- Created by: Callum Hunter
- Created on: 04-01-12 17:59
Igneous - formed by cooling lava. If it happens underground, it is intrusive, but if it happens above ground, it is extrusive. They are resistant to erosion and formed by interlocking crystals.
e.g. Basalt, granite and gabbro
Sedimentary - formed typically in the sea, as sediments layer on top of each other on the seabed and form layers called beds. They often contain fossils of sea creatures. Usually a weaker rock.
e.g. sandstone, limestone and clay
Metamorphic - formed under extreme heat or pressure on existing rocks. Also crystalline, like igenous rocks. Very tough and resistant to erosion.
e.g. slate, gneiss and schist
The rock cycle is the link between the three rocks. Igneous rock is formed by volcanic activity, which is then transported down into the sea and creates beds of sediments, turning into sedimentary rock. This rock is then pushed under the surface and exposed to great pressure and heat, turning it into metamorhpic rock. This metamorphic rock is then melted back into magma.
Also known as physical weathering. It involves the breakup of rocks without any chemical interference. Often results in scree (piles of angular rock fragments) forming at the bottom of rocky outcrops.
Freeze-thaw - involves water freezing in the gaps of rocks, which expands them. Repeated freezing and thawing eventually breaks off the rock, which collects as scree.
Exfolation - happens often in deserts, where repeated heating and cooling of the rocks causes the outer skin to peel away.
Weathering that occurs by a chemical change.
Solution - when rocks dissolve in rainwater, such as when rock salt dissolves in water.
Carbonation - when rainwater becomes a weak carbonic acid, and dissolves rocks that are made up of calcium carbonate.
Biological Weathering: involves plant roots and animals burrowing into
Granite is an intrusive igneous rock, that has been exposed to the surface by erosion of the overlying rocks.
It is very resistant to weathering and so forms many upland areas. It contains cracks and joints - vertical ones are made when it cools and contracts, and horizontal ones are made by pressure release (from the overlying rocks being removed). These features make granite vulnerable to freeze-thawing.
A Granite Tor is formed when a layer of underground granite has vertical joints, some of which are closer together than others. The part of the granite with close-spaced joints weathers quicker than the other parts, leaving a higher section of the granite. The overlying material then erodes away, exposing the granite.
The movement of material downslope by the force of gravity.
Rock fall: When rocks or scree fall down from cliffs due to weathering
Rock slide: When a larger slab of rock slides downslope, caused by water getting into the cracks
Rock debris avalanche: occurs on failing scree slopes
Earth flows: happens when soil is saturated and flows downslope
Mudflows: similar to earth flows, but are quicker due to involving finer materials
Solifluction: slow flow of material over permanently frozen ground (permafrost). Occurs in periglacial areas e.g. Siberia.
Soil creep: unexplained movement of soil downslope.
Erosion Key Terms
Channel: the part of the river valley occupied by the water itself.
Hydraulic action: the force of the water moving in the river.
Abrasion: when rocks in the water hit the river bed, causing parts to break off
Attrition: parts of the load knock into each other, turning it into smaller parts
Solution: dissolving of certain materials (like chalk) by rainwater. A process of transportation and erosion.
Load: material of any size carried by the river.
Traction: the rolling of materials too heavy to carry along the riverbed.
Saltation: the bouncing of small stones and grains along the riverbed.
Suspension: material carried within the river's flow.
High up the river - Small, narrow channel
Vertical erosion, abrasion and attrition
Some traction and saltation
Large load, so high deposition of large material.
Middle of the river - Wider, deeper channel
Lateral erosion becoming more important
Suspension becoming main transportation, but previous types still present
Deposition becoming more obvious
Load size reduced
End of River - Widest, deepest channel
All erosion is much less important
Suspension now dominant type
Deposition of fine material
Large amount of loud, but size now very small
Long Profile: how high up the river is
Cross Profile: how wide the river is
Why does the amount of water in a river fluctuate?
Precipitation is da rain, it drops water in da river.
Interception is cause of da trees, they stop da water reaching da river.
Surface storage is like da puddles, init. They hold da water.
Infiltration is when da water like, sinks through the ground right.
Soil moisture is da water contained in da soil layer.
Percolation is when the water like, sinks deeper below the surface.
Groundwater is water that's chillin' and stored in da rock.
Transpiration is when the water's lost cause of dat evaporation.
Surface run-off is da water that runs across the top of da ground.
Throughflow is water flowing THROUGH da soil layer!
Groundwater flow is da same, but through da rock!
Water table is da level in the ground where no more water could be saturated!
Things that affect discharge
Rainfall is effective! Higher rainfall means the soil is saturated, so more water flows into the river, increasing discharge.
Higher temperatures mean higher evaporation, so less discharge.
Previous weather affects it, because if has been dry beforehand, it takes longer for the water to reach the river and therefore reduces discharge.
Steep slopes encourage faster movement of water into the river, increasing discharge.
Rock type determines how much stays on the surface and how much infiltrates, so impermeable rocks increase discharge as the water runs directly into the river.
Deforestation and urbanisation affect it - they both reduce the things that can infiltrate water, and cities drain water directly into the river.
Causes of floods
PROLONGED RAINFALL - HEAVY RAINFALL - SNOWMELT - STEEP RELIEF
Example, in Bangladesh, four major rivers are fed by Himalayan snowmelt, and the high relief of that area means the water reaches the rivers very quickly.
Deforestation increases surface run-off, and also clogs up rivers with sediment, meaning the channel size is reduced and floods are more likely.