Glaciation - Unit 5 Flashcards
How does a flowing ice body move?
Through glacial transportation
How does flowing meltwater move?
Through fluvial transportation
Where can rock debris be located and transported?
1- Transported on surface (supraglacial debris)
Glacial and fluvioglacial
2- Transported within (englacial debris)
Glacial and fluvioglacial
3- Transported at the base (subglacial debris)
Glacial and fluvioglacial
4- Transported away from the front (proglacial debris)
Fluvioglacial only
What is lateral moraine?
When supraglacial debris is concentrated in bands at the sides of the glacier
What is medial moraine?
When supraglacial debris is concentrated in the middle of the glacier
Give 2 ways that englacial debris is formed
1- Supraglacial debris that becomes buried by snowfall
2- When 2 separate valley glaciers converge
What 2 processes mainly form subglacial debris?
Abrasion and plucking
Give 4 differences between glacial and fluviglacial debris
- Glacial till is angular
- Fluvioglacial deposits are rounded
- Glacier till is unstratified
- Fluvioglacial deposits are stratified
- Glacial till is unsorted
- Fluvioglacial deposits are sorted
- Glacial till is different sizes
- Fluvioglacial deposits are similar sizes
Why are glacial and fluvioglacial sediment so different?
Glacial - rock debris entrained within glacial ice generally experiences few changes as it’s transported as it is fixed within the ice, with the exception of subglacial debris, which is eroded away due to abrasion as it is dragged over bedrock = produces ‘rock flour’
Fluvioglacial - water has limited ability to transport rock debris. The size of clasts it can transport is a function of the velocity of the flowing water (shown on Hjulstom curve)
Give 6 examples of landforms formed by glacial ice
1- Drumlins 2- Terminal moraine 3- Recessional moraine 4- Lateral moraine 5- Medial moraine 6- Push moraine
Name the landscape where glacial ice landforms are found
Till plain
Give 6 examples of landforms formed by meltwater
1- Eskers 2- Kames 3- Kame terraces 4- Kettle holes 5- Kettle lakes 6- Varves
Name the landscape where meltwater landforms are found
Sandur
What 3 categories can glacial till be subdivided into?
1- Lodgement till
2- Ablation till
3- Deformation till
How is lodgement till formed?
- Forms subglacially
- Plastered onto underlying surface by glacier due to friction
- It is compacted, sorted and stratified
How is ablation till formed?
- Deposited from sub, en and supra glacial debris due to ablation
- It is poorly compacted, unsorted and unstratified
How is deformation till formed?
- If a glacier re-advances over an area of till previously deposited, underlying till sediment can be folded
- It is compacted, contain many rock types and the patterns reflect the stresses involved in its formation
What is a moraine?
An accumulation of glacial debris
What is a drumlin?
An elongated hill, streamlined in the direction of ice flow and composed largely of glacial deposits
What is the deformational theory of drumlin formation?
- Glacier moves over obstacle and till is plastered around it
- Happens when there is a large amount of subglacial debris
How does a terminal moraine form?
- When ice melts and deposits all the moraine it was transporting at the front of glacier
How do recessional moraines form?
- Same manner as terminal moraines but they represent a location where the glacier paused for a considerable time during its retreat
How do push moraines form?
- When a glacier advances over existing moraine, pushing the moraine into a new ridge
How can ice-contact fluvioglacial deposits be deposited?
Subglacially (eskers)
Supraglacially (kames)
What are eskers?
Long, sinuous ridges of sands, gravels and pebbles deposited by meltwater streams/rivers flowing through subglacial, and sometimes englacial, tunnels. They can be up to 20m high and 3km wide
How are eskers formed?
- Subglacial stream forms due to increased pressure
- When glacier retreats, the stream stops flowing as hydrostatic pressure from glacier is lost
- Deposits all its material as it doesn’t have the energy to carry it
Describe the clasts in an eskers sediment
- Rounded
- Sorted
- Stratified layers
Give an example of an esker
Munro Esker
What are kames?
A deposited mound of sediment left in the path of a retreating glacier
How are kames formed?
- Formed supraglacially
- Rock fall from valley enters crevasses in glacier
- Crevasses move closer to the base as glacier melts
- Dumped as a mound of sediment when reached valley bed
What are kame terraces?
A deposited mound of sediment at the sides of the valley
How are kame terraces formed?
- Pressure between valley sides and glacier forms an ice-marginal channel
- As water, carrying sediment, travels into valley, it collects in channel
- Channel is not flowing so it deposits material
- When glacier retreats, it leaves sediment at the valley sides
Describe the clasts in a kame/kame terrace sediment
- Angular
- Sorted
- Stratified
What are kettle holes and kettle hole lakes?
A small lake formed from melted dead ice in the valley
Give an example of where kames/kame terraces are found?
East Lothian, Scotland
How do kettle holes form?
- Glacier retreats, leaving behind dead ice
- Meltwater from glacier deposits sediment around dead ice
- Over time, sediment builds up
- As temp increases, dead ice melts and a small lake is created
Give an example of where kettle holes can be found
North Shropshire
What are varves?
The varying layers of sediment that gets deposited due to seasonal rates of deposition
How do varves form?
- Winter = less deposition as there is less meltwater produced
- Smaller particles are deposited in winter
- Summer = more deposition as there is more meltwater produced
- Larger particles are deposited in summer
- Happens each year, building up varying layers of sediment
What is a sandur/outwash plain?
The flat landscape formed by fluvioglacial deposition in front of a retreating icesheet
