JJC H2 GEO P1 Ans

1 2018 H2 P1 Essay Question 1 a) Explain the characteristics of mass movement processes that occur in the tropics. [12] ** For mass movement types, possible types of mass movement that can occur in tropical regions:  Heave (although more prominent in the temperate regions, can occur in tropical regions when extreme changes in temperatures or alternate cycles of wetting and drying occurs) [Possible in AW climate types where there are temperature and rainfall variations throughout the year]  Flow (Common in Af and Am climates where high and intense rainfall events can occur)  Slides (Common in BS and BW climates where lack of vegetation could induce rock slides along slide plane). May also occur in AW or Am climates where rotational slips could occur in the presence of a curvilinear slide plane  Falls (common in all climate types where weathe ring causes lines of weaknesses to develop and once it gave way along areas of weaknesses, falls occur. ** Need to make some subtle link climatic types where mass movement types could occur. If students merely relate to characteristics w/o the links to the climatic types, maximum of 9 marks. Characteristics of Heave: Speed: Very slow (1mm to 1cm per year) Movement: Particles are lifted perpendicularly and dropped vertically Factors dependent on: Alternating cycles of expansion and contraction which can be attributed to large temperature changes, alternating cycles of wetting and drying Water content: generally low Key features: bent tree trunks, terracettes Material size: Varies from large to small Characteristic of flow: Speed: Generally fast Movement: Materials when incorporated with water, essentially moves as a semi-fluid mass Water content: Very high Factors dependent on: Water content (which determines speed and volume) Material size: Varies (from earthflow (mixed)to mudflow (generally fine)) Characteristic of Slide: Speed: Fast Movement: Along slide plane and in contact with surface Water content: low (may only be present to lubricate the surface Factors dependent on: presence of slide plane Material size: varies (Can be a rock or a consolidated mass) Characteristic of fall: Speed: Very fast Movement: Free fall through sky Water content: Low or absent Factors dependent on: Lines of weakness Material size: varies but usually rather large (rock falls)

2 b) The role of water is important in affecting the different mass movement types that occur in the tropics. Discuss the validity of this statement. [20] The role of water should never always be ignored in mass movements and that water certainly plays an important role in influencing the mass movement types as well as the rate at which mass movements occur in different tropical environments. This certainly means that the effects of water on mass movements should not be ignored. However, it must be noted that the role of water in various mass movement types differ very much depending on the type of mass movement. Strictly speaking, we are also looking at three main kinds of mass movements, namely heave, flow and slide. Supporting Argument  Water, as will be argued, plays the most significant role in flows within tropical regions as humid tropical regions are associated with high precipitation. For example in flows, nearly all movement occurs as turbulent motion within the body of the flowing mass. In the case of flows, the material is essentially semi-fluid. As with flows, an abundant amount of water is usually present.  In the case of mudflow, earthflow and debris flow in humid tropical regions such as Tropical rainforest, Tropical Monsoon and Tropical wet and dry (Savannah), water also plays an extremely important role during wet season or during times of intense precipitation. The main difference between these kinds of flows involves the kinds of materials which consequently has an effect on the speed of movement. However it can be said that in general these forms of flows require water to be present to sustain the mass movement. For example, in the case of mudflows, during an event of a heavy rainfall, exposed regolith becomes rapidly saturated. As such, the cohesion strength between particles becomes virtually lost and unstable resulting in a decrease in shear strength and moves down the slope in a turbulent manner as mudflows. In such an example, water is an extremely important component in the mass movement process.

3  Although water is the main influencing component of mass movement in flows, water also plays a role in heave which is also known as creep. One kind of heave in which water plays an important role is frost creep. In heave, although the main process has been expansion and contraction and the subsequent moving of materials down a slope. In creep, water is important because it is responsible for alternating cycles of wetting and drying or areas that experience temperature fluctuations during the year such as Tropical wet and dry climates. The slope expands when it is wet and contracts when it dries. As a result of this, heave is resulted.  As can be seen, in this kind of heave process, the role that water plays is very important. If both soil creep results from extreme temperature changes or alternate wetting and drying, it can be said that the role of water cannot be ignored.  In the case of slides, although water cannot be seen as the main influencing factor, it plays a supporting role in providing the necessary lubricant that facilitates the mass movement process. Counter Argument  However, it must be recognized that water does not play an extremely important role in all mass movement types. In the case of slides, the main contributing factor has been the presence of a slide plane.  In slides, it involved the movement of a coherent mass of material along a distinct and well- defined failure plane. In slides, as mentioned earlier, water is not essential although we may see it as that it may be necessary to provide a certain level of lubrication to aid in the process. For both rock slides and rotational slips, the main requirement is the presence of a failure plane where materials move in a coherent mass. In such a case, water may not play an extremely essential role in the mass movement process.  Secondly, as in the case of heave, if the cause of heave is largely due to large temperature changes, then the role of water in such an instance may not be that important.  May also want to mention rock slides.  Similarly, the role of water in falls in tropical regions is also not directly important. In the case of falls, it is dependent on the presence of lines of weaknesses present in rocks that eventually break away from the parent rock and falls through the air. The role that water plays many not be so direct. However, water may also be seen as important as it may carry out physical and chemical weathering processes along the rock joints and in time to come, cause the rock joints to widen and break away from the parent rock. The role of other factors

4  Other factors may also be responsible for contributing to mass movements. For example, in the event of an earthquake, the likelihood of mass movements may become more likely. When earthquake occurs, due to the intense shaking of the ground surface, the cohesive strength of the particles may be lost, more lines of weaknesses may also be created, causing the likelihood of rock falls and rock slides more likely.  Clearing of vegetation might also make mudflow and debris flow more likely when bare surfaces are exposed to rain and resulting in oversaturation of the soil. Conclusion  Recognise the important role water plays  Also sought to recognize other factors and how water may not be important.  Discusses how water may not be essential for all mass movement types.

5 Question 2 Explain the dif