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Kvartær Geologi > Strukturer > Flashcards

Strukturer Flashcards

1
Q

What is an erratic block?

A

A block that does not correspond/match the surrounding bedrock. It has been moved there by a glacier

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2
Q

What characterises an erratic block?

A

It differs from the surrounding bedrock.
It is often striated (needs to be large(?))

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3
Q

What are the erosional forms/structures?

A

Striae
Crescentic marks
Grooves
Potholes
Roches moutonneés
Crag-and-tails
Drumlins
MSGL
Flutings
Glacial valleys
Tunnel valleys

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4
Q

What is striae?

A

An erosional form, made by abrasion. It is elongated scratches parallel to ice movement

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5
Q

What kinds of stripes are there?

A
  1. Simple striae
    - Movement underneath the ice
    - can show ice movement changes
  2. Wedge-shaped and nailhead striae
    - carved down
    - dragging line with final impact spot
    - show flow direct
  3. Rat-tail striae
    - positive ridge
    - had something in front to protect from erosion
    - show flow direction
  4. Polished surfaces
    - grinding by silt(?)
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6
Q

What are crescentic marks?

A

Marks on boulders or bedrock from impact. Can show ice direction

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7
Q

How does crescentic marks show ice flow direction?

A

It will show a “steep” and deep ish end and a more flat end. The direction is from the flat to the deep cut end.

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8
Q

What are grooves and how are they made?

A

They are linear depressions or channels.
Made from direct glacial and Meltwater erosion - enhancing each other

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9
Q

What are potholes?

A

Deep holes in the bedrock.
Probably made from meltwater systems close to the ice margin. Has big blocks at the bottom, that was used as grinding material

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10
Q

What forms Roches moutonneés and what does it look like?

A

Formed by the ice moving over it, smoothing one side and plucking/quarrying on the other by the freezing of water.
Flow direction from smooth to rough

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11
Q

What does crag-and-tails consist of?

A

A high point bedrock (hard?) with a “tail” of till behind.
Flow direction from high point to low point (the tail)

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12
Q

What is drumlins?

A

An erosional and depositional structure.
Often made by till, in an elongated ‘drop’ shape, showing the flow direction from wide to thin

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13
Q

What characterises flutings?

A

They are long, small (<1m in height) forms, with an initial boulder at the end - hindered the erosion behind it

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14
Q

What is MSGLs?

A

Big structures parallel with flow direction of the ice

Kinda like gigantic drumlins.

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15
Q

What are the characteristics of glaciated valleys?

A

They are U-shaped
There is erosion on the bottom and the flanks

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16
Q

What are tunnel valleys and how are they made?

A

They are channels made from subglacial meltwater drainage. Carved in soft rocks and indicates a huge amount of water

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17
Q

What is the evidence for tunnel valleys to be glacial and not from ex. rivers?

A
  • They go up and down in typography in a way rivers can’t.
  • they start and end in seemingly nowhere
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18
Q

What depositional structures are there?

A

(till)
(drumlins)
Kames
Kame terraces
Eskers
Crevasse fillings
End/terminal moraines
-
Braided streams
Boulders?

……

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19
Q

What are Kames, and what do they consist of?

A

Ice contact deposit.

Hills consisting of clay, silt, sand and some gravel and till.
Fining upwards - decreasing water flow velocity

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20
Q

How are Kames created?

A

Deposition from meltwater and later geomorphological inversion.

Deposition between deadice blocks. When melted it will create normal faults at the edge, when falling down

21
Q

What are kame terraces?

A

A stair-like depositional meltwater formation. Consist of sand and gravel, maybe till inclusions

22
Q

How are Kame terraces created?

A

Created by deposition of meltwater, between typography and deadice. Melting of the ice in several phases can give several terraces

23
Q

What are eskers?

A

Meltwater deposit. Seen as long narrow ridges, that can be discontinuous.
Consist of poorly sorted sand and gravel. Fining upwards

24
Q

How and where are eskers formed?

A

By deposition, filling glacial channels.
They can be made either subglacial, englacial or subraglacial

25
Q

What is the different kinds of eksers/esker processes?

A

Subglacial:
- R-channel - filling out a channel, later material from the ice will cover it
- N-channel - same as R-channel but the water carved it down into the substratum

Englacial:
- filling out channel inside glacier, material from glacier part above will later cover it

Subraglacial:
- fill out channel on the surface, fall down after melting and not covered

26
Q

What is a difference between eksers and tunnel valleys?

A

Eskers is made on hard bedrock
Tunnel valleys are made on soft bedrock

27
Q

What are crevasse fillings?

A

Meltwater deposit. Short low ridges of unsorted debris.

28
Q

How and where are crevasse fillings made?

A

Sub- or subraglacial, where debris/sediment accumulated in crevasses

29
Q

What are end moraines?

A

Meltwater deposit.
Long linear ridges consisting of poorly sorted gravel, sand, till, and a little amount of fine grained material.
Marks a hold of an ice sheet

30
Q

How are end moraines made?

A

By meltwater deposition of material carried or pushed by the glacier, under a larger hold of the ice advance

31
Q

What is the difference between end and terminal moraines?

A

They are largely the same except a terminal moraine is the maximum extent/hold of the ice advance.

Terminal = end
End ≠ terminal

32
Q

What would be expected from proglacial deposits (braided streams)?

A
  • decresing grain size down-flow
  • increasing sorting down-flow
  • daily/seasonal changes (facies changes, erosional unconformities)
  • vertical trends (ice advance/retreat sequences)
33
Q

What does big boulder deposits indicate?

A
  • dramatic meltwater release event
  • it’s close to ice margin
34
Q

If there is only space between big boulders (no matrix), what does this indicate?

A

A high deposition until the end.
The small grains were carried away after when the velocity was too low to carry the big ones.

35
Q

What landscapes/structures does the periglacial zone create?

A

Cryoplanation
(- congelifracts
- frost cracked stones)
Rock glaciers
Cryotutbation
Solifluction
Frost fissures and ice wedges
Patterned ground
Sorted polygons
Pingos
Palsas
Thufur
Growing stones

36
Q

What is cryoplanation?

A

Formation of flat land surfaces

37
Q

What happens in the process of cryoplanation?

A

Disintegration of rock into congelifracts. Fractured boulders by frost.
Creates (in situ) boulder fields, and vertical sorting.

38
Q

What are Rock glaciers?

A

A toungeshaped mass of frozen debris (including ice - not like glacier).
Happens in permafrost conditions due to slow deformation of ice core.

39
Q

What is cryotutbation?

A

A soil process, mixing and disturbing the layers due to freezing/thawing cycles.

40
Q

How does cryotutbation happen?

A

Heterogeneous soils:
Different grain sizes and water content = different freezing rates -> different volume increase -> deformation

41
Q

What is solifluction and how does it happen?

A

Slow creep of soil over permafrost.
Happens downslope, bc of high water saturation of the active layer (low shear strength)

42
Q

What are ice wedges?

A

It is the presence of ice in a frost fissure, preventing the crack from closing and instead growing.

43
Q

What are the different types of ice wedges?

A

Epigenic: several generations growing outwards, youngest in middle

Syngenetic: sediments on top, grows upwards, oldest at bottom

Anti-syngenetic: erosion, crack grows downwards, oldest at top/outwards

44
Q

How is patterned ground created?

A

From ice wedges and freeze/thawing cycles, on horizontal surfaces

45
Q

What is sorted polygons?

A

Rings of coarser grained material with fine grains in the middle

46
Q

What is a Pingo?

A

A hill with ice at its core - will collapse after melting

47
Q

What are palsas?

A

Very small hills (pingo-like structures) caused by uneven snow coverage, freezing soil inbetween (expands)

48
Q

What is Thufur?

A

Smallest structure, small “bulges” of the ground in fine grained sediment (fields)

49
Q

What are growing stones?

A

Rocks moving up from the soil due to freezing/thawing

Kvartær Geologi (8 decks)

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