3.1 How Can Dryland Landscapes be Viewed as Systems? Flashcards

Question

What are common features of semi-arid environments?

Answer 1

Drought, variable rainfall, dust storms, and floods during rainy seasons are common in semi-arid environments.

Answer 2

- Winds from Siberia bring snow- 50 m/ph - Snow never melts, winds too cold and dry, sun rays evaporate it. - Summer= 50 degrees, winter= -40 degrees. - Camels- lack of water- eat up to 10 litres of snow for water

Answer 3

- Himalayas cause a lack of precipitation- rain shadow. - Sandstorms create dunes which can be 300m high, dust blown 5000m into sky. - Subtropical deserts are found between 15 and 30 degrees North and South of the equator: 1. Hot air rises 2. Air cools and heavy rains 3. Drier air moves away from the equator 4. Near tropics air falls and warms up 5. This air has the formation of clouds. 6. Little rain

Answer 4

- Driest desert in the world- some areas haven't had rain for 50 years - Cold sea currents parallel to the land cools the air and produces fog. Fog produces precipitation, but further inland the fog is not condensed to precipitation.

Answer 5

- Every hour temp rises by 5 degrees - Temp on the ground can be 70 degrees - Kangaroos lick saliva onto their arms where the blood vessels are closest to the skin to cool blood down.

Answer 6

- Flash floods help to maintain green grass and provide food and water for animals.

Answer 7

- hottest desert on earth - When air hits a mountain range it must rise, cooling and forming clouds that rain on the wind facing slopes. When the air moves over the mountain there is little moisture. Air warms up and clouds don't form.

Answer 8

Erratic rainfall

Answer 9

Ground heats air forming visible waves

Answer 10

An area that is spatially heterogeneous (varied) in at least one factor of interest. Are open systems and vary in structure and functions due to natural and human factors.

Answer 11

They support 2 billion people, 90% who live in developing countries. Act as the foundation for rural and urban communities- eg. Cairo and Mexico City 6 million km squared of drylands (10%) bear a legacy of land degradation.

Answer 12

- REG (stones) - ERG (sandy) - Hamada (rocky)

Answer 13

- Earths curvature results in radiation at higher latitudes being spread out across a larger surface area. - The angle at which incoming solar radiation hits earth's surface determines whether more or less of it is absorbed or reflected. This is called the angle of incidence. - Differential heating= some parts of the earths surface are heated more than others. - Hadley Cell- air rises, cools and condenses, air diverges to create high pressure regions of no clouds. Cool air sinks and air warms to form low pressure regions.

Answer 14

- Albedo is the percentage of the incident sunlight or radiation that is reflected. - Sand has an albedo of 30-35%, while snow has an albedo of 80-90%. - There is a trend of increasing albedo with increasing latitude.

Answer 15

Wind is the perceptible natural movement of air in the form of currents and is driven by differences in atmospheric pressure- high pressure moves to low pressure and vice versa.

Answer 16

- Red saharan dust deposited in southern europe and occasionally even the UK- (Loess) Surface creep- wind rolls heavy particles of coarse sand and pebbles (0.25mm-2cm) across the dryland surface which can be sped up by the interaction of particles being moved in saltation. Saltation- Fine sand (0.15-0.25mm) is transported when the wind moves the sand short distances before depositing it when the wind velocity decreases and energy is reduced. The sand is picked up again when the wind velocity increases and is moved further. Suspension- Light loess (under 0.15mm) is transported in suspension being picked up and carried high into the atmosphere. Wind direction, velocity and frequency determines the direction and rate of transportation.

Answer 17

- Most rainfall in deserts occurs in low intensity forms. - Sometimes there are more sudden and isolated heavy downpours. In upland areas water is often dominant as an erosional agent. In lowland areas it is common in deposition. Rainfall variability= mean deviation from the average/ the average x 100.

Answer 18

- Very few deserts have rivers that flow permanently due to low levels of precipitation and high levels of evaporation. - However, desert thunderstorms can drop over 25mm of rain in a few minutes. Discharge is irregular in terms of frequency and amount and many rivers evaporate before they reach the sea or flow within basins of inland drainage, usually into a lake. High rates of evaporation lead to some of these becoming inland lakes.

Answer 19

- Deserts have little or no vegetation to intercept so the rainfall is unimpeded and hits the ground with force leading to rain splash erosion as the raindrops dislodge soil particles, making them more susceptible to movement by overland flow. The loosened particles that are not washed away can form a muddy slick that fills and clogs soil pores and reduces soil permeability, reducing infiltration and increasing run off.

Answer 20

High rates of surface run off form streams that lead quickly to the river channel. These carry sand and mud as there is a lot of loose material which erodes rock through abrasion and hydraulic action - Weaker areas of rock such as joints and faults are eroded into very narrow canyons, often less than 1 metre wide. Over time, these develop into wadis. When it rains these canyons fill quickly and channel the water creating flash floods.

Answer 21

They show the water surplus, soil moisture utilisation, soil moisture recharge, water deficit, precipitation, PET and moisture totals.

Answer 22

- These are perennial rivers (they flow all year round) - These rivers rise in wetter areas outside the arid zone and due to a large number of tributaries that join they are able to flow into the sea - Eg. The Colorado River, USA. This river is heavily dammed for domestic, agricultural and industrial use eg. the hoover dam. Since 1963, the Colorado has connected with the sea only a few times but due to co-operation between Mexico and the USA the river is being restored.

Answer 23

- These rivers never reach the sea as their mouth is an inland lake - In desert areas most rivers drain into inland lakes because of high rates of water loss due to evaporation and infiltration. - Eg. The river zin, Israel. This river flowed in 2014, but prior to this there had been drought for many years. The return of the river was predicted and celebrated by locals.

Answer 24

- These are typical of desert areas as they only flow after rainfall and the channels are dry for most of the year. - They tend to have high sudden discharge and high sediment loads after heavy rainfall caused by a thunderstorm. Rainfall can't infiltrate the baked hard ground and there is little vegetation to intercept the surface run off. - Eg. The river Syr Darya flowing into the North Aral sea. Water from this river is over abstracted and flow is reduced so management is in place.

Answer 25

- Temperature decreases with height in the lower atmosphere. So, areas at high elevations would tend to experience lower temperatures than nearby areas at much lower elevations. In the lower atmosphere, temperature decreases at a rate of 6.5 degrees Celsius per km- lapse rate. Every 150m the temp drops by 1 degrees Celsius. - Air rises as it expands and molecules move further apart and it gets colder. - Some deserts are at a high altitude eg. Gobi - Some deserts have a high plateau within them. - Altitude impacts desert climate

Answer 26

- The thermal characteristics of drylands are variable. - Temperatures are most strongly influenced by latitude, except the Namib and the Atacama that are coastal.

Answer 27

- Temperature decreases as latitude increases - Places at the same latitude can have different temperatures and precipitation amounts. - The temp and precipitation per month have a high variation due to the large impact of axial tilt and rotation around the sun (greater seasonality).

Answer 28

* This means the daily difference in temperatures. (between the highest and lowest temperatures) * In the Sahara – the world’s largest hot arid region, the diurnal range can be as extreme as 37.5°c to −0.5 °C but is normally around 15°c to 20°c. Deserts close to the sea have lower diurnal ranges.

Answer 29

- Air rising near the equator to the tropopause is then transferred pole wards at heights of 10-15km and eventually sinks back to the surface between latitudes 20 and 30 degrees in each hemisphere. Warmed by compression, the sinking air creates cloud free conditions, permanent high pressure and extreme aridity at the surface. - Latitude impacts the amount and intensity of incident solar radiation. So, high latitude receives less solar radiation than low and mid latitudes, and average temp generally decreases pole wards.

Answer 30

- Rock lithology refers to the physical and chemical composition of rocks. - Rock structure is the properties that make up individual rock types.

Answer 31

- In rocks with a weak lithology the bonds between the particles that make up the rock are quite weak, as in clay. - Others, such as basalt, made of dense interlocking crystals, are very resistant. - Some such as chalk are largely composed of calcium carbonate and so soluble in weak acids making them prone to chemical weathering. Resistant rocks could provide the high mountainous areas which are not rapidly eroded, whereas the weaker or jointed rocks provide the deeply cut valleys and canyons. If a valley floor is made up of different geologies, some weaker than others, then the canyon sides may be stepped.

Answer 32

Jointing cracks (usually vertical) in rock caused by shrinkage or release of pressure as rocks above are eroded away.

Answer 33

Bedding layering formed in sedimentary rocks as the rate of sediment deposition varies. Layer boundaries are called bedding planes.

Answer 34

Folding bending of rock layers caused by compression of rocks, usually as part of mountain-building when tectonic plates collide.

Answer 35

Faulting deep cracks caused by movement of rock during earthquakes. Different rock types are often seen on each side of a fault.

Answer 36

- Lithology, not structure determines the porosity or permeability of rocks. - Poorly cemented silt and clay rocks which are highly impermeable, create rapid run-off - Rocks with high levels of porosity and permeability create drought at the surface. Both lithology and structure are the primary controls on water transfer in drainage basins. Dryland landscapes are therefore shaped by their geology as they will contain different landforms and relief patterns due to the potential for weathering and erosion to break down and wear away the rocks.

Answer 37

- Freeze-thaw weathering (cold climate) and thermal expansion (warm climate)

Answer 38

Vegetation (roots) and animals (eg. burrows)

Answer 39

Solution- action of acid in the rain

Answer 40

Aspect is the direction that a slope faces. Some slopes may face the prevailing wind and be subjected to more erosion. Ventifacts are rocks with one side eroded by wind abrasion into a smooth flat face. Sometimes the wind blows them over, exposing another face to the abrasion of the wind which also then becomes smoothed. Insolation weathering will be greater on sloped that face the sun as the diurnal temp range will be higher.

Answer 41

Sediment compromises rock particles of varying size derived from weathering and erosion processes, transported and ultimately deposited by rivers, winds and mass movement processes.

Answer 42

REG (rocky or stony)- In some drylands sediments are scarce and the ground may be covered with tightly packed stones forming desert pavements. This rocky surface is known as reg. Most deserts are rocky rather than sandy, suggesting that finer sediments are often have been removed by wind action.

Answer 43

The generic term describes large expanses of sandy deserts.

Answer 44

- Weathering - Mass movement - Erosion - Transport - Deposition The agents are wind (aeolian) and water (fluvial) for transportation and deposition.

Answer 45

- Insolation weathering - Exfoliation - Block disintegration - Granular disintegration

Answer 46

- Rock surface heats up and expands - Rock surface cools and contracts - Joints form in the outer part of the rock - Outer shell of the rock breaks This is a sequential process which is diurnal where rocks are a poor conductor of heat.

Answer 47

During the day the surface layers expands in response to the higher temperatures to a greater extent than those concealed beneath the surface. At night, cooling and contraction occurs at different rates. This causes the surface layers to peel away from the lower layers - the process of exfoliation. Different minerals can heat and cool down at different rates (variation of coefficients of minerals) within a rock eg granite

Answer 48

Caused by heating and cooling of rocks that are well jointed. Rocks breakdown along the joints and bedding planes as these are lines of weakness Eg, with a mesa and bute: - Free face: is being weathered, vertical and horizontal joints - Cap rock: harder rock protecting softer rock - Talis slope: debris, fallen from the free face

Answer 49

Rock type with separated grains in it. Doesn't happen in igneous rocks, only sedimentary rocks.

Answer 50

Salts are common in deserts because they are drawn up to the surface by capillary action in solution and high evaporation rates leave salts on the surface rather than the salts being transported in solution. Rocks are impregnated with soluble salts. Salts disintegrate rocks by the growth of salt crystals which can grow by 300% and this creates stress in the rock causing it to disintegrate = haloclasty.

Answer 51

In high or mid latitude deserts with high diurnal temperature range= shattering and scree. Freeze-thaw weathering can also be called frost shattering. Water may get into a crack in a rock and freeze when the temperature drops. As the water turns to ice it expands and causes the crack to open a little When it thaws ice melts and changes back into water. Repeated freezing and thawing weakens the rock and splits it into jagged pieces. This type of weathering is common in mountainous areas where temperatures are often around freezing point.

Answer 52

Chemical weathering happened more historically (in pluvial times) 1. Solution - More important in deserts - Overlaps with mechanical weathering - Carbonation where limestone is present 2. Oxidation - Namibia star dunes- red colour. - Oxygen dissolved in water reacts with iron to create iron oxides. Minerals oxidised increase in volume. - Eg, Ulluru 3. Hydrolysis - Involves the dissolving of feldspar minerals in granite by hydrogen. - The feldspar reacts with hydrogen in water producing kaolin. - Fieldspar + hydrogen ions + water= clay and dissolved ions - eg. death valley 4. Hydration - Affects rock minerals which have the capacity to take up water. They increase in volume, which sets up stresses within the rock eg. Conversion of iron oxides to iron hydroxides. Causes granular disintegration, surface flaking, similar to salt weathering

Answer 53

- Very localised (desert plains, oasis and wadis) due to lack of moisture and sparse vegetation - Roots prising rocks apart in wadis (tap roots) and wind shear transferring stress - Chelation- humic acids produced when vegetation breaks down - Action of animals- burrowing at night, goats, camels, humans. - Lichens and algae cause micro-morphological changes to rock.

Answer 54

Dark film of iron and manganese oxides. a. ‘sweating’ of minerals to rock surfaces. b. external deposition (wind blown dust / pollen). c. microbiological weathering The varnish is made mostly of silica, which can fall from the atmosphere or leach from the rock itself. Over time, silica breaks down into a gel like form and hardens. It traps amino acids, DNA fragments, and even microorganisms from past eras that lived on the rocks or simply became stuck to them. - DESERT PAVEMENTS eg. Valley of fire, Las Vegas, USA

Answer 55

Alveoles are small hollows or cavities (5-50 cm) that occur in clusters. They are a subcategory of tafoni that consists of regular, tightly adjoining, and commonly patterned cavities that are developed in weathered bedrock. Tafoni are small cave-like features in granular rock with rounded entrances and smooth walls. They occur in clusters. This formation is easily recognized due to its honeycomb, or sponge-like, appearance. Several theories have been put forward, but it is widely accepted that they are caused by a form of salt weathering (solution). It occurs when salt collects on the surface of permeable rocks, usually by ocean waves, mist, or wind. As the saltwater evaporates, it leaves the salt behind. The salt works its way into the rock pores, where it crystallizes and pushes the pores open further. These enlarged rock pores become susceptible to additional weathering, including freeze-thaw cycles. eg. The Arches National Park in Utah, USA

Answer 56

Large dome-shaped rock mass (of granite) The rock mass at depth is under high pressure from overlying rocks. It tends to be uniform and lack fractures. As progressive erosion occurs, the rock mass is subjected to progressively lower pressure of overlying rocks which leads to tension in directions at right angles to the land surface. This tension is relieved by formation of cracks which follow the land surface - they are relatively flat on plateaus, but can be steep on the flanks of mountains which are called exfoliation domes. Once the cracks develop, water enters and causes chemical weathering leading to the formation of new low-density minerals. This enhances the cracks and encourages slabs of rock to detach from the surface. eg. Yellowstone National Park, USA

3.1 How Can Dryland Landscapes be Viewed as Systems? Flashcards

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