Unit 3 Glaciated landscapes

processes of glacial weathering, erosion, and the characteristics and formation of landforms and landscapes

what is the difference between weathering and erosion?

weathering is the break down of rock in situ

erosion is the removal of rock by wind, water, ice or gravity

WEATHERING: what is freeze thaw weathering?

physical weathering where water enters cracks in rocks, freezes and expands, causing the rock to break apart as it thaws.

how do rock characteristics affect freeze thaw weathering?

softer rock which is less resistant to weathering

permeability- more permeable means more rock can be absorbed

damaged rock- more prone to weathering

how does climate affect freeze thaw weathering?

• colder environment

• lots of precipitation

how does altitude/aspect affect freeze thaw weathering?

higher altitude

orientation of the slope- facing the sun will reduce freeze-thaw weathering

WEATHERING: what is the process of dilatation?

the process of rocks fracturing when the overlying pressure is reduced

• this occurs when a glacier is melting, losing weight and hence exerting less downward pressure

• rocks will expand and fracture, as this happens with the fractures tending to be parallel to the surface

EROSIONAL: What is abrasion?

• as a glacier moves, the weathered ricj debris embedded in its base scrapes against the bedrock and wears it away

• large peices of rock debris scratches the bedrock

• finer sand, silt and clay particles tend to smooth and polish the rock- a sandpapering effect

• subglacial debris itself is worn down and converted into tiny clay particles known as rock flour

what factors affect abrasion?

• spped of glacier movement

• ice thickness

• subglacial meltwater

• relative hardness of debris and bedrock

• supply of debris

EROSION: what is plucking?

occurs when meltwater seeps into cracks in the rock of the valley floor and sides. The water then refreezes causing freeze thaw weathering. as the glacier moves, it plucks peices of bedrock.

plucking also occurs on the down valley side of rock obstacles that the ice is moving over by the process of regelation slip.

plucking is effective at the base of glaciers due to the presence of meltwater due to pressure melting

EROSION: what is subglacial meltwater?

• meltwater may get channeled beneath a glacier before emerging at the snout of a glacier as a proglacial lake

• high-velocity meltwater can erode material at the glacier’s bed or widen and deepen channels in the bedrock.

• can result in large subglacial meltwater channels, e.g. Gwaun Valley In South Wales

Macro Scale Erosional Landforms: what is a cirque and what are the 2 distincy stages?

a large ampitheatre shaped hollow found at the head of a valley glacier.

1) development of a nivation hollow

2) glacial erosion deepening the hollow

how does a nivation hollow form? (stage 1)

1. im small hollows on north facing slopes, cold glacial periods cause freeze thaw weathering to occur which causes rocks to disintegrate

2. summer meltwater renives the rock debris which in turn enlargens the hollow

3. this process is known as nivation.

How does a cirque form (stage 2)

1. further accumulation ice will add weight to the glacier will cause the ice to rotate which is aided by meltwater from pressure melting

2. as the ice rotates, it removes rock fragments from the back wall of the hollow through plucking- backwall therefore becomes steep and jagged

3. removal of these rock fragments are then transported by the rotating ice. this causes abrasion of the corrie’s floor and further deepens the hollow.

4. Further rotational movement is aided by meltwater that enters the system through the backwall by a crevasse known as a "bergschrund". This meltwater increases lubrication, enhancing the glacier's ability to erode the bedrock.

5. as erosion enlargens the cirque, pressure release causes dilatation cracks to form in the underlying rock, parallel to the floor of the cirque. this weakens the underlying rock further allowing for more erosion

6. as the growing cirque rotationally slips it may start to move over the corrie lip and out of the rock basin. the lip of the corrie may exhibit anrasion on the up glacier side and plucking on the down side.

why are cirques usually orientated between North West through to N. East to the S.East?

• NE direction as it is shaded from the sun meaning there is little insolation.

• this leads to less melting and more accumulation of ice which grows the hollow quicker

What is an arete and how does it form?

a sharp knife edge ridge which has been produced by two corries eroding back toward each other. Frost shattering makes the peaks jagged giving it its signature knife edge

how does a pyramidal peak form?

• where 3 or more corries around a mountain have been formed as they continue to develop back to back

• the remaining central area of the mountain becomes sharper and steepened.

• further frost shattering will enhance the shape further.

EXAMPLE: Gylder Fawn

How does a glacial trough form?

• glacial troughs develop where glaciers flow into pre existing river valleys

• they alter the valley beyond recognition

EXAMPLE: Yosemite Valley, California

how are truncated spurs formed?

as a glacier moves down a river valley, it erodes rach spur produced by river erosion

over time the interlocking spurs become eroded back to become truncated spur which have a steep cliff face

EXAMPLE: Yosemite Valley

How do hanging valleys form?

• large glaciers have smaller glaciers joining them

• the smaller glacier may have its flow impaired by the larger glacier it is joining meaning it possess less erosive potential and therefore it will not carry out as much vertical erosion down into the bedrock

• as a result after the ice has gone, the smaller glacier valley is left hanging above the much deeper main valley

EXAMPLE: Yosemite Valley

How do ribbon lakes form?

• long narrow lake usually found in a glacial trough

• certain parts of the valley are more likely to be eroded more deeply due to areas of softer rock

FORMATION:

• glacier moves over an area containign alternate bands of hard and soft rock.

• glacier will erode the softer rock more easily, creating a rock basin and leave bars of the harder rocks sticking out on either side called rock bars which act as a damn for meltwater that collects in the rock basin

EXAMPLE: Buttermere, Lake District

MESO SCALE EROSIONAL LANDFORMS: What are roche moutonees

• peice of resistant rock on the floor of a glacial trough that has undergone ABRASION on the upvalley side and PLUCKING on the down valley side.

• typically 1-5 metres in heigh

• 5-20 metres in length

• formation is linked to the process of regelation slip

How do crag and tails form?

1. When a glacier moves over alternating bands of hard and soft rock.

2. the glacier erodes the first band and soft rock more quickly but the middle band of hard rock protects the second band of soft rock from being eroded completely.

3. the CRAG is the hard rock and the TAIL is the soft rock. the crag has steep sides and has cracks in it from plucking.

MICRO SCALE EROSIONAL LANDFORMS:

what are straitions?

• scratches on hard bedrock produced by the process glacial erosion

• debris has frozen in basal ice layer and is dragged across the bedrock to produce them

• they give clear indication of which way the ice was moving

EXAMPLE: Isle of Skye

what are chatter marks?

• small intermittent chips in the bedrock formed when the basal debris within the ice is not in continuous contact with the bedrock

EXAMPLE: Yosemite National Park

what is polished rock?

• glacial ice can also polish rock if sand and silt are entrained within the glacier

EXAMPLE:

Central Park, New York.