


- end moraine [is] an accumulation of unconsolidated material deposited at the snout end of a glacier. There are two types: terminal moraines and recessional moraines.

- terminal moraine marks the farthest extent of glacial advance and thus is the end moraine located at the lowest elevation.

eg Moraine of a piedmont glacier, Bylot Island, Nunavut

Courtesy: Geological Survey of Canada

- recessional moraines form as glaciers pause during periods of retreat, and thus are located at higher elevations than terminal moraines.

eg Garibaldi Provincial Park, British Columbia (two recessional moraines)


Courtesy: P. Mleziva

- streams blocked by terminal moraine form finger lakes
eg Lake Louise, Alberta


Courtesy: The Fairmont Chateau Lake Louise

- a fiord results from the drowning of a U-shaped valley by the sea

eg Shark Fiord, Cumberland Peninsula, Baffin Island, Nunavut

Courtesy: Geological Survey of Canada


eg The formation of Howe Sound, British Columbia - a fiord.
Glaciation - 15 000 years ago


Courtesy: Geological Survey of Canada

Glaciation - 12 000 years ago

Courtesy: Geological Survey of Canada

Howe Sound Today

Courtesy: EHABWEB.NET

- alps are high altitude pastures eg Swiss Alps

- crevasses are cracks that occur as a glacier moves into a wider part of the valley or encounters a change in slope

eg Eastern Baffin Island, Nunavut

Courtesy: Geological Survey of Canada

 

B) Continental Glaciation

- two areas in the world that are experiencing an ice age at present: Greenland [below] and Antarctica


Courtesy: USGS

Features Produced by Continental Glaciation

- glaciers scrape and scour

Canadian Shield: a scoured region; little soil cover, dotted with lakes occupying depressions formed by the scouring action of glaciers

striations: glacial scratches on exposed rock

eg Indian Peaks Wilderness, Utah

Courtesy: Karen A. Lemke, University of Wisconsin-Stevens Point,
and The Virtual Geography Department Project


glacial till: Unsorted glacial debris deposited directly by the ice and consisting of clay, sand, gravel, and boulders intermingled in any proportion. Note : river deposits are generally rounded and sorted.

ground moraine: layer of till that covers the underlying bedrock (several centimetres or metres thick)

erratic: isolated boulder or misfit left by a glacier

eg an erratic near Vernon, B.C.

Courtesy: P. Mleziva

terminal moraine: line of hills marking the maximum extent of the ice sheet

recessional moraine: debris left by a glacier that maintained a constant position for a considerable length of time

interlobate moraine: debris left between the space of two glaciers which closely approached each other eg Oak Ridge moraine in S. Ontario

drumlins: odd tear-shaped hills (altitude: 7.5 to 30 m); steep end faces the direction the ice came from.

eg a drumlin near Separation Lake between Merritt and Kamloops, B.C.

Courtesy: P. Mleziva

eg Drumlinoids near Merritt, B.C.

Courtesy: P. Mleziva

Forms Resulting from the Melting of Ice

- as an ice sheet melts, water pours from it carrying debris and depositing it at the edge of the ice forming an outwash plain

eg in Nunavut

Courtesy: Geological Survey of Canada


- kettle lakes are formed by the melting of stagnant blocks of ice.

eg a kettle lake north of Okanagan Falls, Interior B.C.

Courtesy: P. Mleziva

eg a kettle depression near Kamloops, B.C.


Courtesy: P. Mleziva

- a spillway is a valley formed by a river of meltwater carving into the landscape

eg Glacial spillway, Sachigo River, Ontario.

Courtesy: Geological Survey of Canada


- misfit streams now occupy these spillways; they look like misfits because they are so small in comparison to the size of the valley they are flowing in; the original river which formed the spillway would have been much bigger

- eskers are long snake-like formations consisting of sands and gravels left by streams flowing inside the glacier; serve as road building materials.

eg a gravel quarry cut into the Coutlee Esker west of Merritt, B.C.

Courtesy: P. Mleziva

eg trees grow on an esker near Winfield, B.C.
Eskers drain well as a result of consisting of sands and gravel. Consequently, grasses growing on an esker will often turn brown first before the surrounding grasses.

Courtesy: P. Mleziva

glacial ponding: body of water formed as a result of meltwater not being able to flow away.

kame: low, steep, rounded hill or ridge of layered sand and gravel developed from deposits carried by glacial meltwater.

eg
Kames near Lake O' Laws, Cape Breton Island, Nova Scotia
The terraces mark levels of the meltwater stream which flowed beside and over the deposit.

Courtesy: Geological Survey of Canada


NOTE: Features shared by both alpine and continental glaciers:
- till, striations, terminal moraine, erratics, crevasses

 

The Geographical Significance of Glaciation in Canada

- glaciers removed fertile soil from the Canadian Shield exposing bedrock containing valuable minerals

- rivers and lakes that resulted from glaciation act as a source of hydroelectric power

- Canadian Shield with its many lakes is a tourist attraction

- glacial till of S. Ontario formed a gently rolling landscape with good drainage and easily cultivated soil

- till derived from limestone bedrock; therefore built in fertilizer

- Great Lakes surrounded by fertile plains of clay and sandy loams

- deepening of river valleys by glaciers allowed the Great Lakes to form along with the St. Lawrence seaway which is one of the most important inland waterways in the world

- Prairies received valuable soil deposits carried by glaciers

- alpine glaciation:
- made the Rockies a big tourist attraction
- transportation routes in troughs left by the ice
- fiords act as sheltered harbours for boats and fish farms

- in parts of Canada the depressed land continues to rise after the mass of the glaciers has been removed (i.e. isostatic rebound); around Hudson Bay this could eventually cause some rivers to switch their direction of flow from north to south

- isostatic rebound has been responsible for landforms such as raised beaches; for instance, the raised beaches at L'Anse aux Meadows National Historic Site, Newfoundland.


Courtesy: Geological Survey of Canada

"The 1000 year old Norse settlement (being excavated just beyond the building) is founded on a raised beach, which has been lifted 4 m above present sea level by postglacial rebound. Before rebounding, the currently rocky bay offered sufficient draft for their boats. The total postglacial emergence in this area is 154 m" (Geological Survey of Canada).




Assignment Work

Note: E-mail your work to your instructor for Parts A, C, and D as a word document attachment. This assignment is worth 20 marks.

Part A
Read through the information above and design twenty five study questions. These are questions that you think could be put on a test based on the information given. Include the answers with the questions.

Part B
Click on the "Practice Questions: Glaciers and Glaciation" link above and try the questions.

Part C
Download and open the topographic map and air photo of Waterton Lakes National Park, Alberta and answer the following questions:

1) What is the direction from Bertha Peak (8536) to Mount Boswell (9032)?
A. northeast
B. northwest
C. southeast
D. southwest

2) The elevation of Mount Boswell (9032) is
A. 7410 feet.
B. 7800 feet.
C. 8010 feet.
D. 8610 feet.

3) The area of Middle Waterton Lake is approximately
A. 2.5 sq. km.
B. 5 sq. km.
C. 7.5 sq. km.
D. 10 sq. km.

4) Alderson Lake (825350) is an example of a(n)
A. tarn.
B. playa.
C. finger.
D. oxbow.

5) The cultural feature at X on the air photograph is a
A. clear-cut.
B. golf course.
C. campground.
D. waste treatment pond.

6) The main economic activity in the Waterton region is
A. tourism.
B. forestry.
C. open-pit mining.
D. power production.

7) What type of lake is Upper Waterton lake?

8) What glacial landform feature is Bertha Creek (8535, 8635) flowing in?

9) What glacial landform feature is located at Y on the air photograph?

10) What glacial landform feature is located at Z on the air photograph?

Part D
Explain how the physical and human characteristics of the Waterton Lakes National Park have influenced land use. Answer in two well written paragraphs.

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