Glaciation Pack I Flashcards
What does moraine refer to?
Distinct ridges or mounds of debris that are laid down directly by a glacier or pushed up by it
- Ice contact
- Unsorted
Where are the 5 types of moraine found?
Lateral - along the glacier/valley side
Medial - in the middle of the glacier surface (supraglacial)/middle of the valley floor
Terminal - at the glacier terminus (furthest point the glacier reached)
Recessional - behind a terminal moraine
Push - at the snout of active glaciers
What leads to the 5 types of moraine?
Lateral:
- Consists of debris that falls or slumps from the valley wall or flows directly from the glacier surface
- Exposed rock on the valley side is weather and fragments fall
- Carried along the glacier and deposited when the ice melts
- Parallel to ice flow
Medial:
- Two valley glaciers converge
- Form when lateral moraines meet and combine at the confluence
- Parallel to ice flow
Terminal:
- Marks the maximum limit of glacier advance
- Advancing ice carries moraine forward and deposits it at the point of maximum advance when it then retreats
- Transverse to ice flow
Recessional:
- Form during short-lived phases of glacier advance or standstill that interrupt a general pattern of glacier retreat
- Transverse to ice flow
Push:
- Rock and sediment debris at the ice margin is moulded into ridges by the bulldozing of material by an advancing glacier
- Transverse to ice flow
What is a ground moraine?
- An uneven blanket of till deposited in the low-relief areas between more prominent moraine ridges
- Forms at glacier sole due to the deformation and eventual deposition of the debris under the glacier
What is a kame and how can a kame be described?
Rounded mound or conical hill of fluvioglacial deposits that were once in contact with the ice
What is an example of a kame?
Fonthill Kame, Niagara, Canada
What are the characteristics of a kame?
- Ice contact
- Fluvioglacial deposition
- Under or next to a glacier
- Near the end of the former glacier as it began to retreat
- Stratified
What causes kames to form?
- Deposition of material in ice (hollows such as crevasses or moulins)
- Gradually gets lower as the ice melts
What is kame terrace and how can a kame terrace be described?
Relatively continuous bench-like features along the valley side
What is an example of a kame terrace?
Loch Etive, Scotland
What are the characteristics of a kame terrace?
- Parallel to the valley
- More rounded
- May be sorted
What causes a kame terrace to form?
- A gap or lake between the valley side and the ice margin is filled with fluvioglacial deposits
- Meltwater runs between the glacier and the side wall
What is an esker and how can an esker be described?
A long, sinous ridge of sands and gravel deposited by meltwater flowing through subglacial or englacial tunnels
What is an example of an esker?
Thelon Esker, Canada (800km)
Munro Esker, Canada (400km)
What are the characteristics of an esker?
- Ice contact
- Fluvioglacial deposition under the glacier
- Parallel to former ice flow
- Usually at margins of warm-based glaciers
- Horizontally sorted
- Rounded deposits
What causes eskers to form?
- Meltwater flows in or under glaciers in tunnels
- The meltwater carries material
- When velocity falls, sediment will be laid down on the floor of the tunnel
- If a tunnel becomes blocked by sediment or ice, water and sediment is ‘ponded’ behind the blockage
- A tunnel on the base of the ice will preserve sediments
- A tunnel lying within the ice will disturb sediments as ice melts and sediments drops to the valley floor
What is a sandur and how can a sandur be described?
A flat expanse of rounded, sorted and stratified sands and gravels and is a fluvioglacial landform created by deposition by meltwater
What is an example of a sandur?
Porsmork Valley, South Iceland
What are the characteristics of a sandur?
- Proglacial
- Depositional
- No ice contact
- Stratified
What causes sandurs to form?
- When meltwater emerges from the snout, it loses energy as it is no longer flowing under hydrostatic pressure
- The material it is carrying is deposited, largest first and finest material carried furthest
- Sediment is laid down in layers during annual flood events and during periods of higher discharge (in summer)
- Highly variable discharge causes rivers to split in smaller streams to travel around areas of deposition, known as braided streams
What is a varve and how can a varve be described?
A pair of thin layers of sediment, of contrasting colour, texture and size
What is an example of a varve?
Sandend Bay, Scotland
What are the characteristics of a varve?
- Proglacial
- Depositional
- No ice contact
- Stratified
What causes varves to form?
- Proglacial lakes develop in front on glaciers in depressions in the ground which meltwater flows into
- Seasonal changes in deposition happen due to the varying amounts of meltwater
- In the melting season, there is a lot of meltwater and lots of material is transported
- A lot of heavier material will be being carried so this is deposited in a thicker layer of larger material
- In the non-melting season, there is very little meltwater so very little material is carried
- Fine sediment particles (e.g. clay) will be laid down
- Winter deposition is thin clay beds, whereas summer deposition is thicker sand and gravel beds
- Build up year after year
