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geo > Rocks And Weathering > Flashcards

Rocks And Weathering Flashcards

1
Q

Oceanic Crust

A

6 - 10km
3g/cm3 (density)
Basaltic
200 million years old (younger)

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2
Q

Continental crust

A

35 - 70km
2.7 g/cm3
Silica, oxygen, aluminium
1500 million years old (old)

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3
Q

Tectonic plates

A

Sections of the lithosphere that move as a single unit

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4
Q

Sea floor spreading

A

The formation of fresh areas of oceanic crust which occurs through the upwelling of magma at mid ocean ridges

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5
Q

Benioff zone

A

A zone of earthquake foci caused by a subduction oceanic crust

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6
Q

Accretionary wedge

A

Where sediment on the ocean floor and some of the oceanic crust are scraped off and forced onto the other plate

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7
Q

Metamorphosis

A

When rocks compress and form new rocks under high heat or pressure

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8
Q

Epicentre

A

The point of the surface directly above the focus

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9
Q

Transform fault

A

When 2 plates slide past each other causing friction

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10
Q

Convection current

A

The rising, spreading and sinking of the mantle driven by heat by the core

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11
Q

Weathering

A

The disintegration of material in situ

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12
Q

Mechanical (physical) weathering

A

Rocks broken down without a change in the composition of the rock

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13
Q

Chemical weathering

A

Rocks are broken down by chemical reactions

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14
Q

Regolith

A

The name given to weathered material

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15
Q

Scree

A

The collection of weathered material on a slope

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16
Q

Talus

A

Broken down material that remains next to the original rock

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17
Q

Joint

A

Fracture in rocks

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18
Q

Fissure

A

A large scale weakness in a rock

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19
Q

Batholith

A

A rock formed underground by cooled magma

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20
Q

Exfoliation

A

Outer ,Ayers of rock that are weathered and peeled away

21
Q

Block disintegration

A

Sedimentary rock weathers in large sections (homogenous rock eg limestone )

22
Q

Granular disintegration

A

When rocks break away in small fragments ( heterogenous rock eg granite)

23
Q

Diurnal temperature range

A

Different in lowest and highest temp during the day

24
Q

Thermal expansion + contraction (type and describe)

A

Mechanical type of weathering
- absence of clouds
- suns heat causes outer layers of rock to expand
- radiation cooling at night causes rock to contract
- repeated daily causes outer layers of rock to be weathered

25
Q

Oxidation

A

Chemical
- when rock contains iron, water is present, oxygen is present in soil or atmosphere
- iron (Fe) oxidises to produce hematite (Fe2O3) or magnetite (Fe3O4) rusting

26
Q

Vegetation root action

A

Mechanical
- roots have ability to grow in cracks and joints in rock
- force cracks and joints to widen overtime
- causes rock to break apart

27
Q

Organic weathering

A

Chemical
- humus is dark organic matter formed from plant and animal decays
- during decay, humid acid is released
- humid acid contains organic chelating agents like peptides and sugars
- these extract metal ions from minerals and rocks

28
Q

Carbonation

A

Chemical
- CO2 is dissolved in water forming carbonic acid
- carbonic acid reacts with calcite (calcium carbonate) forming calcium bicarbonate (calcium hydrogen carbonate)
- calcium bicarbonate is soluble (forms limestone pavement)
Occurs with chalk and limestone

29
Q

Frost shattering / freeze thaw

A

Mechanical
- when water in joints freezes at 0 degrees
- fluctuations around freezing point
- water expands by 9% when frozen
- pressure causes rocks to break

30
Q

Pressure release

A

Mechanical
- huge pressure releases occur when layers of rock or ice that lie on top of another rock are removed
- lower rock expands as pressure decreases and fractures occur along lines of weaknesses (bedding planes)
- can eventually break off, called exfoliation joints

31
Q

Hydrolysis

A

Chemical
- feldspars make up 40% of the earths continental crust
- reacts with acidic water, forming kaolinite which can be dissolved

32
Q

Salt crystallisation

A

Mechanical
- water evaporating leaving salt crystals
- temp rises, salt crystals expand and exerts pressure on rock
- in areas 26 - 28 degrees, sodium sulfate and sodium carbonate expands by 300%, forcing joints to crack opem

33
Q

Wetting and drying

A

Mechanical (common at coasts)
- clay rich rocks are pront to expand when they’re wet and contract when dry
- creates cracks which are vulnerable to freeze thaw and salt crystallisation

34
Q

Hydration

A

Chemical
- additional of water to rocks, clays or soils
- some minerals increase in volume
- anhydride expands by 0.5% to become gypsum

35
Q

Slope

A

An inclined surface

36
Q

Slope evolution

A

The development of slopes overtime

37
Q

Slope form

A

The shape of the slope in cross section

38
Q

Slope processes

A

Activities acting on the slope

39
Q

Unconsolidated sediment

A

Loose and not bound together material eg gravel

40
Q

Rock juxtaposition

A

Ore resistant rock over less resistant rock

41
Q

Heave / creep

A

Slow process where small particles eg soil zigzags down a slope due to expansion and contraction

42
Q

Flows

A

When’s there’s a high water content and materials flow down a slope

43
Q

Slumps

A

When there’s a high water content which lubricates a slope and a whole section moves down as one mass

44
Q

Slides

A

Mass moves as a single block down a slope

45
Q

Rock falls

A

Rapid fall of material down a steep slope

46
Q

Surface wash (channelled flow)

A

When the soils infiltration capacity is exceeded and overland flow carries sediment creating cracks / channels on the surface

47
Q

Sheetwash (unchannelled flow)

A

Areas of high velocity where material is dislodged by rain splash and water flows overland instead of in channels. Rills can form

48
Q

Rills

A

A relatively shallow channel, generally less than tens of centimetres deep and carrying water and sediments for only a short period of time

49
Q

Rain splash

A

The weight of raindrops dislodges material

geo (3 decks)

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