2.3 Arid landscape development in contrasting settings

what are bajadas? WATER

A bajada consists of a series of coalescing alluvial fans along a mountain front. These fan-shaped deposits form by the deposition of sediment within a stream onto flat land at the base of a mountain

what is scree? WATER

A collection of broken rock fragments at the base of crags, mountain cliffs, volcanoes or valley shoulders that has accumulated through periodic rockfall from adjacent cliff faces

what is a deflation hollow? WIND

A depression in the landscape of a desert caused by wind, erosions. In deserts the wind erodes loose material from flat areas which have, uncemented sediments such as those occurring in a tropical desert

what are desert pavements? WIND

A desert surface covered with closely packed, interlocking angular or rounded rock fragments of pebble and cobble size. They typically top alluvial fans

what are parabolic dunes? WIND

A horseshoe-shaped dune where the open end faces upwind. These are generally relatively stable features that have been colonised by vegetation, and occur where there is a constant supply of sand, often in coastal locations

What is graded sediment? WATER

A sedimentary deposit which is sorted with the coarsest material left at the upstream end of the fluvial fan and the smallest material on the downstream of the fan

what is pediplanation? WATER

An extensive, thinly alluviated erosion surface found generally in desert, semi-arid and savannah regions. It is considered to be formed by the coalescence of 2 or more adjacent pediments and to represent the end result of the mature stage of the arid cycle of erosion

what is shamal?

Arabian gulf blowing over Iraq and the Persian Gulf from late May to early July

why is wind strong in deserts?

As the great diurnal temperature range (during the day temperatures within hot deserts can be 40 degrees plus and at night then can be down to close to or below 0 and this means as the air temperature varies, the ground temperature takes a longer time to vary so the differences between the ground and the air temperature mean the great winds are created both during the day and during the night (creating strong winds)

what are badlands? WATER

Badlands are a type of dry terrain where softer sedimentary rocks and clay-rich soils have been extensively eroded by wind and water.They are characterised by steep slopes, minimal vegetation, lack of a substantial regolith, and high drainage density.

What are barchan dunes? WIND

Crescent-shaped, form in areas of limited sand supply and unidirectional winds. Move downwind over a flat surface of pebbles or bedrock The points of the crescent are directed downwind. One of the most interesting is the graceful Barchan, whose horns face down wind and form when there is limited sand supply. They move across country and may eventually destroy themselves if they encounter a highway or other obstruction. Windward side has the shallow slope and the steep slip face is the opposite side of the direction of flow of wind Left side is the windward side right is the leeward side There are also perpendicular dunes relative to wind direction

in what direction do desert winds tend to blow?

Desert winds tend to blow from the centre towards air margins. This is because the centre is the highest air pressure and desert margins is an area of lower air pressure.

what is the irifi?

Easterly winds that blow in the western Sahara around march

what are buttes? WATER

Formed in regions where the bedrock is sedimentary with horizontal bedding planes with a resistant cap rock, fluvial erosion creates a butte. They closely resemble a mesa but are much smaller but more elevated. They are thought to be the remains of heavily dissected plateau where the water has eroded all but a thin isolated rock pillar.

what are mesas? WATER

Formed in regions where the bedrock is sedimentary with horizontal bedding planes with a resistant cap rock, fluvial erosion creates a mesa. It is an isolated flat-topped plateau or hill-like features, with steep slopes or cliffs on at least one side, often falling away to a wadi or canyon.

what is a pediment? WATER

Gently sloping areas (less than 7º) of bare rock and debris. They are believed to be formed through a range of processes including fluvial erosion, alongside the deposition of material washed down from the uplands and deposited as the capacity and competence of the water is suddenly reduced by the abrupt change in slope angle

what are Hamadas? WIND

Hamadas are elevated plateaus of rock, these include the Atlas Mountains

what are sief dunes? WIND

Knife-edged ridges of sand or longitudinal dunes form long parallel ridges of sand separated by wind-scoured depressions. Groups or chains can extend over 100km and 300km in height and length. The tops and sides of such dunes are often serrated due to local wind action and eddying.

what are ergs? WIND

Large sand dunes- Ergs makeup 20% of the Sahara and are Sand Dunes that reach heights of up to 300 metres. They cover vast expanses of Algeria and Libya as well as Mali and Nigeria

what are regs? WIND

Regs are a mixture of sand and gravel, often described as a desert pavement of loose stone. They makeup 70% of the Sahara and are the historic remnants of river and sea beds

what are transverse dunes? WIND

Resembles large scale sand ripples, these are large ridges of sand with a steep downward face and form in large groups or fields of dunes. They occur in areas with an abundant constant supply of sand, and can be the result of barchan dunes merging if their supply of sand increases significantly

what are inselbergs? WATER

Rounded steep-sided hills that rise abruptly from a lowland plain. They are characteristic of tropical savannah zones but are found in a range of climatic zones and are generally composed of solid crystalline rocks such as granite. The relic features are thought to be due to geomorphological processes. All theories suggest that the desert environments that inselbergs are found in today were once more humid, supporting the theory that deserts experienced wetter periods (pluvial) in the past

what is the harmattan?

Sahara blowing in the winter months from November to march

What are braided streams? WATER

When ephemeral channels (wadis) appear on a valley floor, they are often braided due to the large amounts of previously deposited material that they have to find a pathway through. The stream pattern will change following each flash flood

what are braided streams? WATER

When ephemeral channels appear on a valley floor, they are often braided due to the large amounts of previously deposited material that they have to find a pathway through. The stream pattern will change following each flash flood

what are some of the significant changes in the areal extend of extreme deserts due to natural climate change processes?

changes in the earth-sun geometry changes in solar output changes in volcanic emissions continental drift changes in albedo

examples of aeolian landforms in the Mojave?

deflation hollows= rainbow basin desert pavement= ventifacts= ventifact ridge yardangs= roggers lake zeugen= white tank arch barchans= sief/star dunes= Kelso dunes (shelter from the prevailing winds)

what are yardangs? WIND

landforms created by erosion. the agent of erosion is wind and it is formed by deflation. they are formed in rocks that have vertical bands of hard and soft rock. the weaker rock is removed from abrasion, leaving edged of harder rock. they vary in size from being a few cm to tens of metres. some are so big you can see them from satellite imagery and they look like a streamlined parallel ridge of rock (rounded upwards face and long ridge downstream) and are aligned in the direction of the prevailing winds. however, it takes millions of years for them to take their current form

what is the distribution of hot deserts presently?

located between 15° and 30° north or south of the equator. This is a zone of subsiding or sinking air. Air that rises due to the intense heat at the equator divides to flow north and south. When it reaches 15° to 30° it begins to sink because it has lost so much of its heat

what is the term for loose material deposited in deserts?

loess

what is the term given to the rock that has been broken down by weathering?

regolith

what are playas/chotts/salt lakes? WATER

salt flats. Form when ephemeral streams flow into inland basins or depressions. A dry lakebed at the bottom of a desert basin (sometimes temporarily covered with water) they have no vegetation and are among the flattest geographical features in the world. Following the rare periods of rainfall, the water quickly evaporates due to the intense heat, leaving a dry lakebed behind. They consist of salts (evaporites) that were carried in by the streams and precipitated during the evaporation (sodium chloride is the most common precipitate and other salts include magnesium sulphate and sodium sulphate). These are often exploited as they are rich salts

what was the distribution of hot deserts in the early Holocene?

the distribution of hot deserts was dramatically reduced

what is kharif?

the easternmost extension of Africa in northern Kenya. In the Somali-Chalbi desert blowing June to September

what was the distribution of hot deserts in the last glacial maximum?

the hot deserts were much more extensive

What is spatial variations in desert landscapes?

the variation in hot deserts across space, or across the earths surface eg. the differences between ergs, regs and Hamadas and badlands. it can also refer to the spatial variation across a single hot desert

what is a wadi? WATER

Steep-sided, wide-bottomed, gorge like valleys formed by fluvial (water) erosion in arid and semi-arid regions. wadis are rarely filled with water the valley walls are steep and often covered with thick layers of weathered material, with a build-up of sediment on the valley floor. These valleys are either permanently dry, due to climate change and the drying up of former rivers, or only occasionally occupied by ephemeral streams, which can flow as a torrent ( a strong and fast-moving stream of water) with very high levels of discharge following sudden storms. They can range from small channels a matter of metres in length to complex channel systems over 100km long.

what is the haboobs?

Sudanese Sahara. More localised winds generated in the Sudanese Sahara

what factors affect the amount of sediment transported and how far it travels?

The amount of material and how far it gets moved is dependent on a number of things: speed, direction of the wind, turbulence within the wind, duration and over and what type of surface (regolith) and the presence of vegetation (or lack of)

what is pluvial?

The theory that deserts experienced wetter periods in the past

what are star dunes? WIND

These have variable slip face directions as they occur in areas with an abundant supply of sand but variable wind directions. These are often quite massive and permanent dome-like features extending over hundreds of kilometres and being hundreds of metres high, creating a draa landscape

what are ventifacts? WIND

They are exposed rocks lying on the desert surface that have been abraded or shaped by wind-blown sediment. This is usually sand, or finer silt and clay-sized particles and is often linked to a sand-blasting effect. Ventifacts can range in size from pebbles as small as a centimetre to huge boulders many metres in diameter. They are characterised by smooth and flattened sides and sharp edges or ridges. There are many recognised 'faceted types' with different numbers of flattened sides and sharp edges

what are the processes that impact sediment in hot deserts?

Weathering (breakdown of rocks by the processes of mechanical, biological or chemical) Erosion (the breakdown of the surface into sediment) Transportation (moving material from where is was eroded to the site of deposition) Deposition ( laying down of sediment as the process of transportation has lost the required energy)

what is an eddy? WIND

a circulation that develops when the wind flows over or adjacent to rough terrain or other obstructions. They generally form on the lee (downwind or sheltered) side of these obstructions. The size of the eddy is directly proportional to the size of the obstruction and speed of the wind. Eddy's may have horizontal or vertical circulations that can either be cyclonic or anticyclonic. Horizontal eddies form in sheltered areas downwind of rough coastlines or mountain chains.

what are the 3 types of inputs of loose sediment in deserts?

aeolian (comes into the system via wind) weathering of underlying bedrock fluvial (comes into the system from rivers)

when does geological change happen in hot deserts?

after tectonic uplift

what is tectonic uplift in hot deserts?

after tectonic uplift which will occur when the earths plates move and when they collide or converge, sections of the plate will be lifted up forming mountains and that will trigger intensive weathering, mass movement and erosion (primarily water) resulting in the increase of gradient and also the increase in precipitation as a result of relief precipitation.

what happens to hot deserts over time after tectonic uplift?

the water erodes vertically, by abrasion, attrition, hydraulic action and solution to form valleys which cause steep-mountain slopes that are then weathered down in the valley to form pediments. over time, the pediments eroded wider and cut back into the mountain forming gentle slopes with increasing numbers of fluvial landforms on them including inselbergs (as the mountains become isolated) and eventually a playa will form which will feature the lowland landforms and across a surface known as a pediplain. with further uplift the whole process will start again. the landscapes will change for very long periods of time as a result of geological forces

what are zeugens? WIND

they are landforms created by erosion. the agent of erosion is the wind and the action of abrasion creates them. zerugens form in rocks that have horizontal bands of soft and hard rock- almost all rocks and joints have cracks in them. in deserts, these joints are made wider by the effects of the different forms of weathering. once these joints are widened, they further enlarge by abrasion. the remaining hard rock is left standing and is called a zeugma. they can be 30m high. eventually the base is weakened by abrasion, the top collapses.

what is temporal variations in hot deserts?

variation over time

what are examples of fluvial landforms in the Mojave?

wadis=Ivanpah valley Badjas= Lucy grey fan (alluvial fan) pediments= Cima dome Playas= soda lake inselbergs= teutonia peak

What are aeolian processes?

wind action