Glacial Processes Lab
Before any glacial valley exists, ice has to break the rock, drag the pieces along and drop them again. Freeze-thaw weathering, the two glacial erosion processes told apart precisely, and how a glacier carries and deposits its load.
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What a glacier does to rock
The scenery of a glaciated upland gets most of the attention, but a valley shape is only ever the result of rock being broken, carried and dropped. This module stays with those processes. Freeze-thaw weathering shatters the rock where it sits. Plucking and abrasion are the two ways moving ice wears the land away. Transportation carries the loose rock inside and on top of the ice. Deposition drops it again when the ice melts. Get the processes right and the landforms explain themselves in the next module.
Glacial process words
Learn these five before you sort any description. Each one does a different job, and exam questions ask which one is acting rather than asking you to list them all.
Plucking against abrasion
These two erosion processes are the ones learners mix up, because both wear the land away as the ice moves. The difference is what happens to the rock, so read both columns and remember which one grinds.
How to name the process
Ask what is happening to the rock. Is it being shattered where it sits without moving anywhere? Is a moving agent tearing whole pieces off, or is it grinding the surface with material it already carries? Is loose rock being carried along, or dropped when the ice runs out of energy? Match the description to the job and the name follows. The landforms these processes create, such as corries and glacial troughs, are studied in the next module.
Match the process to its job
- freeze-thaw
- plucking
- abrasion
- deposition
- shatters rock in place as water freezes in a crack
- pulls loosened rock away after it freezes to the ice
- grinds the surface with rock held in the ice
- drops the carried load as the ice melts
Which process is this?
A glacier moves and rock that is frozen into its base scratches long grooves into the valley floor below. Which process is acting?
- Abrasion, because carried rock scrapes the surface.
- Plucking, because rock is torn away.
- Freeze-thaw, because water is freezing.
- Deposition, because material is left behind.
Pick the erosion processes
Select the TWO processes by which moving ice erodes the land.
- Plucking
- Abrasion
- Deposition
- Freeze-thaw
Read the map scale
On a map, 1 cm represents 2 km on the ground. A glaciated valley measures 3 cm along the map. Multiply to find its real length in km. What is the answer?
Order the freeze-thaw steps
Put the steps of freeze-thaw weathering in order, earliest first.
- Water collects in a crack in the rock
- The temperature drops below freezing and the water freezes and expands
- The ice pushes the crack wider
- The ice melts and the cycle repeats until a piece breaks off
Complete the process facts
Water freezing again and again in a crack shatters rock by _____ weathering. When meltwater freezes onto rock and the moving ice pulls it away, the process is _____. When rock carried in the ice scrapes the surface below, the process is _____. When the ice finally melts it drops its load, which is called _____.
Match the description to the process
- long scratches gouged along a smoothed valley floor
- a jagged back wall where blocks have been ripped out
- a pile of shattered angular rock below a frost-cracked face
- a spread of unsorted rock and clay left as the ice retreats
- abrasion
- plucking
- freeze-thaw
- deposition
Spot the erosion processes
Tap the TWO processes that erode the land as the ice moves.
- plucking
- abrasion
- freeze-thaw weathering
- deposition
Name the process at work
Read each description and choose the process that is acting.
- On a high peak, water seeps into a crack, freezes below freezing overnight, thaws by day, and after many nights a lump of rock splits away. Which process is this?
- Meltwater at the base of a glacier freezes around blocks of rock, and as the ice moves forward it drags those blocks away from the bedrock. Which process is this?
- A glacier in the Lake District melts at its snout and leaves behind a jumble of rock and clay of every size, all mixed together. Which process is this?
Explain the glacial processes
Explain the processes that shape a glaciated upland, from the breakdown of rock to the dropping of material. Say what each process acts on.
- Explain what freeze-thaw weathering is and why the ice does not need to move for it to work
- Explain what plucking is and how meltwater makes it possible
- Explain what abrasion is and what it leaves on the rock surface
- Explain clearly the difference between plucking and abrasion
- Explain how a glacier carries its load and when deposition happens
- Finish by explaining why glacial till is unsorted