unit three

Question 1

define weathering

Answer 1

the breakdown of rock where it is located involving physical processes such as freeze thaw weathering and chemical processes such as carbonation

Question 2

what are the two processes of weathering (physical and chemical)?

Answer 2

physical: freeze thaw weathering
chemical: carbonation

Question 3

define erosion

Answer 3

the removal of rock by ice water wind or gravity

Question 4

what are the two key weathering processes?

Answer 4

freeze thaw weathering and dialation

Question 5

describe freeze thaw weathering

Answer 5

when water freezes it expands by 9% in volume, and exerts pressure on any cracks or crevasses on the glacier. repeated freeze thawing eventually causes the rock to fracture

Question 6

by how much does water expand by when frozen?

Answer 6

9%

Question 7

what conditions must be met for freeze thaw weathering to occur?

Answer 7

• the rock must be permeable to allow movement of water
• precipitation must occur
• temperatures must fluctuate
• the altitude must be high enough to drop below freezing

Question 8

what is dialation?

Answer 8

when rocks fracture due to overlying pressure being released. this typically occurs when a glacier is melting and exerting less downwards pressure. the rock then expands and fractures to release pressure

Question 9

what is the dialation process sometimes called?

Answer 9

pressure release or unloading

Question 10

what are the three types of erosional processes?

Answer 10

abrasion, plucking and subglacial meltwater erosion

Question 11

describe the process of abrasion

Answer 11

as a glacier moves the embedded rock debris in its base scrape against the bedrock wearing it away

Question 12

how does rock flour form?

Answer 12

during abrasion the subglacial debris are worn down and this is converted into tiny clay particles or rock flour

Question 13

what are the factors that affect abrasion?

Answer 13

• the speed of glacial movement
• the ice thickness/weight
• the amount of meltwater
• the hardness of the debris/rock
• the shape/supply of debris

Question 14

how does plucking occur?

Answer 14

when meltwater seeps into cracks in the rock of the valley floor and sides and unfreezes causing freeze thaw weathering. as the glacier moves it “plucks” pieces of bedrock

Question 15

where does plucking occur?

Answer 15

on the down valley side of rock obstacles that the ice is moving over via regelation slip. it occurs at the base of the glacier

Question 16

how does regelation slip cause plucking?

Answer 16

regelation slip occurs when the pressure melting point is close to the temperature at the base of the ice, resulting in increased pressure which creates crevasses. the meltwater then fills into the crevasses and freeze thaw weathering occurs, which then results in plucking as it moves

Question 17

what is attrition?

Answer 17

when rocks and pebbles wear down on eachother, becoming smaller and rounder

Question 18

what is corrosion?

Answer 18

chemical erosion of rocks

Question 19

what is hydraulic action?

Answer 19

when water crashes against something causing material to become dislodged and carried away

Question 20

why are subglacial streams powerful?

Answer 20

they form a system of tunnels with water flowing under extreme pressures. the flow direction is also determined by the pressure gradient and topography, not gravity.

Question 21

what are the two stages of cirque formation?

Answer 21

1. the development of a niviation hollow
2. the enlargement of the hollow after a cirque begins to move

Question 22

describe the formation of a niviation hollow

Answer 22

1. north facing slopes recieve little insolation and so the temperature remains pretty cold even during the summer
2. freeze thaw weathering occurs due to temperature fluctuations which results in loose material
3. the surface of the glacier thaws in the summer producing meltwater which removes rock debris in the solifluction stream

Question 23

describe stage two of cirque formation

Answer 23

1. further accumulation of ice adds weight resulting in the rotational movement of ice which is aided by the meltwater caused by pressure melting
2. as the ice rotates it removes rock frangments from the back wall, this plucking occurs a steep, jagged and angular backwall
3. the rock fragments picked up by plucking are transported by the rotating ice causing abrasion of the floor, deepening the hollow
4. as erosion enlarges the hollow pressure release causes dialation cracks to form in the underlying rock, weakening it aiding further erosion
5. as the glacier continues to slip it moves over the cirque and out of the basin creating a lip, which may experience abrasion as pressure icreases

Question 24

what are aretes?

Answer 24

sharp, knife edge ridges which have been produced by two cirques eroding back into eachother

Question 25

what are pyramidal peaks?

Answer 25

pyramidal peaks are where three or more cirques around a mountain have been formed, eroding the centre creating a sharp and steep central area. frost shattering enhances the shape further

Question 26

what are glacial troughs?

Answer 26

glacial troughs are formed when glaciers flow into pre-existing river valleys and alter them

Question 27

what are truncated spurs?

Answer 27

in a normal river valley interlocking spurs are created as the river erodes downwards and meanders from side to side, however as a glacier moves down a river valley it erodes each spur and over time create truncated spurs which have a steep cliff face

Question 28

what are hanging valleys?

Answer 28

just like large rivers have smaller tributaries which join them together, glaciers have smaller glaciers joining them, however the smaller glaciers may have their flow impaired by the larger glacier and this causes less erosive potential. this causes ice to hang above the much larger main valley after the ice has gone.

Question 29

what do hanging valleys sometimes create?

Answer 29

smaller waterfalls

Question 30

what are ribbon lakes?

Answer 30

ribbon lakes are long narrow lakes found in a glacial trough, certain parts of the valley erode more deeply through abrasion than others due to thicker ice or areas of softer rock and this creates a hollow called a rock basin. the harder rock on either side are known as rock bars which act as dams which fill up with rainwater

Question 31

what are the macro scale landforms?

Answer 31

cirque, arête, pyramidal peak, glacial trough, hanging valleys, truncated spurs and ribbon lakes

Question 32

what are the two meso scale landforms?

Answer 32

rouhee moutonees and crag and tails

Question 33

what are the micro scale landforms?

Answer 33

striatations, chatter marks and polished rock

Question 34

what are rouché moutonees?

Answer 34

a peice of resistant rock on the floor of a glacial trough that has undergone abrasion on the upper valley side and plucking on the down valley side

Question 35

what process allows rouche motonees to form?

Answer 35

regelation slip

Question 36

how do rouche moutonees form?

Answer 36

- plucking takes place on the downside of the glacier. pressure water seeps into the cracks in the rocks and re freezes due to reduced temperatures, which causes water to expand, then debris break off and are plucked away causing a jagged side - abrasion takes place on the upper glacier side where high pressures push debris into the obstacle which polishes it giving it a smooth side - pressure melting occurs due to meltwater allowing the glacier to slide

Question 37

when do craig and tails form? (not how)

Answer 37

when a glacier moves over a band of resistant rock surrounded by less resistant rock

Question 38

how do crag and tails form ?

Answer 38

• plucking and abrasion erode the stoss side of the rock • the less resistant rock gives the tail which has a gentler gradient • moraines are often found on the top of the tail

Question 39

what are striations?

Answer 39

scratches on the hard bedrock produced during abrasion. debris frozen in the basal ice are dragged across the bedrock to produce them and they give a clear indication of what direction the ice was moving

Question 40

what are chatter marks ?

Answer 40

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

Question 41

describe the micro scale landform: polished rock

Answer 41

as well as scratching and gouging the rock the ice can polish it if sand and silt are found in the basal ice layer as opposed to angular rock fragments

Question 42

where is our example of a rouche mountonee?

Answer 42

at the floor of the nant ffrancon valley

Question 43

where is our example of an arête ?

Answer 43

cwm idwal

Question 44

where is our example of lateral morraines?

Answer 44

cwm idwal

Question 45

where is our example of a pyramidal peak?

Answer 45

cwm idwal

Question 46

where is our example of a cirque?

Answer 46

cwm idwal