2023 HCI J1 Promos Ans Key

HWA CHONG INSTITUTION JC1 Promotional Examination Higher 2 SUGGESTED ANSWERS AND COMMENTS Section A Answer both questions. Cluster 2 Tropical Environments 1 Resource 1 shows the Inter-Tropical Convergence Zone (ITCZ) and wind direction over the African continent in June to September, and January to March. The locations of Ouagadougou (12.4°N), capital city of Burkina Faso, and In Salah (27.2 °N), an o asis town in central Algeria, a re also shown in Resource 1. Resource 2A is a cross -section schematic diagram of the drainage basin system in Ouagadougou while Resource 2B shows that of In Salah. Resource 3A shows a mass movement that had occurred in Ouagadougou, and Resource 3B shows a mass movement that had occurred in In Salah. (a) Describe the changes in winds over Ouagadougou and In Salah from June to January shown in Resource 1. [4] Award 1m for changes, to a maximum of 2m for winds in Ouagadougou, and maximum of 2m for In Salah. Possible observation of changes in winds include:  Onshore or offshore: e.g. Ouagadougo experiences onshore winds from Atlantic Ocean in June, but offshore from dry continental interior in Jan.  Wind direction: e.g. In Salah experiences predominantly easterly winds in June, but in Jan, little/no winds as it is dominated by high pressure cell (b) With reference to Resource 1, suggest reasons for the differences i n rainfall characteristics between Ouagadougou and In Salah. [8] Award maximum of 2m for description of and differences in rainfall characteristics of Ouagadougou (marked seasonality of wet season in June, dry season in January) and In Salah (arid throughout year, with very low total annual rainfall) Award 1m for a valid suggested reason with an additional 1 to 2m for development of point. Maximum of 6m for explanation (as 2m is needed for description) Possible reasons:  Aridity of In Sal ah: dominance of high pressure belt shown by wind direction; ITCZ does not move into the region  Seasonality of rainfall in Ouagadougou: Onshore winds: moisture laden winds forced to rise over any elevation or possibly uplifted by ITCZ low, resulting in expansion of air mass, adiabatic cooling to saturation, forming rainclouds.  Proximity of Ouagadougou to ITCZ accounting for wetter climate (c) Describe the differences between the two drainage basin systems of Ouagadougou and In Salah shown in Resources 2A and 2B respectively. [4]

2 © Hwa Chong Institution 9173 / 01 / C1 Promo Exams 2023 Award 1m for each difference with an additional 1m for development comparing the two (only if applicable and clearly a development of point), to a maximum of 2m for each difference. Possible differences include:  Much higher water table in Ouagadougou than in In Salah (which is below level of river bed)  Baseflow in ground water storage in Ouagadougou feeds river, while in In Salah, no baseflow feeding river (d) From Resources 1, 2A and 2B, suggest why overland flows may be more common in Ouagadougou than in In Salah. [5] Award 1m for each suggestion with an additional 1m for explanation and development of reason (i.e. showing understanding of drainage basin water balance). Possible suggestions include:  High seasonal rainfall (especially monsoonal) contributes to high average monthly rainf all in months of June-Sept, inability for all precipitation to infiltrate and percolate into soil moisture and ground water storage respectively, flow over surface as IEF  SOF very possible also due to high water table in Ouagadougou: very easily prolonged monsoon rainfall can raise water table by percolating rainfall, raising water table to intersect at surface, resulting in saturated over land flow  In Salah: low water table, hence SOF extremely unlikely  Arid climate of In Salah means very low occurrence of precipitation which could contribute to IEF (e) Compare the key characteristics of the two mass movements shown in Resources 3A and 3B. [4] Award 1m for each comparison of characteristic with further 1m for development, up to a maximum of 2m for each characteristic. Maximum 3m for similarities / differences. Possible suggestions: Differences  Angle of slope of failed material: near vertical and even overhanging slope at In Salah vs ~25 at Ouagadougou  Amount of water: predominantly dry in In Salah vs wet slurry of Ouagadougou Similarities  Both fail under shear stress due to the pull of gravity  Both leave behind scars (bare slope without vegetation) on the slopes and scarps. (f) With reference to Resources 1, 2A and 2B, explain why mass movement processes may differ between Ouagadougou and In Salah. [5] Award 1m for each suggestion with addition 1-2m for further development of point up to a maximum of 3m for each suggestion. Students to be able to explain the mechanism and process of mass movement – one being a wet flow vs a high speed dry rockfall, with reference to shear strength (e.g. friction between soil grains or internal strength of rock) vs shear stress (gravity acting on slope). Possible suggestions include:

3 © Hwa Chong Institution 9173 / 01 / C1 Promo Exams 2023  Amount of water: high precipitation not only adds weight to slope, increasing shear stress (gravity!) but also breaking frictional bonds between soil grains holding slope in place. With saturation of upper layer of slope, grains of soil cannot be held in place and fails as a slurry 2 Resource 4 is a map of Peninsular Malaysia showing the locations of limestone hills. Kinta Valley ( 4.4°N) in Perak state, is indicated in the box. Resource 5 shows Gua Tempurung, a limestone cave in Kinta Valley. Resource 6 is a photograph of a quarry – a mining site – at Gunung Kanthan, northern Kinta Valley. (a) From Resource 4, describe the distribution of limestone hills in Peninsular Malaysia. [2] Award 1m for each valid description. Possible descriptions include:  Limestone hills generally clustered  Located in central and northern Peninsular Malaysia (b) With reference to Resource 4, explain the dominant type of weathering that is likely to occur in Kinta Valley, Malaysia. [4] Award 1m for a possible valid weathering process, 1m to account for why this is likely to occur in Kinta Valley, and up to 2m for explanation. Indicative content:  Dominant type of weathering is either chemical weathering or specifically carbonation (or solution).  This type of weathering is likely to occur in Kinta Valley due to either its low latitude (seen in Resource – Malaysia is at about 5 °N, hence indicating an Af climate) and/or presence/dominance of limestone rock in Kinta Valley.  High total annual rainfall provides the high amount of running water to dissolve minerals in rocks, specifically calcium carbonate when water is slightly acidic (due to CO2 dissolving in it as rainwater percolates through soil) (c) Describe the limestone features as seen in Resource 5. [4] Award 1m for each valid description. Indicative content:  Large cavernous underground chamber, more than 20m high  Base of cave is wider than the ceiling  Visible cracks on limestone walls  Numerous tapering hanging structures from roof of cave, some longer than 2m (d) With reference to Resource 5, explain the formation of the features shown. [7] Possible features to explain are: underground cave and speleothem Indicative content:  Carbonation process occurring only along structural weakness of limestone, i.e. intersecting joints, cracks and bedding planes, a