Moraines Flashcards
What do end moraines mark?
The ice marginal position
When the moraines are at the side of the glacier they’re called
lateral moraines.
You can tell if a moraine has lots of ice in it because…
it’s covered in debris- ice is protected by debris so can last for a long time (can’t tell you of age therefore).
Glacier advance
Positive mass balance
Can advance over previous moraines
Glacier in balance
Glacier stay in one position and build up a large moraine
Glacier retreat
Leave a series of moraines marking it’s retreat.
End moraines general term for moraines that
Surround the glacier
End moraines are formed by…
Melt (dump)
Freezing on
Push
Melt-out Moraines
After a few years…
As a glacier melts out the debris will avalanche down the front, collecting, and forming an apron down the front (supra glacial source).
Subglacial/englacial source
they become vegetated and stablished- becomes harder for them to be washed away.
Freezing on
Underlying sediments are freezed on.
In summer this will be melted out, forming a moraine.
Push moraines
Another way in which moraines are formed is when there is some kind of subglacial source being pushed underneath towards the front, pushing up the sediment beneath it.
In this example the glacier is completely clean at the front (must have come from beneath).
Glaciotectonics
Proglacial deformation
Deformation in front of glacier
Compressed is…
Extended is…
Negative
Positive
Styles of deformation
Open folding and nappes (ductile deformation)- where something is pushed and ‘bends’
Listric thrust faulting (brittle deformation)
Faulting
Sometimes the sediment is too strong- instead of bending it snaps.
Push Moraine formation
Bulldozed push moraines- frontal pushing
Deforming bed push moraines- frontal pushing + lateral stresses transmitted through the deforming mass
Landsystems
Facies = individual sedimentary deposits
Facies assemblage/sediment landform association = facies laid down next to each other or in a vertical sequence
Landsystem = Large scale groupings of facies deposited in same environment plus erosional landforms from same time
Hard bed rock glacier
Low debris supply- alpine
High debris supply - Ghulkin-type
They have so much debris because of being formed in new tectonic areas
Big contrast in summer and winter temperatures
Can dam
Soft bed rock glacier
Marginal ice sheet
Typically a series of push moraines, stagnant ice till underneath the glacier
Push moraines are only formed by glaciers that…
have retreated and then advance again.
The existence of a push moraine is usually evidence of…
the climate becoming poorer after a relatively warm period.
Why are there characteristic differences in the orientation of rocks within a push moraine?
Material that had already been deposited is shoved up into a pile as the ice advances, and because most moraine material was deposited by falling down not pushing up, there are characteristic differences in the orientation of rocks within a push moraine.
