Lecture 5-3 Glacial systems

Question 1

What is a glacier?

Answer 1

A mass of ice (>.1 km2) that has its genesis on land and that represents a multiyear surplus of snowfall over snowmelt
- perennial ice covers about 10% of the land areas of earth

Question 2

How do glaciers form?

Answer 2

Snow accumulation doesnt melt in the summer, recrystalization of snow to form large crystals of ice (rough and granular) called Firn
-Lower layers turn to Solid Ice under the weight of overlying firn and snow

Question 3

What are some properties of ice?

Answer 3

Has a density of .9g/cc (it floats)
its a weak solid and will not hold a vertical cliff higher than 40m
ice will flow under its own weight
pressure can cause local melting

Question 4

What are the 2 types of glaciers?

Answer 4

Alpine and Continental

Question 5

What are Alpine Glaciers?

Answer 5

Long and narrow mountain glaciers, slow-moving, wedge-shaped streams of ice

• small= 1-2 km long, 100’sm wide, 100’sm deep
• Large= over 100km long x 100’sm deep

Question 6

What are continental glaciers?

Answer 6

Very old (1000’s of years), thick (1000’s of m) mass of ice covering almost and entire land mass

• Greenland and Antarctic
• Ice cap: dome shped glacier which buries the landscape
• Ice sheet: <50,000km2, flattened dome in shpe, burrie underlying relief

Question 7

What are Alpine cirques?

Answer 7

-Semi-cicular shaped bedrock feature created as a glacier scours back toward the mountain
Found at the head of glacial trough, hollows
they occur just below the high peaks and have shape that vary depending on:
-Pre-glacial topography at the valley head
-level of activity by the alpine glacier
-duration of glaciations
-composition and structure of the bedrock

Question 8

What is ablation?

Answer 8

The loss of snow and ice by melting and evaporation. most melting occurs at the glacial snout

Question 9

What is Glacier Mass balance?

Answer 9

The change in mass (diff between total accumulation and gross ablation) of a glacier over some defined interval of times, determined either as a value at a point, an average over an area, or the total mass change for the glacier
-provides measure of glaciers condition, is it gaining or losing mass?

Question 10

What are the 4 parts of glacial zonation?

Answer 10

1) Accumulation zone: the upper part of the glacier
2) Firn: granular old snow that forms a surface layer in the accumulation zone
3) Equilibrium line: line that separates the accumulation zone from the ablation zone
4) Ablation zone: the lower part of the glacier

Question 11

What makes glaciers move?

Answer 11

Weight: the weight of the overlying mass forces the ice to spread out
Flow: ice is slippery. flows over underlying rock/soil
Crevasses form along steep slopes

Question 12

How far do glaciers move?

Answer 12

Below snowline: glaciers begin to melt and evaporate, thining out (lower elevation/latitude)
Ice front: The front edge of a glacier
Melting=movement: stationary ice front
Extended to the sea: break off (calving)

Question 13

What is ice velocity dependant on?

Answer 13

Distance from bed and valley sides
accumulation vs. ablation zone
free water -temperate glaciers
Stresses cause the surface to crack (crevasses)

Question 14

How does glacial erosion take place?

Answer 14

Ice push: the glacier acts as a bulldozer and may be capable of pushing a limited amount of loose rock debris
Plucking: involves removal of blocks of rock from outcrops. the glacier exploits rock weaknesses along fractures to pull the rock loose

Question 15

What is Glacial Abrasion?

Answer 15

Glacially transported rock fragments that show polish, striations and grooves. both clasts and bedrock are likely to show these features

Question 16

What factors influence abrasion?

Answer 16

• Amount of debris
• basal sliding velocity
• ice thickness to apply normal pressure
• hardness of bedrock
• basal water pressure (enough to increase sliding velocity but not so much that friction is needed)
• removal of rock material by melt water

Question 17

What is Arete:

Answer 17

Steep-sided, sharp-edged bedrock ridge formed by two glaciers eroding away on opposite sides of a ridge.

Question 18

What is a col?

Answer 18

Low areas, or passes, through a ridge that once had glaciers on either side

Question 19

What is a horn?

Answer 19

3 or more cirques adjacent to one another (A jagged peak that has survived the glacial erosion all around it)

Question 20

What is a tarn?

Answer 20

A small lake that occupies a rock basin in a cirque or glacial trough

Question 21

What are Erratics?

Answer 21

A boulder-sized rock dumped by a glacier. the rock is usually of a different type than the surrounding rock

Question 22

What are evidence for glaciers?

Answer 22

Unsorted materials, Erratics, Striations, polished bedrock

Question 23

What are striations?

Answer 23

Grooves carved into the bedrock by pebbles and cobbles carried at the bottom of a glacier

Question 24

What is Polished bedrock?

Answer 24

smooth rock surfaces created as glaciers flow over bedrock

Question 25

What are glacial troughs

Answer 25

The longitudinal profiles are steep, irregular and stepped

U-shaped and typically straight

Question 26

What are hanging troughs

Answer 26

Is a tributary that no longer meets the main valley accordantly, often the sites of waterfalls

Question 27

What are Fiords?

Answer 27

Troughs partially filled with an arm of the ocean

Question 28

What is glacial Till?

Answer 28

unsorted/unstratified material left over by glaciers

Question 29

What is Outwash?

Answer 29

Deposits made by streams after glaciers melt (sorted/stratified)

Question 30

WHat is glacial drift and what are the two types? What is Lodgement till?

Answer 30

Rock debris deposited by glaciers
-stratified drift- layers of sorted and stratified debris of varying sizes
- till- unstratified debris of varying sizes deposited directly by the glacier and not streams
Lodgement till: underneath; dense and rich clay; deposited by previous glacier

Question 31

What are moraines and the different types?

Answer 31

Piles of sediment that are deposited

• Ground moraine: carried in the bottom of a glacier pre-deposition
• Lateral Moraine: pile up along the sides
• Medial Moraine: material within the glacier (two come together)
• Terminal moraine: occurs at the ice front and marks the glaciers farthest advance
• Recessional moraine: slowly retreat of end moraine leave smaller rows of sediment behind

Question 32

What is a Drumlin?

Answer 32

Low rounded oval hills formed under the glacier and molded by its movement

Question 33

What is a kettle?

Answer 33

A basin formed where and ice block was buried by till or ice-contact deposits and then melted. this is the principle ice-stagnation landform, and is usually occupied by a lake

Question 34

What is a Kame?

Answer 34

An isolated hill of stratified drift deposited in opening within or between ice blocks
kame deltas are flat-topped hills deposited in standing water at an ice margin

Question 35

What is an esker?

Answer 35

a winding, rounded ridge that is generally 30-70m wide, height 17-33m,

Question 36

What are outwash plaines?

Answer 36

Depositional plains of outwash