4. Origin of tills, deposits, and landforms Flashcards
Origin of tills, meltwater-, glaciolacustrine- and glaciomarine deposits, and landforms they build
What are some typical properties of most tills?
Deposited directly by a glacier
(with little or no sorting by water)
- diamictic (clay to boulders)
- cohesive
- massive (=structureless)
- mixed lithological and mineralogical components
What does the colour of a till indicate?
Weathered = more brown
Young and fresh = gray greenish colours
What can classify a deformation till?
- local material
- deformation structures
- heavily abraded stones
- compact appearance
- elongated stones strongly aligned parallel to ice movement
What can classify a lodgement till?
Related to a deformation till
- local and far-travelled material
- massive structure
- elongated stones aligned parallel to ice movement
- bullet-shaped and imbricated stones
- relatively fine-grained
What can classify a melt-out till?
When the ice doesn’t move anymore
- far-travelled components
- unabraded stones
- stringers of sand (washing)
What can classify a flow till/gravitational deposit?
- folds (bc of flow down)
- heterogenous appearance
- loose structure (haven’t been underneath the ice)
- inconsistent orientation of
elongated stones - far-travelled components (material transported from far up the glacier)
- some sorting by water
- relatively coarse-grained
- strongly variable thickness
What classifies waterlain tills?
Deposited in water
- in proglacial lakes and in ocean/sea at the ice margin
- in subglacial lakes and cavities
Can have oversized boulders → dropstones
What is a kame?
- Moundlike hills composed of clay, silt, sand and to some extent gravel and till
- Formed by geomorphological inversion (dead-ice blocks on either side of a ‘block’ of sediments)
- Frequent normal faults at the flanks
- Grain-size fining upwards (decreasing water flow velocity)
What is kame terraces?
Ridges of sand and gravel along valley flanks.
Some till inclusions.
What is an esker?
- Long, narrow ridges of poorly sorted gravel and sand; infill of glacial channels
- Can be up to 50 m high, 100’s km long
- Oriented perpendicular to glacier margin (= parallel to ice flow)
- Grain-size fining upwards (decreasing water flow velocity).
What does a supraglacial esker look like?
The esker is deposited on top of a till and with another till at the sides of the esker (so the top of the esker is exposed)
What does an englacial esker look like?
The esker is deposited on top of a till and coated with another till
What does a subglacial esker look like?
The esker is deposited on the bedrock and coated with a till
What is a crevasse filling?
- Linear, short, low ridges
- Unsorted debris accumulated in supraglacial crevasses lowered onto the ice bed during deglaciation, or accumulated in subglacial crevasses.
What is a terminal moraine?
The reach at the outermost extend
