P.1
Shatin Pui Ying College
F.7 Geography Paper 2 Mock Exam (2003-04)
Suggested Solution
Section ANatural Landscapes
1.‘The location and climatic characteristics of a biome are results of their geographical position relative to the global pattern of air circulation.’
Using any one biome in the tropics as an example, discuss the validity of this statement.
Explanation5
Description3+7
Discussion6
Examples4
A.Explanation : Global pattern of air circulation
-Hadley Cell
-Ferral Cell
-Polar Cell
-Annotated diagram
-Focus put on Hadley Cell (biome in the tropics) (5)
B.Selection of biome
-tropical rainforest, or
-tropical desert
C.Description : Location / Spatial characteristics
-TRF -low latitudes, around the equator in the tropics
within 10N & S of the equator
E.g.Amazon Basin in Brazil, S America
Congo Basin and Zaire Basin in W. Africa
Southeast Asian countries, e.g. Thailand, Indonesia, the Philippines
location relative to Hadley Cell
-TD -20-30N & S of the equator
E.g.Sahara Desert of N. Africa
Kalahari Desert of S. Africa
Mojave Desert of N. America
location relative to Hadley Cell (3)
D.Description & Explanation : Climatic characteristics
-TRF -Temperature
high temperature (around 26-27C) throughout the year
small annual (2-5C) and daily (5-10C) range of temperature
strong insolation
due to high angle of the sun,
short distance travelled by sun’s ray through the
atmosphere
vertical sun’s ray
absence of seasonality
Precipitation
high annual precipitation, over 2000 mm
due to its location at the rising lime of the Hadley Cell
the influence of Equatorial Low
evenly distributed precipitation, with double maxima
convection rain is common
-TD -Temperature
high temperature (around 40C) throughout the year
large annual daily (over 20C) range of temperature
due to the absence of blanket effect from the clear sky
strong insolation
due to absence of cloud cover
Precipitation
low annual precipitation, around / less than 250 mm
due to its location at the sinking lime of the Hadley Cell
the influence of Subtropical High
unevenly distributed precipitation
unreliable precipitation
sudden torrential downpour is common (7)
E.Discussion : Factors leading to local variation
-Aspect
-Distance from the sea / Maritime influence / Continentality
-Altitude
-Vegetation cover
-Human factor(6)
F.Examples(4)
max. 25
- Compare and contrast the weathering processes in tropical humid environment and tropical arid environment. Explain why within the same climatic zone, there will be local variation in the work of weathering.
Ref : 94#2Comp & Cont12 (D & E)
90+1Exp10 (local variation)
89+1Egs. 3
I.Intro
- Def. of weathering :
disintegration (physical break down) or decomposition (chemical decay) of rock in situ
- Types : physical, chemical + biological weathering
- Relative importance differs in TRF and TD : TRF : C > P; TD : P > C(4)
- A. Compare & contrast : weathering processes in TRF + TD
TRF / TD
Chemical Weathering
1. / stronger hot + wet climate / 1. / weak aridity Ep ＞ppt.)
constantly Tº(26-28℃) +
ppt. (＞2000 mm annually) / Tºfavours chemical weathering but
restricted by extremely low annual ppt ＜250 mm
2. / Tº control level of chemical activities
3. / ppt. chemical processes, e.g. solution, hydration, hydrolysis, oxidation + carbonation (limestone region) spheroidal weathering, honeycomb weathering
4. / Biologically, Tº + ppt. fauna + flora
excretion of organic acid for chemical weathering
Physical weathering
1. / weak small annual range of Tº (2℃) though / 1. / strong large daily + annual range of Tº (＞50℃)
assisted by the presence of moisture
2. / ,hot + wet climate dense veg.
range of Tº / 2. / aridity barren land without / with sparse veg.
range of Tº
3. / biologically, dense veg.
roots
physical exertion of pressure upon rocks / 3. / physical weathering processes,
e.g. block disintegration, granular disintegration, salt crystallization, onion-skin weathering,
e.g. exfoliation dome in the Outback of Australia (Ayers Rock)
(8)
B.Factors causing local variation
1. a.Rock type : composition + mineralogy
-quartz more resistant to weathering
-heterogeneous rock favours granular disintegration (P) + honeycomb weathering (C)
homogeneous rock favours exfoliation (P)
b.rock structure : joints water seeps along joints for speroidal weathering (C)
2.Topographic factors :
a.altitude / height : alt. :Tº fluctuate around 0℃ frost action (P)
range of Tº (P)
wind velocity desiccation (C)
b.aspect : sun-facing :Tº(C)
veg. (P) : plants’ roots + micro-organisms ‘ burrowing
(C) : organic acids
c.relief : steep relief : soil depth + soil moisture (C)
veg. (buffer) range of Tº (P)
d.site :along rivers /coastal areas : R.H. (C)
- Biotic factor – human’ devegetation exposure to air + water rate of weathering
- plants + micro-organisms rate of weathering(10)
Examples (3)
Max. 25
3.With reference to oxisol and aridisol, describe their pedogenic processes. Evaluate
the relative importance of physical and human factors in contributing these
processes in the tropics. To what extent is soil conservation effective in slowing
down the degradation processes? Illustrate your answer with examples.
Ref :98#2Des 5+5
00#3Eva 4+5
01#3Ass 6
02#3Egs.
- Intro :
1.Oxisol : tropics, e.g. savanna, usually with a short dry period for oxidation reddish brown colour + formation of oxic / plinthite layer by the process of plinithization
2. Aridisol : arid zones, e.g. TD or, areas with continental climate capillary action duricrust formed by salinization (salt crust) and calcification (caliche)
II.Content :
A.Description : Pedogenic processes of oxisol in the tropics(Fig 1)
1.Oxisol is formed in the tropics with alternate wet and dry seasons
2.Hot and wet seasons: hot (annual mean T 27-28C) + wet : annual ppt > 2000 mm
water surplus some minerals are removed as the excess water percolates through the soil to the ground water zone, i.e. intense leaching
3.hot + wet dense vegetation + active bacterial activities chemical weathering release of clay + sesquioxides of Fe + Al
4.clay breaks down to form silica which is leached out by heavy rainfall by the process of desiliccation; leaving behind sesquioxides of Fe + Al reddish brown in colour
5.Dry season high concentration of sesquioxides of Fe and Al plinthite / oxic layer (> 30 cm thick, at 2m below ground surface) hard pan called laterite is formed by the process known as plinthization/ laterization.
Fig. 1
(5)
B.Evaluation : Physical factor (oxisol)
aridity ∵natural climatic changes, e.g. El Nino quickens the drying up of sesquixides of Fe + Al hardening of oxic layer
C.Evaluation : Human factor (oxisol)
- Mekong Project in Vietnamdeforestation + fluctuation of groundwater table alternate reduction and oxidation
2.Devegetation for construction, industries, transport development, e.g. Trans-Amazon Highway; cattle ranching e.g. in Brazilian Highland; plantation, e.g.rubber plantation in W. Malaysia; commercial lumbering, e.g. for ramin in Kalimantan, ebony in Sulawesi, mining ores, e.g. tin in Sungai Lembing, iron ore in Gambang, etc.
Deforestation exposure to air ↑plinthization / hardening of oxic layer
Evaluation : relative importance of physical and human factors in contributing oxisol
- Physical factors promote the formation of aridisol gradually.
2Physical factors only provide the necessary condition.
3.Human factors accelerate plinthization and the formation of oxisol.(4)
D.Description : Pedogenic processes of aridsol in TD or areas with continental climate(Fig 2)
1.Low annual ppt, 250 mm for TD; 250 – 1000 mm for areas with continental climate) potential evapotranspiration > ppt (water deficit); or areas with continental climate in the interior
2.High water table/ Water table near to the ground surface
3.Poor / inland drainage, e.g. valley floors, flat basins in the continental interior,
e.g. Qinghai, Xinjiang water is available for intense evaporation
4.Release of soluble salts, e.g. Ca and K, by weathering, or extinct lakes
- Rainfall is too low for leaching
- Intense insolation + T evaporation + capillary action TD : salinization : salt solution is drawn upward water loss by evaporation mineral salts precipitates on the ground surface as a hard pan (whitish salt crust).
- Areas of continental interior, with limestone (containing calcium carbonate) : calcification evaporation + capillary action hard pan called, caliche / calci layer in B horizon (15 – 30 cm below ground surface)
e.g. Calcification in China brown soils in desert areas of Inner Mongolia
Fig. 2
(4)
E.Evaluation : Physical factor (aridisol)
1.Prolonged drought due to climatic change
E.g. : Severe drought in Sahel region, including Ethiopia in 1968-73 1980-84.
- vegetation exposure to wind and sun capillary action
- vegetation wind velocity active wind erosion + desiccation
F.Evaluation : Human factor (aridisol): Human misuse of resources
1.nomadic herding overgrazing, e.g. the Rendille of N. Kenya
2.oases + marginal farming overcultivation, e.g. along the R. Nile in Egypt
3.Devegetation for firewood as fuel devegetation
4.Mining, e.g. rock salt in Sahara + opal in Great Australian D.
Activities1. 4.Devegetation exposure to wind and sun baking
5. Improper irrigation
-excessive irrigation without proper drainagewater available for capillary action water table
6.Construction of reservoir + dam in semi-arid lands, e.g. Tarim Basin
water available for capillary action soil moisture content
Evaluation: relative importance of physical and human factors in contributing aridisol
- Physical factors promote the formation of aridisol gradually.
2Physical factors only provide the necessary condition.
3.Human factors accelerate salinization and the formation of aridsol.(5)
G.Assessment : Soil conservation measures
1.adopt better farming methods
- tillage
-protect the soil by residue cover / mulch
-plant soil-improving crops, e.g. legumes (N-fixing bacteria)
-crop rotation
-contour ploughing / terracing on slopes
2.Set up windbreaks slow down the degradation process
-Reclamation with salt-tolerants, grasses and shrubs, e.g. Phragmites spp.
surface roughness to stop the advancing sand dunes
E.g. In Iran, advancing dunes have been stopped by spraying them with petroleum residue; when the spray dries, it forms a mulch that retains moisture and allows vegetation to grow.
(3)
H.Other measures to alleviate soil degradation
1.Overgrazing
herding size to meet the carrying capacity of land by legislation + education
2.Devegetation for firewood as fuel
develop alternative sources of energy, preferably renewable resources, e.g. wind power + solar energy as substitutes
3.Improper irrigation
-Adopt irrigation with proper management, i.e. proper drainage +
-avoid the use of salty water +
-practice drip irrigation
4.Construction of dams + reservoir
-Avoid construction of dams + reservoir upstream of inland river
5.Develop secondary + tertiary industries pressure on land
6.Birth control + family planning through education is a long term solution to pressure on land
(3)
III.Conclusion
Assessment
Effectiveness of measures depends on the willingness of Government, availability of capital, citizens’ cooperation + technical support form foreign countries
Max. 25
3.With reference to oxisol and aridisol, compare the ways in which climate and other environmental factors interact to produce these two distinctive soils. Discuss how people induce soil degradation in the tropics. Illustrate your answer with examples.
Ref :98#2Comp12
00#3Dis8
01#3Eg.5
I.Comparison : Oxisol (latosol in TRF + ferruginous soils in savanna)
- Climatic factors
1.Oxisol is formed in the humid tropics intense chemical weatheringfine texture clay soil (with high moisture + nutrient holding ability) + thick soil profile (up to 30m)
2.TRF
hot (annual mean T 27-28C) + wet : annual ppt > 2000 mm
water surplus some minerals are removed as the excess water percolates through the soil to the ground water zone, i.e. intense leaching
3.hot + wet dense vegetation + active bacterial activities chemical weathering release of clay + sesquioxides of Fe + ‘Al (Fe2O3 and Al2O3)
4.clay breaks down to form silica which is leached out by heavy rainfall by the process of desilication; leaving behind sesquioxides of Fe + ‘Al reddish brown in colour (Fig.1)
5.Savanna
alternate dry and wet seasons, dry season High concentration of sesquioxides of Fe and Al plinthite layer hard pan called laterite is formed by the process known as plinthization/ laterization. (Fig. 2)
Fig. 1Fig. 2
- Environmental factors
1.Luxuriant vegetation + abundant fauna, especially fauna, soil micro-organisms
hot wet climate active bacterial activities decomposition
2.Even so, plants take up a lot of nutrients from the oil and store them in plant
tissues infertile soil
Examples :Leizhou Peninsula of Guangdong, SW Taiwan(6)
II.Aridisol (Desert soils in TD)
A.Climatic factors
1.Desert climate : annual ppt 250 mm; potential evapotranspiration (Ep) > ppt
water deficit
2.Release of soluble salts, e.g. Ca and K, by weathering, groundwateror extinct lakes
3.Rainfall is too low for leaching
4.Intense insolation evaporation + capillary action
salt solution is drawn upward to from hard pan, or whitish salt crust. (Fig. 3)
5. aridity soil is affected by desiccation (as infiltration is prevented)
biological productivity desertification
Fig. 3
B.Environmental factors
1.Salinization or the formation of aridisol is further enhanced
a)in areas with high water table and
b)poor drainage, e.g. valley floors, flat basins in the continental interior water is available for intense evaporation
- Scanty vegetation aridity barren direct exposure to wind + sun baking rainsplash effect + soil erosion + gullies + badland, i.e. aridisol is easily susceptible by erosion
Example : Qinghai, Xinjiang(6)
- Discussion : man induces soil degradation in the tropics
A.TRF / Savanna
1.Mekong Project in Vietnamdeforestation↑plinthization
2.Devegetation for construction, industries, transport development, e.g. Trans-Amazon Highway; cattle ranching e.g. in Brazilian Highland; plantation, e.g. rubber plantation in W. Malaysia; commercial lumbering, e.g. for ramin in Kalimantan, ebony in Sulawesi,. Mining ores, e.g. tin in Sungai Lembing, iron ore in Gambang,etc.
B.TD / Semi-arid zones in the tropics
1.Improper irrigation
- excessive irrigation without proper drainage
- use of salt-laden moisture on irrigation
2.Construction of reservoir + dam in semi-arid lands, e.g. Tarim Basin
water available for capillary action under intense insolation salinization
3. men fail to identify fragility of environmentoveruse resources
a)They practise nomadic herding e.g. by Rendille of N. Kenya
-Population explosion in N. America and Middle East herding size, e.g. 62% in Mali and 125% in Mauritania in 1955-70 overgrazing trampling
b)oases + marginal farming overcultivation
e.g. along the R. Nile in Egypt
-population demand for food fallow period overcultivation biological productivity can’t support crops + vegetation again barren capillary action + salinization
c) devegetation for firewood as fuel devegetation
low technological level over 90% African people depend on wood for cooking and heating
d)Mining
e.g. rock salt in Sahara + opal in Great Australian D.
All these activities Devegetation, overgrazing (trampling), over-cultivation soil erosion
i) exposure to wind and sun baking + soil is compacted + dries up
wind erosion gullies + badland
ii)lacks plants roots to bind soil particles together +
iii)rainsplash effect(8)
IV.Examples(5)
Max. 25
4.The extent of man’s exploitation of natural resources should be balanced against the fragility of an ecosystem, or else, havoc will follow.
Under the light of this statement, evaluate the relative importance of human activities in causing desertification.
Ref :90#4Des.4 (def.)
91#4Exp.8 (process of desertification)
98#3Eva.5+2+2 (causes + assess.)
99#3Egs.4
A.Definition of desertification
- It is the intensification of desert condition or
- The extension of desert-like conditions into previously non-desert areas.
- It mainly occurs in the semi-arid lands, e.g.savanna, with annual rainfall between 250 and 375mm, bordering the true (climate) deserts, e.g. the Sahel regions.
- Although it supports more lives than that of the desert ecosystem, its carrying capacity and diversity is still low and it is inherently unstable and fragile (scarce and unreliable rainfall, rapid rate of evaporation, sandstorms, strong wind). It is sensitive to disturbances and its equilibrium can easily be upset.
- As man fails to recognize the limited productivity of the dry lands, rapid degradation results.
- It involves a degradation of soil and plant cover and reduced productivity of the land.
- The once green landscape becomes parches, leafless, treeless and sandy or pebble-covered surfaces.
(4)
Evidence of desertification
The southern edge of Sahara desert has been gradually shifting southward and about 650,000 km2of cultivated land has been desertified to the Sahara over the past 50 years along the southern fringe.
B.Human overexploitation of natural resources
- Nomadic herding →overgrazing
a)practiced by native tribes, e.g. the Bedouins of Saudi Arabia , the Tuaregs of the Sahara and the Rendille of N. Kenya.
b)demographic explosion in N. Africa and Middle East : population growth rate reaches 3-3.5% with a doubling in 20-30 years
c)→herding size ↑
no. of herds increased by 62 % in Mali and 125% in Mauritania in 1955-70.
→Pastures are thereby removed for overgrazing→soil dries up
2.Oases and marginal farming →overcropping
a)e.g. along the River Nile in Egypt
b)demographic exploitation → ↑demand for food →overcropping
e.g. In Rajasthan, population↑rapidly in 1951-71 →land / family from 14 to 10 ha.
c) continuous cultivation exhausts the soil and accelerates erosion.
e.g. Ethiopia’s cultivated areas lose more than 1000 million tonnes of topsoil annually. Worn-out soil cannot support intensive cultivation and crop yields fall. e.g.Sudan produces 50% less grain /ha. than it did 10 years ago.
d)Improper irrigation, e.g. use of too salty water causes salinization + alkalinization
→land productivity
3.Firewood collection as fuel →devegetation
a)This is associated with low technological level and low standard of living.
b)Over 90% of people in Africa’s developing countries depend on wood for cooking and heating.
4.Mining of minerals→devegetation
Minerals, e.g. rock salt and opalare often mined in the Saharan Desertand the Great Australian Desert respectively; and oil is exploited / drilled in Saudi Arabia + Kuwait
5.To make full use of the extensive land with unique landform features and high degree of confidentiality with clear sky, other activities, e.g. tourism + retirement centers, e.g. Tripoli, a port of Libya; industrial development,e.g. petrol-chemical industries in Egypt, Libya + Algeria; setting up of satellite observation + space industry, military industry in NW China and nuclear testing ground →devegetation (pollution, esp. air, water, land) and leakage of radioactive materials (5)
C.Physical factor in causing desertification
Desertification is also caused by natural climatic change : increased aridity, about 5000 years ago. For example : (any 2)
- Studies oftree-rings in the SW of the USA indicated the occurrence of several periods of deficient rainfall in recent centuries, notably at the beginning of the 19th century.
- Inscriptions on rock along the Nile in Nubia indicated that there was a reduction in the flood levels.
- On both sides of the Sahara and North Kenya, lakes dried up and sand dunes extended outwards from the heart of deserts.
- Between 1968-74, there was a long period of drought in the Sahel district of Ethiopia. The rain failed again in 1980-84. (2)
D.How physical factor and human misuse of resources cause desertification(Fig. 1)