Rocks and weathering Flashcards
Freeze Thaw Weathering
When Water enters a crack in the rock, freezes, expanding the crack. Then it melts causing the rock to break apart.
Where: Locations where temperatures drop below 0 at night
Influenced by:
- Freeze thaw weathering is faster in colder places
- Rock type: some rocks are harder to erode and are less likely to have cracks
Heating and Cooling weathering
Insolation causes the rock to expand, creating cracks within the rock. The cold of the night causes the rock to contract.
This repeats, expanding the cracks causing the outer shell to weather away.
Where: moderate heat/cold (usually found in semi arid environments)
Influenced by:
- Amounts of rainfall
- Temperature change
Salt Crystalisation
Salt crystal growth happens when salt particles enter a rock’s pores. As temperatures rise the salt crystals expand, exerting pressure on the rock
Where:
- Coastal environments (sea spray), anywhere with very salty water.
Influenced by:
- Higher evaporation rates lead to more salty water, leading to more salt crystal growth
Pressure release, Dilatation
(whatis it, where is it found, what does it influence?)
Pressure release takes place when rocks under a heavy load have this released, causing them to expand and crack
Where:
- Caused by the removal of a pressurising force, normally in rocks near the surface of solid rock
What does it influence?
- Increases the rate of other weathering processes such as chemical weathering by increasing surface area exposed as rock cracks.
Vegetation root action
What is it, where is it found, what does it influence
Vegetation root action is weathering caused by pressure placed on rocks through the growth of plant roots and can eventually cause the rock to break apart
Where:
- Normally takes place in forested areas with large trees that will be able to grow strongly enough to exert pressure on rock, more erodible rock types such as sandstone and limestone are susceptible
What does it influence:
Breaks large bodies of rock up into smaller pieces and can cause large cracks,
Hydrolysis
What is it, where can it be found, what influences it?
Hydrolisis is when rocks react with water. E.G, soluble rocks dissolving into water.
Where:
Anywhere with rocks, such as granite, which react with water.
What inluences it?
-Rock type, Quartz is not affected
-Water reacts with Feldspar minerals in granite to form clay
- relief, water will not permeate the ground and react, it will instead run off.
Carbonation
What is it, where is it, what is it influenced by
Acidic rainwater breaks down limestone and chalk.
carbonic acid in rainwater reactswith calcite creating calcium bicarbonate which is then removed by percolating rainwater
Where is Carbonation found?:
- anywhere where water comes into contact with rocks.
Influenced by:
- rainfall
- temperature: Van’t Hoff’s law, the rate of chemical weathering increases 2-3 times for every increase of temperature of 10degrees
Hydration
What is it, where can it be found, what influences it
Hydration is when a rock absorbs water, reacting with it, leading to the rock swelling, creating cracks.
This can make the rock more susceptible to other types of weathering.
E.G Anhydrite reacts with water to form Gypsum.
Where:
- anywhere with permeable rocks and precipitation
What is it influenced by:
- relief
- precipitation rates
how do different factors increase/decrease the rate of weathering?
-A steep gradient increases physical weathering but decreases chemical weathering as water needs to be relatively still.
Vegetation:
- high levels of decomposition can generate lots of humic acid, leading to hydrolysis.
- Insulate rock from large temperature ranges, reducing some physical weathering.
Temperature:
- Van’t Hoff law for temperature as well
What are the 4 mass movement types?
Falls
Slides
Flows
Heaves/Creeps
What is a rock fall?
The movement of rocks under gravity.
What are rockslides/landslides?
an entire mass of material moving along a slip plane.
Heaves/Creeps
A slow movement of material up or down a slope.
What are flows?
The movement of a mass of rock/soil that contains a significant amount of water.
Vajont dam (mini case study)
-A dam built in northern (shit) Italy built after World War 2
-Officials attempted to drawdown the reservoir (reduce capacity), but didn’t reduce it enough
-The landslide displaced water in the reservoir and created a megatsunami that destroyed the town of Casso and some towns in the Piave valley
How does water increase the likelihood of a landslide?
The added weight of saturated layers can increase the loading on the slope.
It can also reduce the cohesive strength of soil particles (e.g. clays) by decreasing the friction strength. This is especially true when saturation occurs and the soil pores are completely filled as pressure is then applied outwards, forcing the soil particles to separate.
Water can also act as a lubricant between distinct layers (i.e. permeable vs impermeable) facilitating the glide horizon.
What is rainsplash
(explain)
When rain hits a surface, the impact of the rain droplets can be enough to displace the soil particles and detach them from the rest of the ground. As the water hits the slope, the force of gravity causes the water and the displaced soil granules to move downhill.
Surface runoff
Type: overland flow
A shallow sheet of waterflows over the surface of a slope, causing the top layers of the slope to be transported downhill. This occurs when water cannot infiltate into the slope, therefore flowing over it instead.
What is pinning?
This is where people drill into cliff faces and put big bolts in the hole. This transfers the pressure from the outside of the rock face to the really rigid stable interior of the rock.
However, this only works with bedrock, because the poles need to perch onto hard rock.
What is netting?
Netting helps contain loose material and catch debris. However, it only works up to a point. If a big boulder falls then the net will break. It can be contoured to slopes to prevent larger movements, and tensioned to restrain the movement of the rock face.
What is Grading?
Grading refers to the reprofiling of slopes so that they become more stable, by decreasing the gradient of the slope, infiltration is increased (as higher GPE) and surface runoff is reduced. It can also allow for afforestation.
At the end of the process, the slope is smoothed by a long reach digger
What is Afforestation?
This refers to the planting of trees to reduce the amount of moisture in soil.
Roots also increase the stability of soil and hold it in place
However:
You have to have a relatively flat surface to plant loads of trees.
What are the 3 types of plate boundary?
- Divergent
- Convergent
- Conservative
Characteristics of divergent plate boundaries
(what is it and what landforms are associated with it
- 2 plates moving in (relatively) opposite directions.
LANDFORMS:
- Sea Floor Spreading
- rift valleys
- Mid ocean ridges
- Volcanoes
