Mass Balance, Transport and past glaciations Flashcards
Mass balance (b)
= accumulation (c) + ablation (a)
Mass balance (b) = accumulation (c) + ablation (a) Positive mass balance
More accumulation than melting
Glacier advance
Mass balance (b) = accumulation (c) + ablation (a) Negative mass balance
More ablation than accumulation
Glacier retreat
Measuring mass balance
Manual collection of mass balance
Accumulation zone
Pits (to check how much snow has fallen)
You can dig down into the glacier and see how much snow is deposited each year (quite easy to see)
Measuring mass balance
Manual collection of mass balance
Ablation zone
Stakes
You can dig down into the glacier and see how much snow is deposited each year (quite easy to see)
Positive mass balance measurements are very…
detailed
Negative mass balance measurements are very…
very slow and expensive, small scale
Positives of remote sensing
potentially cover large huge areas, could be semi automatic
Negatives of remote sensing
may be problems with technique on small glaciers
What is Global Land Ice Measurements from Space (GLIMS) used to do?
Using the World’s Glaciers to Monitor Climate Change
Glacial transport paths
Supraglacial
Englacial
Subglacial
Sediment sources
Supraglacial debris Subglacial debris - Regelation - Shearing - Freezing on
Pressure melting point
The pressure melting point is the temperature at which ice melts at a given pressure.
Positive mass balance
More accumulation than melting
Glacier advance
There is more accumulation than melting so glacier advance
Negative mass balance
More ablation than accumulation than accumulation
Glacier retreat
More ablation meaning the glacier retreats
The glacier is always moving forward (but it may retreat)
In the summer, the snow melts back at the front
In the higher part there is more accumulation (accumulation dominant)
The lower part is more ablation (called ablation dominant)
Transport
What does englacial mean?
When material passes through the glacier
When it pass along the base it is sub-glacial
When material travels along the top it is supraglacial
Transport
What does regelation mean?
Means refreezing
Water has to flow up hill which causes melting and then it refreezes when it gets to the other side
Transport
What does shearing mean?
When there is a crack in the ice at the bottom and then there is sediment the protrudes into the base of the ice
Transport
What does freezing on mean?
Where sediment gets frozen onto the glacier because it is so cold
What is the Anglian?
a line that differentiates where the glacier was
When was the most recents ice age in the uk?
10,000 years ago
What did the recent ice age create?
Boulder clay deposits in eastern UK
What was the Pleistocene?
A glacial period around 25,000 years ago when 30% of the earth’s land surface was covered by ice (mainly in the N. hemisphere) and most of Britain was covered by ice that had extended South from the Arctic in a colder glacial period.
How did the Pleistocene end?
When the climate warmed (about 10,000 years ago)
What is the ice sheet that covered the UK?
Devensian/ The Scandinavian
Describe the maximum extent of the ice covering the UK 25,000 years ago
The ice covered The Wash in the East and South Wales in the West
What are the 5 glacial processes?
1) Freeze-thaw weathering
2) Glacial Erosion
3) Movement
4) Transport
5) Deposition
What causes freeze-thaw weathering?
Temperature changes
Moisture changes
Chemical processes by mild acid
Describe the freeze-thaw weathering process
1) Water seeps into cracks in a rock face
2) The temperature falls at night, causing the water to freeze
3) Water expands - this expansion puts pressure on either side of the crack , causing it tear wide open
4) During the next 24 hour cycle, the ice melts, sinks deeper into the crack and freezes again
5) Over time, large blocks of rock can be shattered apart by repeated cycles of this weathering process
What is the evidence for freeze-thaw weathering?
Scree slopes and blockfields (rock debris which cover large upland areas)
Why is freeze-thaw weathering important?
It helps to shape jagged glacial mountain landscapes
What are the two main ways in which ice is eroded?
1) Plucking
2) Abrasion
What is plucking?
When ice moves over the rock surface and meltwater freezes around loose sections, pulling them away. It’s effective when the rock contains many joints (cracks) which the rock can seep into
What is abrasion?
Caused by rocks and boulders embedded in the base of the glacier which act like sandpaper, scratching and scraping the rocks - causing striations
Glaciation of Britain – glacial and inter glacial
Many potential glaciations
- A lot of potential glaciations with little evidence
- Old glaciation – Anglian 450ka
- Young glaciation – last glacial maximum (LGA) or Devensian 18ka
The glacier extent is disputed – more recent research suggests it stretched further into the north sea
British and Irish ice sheet (BIIS)
Most recent – Lock Lomond / Younger Dryas (12.9 – 11.5ka) – it becomes cold again for about 1,000 years and glaciers re-grow in mountainous areas
Cullins, Skye – you can see where the glacier was and the moraine at the front
