Glaciers Flashcards
What is a glacial period
When the temperature has dropped significantly low and ice advances
The last ice age was 22,000 years ago
What is an interglacial period
When the temperature is warmer for extended periods of time marked by the retreat of ice to higher altitudes or latitudes
What caused the ice age
The orbital theory (Milankovitch)
What 3 changes are part of the orbital theory
Eccentricity - circular/oval orbit around the sun (100,000 yrs)
Obliquity - tilt of the axis (41,000 yrs)
Precession - earths wobble (23,000 yrs)
These 3 changes alter the amount of sunlight the earth receives and where the sunlight falls in the earth
Formation of glaciers
- Glaciers form when snow remains in the same area all year round, slowly transforming into ice
- Each year, new layers of snow bury and compress previous layers
- This compression forces the snow to re crystallise, forming grains
- Gradually the grains grow larger and the air pockets between the grains get smaller, causing the snow to compact and become denser
- After about 2 winters the snow becomes a middle state between snow and glacial ice
- This process usually takes >100 yrs
Define weathering
The breakdown of rocks without moving them by the action of rain water, extremes of temperature and biological activity
E.g. freeze thaw weathering
Freeze thaw weathering process
- Water enters a crack in the rock
- When it freezes it pushes the rock apart (ice expands by 10%)
- The ice then melts, leaving the rock broken up
Glacial erosion definition
The wearing away and removing of the land by flowing water, ice or wind
(There are two erosion processes - plucking and abrasion)
Plucking
Where a glacier moves over an area of rock
Due to friction the bottom of the glacier melts and water seeps into cracks around the rock below
The water refreezes and the rock effectively becomes part of the glacier and is ripped out when the glacier advances
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 (striations)
3 ways that that till is transported by a glacier
Supraglacial material - carried on top (material falls onto ice)
Englacial material - carried inside (material falls into crevasses)
Subglacial material - carried below (material is plucked or abraded)
Glacial till
Sediment transported by ice
Can be deposited to form moraines: (recessional, lateral, terminal, medial)
Outwash
Sediment transported by meltwater rivers - more rounded than till due to attrition by river erosion
Bulldozing
When a glacier moves forward it acts like a bulldozer, moving piles of debris in front of it to create a high ridge (moraine)
The furthest advance of ice is marked by terminal moraine
Glacial deposition
When the ice is losing energy it starts to drop material
(Till)
Drops any size anywhere
Till points in the direction that the glacier flows
Deposited in landforms known as moraines
What is a corrie
Bowl shaped hollows with a steep back wall and ridges, sometimes containing a small, round lake called a tarn
Formation of a corrie
- Snow accumulates (normally on a north facing slope)
- Over time the snow becomes glacial ice and there is more ice than the depression can hold. Some starts to flow to different levels
- Plucking occurs on the back wall of the glacier, making it steeper
- Freeze thaw occurs on the top of the slope, producing scree which gets incorporated into the glacier
- Ice mass slides down the hill slowly due to its own weight. Abrasion wears down the corrie’s base, making it deeper
- There is less erosion at the front so a rock lip forms
- Tarn (lake) forms after all ice has melted
What are Arêtes
A ridge formed by 2 back to back corries
What are pyramidal peaks
A ridge formed by 3 back to back corries - grow in hollows on all sides of a mountain
Ribbon lakes
Differential rates of erosion can occur (hard and soft rock)
This means that some parts of the valley floor are deepened, allowing the creation of ribbon lakes
There are long and thin lakes that collect from meltwater and rainwater after the glacier has melted
Example of hard and soft rock
Hard - graphite
Soft - clay
Truncated spurs
Whilst rivers meander around spurs of land, ice has the erosive power to remove any obstacles in its path - truncated spurs can be identified along the sides of a glacial trough
Hanging valley
The portion of a tributary that still remains
Within glacial valleys there are main glaciers and smaller tributary glaciers
The main glacier can erode its valley to a greater extent as they have more mass
This means that the main valley is much deeper, wider and steeper
The smaller valleys are called hanging valleys
U shaped valley
Also known as the glacial trough
