MIDTERM CHP 8

Question 1

Glacier?

Answer 1

A mass of ice on land that formed by the accumulation of snow.

Question 2

Where does a glacier form?

Answer 2

They form at high elevation (alpine glaciers) and high latitude (continental glaciers)

Question 3

How does a glacier form?

Answer 3

Glaciers form when snow accumulates and remains year round, and new layers of snow bury, compress and insulate the previous layers.

The new layer forces the snow to accumulate and recrystallize as it transforms into ice.

Question 4

Unique properties of glacial ice

Answer 4

• Glacial ice is very much in a state of transition. While it is a solid it is very close to being a liquid.
• It forms at 0°c and more or less remains there. It will melt where pressure is applied.
• This also means that ice will “flow” even though it’s a solid.

Question 5

How does glacial ice move and how does the velocty of the ice vary within a glacier?

Answer 5

Ice moves slowest at the bottom, fast at the top (typically top center).

A glacier will advance at different rates depending on the season.

The absence or presence of meltwater will also determine how fast and how far a glacier will move.

Question 6

Regelation

Answer 6

Way that a glacier moves around an obstacle by melting and refreezing.

Question 7

Roche Moutonnee formation?

Answer 7

1. The ice encounters an obstacle it cannot move. The ice slows down and pressure increases. The ice here then melts.
2. The solid ice eventually slides forward and around the obstacle. At the same time meltwater moves down and around the obstacle.
3. The meltwater is now down at the lee-side of the obstacle. Here, under lower pressure the meltwater re-freezes.
4. The bedrock at the lee-side of the obstacle is physically weathered creating more angular rock fragments.

The end result is the formation of a ROCHE MOUTONNET

Question 8

8. What is a cold based glacier? How does velocity vary with depth within this ice?

Answer 8

Glacier where the ice is frozen to the underlying bedrock.

The glacier deforms as it moves.

Average ice velocity is slow.

The bottom is slow, the top is fast.

Question 9

9. What is a warm based glacier and how does velocity vary with depth within this ice?

Answer 9

Glacier where the ice is NOT frozen to the bedrock beneath it.

The ice does not deform internally. Instead it slides slides along as a single mass on a layer of melt water.

Average velocity is faster.

Question 10

10. How does sediment form at the base of a glacier as it forms?

Answer 10

The glacier forms as snow accumulates. During this process, meltwater is sometimes present.

As meltwater reaches the bedrock beneath the snow/ice and refreezes, it physically weathers the bedrock (frost action).

As a result, large angular pieces of sediment are created.

Question 11

11. How does sediment form at the base of a glacier as it moves?

Answer 11

As sediment at the base of the ice is set in motion, it moves with the ice.

Where a piece of sediment within a glacier contacts the underlying bedrock, abrasion weathering can occur.

At contact, the moving sediment abrades against the bedrock, creating very fine sediment.

Question 12

12. Striation

Answer 12

Striations are are straight, long (<10 m), shallow (<1cm) engraving or scratched in the bedrock caused by the passage of a rock embedded in the base of a glacier.

Question 13

Striations are used for?

Answer 13

Striations are very good at indicating ice flow direction,

Question 14

Chattermark

Answer 14

These are crescent shaped “holes in the bedrock that can be concave up-ice or concave down-ice.

(asymmetrical shape in cross-section)

Question 15

Chattermark formation

Answer 15

Instead of the ice going around the rock fragment (regelation) or eroding the rock fragment once again, it is possible that the bedrock may break from shear stress.

If this happens when the bedrock is broken (physically weathered) such that a friction crack or “chatter mark” is formed

Question 16

Lodgement Till

Answer 16

Till deposited beneath a glacier.

• It is compressed, very dense and very hard.
• contains all the original grain sizes it had when it was in transport and often has an ‘internal fabric created by the ice as it passes after deposition.
• This internal fabric may include alignment of some rock fragments or grooves left in the surface of the till.

Question 17

Lodgement Till formation

Answer 17

If there is a high enough concentration of sediment at the base of the glacier the ice may not be able to move it.

Eventually the ice will detach from the sediment, leaving it behind as it continues to flow forward.

Till may also be deposited in and around irregularities in the bedrock. (Till deposited in this way is Lodgement Till)

Question 18

Ablation Till

Answer 18

Till deposited at the edge of a glacier.

• Not compressed (not dense) nor hard like lodgement till.
• Often has been reworked by meltwater and gravity so that the finer gain sizes have been removed.

Question 19

Ablation Till Formation (SEE DIAGRAM)

Answer 19

1. At A the glacier is warm-based (not frozen to the bedrock) because of pressure melting.
2. At B the glacier is cold-based (it is frozen to the bedrock) because the glacier is thinner, pressure is less and cold air temperatures can penetrate into this thinner, less insulated ice.
3. At C: as the ice at the edge of the glacier slows down, it is pushed by the faster ice behind it. This causes ice and sediment to move up and way from the bedrock.

As a result of all this movement, sediment is carried onto the ice (supra-glacial), in the ice (englacial) and beneath the ice (subglacial) is concentrated at the edge of the glacier (C).

Question 20

What is a till plain?

Answer 20

Area large area of land covered in till. They often have irregular or hummocky topography. (Their surface is often irregular with lots of small highs and lows that are a result of uneven deposition and the formation of kettles)

Question 21

Why do till plains often have a hummocky topography?

Answer 21

As a glacier melts it may leave blocks of ice stranded on the ground in front of it.

This ice block may be completely or partially buried by sediment (till) from the glacier.

When this ice block melts a basin or depression is left behind.

If his basin fills with water it is a kettle lake.

Question 22

What are the sources of liquid water in a glacial environment?

Answer 22

• Meltwater. Derived from rain, melting snow or melting ice, and pressure melting in the glacier.
• arguably, a geothermal gradient could be contributing to melt.
• Meltwater itself can contribute to more melting.

Question 23

What does liquid water have that solid ice does not? How does liquid water affect the behaviour of glacial ice?

Answer 23

? IDK

Question 24

20. What happens to a glacier when it reaches the ocean?

Answer 24

Upon reaching he ocean the ice begins to float and melt.

The ice will also break apart to create icebergs.

The rise and fall of sea level with tides will help to break the ice.

(A) While sediment may be released from the entire glacier, more is released from the base of the glacier.

(B)
Sediment is also carried by icebergs and eventually deposited as they melt.

Question 25

What is an esker and how does it form?

Answer 25

A long linear ridge of sediment deposited by meltwater in tunnels at the base of the glacier.

Question 26

Drumlin

Answer 26

An asymmetrical teardrop shaped hill composed of till that is deposited beneath an advancing ice sheet.

Question 27

Kame

Answer 27

A mixture of sediment deposited at margin of an ice sheet where meltwater and gravity have concentrated the sediment.

These are often larger, taller hills of poorly sorted sediment.

Question 28

Briefly describe the formation of glacial lake deposits

Answer 28

With the passage of each year, alternating summer and winter layers are deposited in the lake (rhythmites).

During the summer, in addition to sediment and meltwater, pieces of glacial ice are transported into the lake. This glacial ice often carries sediment, some of it coarse, which drops into the lake when the ice melts.

The presence of large drop stones in finer summer and winter layers makes these deposits VARVES which are exclusive to a glacial lake environment.

Question 29

Glacial Lake Deposits - Summer conditions

Answer 29

During the summer the surface of the lake is ice free. Water and sediment enter the lake but only the coarser sediment (i.e. silt) settles to the bottom.
(silt in suspension does not settle to the bottom.)
This creates a coarser grain, lighter coloured summer layer on the lake bottom.

Question 30

Glacial Lake Deposits - Winter Conditions

Answer 30

during the winter, the lake is covered in ice. Water in the lake is isolated and circulates very little. Now the finest sediments (i.e. clay, organic material) carried in suspension are deposited created a fine grained, dark coloured winter layer.

Question 31

Paraglacial environment

Answer 31

Cold environments that persist after a glacier is gone.

Question 32

Periglacial environment

Answer 32

Cold environments that do not always experience freezing conditions.

Question 33

Nivation Hollow

Answer 33

Gravity, and perhaps some meltwater, erodes and transports this sediment to create a shallow depression in the hillside called a nivation hollow on this slope.

Question 34

Nivation Hollow

Answer 34

In the northern hemisphere, a north facing slope will be colder as it gets less sunlight.

More snow will accumulate and persist longer on this slope.

Here, as the base of the snow pack there is repeated freeze thaw cycles which physically weather the bedrock.

Gravity, and perhaps some meltwater, erodes and transports this sediment to create a shallow depression in the hillside called a nivation hollow on this slope.

Question 35

Permafrost

Answer 35

Ground that has been frozen for at least 2 years.

Question 36

Why is permafrost important in Canada?

Answer 36

• it is a major feature in the Canadian landscape.

Question 37

Patterned ground and how it forms

Answer 37

These are regular, repeating patterns in sediment that are caused by freeze-thaw cycles.

mixing in the form of convection currents is the result of repeated expansion and contraction cause by freeze-thaw cycles. At the surface, the larger grains are pushed further to form a ridge (A)

Question 38

Two ways a rock glacier can form

Answer 38

They form in one of two ways:

1. When a typical glacier accumulates more and more sediment until it is mostly rock fragments
2. When a deposit of rock fragments becomes impregnated with snow and ice such that it begins to flow..

Question 39

Closed systems for pingos

Answer 39

In a closed system, pingos form when a lake drains.

Permafrost beneath a lake occurs at greater depthe because of the heat holding capacity of the water.

Once the lake is drained, the exposed ground beneath the lake freezes - the surface of the permafrost rises.

Water between the lake bottom and the surface of the permafrost is trapped. It eventually freezes to form ice that pushes the ground up.

Question 40

Breaker zone landform

Answer 40

ripple bedding (including: asymmetrical, symmetrical ,crescent, long or short)

Question 41

2)Swashzone

Answer 41

Thin laminations - layers in fine sediment tilted toward the ocean

Question 42

3) dunes

Answer 42

large riples - formation of sand controlled by wind