❄️ Physical: Glaciated Landforms Flashcards
What caused the last ice age?
Every 100 years the Earth’s orbit becomes slightly elongated, making summers shorter and cooler and winters snow fails to melt. Temperatures dropped and ice grew
What is a glacier?
A slow moving mass of ice downhill under the influence of gravity.
How do glaciers form?
- Glaciers form when snow remains in the same area year-round, slowly transforming into ice
- Each year, new layers of snow bury and compress the previous layers
- This compression forces the snow to re-crystallise, forming grains similar to sugar
- Gradually the grains grow larger and the air pockets between them get smaller, causing the snow to slowly compact and increase in density
- After about two winters, the snow turns into firn - a middle state between snow and glacier ice
- For most glaciers, this process takes more than 100 years
What is weathering?
The breakdown of rocks in-situ by the action of rain water, extreme temperatures and biological activity.
Explain the process of freeze-thaw weathering.
- Rain water falls into a crack in a rock
- The water freezes and causes the rock to expand
- The rock then breaks into tiny pieces
What is plucking?
Where a glacier moves over an area of rock and due to friction, the glacier melts and water seeps into cracks around the rocks below. The water refreezes and the rock effectively becomes part of the glacier and is ripped.
What is abrasion?
Where rocks at the bottom of the glacier act like sandpaper - grinding over the bedrock. This can polish the rocks or create sharp grooves called striations.
What are the 3 different ways glaciers can transport debris (till)?
- Supraglacial material: On top
- Englacial material: Inside
- Subglacial material: Under
What is bulldozing?
When a glacier moves forward it can act like a giant earthmover, bulldozing piles of rock debris in front of it to create a high ridge called moraine.
What is outwash?
The sediment meltwater rivers carry.
Why is outwash more rounded?
Attrition in the river which erodes their sharp edges.
What is a landform?
A natural feature on the Earth’s surface caused by geographical processes.
What are corries?
Bowl shaped hollows with a steep back wall and ridges, forming an armchair shape around a hollow. Sometimes containing a small round lake called a tarn.
How is a corrie formed?
- Snow accumulates in depressions high up, predominantly on north facing slopes
- Over time the snow becomes glacial ice and there’s more ice than the depression can hold and some starts to flow to other levels
- Freeze-thaw weathering occurs at the top of the slope producing scree which becomes incorporated into the glacier
- The hollow deepens where the ice is thickest due to abrasion. Rock debris acts as tools to wear away the bottom of the hollow
- Ice becomes frozen to the back of the hollow and plucking occurs as blocks of rock are pulled away as the ice moves downhill. This makes the back wall steeper and these rock fragments become incorporated into the glacier.
- There is less erosion at the front where the glacier leaves the corrie hollow to flow down the valley; a rock lip forms here as a result of less powerful erosion
- When all the ice has melted a tarn forms
What are aretes?
A narrow ridge formed when two corries meet back to back.
What are pyramidal peaks?
When three or more corries form a single peak where the aretes meet.
What is an example of an arete?
Crib Goch in Wales
How are ribbon lakes formed?
- As a glacier flows it travels over hard and soft rock
- Softer rock is less resistant to erosion, so the glacier will carve a deeper trough over it
- When the glacier has melted, water collects in these deeper areas, creating a ribbon lake
What are the characteristics of ribbon lakes?
- Long
- Thin
- They’re in U shaped valleys/glacial troughs