Fluvioglacial Landscapes Flashcards
What is glaciolfluviol action
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
How does glaciofluvial erosion occur
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.
Give the two main sources of meltwater from glaciers
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
What are supraglacial channels
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
What are englacial streams
Surface streams may plunge down into the ice where there are crevasses, or through cylindrical vertical tunnels called moulins
What are subglacial tunnels
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
What is glaciofluvial deposition
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
What is an outwash plain and how is it formed
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
What is an esker and how is it formed
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.
What is a kame delta and how is it formed
A small feature that forms when a stream deposits material on entering a marginal lake
Form small, mound-like hills on the valley floor
What is a kame terrace and how is it formed
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
What is a crevasse kame and how is it formed
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
What are varve deposits
Layers of deposition at the bottom of a lake
How do you distinguish between glacial and fluvioglacial deposits
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
Explain the development of cold-based glaciers (5)
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
The movement of ice varies whether it is a …..based or a …..based glacier
Cold
Warm
How much does a cold-based glacier move per day
2-3cm - no meltwater so high friction between the glacier and rock surface
What is a glacial surge
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
Where does the ice move fastest (warm based)
At the centre and the highest point of the glacier, due to the lack of friction and contact between the mountain surface and sides.
How far do warm-based glaciers move per day
4m
Give two types of internal deformation
Laminar flow
Intergranular
Give 3 ways glacier move through basal movement (warm-based)
Basal Sliding
Creep
Sub-glacial deformation
Give 3 other ways glaciers move
Extending
Compressing
Surging
Give the 5 types of moraine
Ground Moraine Lateral moraine Medial moraine Recessional Moraine Terminal moraine
What is ground moraine and how is it formed
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
What is lateral moraine and how is it formed
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
What is medial moraine and how is it formed
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
What is terminal moraine
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
What is recessional moraine
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
What are erratics
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
