Deserts Flashcards
What are pediements (Name the type of erosion that causes them)?
- Water erosion
- Pediments are gently sloping areas of rocks caused by erosion of rocks by sediment in sheet floods.
What are Playas? (Name the type of erosion that causes them)?
- Water erosion
- Flat depressions at low pediment - Lake periodically form in them when water drains into them after rain events.
What are inselbergs? (Name the type of erosion that causes them)?
- Water erosion
- Steep sided hills that rise up from pediments - made up of hard rock that is more resistant to erosion than surrounding rock, which will stand out.
What desert is the largest in the world?
- The largest hot desert in the world is the Sahara desert.
Why does the Sahara desert recieve such little rainfall
- The Sahra desert is located in a high pressure area on the tropics where air which has risen from the equator loses moisture by the time it has reached the tropics.
How many mm of water does the Sahara receive a year?
- Less than 100mm.
What are 2 characteristics of the soil in the Sahara?
- The soil is dry with little organic matter.
- The soil is quite often saline.
What are 2 characteristics of vegetation in the Sahara?
- The vegetation is sparse and there is a low diversity of plant life
- However, vegetation cover can increase temporarily after rainfall.
How does large temperature range affect the Sahara processes?
- Leaves rocks more vulnerable to thermal fracture and frost weathering.
How does infrequent rain affect the Sahara processes?
- Processes caused by water operate intermittently but are powerful when they occur.
How does high temperatures and low rainfall mean affect the Sahara processes?
- Means that sediment is very mobile, being easily eroded and transported by strong winds.
What is an example of a deflation hollow in the Sahara desert? (why may it have occured)
- The Quttara Depression (133m, below sea level)
- May have been caused when the climate was wetter but eventually became drier, therefore deeper and wider.
Why were wadis formed in the Sahara?
- Formed when the Sahara had a wetter climate.
- Wadis form intermittent, ephemeral streams.
Why were yardangs formed in the Sahara?
- Wind from one direction eroded the rocks by abrasion.
What is an example of a dune in the Sahara? (state how much land it covers)
- Great Sand Sea (Dune Field covering 72,000km^2) (Located in Western Egypt and eastern Libya)
What was the trend of deserts 9000 years ago?
- The presence of deserts wasn’t as widespread as it is today.
What is desertification?
- The degradation of semi-arid land by human activities plus changes in climate.
Why is desertification an issue (simple)
- It causes the land to become unproductive which leads to a number of issues
What % of Africa is at risk of desertification?
- 46%
How does lower rainfall increase desertification?
- Less rain results in less surface water and groundwater.
- So less water for vegetation growth.
- Leads to soil erosion because there are less roots to bind the soil together.
How does higher temperatures increase desertification?
- Higher temperatures result in the rate of evapotranspiration
- Means less water for the growth of vegetation.
Why is overgrazing a cause of desertification?
- Reduces vegetation causes soil erosion
- More trampling causes the compression of soil.
Why is overcultivation a cause of desertification?
- Soil doesn’t have time to recover and doesn’t have enough nutrients to support the plants/
Why is deforestation a cause of desertification?
- Exposes the soil to rain and removes the trees and roots.
How does overpopulation growth increase desertification?
- Increases the pressure on the land, leading to more overcultivation, overgrazing, deforestation and irrigation.
Why does desertification shape sedimental landscapes?
- The ground becomes more exposed to erosion
- Increased erosion exposes bedrock
- Higher wind speeds and more sediment cause more sand to be blown into an area.
How does desertification shape ecosystem health?
- Desertification causes the land to become less fertile so less plant life will grow.
- Less vegetation means less animal life Is supported.
- Animals may migrate/die out due to desertification.
- Desertification releases carbon into the atmosphere, contributing to climate change.
How does desertification shape populations?
- Agricultural productivity decreases so there’s loss food security for families.
- Therefore, families need to move into large cities
- Puts pressure on urban areas through overcrowding
What are 4 effects of not acting on desertification?
- Desertification will continue
- There’ll be a reduction in agricultural yield, decreasing food security and hindering development.
- Urban areas may be overcrowded
- Leads to conflict between desertified countries.
What are 3 actions of stopping desertification?
- Locally, the planting of vegetation can act as windbreakers
- Farmers can rotate crops to allow soil recovery.
- If the world reduces greenhouse gas emissions then temperatures rise and rainfall decline will stop getting worse. `
What are 2 ways local populations can adapt to desertification?
- Diversifying farms to contain livestock which is less vulnerable to desertification.
- Improvements in agricultural technology which increases crop yields and prevents food insecurities.
What % of Spain is arid?
- 50%
What % of Spain is at risk of desertification as of 2008?
- 37%
How is climate change a cause of desertification in southern Spain?
- Evapotranspiration rate increased due to Spain’s 1.5 degrees celcius increase in temp.
- Rainfall decreases in the south
- Less water so less plants grow.
What % decrease of fresh water in Spain?
- 20%
How is Spain’s agricultural innovations caused desertification?
- Overcultivation reduces nutrient content.
-In Andalusia, there is overcultivation of olive trees. - Overgrazing reduces vegetation cover.
Where in Spain isn’t suited for agriculture and what figure shows the areas importance?
- Almeria ($1.5 billion made for the economy but the climate isn’t suited for agriculture)
What are 3 impacts of desertification in Spain in regard to undrinkable water, illegal selling of water and biodiversity?
- Salinisation is happening so water i becoming undrinkable.
- Black market is developing which makes it illegal to use water in certain boreholes.
- Reduction in biodiversity ruins ecosystems.
What is the Government proposing to do in Spain in response to desertification?
- Transfer water from areas of high water content to areas of low water content.
How are Spain mitigating desertification?
- Indentifying areas of high risk to help improve defence plans and limit the impact on vegetation.
How are Spain adapting to desertification?
- An official water trading scheme has been put in place that allows farmers to buy water that isn’t illegal but is 3 times the price.
What percentage of reforestation is happening between 1990-2015?
1990 - 27.6%
2015 - 36.8%
How much rainfall does the Sahara recieve?
- Less than 100mm a year
What is the average temperature in the Sahara?
- 30 degrees celcius
What is the soil like in the Sahara?
- Dry with little organic matter
- Saline
How does climate affect Saharan desert processes? (3 points focussing on temperature, rainfall)
- Large temperature range means rocks are vulnerable to thermal fracture and frost weathering.
- Infrequent intense rainstorms mean that processes caused by water operate intermittently
- High temperatures and low rainfall mean that sediment is very mobile, being easily eroded and transported.
What other landforms found in the Sahara?
- Deflation hollows
- Yardangs
- Wadis
- Dunes
Example of deflation hollow in sahara?
- Quattara Depression (133m below sea level)
What is deflation?
- The removal of fine material by the wind?
What are deflation hollows?
- Huge depressions in the ground when a lot of fine material is removed from one place.
What are desert pavements?
- Surfaces of interlocking stones.
- Form when wind blows silt and sand away, leaving gravel, rocks and pebbles.
What are yardangs?
- Streamlined ridges formed by a unidirectional windH
How are yardangs formed?
- The wind carries sand in suspension, which erodes rocks by abrasion
- Softer rock is more easily eroded than harder rock.
What are zeugens?
- Hard rock above soft rock, if cracks form then wind can pass through and erode the softer rock.
What are ventifacts?
- Individual stones with smooth sides that have been abraded
- Sides facing the prevailing wind are abraded the most
- However, the rock may move or the prevailing wind may change.
How are sand dunes formed?
- Wind slows down so sand gets increasingly deposited.
What are seif dunes?
- Dunes that are wiggly lined.
- Formed from barchan dunes when the prevailing wind changes causing the arms of barchan dunes to elongate.
What are barchan dunes?
- Crescent shaped dunes that form in the direction of the prevailing wind.
- Swirling winds help to keep the slope steep.
What are Wadis?
- Ravines that were eroded when deserts had wetter climates.
What are alluvial fans?
- Flat desert plain at the mouth of a wadi leads to sediment being deposited as energy from water is dissipated.
What are bahadas?
- Several alluvial fans which have spread out and joined together to form a uniformed shape.
What is weathering?
- The break down of rock.
What is thermal fracture?
- When at higher temperatures rocks expand and at lower temperatures rocks contract.
What is freeze thaw?
- Happens when water enters rocks crack
- Water below 0 degrees celcius causes thawing causing pieces to fall off.
What is salt weathering?
- When saline water enters
- High temperatures cause water to evaporate
- Salt crystals expand, increases pressure on rocks and causes pieces to fall off.
What happens when iron reacts with oxygen?
- Iron oxide causes rocks to crumble.
What happens when CO2 dissolves in rainwater?
- Carbonic acid is form which can react with rocks such as limestone which contain calcium carbonate causing the breakdown of rock.
What is exofiliation ?
- The peeling of the rock’s outer surface
What is granular disintegration?
- Disintegration of individual grains.
What is abrasion?
- Erosional Scraping of particles from the rock surface
What is suspension?
- The transportation of small particles picked up and carried.
What is saltation?
- When small particles are temporarily lifted and bounce
What is traction?
- The transportation of heavier material.
What are exogenous rivers?
- Where water is sourced outside the desert region
What are ephemeral rivers?
- Where water is intermittently flowing through the river
What are endoreic rivers?
- Where river terminates inland.
What is the aridity index based off?
- The difference between the amount of precipitation and the potential evapotranspiration.
Why are deserts found at the tropics?
- Air rises at the equator
- Air cools as it rises
- When it sinks, the air is dry
- Dry air descends around 30 degrees north and south of the equator
- Air descends at areas of high pressure so the wind blows outwards and no moisture is brought in.
- Low precipitation
Explain cold ocean currents?
- Wind travels above cold oceans, reduces the temperature.
- Reduces its ability to hold moisture
- Moisture is released as precipitation
- Dry by the time it reaches the land.
What is the rain shadow effect?
- Where tall mountains force wind upwards which cools it forcing precipitation to be released
- By the time wind reaches inland areas, there is very little moisture.
Why are deserts found in the middle of continents?
- Central parts of the continents are more arid than coastal areas.
- Moist wind from the sea moves inland and is dropped as precipitation.
- Little rain will fall.
- An example would be the Gobi Desert.
What is rainfall like in deserts?
- Little rainfall which is infrequent
What is flash flooding?
- When there is sudden, high intensity flows of water through channels.
- Heavy rainfall can’t be absorbed by the dry, baked soil.
- Flash floods have enough energy to transport large pieces of desert rocks by traction.
What is sheet flooding?
- Flooding that doesn’t occur through a channel.
- Spreads across a desert plain rather than through a channel so has less energy than flash floods whilst still being able to transport pebbles, gravel and sand.
What is block disintegration?
- When larger chunks of rock are broken off.
What is deposition?
- Desert material which eventually is dropped.
What factors lead to deposition?
- Sediment load exceeds the ability of water/wind to carry it.
- Happens when water slows down as the flow is reduced, which can happen if it leaves a channel and spread outs.
What is mass movement?
- The movement of material down a slope due to gravity.
Where does mass movement occur the most?
- Landforms with steep sides such as inselbergs, potentially wadis.
What are 3 inputs of the desert?
- Water, wind, sun
What are the stores of the desert?
- Landforms store lots of sediment
- Water stores in the ground and rivers
What are the flows of the deserts?
- Sediment moved by erosion/deposition/transportation/weathering
What are the outputs of the desert?
- Water evaporating rapidly
- Runoff
- Sediment
What does it mean that deserts are open systems?
- Energy and matter can move in/out.
What is an example of a negative feedback loop in the desert?
1) Temperature increases
2) Evaporation increases so the ground is drier.
3) Drier sediment gets more easily eroded so dust clouds form.
4) Dust clouds block solar radiation.
