GEOG: Ch. 19 - Glaciers

Driftless area

The greatest total area of ice-covered land was in North America.

–For reasons not understood, a small area in NW Canada, northern and western Alaska, and SW Wisconsin was left uncovered by glaciers.

indirect effects of Pleistocene glaciation

1.  Periglacial processes.

2.  Sea-level changes.

3. Crustal depression.

4.  Pluvial (increased rain) development.

1.  Periglacial processes.

•Was never touched by glacial ice but where indirect influence of the ice was felt.

•Most important process was the erosion and deposition done by meltwater.

•Frost weathering was also important.

2.  Sea-level changes.

•There was a worldwide lowering of sea level during glacial advance due to a buildup of ice and less water draining into the seas.

3. Crustal depression.

•The weight of the ice caused portions of the crust to sink as much as 4000 feet in some places.

4.  Pluvial (increased rain) development.

•All continents experienced an increase in moisture.

•This increase was caused by a combination of meltwater runoff, increased precipitation, and decreased evaporation.

•A prominent features was the creation of many lakes where none had been.

Outlet glaciers

long tongues of ice, are found around the margin of the sheet.

–Extend between rimming hills and the sea.

ice shelf.

When ice reaches the ocean along a massive front and sometimes projects out over the sea

icebergs

When great chunks of ice fall off the shelf into the sea

Two types of mountain glaciers

1.  Highland icefields.

2.  Alpine glaciers.

1.  Highland icefields.

•Ice accumulations is an unconfined sheet that may cover a few hundred to thousand square kilometers.

•Found in the high country of western Canada and southern Alaska and Iceland.

Valley glaciers

outlets that are often tongues of ice that travel down valleys in the mountains.

piedmont glacier.

If the leading edge of a valley glacier reaches a flat area and escapes the confines of the valley walls

2.  Alpine glaciers.

Those that develop individually high in the mountains rather than as part of a broad icefield, usually at the heads of valleys.

Cirque glaciers

very small alpine glaciers confined to the basins where they originate

•Normally they flow as long, narrow valley glaciers.

accumulation

addition of ice by incorporation of snow

ablation

wastage of ice through melting and sublimation

The persistence of any glacier depends on…

the balance between accumulation) and ablation

neve or firn

Continued compression creates a material called…

zone of accumulation

upper portion of glacier

ablation zone

lower portion of glacier

abrasion

–Bedrock is worn down by the rock debris being dragged along in the moving ice.

–Tends to produce striations, polishing, and grooves.

Drift

general term for all material moved by glaciers.

Till

the name for all rock debris deposited directly by moving or melting ice with no meltwater flow involved.

–Accomplished whenever debris is dropped on the ground beneath the ice.

–Debris is unsorted.

glacial erratics

outsized boulders that are included in the glacial till, which may be different from the local bedrock

U-shaped troughs

The most conspicuous erosional features are valley bottoms,  gouged and deepened by moving ice.

roche moutonnee

often produced when a bedrock hill is overridden by moving ice.

till plain

consists of unsorted glacial deposits. 

–Deposition tends to be uneven, producing an irregularity undulating surface of broad, low rises and shallow depressions.

Moriane

a general term for glacier-deposited landforms composed entirely or largely of till.

–Usually much longer than they are wide.

–Tens of meters to a few kilometers high.

4 types of moraines exist:

1.  Terminal moraine

2.  Recessional moraines

3.  Ground moraine

4.  Interlobate moraine

•1.  Terminal moraine

a ridge of till that marks the outermost limit of glacial advance.

–Forms when a glacier reaches its equilibrium point and so is wasting at the same rate that it is being nourished.

•2.  Recessional moraines

ridges that mark positions where the ice front was temporarily stabilized during the final retreat of the glacier.

–Terminal and recessional moraines form in the shape of a concave arc (tongue of ice)

•3.  Ground moraine

formed when large quantities of till are laid down from underneath the glacier rather than from its edge.

•4.  Interlobate moraine

formed along the side margins of two glaciers.

–Forms a middle moraine.

Kettles

form as the blocks of stagnant ice, both large and small, included within the till eventually melt.

–Create irregular depressions.

Drumlins

low, elongated hills made of unsorted till.

–Deposited by ice sheets.

–Their origin is not completely understood, but most of them are apparently the result of ice readvance into an area of pervious deposition.

–Usually occur in groups.

–Significant because they tell the direction of ice flow.

outwash plains

most extensive glaciofluvial features