AS Geography - Physical Geography

Terms in this set (189)

• Greatest rates of weathering are found in equatorial regions, because it's humid all year round. Chemical weathering needs water and is the active weathering agent in weathering.
• For every 10 degrees rise in temp. weathering rates increase by 2 1/2 times.
• In colder higher lats and mid lats, weathering is predominantly physical weathering.
• There is anomaly to this relationship. There is chemical weathering in high lats. beneath snow and there are large abounts of CO2 dissolved in the water. This creates carbonic acid from carbonic solution.
• Glacial climates: Susceptibility to frost increases wih increasing grain size. In Taiga claimates fairly high soil leaching, and low rates of organic matter decompose. In Tundra areas low precipitation, low temps and permafrost - moist conditions, slow organic production and breakdown. May have slower chemical weathering. Bacterial weathering may occur. Granular disintegration occurs. Hydration weathering common.
• Temperate climates: Precipitation and evaporation generaly fluctuate. Both physical and chemical weathering occur. Organic content moderate to high, breakdown moderate. Silicate clays formed and altered. In deciduous forest areas biological weathering occurs as well as organic weathering.
• Arid/ semi-arid climates: Here evaporation exceeds precipitation rainfall is low, temps are high and organic content low. Mechanical weathering, salt weathering, and granular disintegration is domiant indriest areas. Low organic input relative to decomposition. Slight leaching CaCO3 in soil. Sulphates and chlorides may accumulate in driest areas. Increased precipitation an decreased evaporation toward semi-arid areas and steppes yield thick organic layers, moderate leaching and CaCo3 accumulation.
• Humid tropical climates: High rainfall often seasonal. Long periods of high temperature. Moisture availability is high. Weathering products are removed or accumulate to create red/ black clay. Organic content high but decomposition high. Usually intense deep weathering.
Limestone is a rock containing at least 80% calcium carbonate and is formed primarily over four geological periods.
Carboniferous limestone:
• Hard, grey, crystalline and well-jointed
• Contains fossils such as coral, crinoids and brachiopods
• The rock must have been formed on the bed of a warm clear ocean
• It has developed it's own unique landscape known as 'Karst' scenery
Magnesian Limestone:
• Contains a high proportion of magnesium carbonate
Jurassic Limestone:
• Similar scenery to that of chalk
Cretaceous Chalk
• It's pure, soft, well-jointed limestone
• It's believed to be composed of the remains of small marine organisms which lived in clear shallow waters
Karst Scenery example: Li Valley, South China
• Limestone covers 300,000 km2 of China
• The limestones that outcrop near Guilin have formed a unique karst landscape
• The massively bedded, crystalline rock, which in places is 300m thick, has been slowly pushed upwards from its seabed origin through tectonic movements formed on the Himalayas and Tibetan Plateau.
• Heavy monsoon rain, exceeding 2000mm, has led to rapid fluvial erosion by the Li River.
• The availability of water together with the high sub-tropical temperatures (Guilin is at 25oN) encourages high active chemical weathering (solution and carbonation).
Carboniferous Limestone

Carboniferous Limestone develops its own unique scenery for three main reasons:
1. It is found in thick beds separated by almost horizontal bedding planes and with joints at right angles.
2. It is pervious but not porous, meaning the water can pass along the bedding planes and down joints but not through the rock itself.
3. Thirdly, Calcium Carbonate is soluble. Carbonic acid in rainwater together with humic acid from moorland plants, dissolve the limestone and widen any weaknesses in the rock. Acid rain also speeds up carbonation and solution. As there is little surface drainage and breakdown of bedrock to form soil, the vegetation cover tends to thin or absent. In winter, this allows frost shattering to form scree at the foot of steep cliffs.
Carboniferous limestone can classify into four types:
1. Surface features caused by solution - Limestone pavements are flat areas of exposed rock. They are flat because they represent the base of dissolved bedding plan, and exposed because the surface soil may have been removed from glacial activity and never replaced. Where joints reach the surface, they may be widened by acid rainwater to leave deep gashes called grikes. Between the grikes are flat topped yet dissected blocks called Clints. In time, grikes widen and the Clints are weathered down until the lower bedding plane is exposed and the process of solution-carbonation is repeated.
2. Drainage features - Rivers that have a source on surrounding impermeable rocks may disappear down swallow holes or sinks as soon as they reach the limestone. The streams flow underground finding a pathway down enlarged joints, forming potholes, and along bedding planes. Where solution is more active, underground caves form mostly above the water table (vadose caves). Corrosion often widens the caverns until part of the roof collapses, providing the river with angular material that is ideal for corrasion. Heavy rainfall quickly infiltrates downwards, so caverns and linking passages may become water filled. Resurgence occurs when the river reappears on the surface at the junction of permeable and impermeable rock.
3. Surface features resulting from underground drainage - Steep sided valleys are likely to have been formed as rivers flowed over the surface of the limestone, when permafrost acted as an impermeable layer. When the rivers were able to revert to their subterranean passages, the surface valleys were left dry (steep gorges). If the areas above an individual cave collapses, a small surface depression called a doline is formed.
4. Underground depositional features - Groundwater may become saturated with calcium bicarbonate, which is formes by the chemical reaction between carbonic acid in the rainwater and calcium carbonate in the rock. However, when the hard water reaches the cave, much of the carbon dioxide bubbles out of solution back into the air. Helped by the loss some moisture through evaporation, calcium carbonate crystals are subsequently precipitated. Water dripping from the ceiling of the cave forms, over time, stalactites. As water drips onto the floor, further deposits of calcium carbonate form more rounded stalagmites that may join the stalactites to form a pillar.
• Granite was formed when magma was intruded into the Earth's crust.
• Having been formed at a depth and under pressure, the rate of cooling was slow and this enabled large crystals of quartz, mica and feldspar to form. As the granite continued to cool, it contracted and a series of cracks were created vertically and horizontally, at regular intervals. These cracks may have been further enlarged by pressure release as overlying rocks were removed.
• The coarse-grained crystals render the rock non-porous but, although some believe granite is impermeable, water can make its way along many cracks making some areas permeable. Despite this, most granite areas usually have a high drainage density and, as they occur upland, they are often covered by marshy terrain.
• Although hard, granite is susceptible to both physical and chemical weathering. The joints, which can hold water, are widened by frost shattering, while the different rates of expansion and cooling of the various minerals within the rock cause granular disintegration.
• The feldspar and mica can be changed chemically by hydrolysis. This means that calcium, potassium, sodium, magnesium and, if the pH is less than 5.0, iron and aluminium, are released from the chemical structure. Where the feldspar changes near the surface it forms white clay called kaolinite. When the change occurs at a greater depth it produces kaolin. Quartz is not affected by chemical weathering and remains as loose crystals.
• Tors form in temperate climates and inselbergs in tropical climates.
• Indeed controversy has surrounded their origin.
If we define a tor as a residual mass of rock capping hills or high ground then many theories can explain their origin. They are not just restricted to granite regions and appear to be found in more than one climatic region of the world. Theories centre on weathering and erosion.
• Consider the granite tor, so characteristic of Dartmoor, Linton's theory advocates deep chemical weathering as the exponent, suggesting that where joints in the rock were closer together the rock would be more deeply weathered and so easily removed by later erosion. He saw a prolonged chemical weathering under tropical conditions as the main factor in tor genesis.
• A second theory favoured by arctic workers suggests mechanical weathering during the ice age was responsible. King's theory advocates tors to be nothing more than the residual remains of sub aerial erosion surfaces.
- Fast, need well lubricated material
- The material behaves like a viscous fluid
- Material size - large boulders - small grains
- The debris avalanche (large boulders) is the fastest of the flows
- Some other types of flows include earthflows and debris flows (small grain sized slows).
- Occurs because there is a decrease in internal/ shear strength. Heavy rain infiltrates the regolith - lubricates the material by filling the pores thus increasing pore pressure. Shear strength < external stress i.e. gravity
- Flows can be triggered by earthquakes would increase shear stress.
- The most important point about flows is that there is a decrease in movement with depth. The top middle moves the fastest and the front extends the furthest (an area known as the 'toe/lobe'). The internal deformation of material down the slope and as the material goes down the slope there is a decrease in velocity. A scar is left at the top of the slope where the flow began. This is a steeper section of the slope.
- The overall impact of the slope: Scar, gentler gradient at the base of the slope and material may spread widening slope foot.
- Mudflows: Rapid movements, occurring on steeper slopes, exceeding 1km/hr. They are most likely to occur following periods of intensive rainfall, where both volume and weight are added to the soil giving it a higher water content than an earthflow
- Earthflows: When the regolith slopes 5-150 becomes saturated with water, it begins to flow downhill at a rate varying between 1 and 15 km per year. The movement of material may produce short flow tracks and small bulging lobes or tongues, yet may not be fast enough to break the vegetation.
Impacts:
• Rains triggered mudslides, landslides and flash floods which claimed the lives of 10,000 -50,000 (unknown accurately as most people were buried under mud or swept to sea) in between the mountains and the Caribbean Sea.
• 150,000 were left homeless by landslides and floods in the states of Vargas and Miranda.
• Slum dwellings were often buried by mudslides (8-10m deep) or swept out to sea. This is why fatalities are unknown as many went missing and entire families went unreported as missing.
• Bridges, roads, factories, crops, telecommunications and the tourism industry (in the immediate future) were destroyed. The international airport in Caracas was closed.
• Containers at the seaport of Maiqueita were damaged. Harzardous material leaked out of these containers. Operations at the port were halted and hampered efforts to bring in emergency supplies. The economic damage was estimated at $3billion.
• 70% of Venezuelan population was living in this small coastal area. The government then made a plan to move some of the population to inland areas.
• As a result of these landslides a plan to rebuild 40,000 homes was created for Vargas. A $100 million extension was planned for the international airport. The country's main seaport in Vargas, was also planned to be modernized. Tourist destinations in Macuto and Camuri Chico were also rebuilt. Towns such as Carmen de Uria were not rebuilt, and instead created into parks & bathing resorts.
• These improvements reduced the number of fatalities to 14 in the next 2005 mudslides in the region.
Riffle and pool sequence: River channels have irregularities in the bed, which cause the thalweg to shift from the middle. These are known as 'pools' and 'riffles'. In a flowing stream, a riffle-pool sequence (also known as a pool-riffle sequence) develops as a stream's hydrological flow structure alternates from areas of relatively shallow to deeper water. This sequence is present only in streams carrying gravel or coarser sediments. Riffles are formed in shallow areas (the shallow points of inflection) by coarser materials such as gravel deposits on river with a turbulent flow with a lower velocity. Pools are deeper and calmer areas of laminar flows with higher velocities, whose bed load (in general) is made up of finer material such as silt. Streams with only sand or silt-laden beds do not develop the feature. The sequence within a streambed commonly occurs at intervals of from 5 to 7 stream widths. Meandering streams with relatively coarse bed load tend to develop a riffle-pool sequence with pools in the outsides of the bends and riffles in the crossovers between one meander to the next on the opposite side of the stream. The pools are areas of greater erosion where the available energy in the river builds up due to a reduction in friction. The material eroded tends to be deposited in the riffle area between pools as energy is dissipated across the riffle area. Pools and riffles are responsible for the initiation of a meander. The pools are areas of high velocity and the thalweg is fast in a pool. Its energy is reduced and diffused (spread out) as it crosses the riffles. This is because the water is shallower; the bed is covered with bed load, is rough and creates turbulent flow. Therefore in order to overcome, these obstacles the river uses up more energy become slower.
Deltas: Deltas are usually composed of fine sediment, which is deposited when a river loses energy and competence as it flows into an area of slow-moving water such as a lake or the sea. When the river meets the sea the meeting produces an electric charge, which causes clay particles to coagulate and to settle on the seabed, a process called flocculation (larger coagulated particles carried out into the shallow water offshore and deposited, and the river loses energy on meeting the sea water). The water flows into a delta via distributaries. They are usually highly populated, not very navigable and have a great risk of flooding. Crops are usually grown on these deltas and are usually staple crops e.g. Rice. Deltas are named after the fourth letter in the Greek alphabet (∆). Yet Deltas range in geomorphology into three main types:
• Arcuate: (Wave dominant) Having rounded, convex outer margins. They also have smooth coastlines and have well developed beaches/ sand dunes. Lagoons form near coastal areas e.g. the Nile Delta.
• Cuspate: (Tide dominant) Where material brought down by a river is spread out evenly on either side of the channel. It is tide dominant and is covered by the high tide and left dry at low tide e.g. the Bangladesh Delta.
• Bird's foot: (River Dominant) Where the river has many distributaries bounded by sediment and which extend out to sea like the claws of a bird's foot. The river has a large load from a huge drainage basin, a low energy river into the Gulf of Mexico, and a small tidal range e.g. Mississippi Delta.
Case Study Physical and human intensification of floods: Mississippi River

• Huge river system - 3800 Km long - 1400 million m3 per day discharge
• Every year there is either flooding or severe drought
• Engineering of the channel to control floods, but this exacerbated problems.
• Natural levees were heightened, but this heightening channeled fast flowing water into the deepened river. The water could not be accommodated in the confined space - discharge levels caused more flooding by overtopping new levees and breaks in the new man made embankments.
• Source is a small glacial lake, Lake Itasca, in Minnesota at 480m above sea level. It takes an average of 90 days for the water in the Mississippi to flow to the Gulf of Mexico.
• Just north of St Louis, Missouri the Mississippi River is joined by the Missouri River. The confluence of the river is now doubled.
• The river is a major transport link for grain from the Midwest and petrochemicals from the Gulf. To help these boats use the river, many dams and locks have been constructed. Also the river had been deepened at least 3m and up to 4m in some places.
• Dykes have been built to prevent the riverbanks from eroding.
• The lower Mississippi has huge sweeping meanders. Some of the channels have been changed to divert the river from this course, to shorten the journey for boats.
• The city of New Orleans is built on a delta about 160 Km from the Gulf. A hurricane in 2005 devastated the city when levees protecting the city had broken.
Droughts

• The hydrological cycle accounts for 1% of the total water on the planet
• The hydrological cycle is a closed system because water is neither added nor lost
• Over the last 300 years the world's population has increased x7 and demand for water has increased x40.
• Severe water stress is experienced by 1.1 billion people in 80 countries

Reliability of rainfall
• Few homes in LEDC's have piped water
• Few developing countries have the money or the technology to build dams to store water. If they have it was mostly like built with foreign aid
• Torrential downpours give insufficient time to infiltrate the ground. Instead surface runoff create flash floods
• The most vulnerable areas are desert margins and tropical interiors where average annual rainfall is low and rainy seasons are short
• Many countries just experience wet/ dry seasons. If rain fails one year, the result of produce can be disastrous
• Deforestation decreases interception rates and increases evaporation rates
• Climate change can also have an effect on length of droughts
• Increased use of water for irrigation, demand for water for home use (population increase) and for manufacturing also can intensify droughts.

Clean Water
• 1.1 billion people lack clean water
• Rural areas use local rivers for drinking as well as washing and sewerage disposal
• Shanty towns lack proper drainage for sewerage which may pollute water ways
• Droughts: Animals die, crops whither, human dehydrate,
• Villagers can help themselves out though by: building wells to reach a permanent supply, lining wells with concrete, using pumps and teaching about proper hygiene, building stone walls, reducing amount of trees cut down, education on droughts, reducing reliance on irrigation, Using more drought resistant HYV plants, changing cultivation techniques, recycling water from showers, baths and washing, water tanks to use during droughts and save water during rainy seasons, de-salination kits.
1) General circulation
• Tri-cellular model
o Hadley Cell
• Moves anticlockwise in the northern hemisphere in convection currents
• Moves between 0-30 degrees and is associated with cumulonimbus cloud formations
o Ferrell Cell
• Associated with warm south westerlies
• Circulates up to 12Km in height and between latitudes 30-600 and in a clockwise direction in the northern hemisphere
o Polar cell
• Circulates in an anti-clockwise direction in the northern hemisphere
• Associated with easterlies
• Circulates between latitudes 60-90 degrees
• Up to 9-10 Km in height
o Depressions
• A mechanism for excess heat to be transferred
o Coriolis force
• Refers to the direction that the water spins in the northern hemisphere compared with the southern hemisphere.
• It is due to the Earth's rotation
• In the northern hemisphere water spins a clockwise direction and in the southern it spins anticlockwise.
• ITCZ
o Trade winds
• Pick up latent heat as they cross warm tropical oceans
• North East in the northern hemisphere and south easterly in the southern hemisphere
o Doldrums
• Gentle variable winds
o Inter-tropical convergence zone
• This is the zone where trade winds meet
• Jet Streams
o Helps in a rapid transfer of energy
o Narrow bands of extremely fast moving air
• Rossby Waves
o Rossby waves are high altitude, fast moving westerly winds, which often follow an irregular path. The path that they take changes throughout seasons.
2) Ocean currents
• The ocean has a greater specific heat capacity than land
• Warm currents carry water pole-wards and raise the temperature of the maritime environment. Cold currents also carry water towards the equator and lower the temperature of coastal areas there.
3) Weather systems
Impacts of Global warming

• Climatic
o Increased storm activity
• Tornadoes in the mid west
• Hurricanes
• Typhoons
• Cyclones
o Temperature increases
• With no action, temperatures will increase by 2.50C in the next 50 years.
o Reduced rainfall
• Leads to droughts
o Rise in sea temperatures
• Other
o Forest fires
• Increase of fires because of dry forests
o Coral bleaching
• From a rise in sea temperatures
• For example reefs on the Great Barrier Reef
o Water shortages
• 4 billion could face water shortages if temperatures increase 20C.
o Changes in agriculture
• Samoln fishing could become obselte
• A 35% decrease in yields if temperatures increase 30C
• However there could be an increase in timber yields
• Increase in growing seasons in temperate and alpine areas
o Flooding
• By 2100 an overall 1m rise in sea levels if no action has occurred.
• Flooding will occur in Delta areas more frequently e.g. New Orleans.
• 4 million km2 is threatened
• 200 million could be at risk of loosing their homes from floods by 2050.
o Changes to Tourism
• Longer tourist seasons for summer tourist destinations
• Winter tourism to ski fields and glaciers may decline.
o Soil erosion
• Especially in areas such as the amazon that is damaged by slash and burn practices
o Spreading of disease
• A 20C rise could increase the number infected by Malaria by 60 million
o Extinction of wildlife
• If temperatures increase by 20C, 40 % of species will become extinct
• Habitats could decrease in range e.g. Polar Bears
• Range of Species could increase e.g. Butterflies in the UK
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