Glaciation Pack H Flashcards
What is till?
The material that gets deposited by a glacier
- Can be fine small particles (like clay, sand or silt) or large clasts (like pebbles, cobbles and boulders)
- Deposited when the ice or water releases the material is was holding (melt-out)
- Unsorted
What three types of till exist?
Ablation till:
- Created when melting happens near the glacier snout in receding or stagnant glaciers
- Deposition happens subglacially from geothermal heat warming the glacier’s sole
- Material on the surface or in crevasses can also be released when solar radiation melts ice
- Whole layers of debris or single clasts
Lodgement till:
- Created when rock debris that is being transported subglacially becomes lodged or stuck in the ground as the glacier moves
- May be due to pressure melting
Deformation till:
- Created when the material that is in front of or beneath a glacier is unable to resist the glacier’s force and is deformed
- Weak rock is then incorporated into the base of the glacier
- Released when the ice melts
What are the characteristics of glacial till?
- Poorly sorted
- Angular or sub-angular due to no attrition
- Dropped in mounds and ridges not layers
- Unstratified
- Elongated particles might be orientated in a particular direction to show direction of ice
- Subglacial till may have been eroded slightly but supraglacial till will be more angular/less spherical
What is drift and how is it sorted?
- Sorted till
- Stratified (in layers)
- Larger material is closed to glacier
Why does drift get deposited?
- Reduction of energy/velocity in meltwater streams
- Meltwater streams lose energy in winter when streams freeze and discharge is low or at night when temperatures are lower
What are the characteristics of fluvio-glacial deposits?
- Material can be deposited from supraglacial, englacial or subglacial streams
- Can be deposited where the glacier is or in front of the glacier
- Large meltwater streams will have the capacity to carry large volumes of rock
- Material is rounded due to attrition from the streams that are under hydrostatic pressure and are very fast
- Sorted as heaviest material is dropped first
- Deposits are layered/stratified vertically as daily and seasonal flows differ
What does proglacial mean?
In front of the glacier
Why is fluvio-glacial material more sorted and more rounded the further from the snout in the distal zone rather than in the proximal zone?
- When streams come out the glacier there is a decrease in velocity as there is no longer pressure from the ice above and around the stream
- At the snout (proximal zone) the deposits are less sorted and more angular as the meltwater has the greatest power
- In the medial zone, particles are less coarse and more rounded
- In the distal zone, it is well sorted and smaller
What is a drumlin and how can it be described?
An oval shaped hills, largely composed of glacial drift, formed beneath a glacier or ice sheet and aligned in the direction of ice flow
What is an example of a drumlin?
Teesdale, North Yorkshire
What are the characteristics of a drumlin?
- Exists as fields or swarms of landforms, known as a basket of eggs topography
- Found in lowland areas
- Steeper, blunt end is the up-glacier side (stoss)
- Gently sloping, tapered end occurs down-glacier (lee)
- Have rock cores surrounded by a concentric sheath or till or are filled with unconsolidated sediments that are poorly sorted
- Vary in size
- Polygenetic as are formed under the glacier
What causes drumlins to form?
Theory 1:
- Glacier normally flows over the till but, when there is heavier, sticker sediment, the glacier moulds the sediment as it flows
- Known as subglacial bed deformation
Theory 2:
- Huge meltwater floods (caused by volcanic eruptions) can cause erosion
- Leaves behind the drumlin
