hot deserts aqa a level geography paper 1

outline a desert landscape system

A desert landscape has inputs like solar energy and wind, stores such as sand dunes, flows including wind erosion and transportation and outputs like sediment blown out of the area.

outline the positive feedback of a desert landscape

Positive feedback is when knock on effects amplify the actions occurring. An example could be desertification. If soil becomes exposed to wind, deflation can occur. This strips soil away from the land leaving it more exposed to deflation and erosion.

explain negative feedback within a desert landscape

negative feedback is when the knock on effect nullify the actions and return the cycle back to its equilibrium state. An example could be redesertiting land.

outline the concept of dynamic equilibrium in a desert landscape

Dynamic equilibrium means the desert system stays balanced over time. Inputs like sediment and wind are matched by outputs like erosion and deposition. If disturbed, the system adjusts to restore balance. For example through dune movement or changes in vegetation.

explain the concept of landform and landscape when describing a desert landscape

A landform is a distinct natural feature in a hot desert shaped by erosion, deposition and weathering. They develop due to aeolian processes, fluvial processes and extreme temperatures. Examples could be sand dunes which are formed by deposition of sand accumulating. They are influenced by climate, temperatures, aeolian and fluvial processes

outline how related landforms combine to form characteristic landscapes

In deserts, landforms like dunes, wadis and mesas are liked by erosional and depositional processes. Sand dunes form from wind transport and accumulate in sheltered areas. Wadis form from flash flooding in dry riverbeds. Together they create a recognisable arid landscape.

explain the global distribution of mid and low latitude deserts and their margins

global distribution of deserts is located in parallel belts 20-30˚ of hot deserts. This is because the global atmospheric circulation here means that it has low humidity meaning minimal cloud cover and low precipitation. They are mostly concentrated on the west of continents with the exception of the Sahara which covers both east and west of Northern Africa. The majority of hot deserts are located in the northern hemisphere.

outline the characteristics of hot desert environments

Hot deserts are very dry with less than 250mm of rainfall per year and temperatures that can exceed 40˚C in the day and have cold nights meaning large diurnal ranges. Soils are often sandy, dry, low in nutrients. Vegetation is sparse and drought resistant

explain how climate characterises a hot desert environment

Hot deserts have high daytime temperatures due to intense solar radiation. Lack of cloud cover causes cold nights. Low rainfall means limited water availability, shaping the sparse vegetation and dry soils typical of deserts.

outline how soils characterise a hot desert environment

Desert soils are dry and sandy with little organic matter. They are often shallow and poorly developed due to low vegetation. Soils may have a high salt content from evaporation, which limits plant growth, reinforcing arid conditions

explain how vegetation characterises a hot desert environment

Vegetation in desert is sparse due to low rainfall. Plant like cactus have adaptations like thick stems and waxy surfaces to store water. Deep or wide roots help to absorb water quickly after rain. This specialised vegetation reflects the harsh desert climate.

explain the concept of the water balance

Water balance is the balance between precipitation and evapotranspiration. In deserts, evapotranspiration is much higher than rainfall, causing a deficit. This leads to dry soils, limited vegetation and intermittent water flow

outline the aridity index

The aridity index is the ratio between precipitation and potential evapotranspiration. It is divided into three categories: hyper arid, arid and semi arid. A hyper arid area rarely receives more than 100mm of precipitation annually. An arid region receives less than 250mm of precipitation per year. A semi arid region receives between 250 and 500mm of precipitation annually.

explain the causes of aridity

One cause of aridity is global atmospheric circulation. This is due to the Hadley cells 20-30˚ North and south of the equator. Here, warm air rises at the equator before cooling at 30˚ N and S of the equator. The air then sinks creating high pressure which prevents cloud formation leaving dry conditions.

outline how continentality causes aridity

Continentality means locations far from the sea have more extreme temperatures. Without moisture from the ocean, air masses become dry. Rainfall is low becuase there's little water vapour to form clouds. This leads to arid desert conditions.

explain how relief causes aridity

Mountains block moist air from reaching inland areas. As air rises over mountains, it cools and falls as rain on the windward side. The dry air then descends on the leeward side of the mountain creating a rain shadow effect. This leads to arid conditions behind the mountains. An example is the Atacama desert in South America.

explain how atmospheric processes relating to wind and pressure cause continentality

Continentality is caused by atmospheric processes as rising hot air in Hadley cells create a low pressure area over desert landscapes. Winds blow cooler high pressure air from the ocean to the land. When the air reaches the land, it heats up and rises

outline the sources of energy in a hot desert environment

One source of energy is insolation, this creates the climate of the deserts as it evaporates moist air in the desert. Another source is wind this helps to shape landforms this is because winds transport and sediment across the desert. This shapes and creates landforms like sand dunes and yardangs A further source is water, this shapes landforms through erosion and transportation of sediment and creates landforms such as alluvial fans and wadis.

explain insolation as a source on energy in a hot desert environment

One way insolation is a source of energy is through

outline wind as a source on energy in a hot desert environment

Wind is an important input of energy in hot deserts. This is because it drives processes of erosion and transportation. This shapes the desert landscape and contours the landforms. Winds in a hot deserts are responsible for forming sand dunes such as barchans and landforms such as zeugens and yardangs. An example is the harmattan winds in the Mojave desert in the USA

explain runoff as a source on energy in a hot desert environment

Runoff is a source of energy in a hot deserts environment as it constructs the landforms within the desert landscape. This is because when rainfall does occur in the desert, it is usually very intense with a high volume meaning that it has lots of power, creating channels through the desert. This is often how landforms such as wadis are formed which are steep sided valleys with ephemeral streams

outline the sediment sources in a hot desert environment

One source of sediment in a hot desert environment is sediment derived from the weathering of underlying parent material. Another source of sediment could be fluvial origin from rivers transporting sediment into the deserts, before drying up and leaving sediment in the riverbeds.

explain cells and budgets in a desert environment

Sediment cells are self contained areas where sediment is eroded, transported and deposited. These include sources, transfers and sinks. The sediment budget relates to the balance between sediment lost and gained. When sediment is gained features like dunes occur as sediment accumulates. However when sediment is lost, features such as deflation hollows occur due to sediment loss.

explain weathering as a geomorphological process

Weathering is the breaking down or decaying of material where it is. It doesn't involve transporting of material. There are 3 types of weathering: mechanical, chemical, organic. Mechanical weathering is the breakdown of rocks into smaller pieces without altering their chemical composition. Chemical weathering is the process of decomposition of rocks due to chemical reactions mostly requiring the presence of water or oxygen. Organic weathering is when plants and animals contribute to the breakdown of rocks through physical and chemical actions.

outline mass movement as a geomorphologcial process

Mass movement is the movement of material downhill under the influence of gravity which could be assisted by rainfall. Due to the limited amount of vegetation and soil in a hot desert, mass movement is occurred by rock falls and rock slides. Rock falls are where small blocks of rock become detached from an exposed cliff face and fall freely to the base of the cliff. Rock slides are where there is a failure throughout teh rock as a whole and the material collapses rather than individual blocks. These create steep slopes with the accumulation of angular material at their base.

explain erosion as a geomorphological process

Erosion refers to multiple processes that wear away the land surface my mechanical action. It often leads to degraded land. There are two erosional processes by wind: abrasion and deflation. Abrasion is when material carried by the wind hits against exposed rock surfaces, creating a range of erosional features. Deflation is when wind removes dry sand, silt and clay particles from the surface and transports it away leaving the coarse and fine pebbles making desert pavement.

outline transportation as a geomorphological process

Transportation is the movement of particles by wind. It is influenced by a range of factors, the most important one being wind strength and direction.

explain deposition as a geomorphological process

Deposition is when wind and water transporting sediment lose energy and therefore they have a reduction in the capacity that they can transport.

outline thermal fracture as a geomorphological process

Thermal fracture is a mechanical weathering process. It involves the break down of rocks due to the cycles of heating and cooling. This causes repeated expansion and contraction leading to stress on the rock. This stress exceeds the tensile strength of the rock and causes fractures.

outline exfoliation as a geomorphological process

Exfoliation is a mechanical weathering process. It involves, the flaking of layers of rock due to the repeated heating and cooling cycles of rocks. Because the expansion and contraction is repeated, weakening in rock layers occurs. This causes the outer layers to crack and peel off hence the name exfoliation.

explain chemical weathering as a geomorphological process

Chemical weathering is the process of decomposition of rocks due to chemical reactions mostly requiring the presence of water or oxygen. Some examples are oxidation and duricrust. Oxidation is when rock turns to be a reddish colour due to the exposure to water and oxygen. Duricrust is accumulations of salt on rock which becomes cemented.

outline block disintegration as a geomorphological process

Block disintegration occurs in areas with high diurnal ranges. This means that rock is repeatedly heated and cooled, causing rock to expand and contract. This puts stress on the rock causing fractures to occur along joints meaning that it breaks into blocks

explain granular disintegration as a geomorphological process

Granular disintegration occurs in coarse grained rocks like granite. When the different minerals in the rock are exposed to heat from the day and cold at night in the desert, the minerals expand and contract. This creates internal stress, leading to the rock breaking down into separate grains over time.

outline the role of wind in deflation

wind removes fine and loose material from the surface. Lighter particles such as sand are picked up and transported elsewhere. Larger and heavier particles are left such as pebbles as the wind isn't strong enough to move them. This shapes desert landscapes by lowering the land exposing bedrock and shaping dunes elsewhere.

explain the role of wind in abrasion

wind carries sand and hits rock surfaces. This weathers the surfaces and acts like sandpaper, smoothing and polishing the rocks. It is most effective close to the ground and shapes landforms such as yardangs and zeugens.

explain the role of wind in transportation through suspension

Suspension occurs by wind lifting dust and fine particles into the atmosphere. These particles are transported over long distances by high velocity winds in the atmosphere. The wind transporting these particles can change the desert landscape by forming deposits of dunes and abrading rock to form features like yardangs or ventifacts

explain the role of wind in surface creep

Surface creep occurs by wind pushing slightly larger grains along the surface of the desert. The force of the wind pushes the grains along a short distance and can help form desert landscapes such as dunes when the wind no longer has enough energy to move the particles.

outline the role of wind in deposition

Wind is the key influence of deposition. This is becuase when the wind loses its energy, it releases larger sediment carried as it is heavier. This forms dunes within the landscape. Smaller particles are carried further and when released forms loess deposits.

explain the origin and development of deflation hollows

Deflation hollows are depressions in the ground formed by wind erosion in desert environments. When the wind blows it picks up loose and fine particles and carries it away. This lowers the ground surface creating a hollow or depression. This is most common in areas without vegetation as the loose material is removed easily. Over time, the wind removes more sediment, deepening the depression.

outline the origin and development of desert pavements

Desert pavement forms when fine particles such as sand and dust are removed by erosion through deflation. This leaves a concentration of larger stones and pebbles on the surface which looks like a pavement. This takes long periods of time to form as continuous wind erosion and transportation is needed and larger rocks can compact the finer material making it more difficult to move.

outline the origin and development of ventifacts

Ventifacts develop through wind blown sediment abrading them. This creates a sandblasting effect. Because the wind blows in a particular direction it leads to one side becoming smooth with sharp edges.

explain the origin and development of yardangs

Yardangs are formed in areas where these is soft, unconsolidated rock with alternating hard rock layers. When abrasion of sediments occur, soft rock is eroded quicker than hard rock leaving those layers behind. Due to wind direction remaining consistent, yardangs become aligned parallel to the prevailing wind. Overtime, continued erosion deepens the troughs and sharpens the ridges. They can range in sizes depending on the extent of erosion

explain the origin and development of zeugen

Zeugen develop in areas with horizontal layers of hard rock over soft rock. Weathering weakens the upper hard rock, exposing the soft layer beneath. The soft layer erodes much faster than the hard rock through abrasion, undercutting the rock, leaving it standing as a ridge with a mushroom like profile.

outline the origin and development of barchans

Barchans develop in areas with a limited supply of sand. A constant wind blows from one direction, this shapes the dune, pushing up the windward slope. Sand slips down the steeper leeward side due to gravity. The horns of the barchan move faster than the central part, so the dune slowly migrates downwind over time.

outline the origin and development of seif dunes

Seif dunes typically develop from barchan dunes that become elongated. They form due to a dominant wind direction with occasional cross winds. The dominant wind shapes the main ridge of the dune, while cross winds stretch and narrow it. The dune becomes aligned parallel to the prevailing wind over time.

explain the sources of water in a hot desert

There are 3 sources of water in a hot desert: exogenous, endoreic, ephemeral. Exogenous water is water that originates externally to the deserts and flows through it. It is a reliable, constant flow of water and an example is the Colorado river. Endoeric water is water that terminates in the middle of the desert. This is due to high evaporation rates. Ephemeral water is water that flows intermittently after storm events. This is often large volumes of water and creates landscapes such as canyons through the high volume of water and lack of vegetation coverage.

outline exogenous water as a source

Exogenous water is water that originates externally to the hot desert. It is a reliable and constant flow of water through a hot desert with the ability to maintain flow throughout the year. An example is the Nile river.

explain endoreic water as a source

Endoeric water is water that terminates in the middle of the desert and therefore doesn't drain into the sea. This is due to high evaporation rates. An example is the campaign sea which is an endoreic basin surrounded by land.

explain ephemeral water as a sources

Ephemeral water is water that flows intermittently after storm events. This is often large volumes of water and creates landscapes such as canyons through the high volume of water and lack of vegetation coverage.

outline the episodic role of water

Episodic role of water typically occurs as sudden rainfall resulting in flash flooding. This causes fluvial erosion to occur to the desert landscape, forming landforms such as wadis. Episodic water is rare and usually is intense rainfall events

explain sheet flooding

Sheet flooding is when rainwater spreads out a thin even layer over the land rather than flowing in channels. It occurs when rainfall is intense and the soil can't absorb water quickly. It's common on flat, bare ground and can cause soil erosion. An example is the Sahel, where sheet flooding damages land and reduces farming productivity.

outline channel flash flooding

Channel flash flooding is a sudden intense flood event where water rapidly fills river channels after heavy rainfall. It occurs in small steep drainage basins with impermeable surfaces leading to fast surface runoff.

outline the origin and development of wadis

Wadis are dry river valleys found in arid and semi-arid regions such as the Sahel. They are formed through fluvial erosion during rare but intense flash floods in desert climates. Overtime, repeated flooding deepens and widens the channel even though the river only flows intermittently. Wadis can remain dry for most of the year but are key features of desert drainage systems.

explain the origin and development of bahadas

Bahadas form in arid regions where several alluvial fans merge at the base of mountains. The develop as flash floods carry sediment down steep slopes and deposit it when the flow slows on flatter ground. Overtime, multiple overlapping alluvial fans create a broad, gently sloping bahada. These features are common in deserts like the Mojave where seasonal rainfall causes repeated deposition

outline the origin and development of pediments

Pediments are gently sloping rock surfaces found at the base of desert mountains. They form through fluvial erosion during sheet floods and extended periods of time. As the mountain retreats due to erosion, the pediment extends outward into the desert. Pediments are typical in arid regions like the Mojave desert, forming part of the desert pediment landscape

explain the origin and development of playas

Playas are flat, low- lying dry lake beds found in desert basins with no external drainage. They form when ephemeral lakes develop after heavy rainfall collects in these basins. Water quickly evaporates in the hot, dry climate, leaving behind salt and sediment deposits. Over time, this creates a hard, cracked surface, common in deserts like the Mojave.

outline the origin and development of inselbergs

Inselbergs are steep sided hills rising abruptly from a desert plain. They form from resistant rock that withstands weathering and erosion better than surrounding landscape. Over time, surrounding rock is worn away by wind, water and temperature changes, leaving the harder rock exposed. Inselbergs are found in deserts like the Sahel.

explain the relationship between process, time, landforms and landscapes in hot desert settings

Processes like weathering, erosion and deposition shape the landforms in hot desert environments over time. Over long periods, processes like wind and water erosion wear down rock surfaces and create landforms such as pediments, inselbergs and wadis. The landscape evolves through continuous interaction between these processes with features like sand dunes and playas forming through repetitive climactic conditions over time.

outline the changing extent and distribution of hot deserts over the last 10,000 years

Over the last 10,000 years the extent and distribution of hot deserts has changed due to shifts in climate. At the end of the ice age, deserts like the Sahara were wetter with vegetation, as the climate warmed, deserts became drier and more arid. The Sahara moved south and other deserts like the Mojave had changing precipitation patterns. Over the years, human activity like overgrazing and deforestation contributes to desertification, expanding desert areas like the Sahel.

explain the causes of desertification

There are several causes of desertification such as climate change, overgrazing, deforestation and agricultural practices. One factor is climate change leads to higher temperature and reduced rainfall, making areas more prone to desertification. Another factor is overgrazing by livestock removes vegetation, leaving soil exposed to wind and water erosion. A further factor is deforestation which reduces tree cover, this leaves the soil unprotected preventing the soil from maintaining moisture. Another factor is agricultural practices. This depletes the soil's nutrients, contributing to land degradation.

explain the human causes of desertification

There are several human causes of desertification. One factor is overgrazing by livestock. This reduces vegetation cover, leaving soil vulnerable to fluvial and aeolian erosion. Another factor is deforestation for agriculture. This removes trees protecting soil, leaving it to dry out and degrade. A further factor is over-cultivation which depletes soil nutrients, reducing its fertility and making it more susceptible to erosion. Another factor is poor irrigation practices. This can lead to salinisation where salts build up in the soil, further degrading its quality.

outline climate change as a cause of desertification

Climate change increases global temperatures, leading to drier conditions and reduced rainfall in vulnerable areas. Higher temperatures increase evaporation rates, drying out soil and reducing moisture availability for plants. Changes in rainfall patterns cause prolonged droughts, making regions more susceptible to desertification. More extreme weather events can damage vegetation and soil, accelerating land degradation

outline the distribution of areas at risk of desertification

Areas at risk of desertification are typically found in arid and semi-arid regions such as parts of Africa, Asia and Australia. The Sahel region of Africa is highly vulnerable due to low rainfall and increasing temperatures. Central Asia is also at risk due to overgrazing and deforestation which has exacerbated land degradation. Australia is also prone to desertification due to droughts, poor land management and climate change.

explain the impact of desertification on ecosystems

Desertification leads to the loss of vegetation, reducing plant biodiversity and disruption to food chains. The loss of soil fertility makes it difficult for plants to grow, leading to desertification as the soil is no longer protected. Water scarcity occurs as soil becomes less able to retain moisture, impacting both plants and animals that rely on the land. Soil erosion caused by wind and water further degrades the ecosystem, removing topsoil and causing habitats to disappear.

outline the impact of desertification on landscapes

Desertification impacts landscapes through Vegetation loss which transforms once productive land into barren exposed soil. Soil erosion removes topsoil, leading to cracks and uneven ground surfaces. Sand encroachment and spread of dunes can cover farmland and settlements, reshaping the landscape.

explain the impacts of desertification on populations

One impact of desertification is food insecurity. This is because the soil will become infertile and have limited supply of water, therefore meaning that crops may fail to grow leading to a decline in crop yields which may cause malnutrition or starvation of populations. Another impact on populations could be urbanisation. Communities may have to move to cities leading to more pressure on cities to expand. A further impact on populations could be declining water supplies. This could lead to a dehydrated population.

outline possible futures for local populations in relation to desertificaiton

One future for locals populations is to collaborate with NGOs which can help protect ecosystems. Another possible future for locals populations is to adapt through irrigation schemes?