Fluvioglacial Landscapes

Question 1

What is glaciolfluviol action

Answer 1

The action of glacial meltwater upon the landscape and the landform this produces.

Glaciofluviol processes are quite different from normal fluvial action due to the high pressure and velocity of the flow

Question 2

How does glaciofluvial erosion occur

Answer 2

The high pressure and velocity of the meltwater beneath glacier ice causes erosion of underlying bedrock by both abrasion, and cavitation, as well as by chemical means

High amounts of glaciofluvial erosion occur in front of glaciers, in areas where the meltwater exiting the ice is channelled.

Question 3

Give the two main sources of meltwater from glaciers

Answer 3

Surface Melting - majority. Only source of cold-based glaciers which are frozen to their beds.

Basal Melting - occurs if the temperature of the ice at the base of the glaciers at the PMP. The weight of the overlying ice, combined with frictional heat

Question 4

What are supraglacial channels

Answer 4

Surface melting - sometimes surface streams form, running along the top of the ice in the ablation zone when the surface melting produces water more quickly than it can percolate through the ice.

Few meters wide and have high velocities because of their smooth sides

Question 5

What are englacial streams

Answer 5

Surface streams may plunge down into the ice where there are crevasses, or through cylindrical vertical tunnels called moulins

Question 6

What are subglacial tunnels

Answer 6

Basal meltwater flows under pressure beneath the glacier and, through the exploitation of weaknesses and fractures in the ice, the meltwater is able to excavate subglacial tunnels beneath the glacier, eventually exiting at openings along the snout

Question 7

What is glaciofluvial deposition

Answer 7

When meltwater deposits material subglacially, englacially, or supraglacially, the material is referred to as an ice-contact glaciofluvial deposit

When glaciofluvial material is deposited at or beyond the ice margin by streams issuing from the glacier, it is known as outwash

Question 8

What is an outwash plain and how is it formed

Answer 8

An extensive and gently sloping area of sand and gravel in front of a glacier

Results from the ‘outwash’ of material carried by meltwater streams. At the end of a glacial period - huge quantities of material will be spread out over the outwash plain by greater torrents of water

Question 9

What is an esker and how is it formed

Answer 9

Long, sinuous ridges made of sand and gravel that can be 30m high and stretch for several km’s. Usually take the form of meandering hills running roughly parallel to valley sides

Formed by subglacial river deposition during the final stages of a glacial period, as the ice was melting and no longer moving forwards.

Question 10

What is a kame delta and how is it formed

Answer 10

A small feature that forms when a stream deposits material on entering a marginal lake

Form small, mound-like hills on the valley floor

Question 11

What is a kame terrace and how is it formed

Answer 11

Most extensive type of kame - on the side of the valley

Results from the infilling of a marginal, glacial lake, trapped between the glacier and the valley side. When the ice melts, the kame terrace is abandoned as a ridge on the valley floor

Question 12

What is a crevasse kame and how is it formed

Answer 12

A disrupted pile of debris at the bottom of the valley floor

Some result from the fluvial deposition of sediment in the surface crevasses. When the ice melts, they are deposited on the valley floor to form small hummocks

Question 13

What are varve deposits

Answer 13

Layers of deposition at the bottom of a lake

Question 14

How do you distinguish between glacial and fluvioglacial deposits

Answer 14

GLACIAL =

• Jagged and angular
• Striations
• Long axis orientation in the direction of glacial flow

FLOVIOGLACIAL =

• Smooth and rounded
• Sorted by size
• Stratified layers
• No noticeable orientation

Question 15

Explain the development of cold-based glaciers (5)

Answer 15

Found in high latitudes, so less seasonal change + higher altitudes

Very limited meltwater

The glacier moves via internal deformation (stick to the rock bellow, gravity rips away the ice from the bedrock) as there is no basal sliding - only moves 2/3cm per day

Mostly formed when snow accumulates on the ground, turns to ice

Question 16

The movement of ice varies whether it is a …..based or a …..based glacier

Answer 16

Cold

Warm

Question 17

How much does a cold-based glacier move per day

Answer 17

2-3cm - no meltwater so high friction between the glacier and rock surface

Question 18

What is a glacial surge

Answer 18

Due to the build-up of meltwater beneath the ice that can’t escape and moves the glacier 60-70m per day, occurring once every 60 years

Question 19

Where does the ice move fastest (warm based)

Answer 19

At the centre and the highest point of the glacier, due to the lack of friction and contact between the mountain surface and sides.

Question 20

How far do warm-based glaciers move per day

Answer 20

4m

Question 21

Give two types of internal deformation

Answer 21

Laminar flow

Intergranular

Question 22

Give 3 ways glacier move through basal movement (warm-based)

Answer 22

Basal Sliding
Creep
Sub-glacial deformation

Question 23

Give 3 other ways glaciers move

Answer 23

Extending
Compressing
Surging

Question 24

Give the 5 types of moraine

Answer 24

Ground Moraine 
Lateral moraine 
Medial moraine 
Recessional Moraine 
Terminal moraine

Question 25

What is ground moraine and how is it formed

Answer 25

A thin layer of till deposited all over the valley floor, often in humockdy mounds measuring up to 5m high

Deposited by a glacier in successive advances and retreats

Question 26

What is lateral moraine and how is it formed

Answer 26

A ridge of till running along the edge of a glacial valley parallel to the direction of ice flow (100m high and several km’s long)

Formed through freeze-thaw weathering on the exposed valley sides above the ice level, causing rock debris to fall onto the glacier ice by rockfall. As the glacier retreats, it is deposited on the valley floor

Question 27

What is medial moraine and how is it formed

Answer 27

Starts at the confluence of two glaciers. Found in the centre of a glacier, visible as a long ridge of supraglacial debris running parallel to ice flow

Formed by the merging of two later moraines where two glaciers meet - rarely distinctive beyond the snout of the glacier

Question 28

What is terminal moraine

Answer 28

A ridge of till extending across a glacial valley, tend to be crescent-shaped, reaching further down the valley in the centre.

Marks the position of the maximum advance of the ice

Question 29

What is recessional moraine

Answer 29

A series of ridges of glacial till running broadly parallel to each other and to the terminal moraine.

Tend to be lower in height to terminal moraine (5-20m high)

Form during a standstill in the glacier’s retreat when material is deposited at the snout of the glacier. For significant ridges to form, pauses need to be long enough to allow till to accumulate and deposited

Question 30

What are erratics

Answer 30

Individual pieces of rock, varying in size from small pebbles to large boulders which have a completely different lithology from that of the area they have been deposited - eroded by plucking, transported within ice to different regions