IN: https://papers.gceguide.com/A Levels/Geography (9696)/2016/9696_s16_in_11.pdf
QP: https://papers.gceguide.com/A Levels/Geography (9696)/2016/9696_s16_qp_11.pdf
MS: https://papers.gceguide.com/A Levels/Geography (9696)/2016/9696_s16_ms_11.pdf
SECTION A
(a) Using Photograph A, name the feature labelled: (i) X; River cliff [1] (ii) Y: Point bar [1]
(b) With the aid of a diagram, explain how the meander shown in Photograph A may have been formed. [5]
Ans from: 9696_SpecimenPaperAnswers_v1.pdf
Meanders form due to areas of deeper and shallower water in the river’s middle course, called pools and riffles. These pools and riffles interact with the flow of the water in this part of the rivers course, causing the fastest flow (thalweg) to swing from one side of the river to another. Erosion is caused on the outside of the bend where the current is fastest which produces the river cliff. By contrast deposition occurs on the inside of the bend where the current slows, forming the slip off slope. This differential movement of water leads to the development of helicoidal flow which accentuates the erosion and deposition.
MS: The better answers will refer to pool and riffle sequence. The different characteristics lead to the fastest flow swinging from one side of the channel to the other. The pools, being an area of less frictional resistance, is a place where erosion takes place. The pool is deepened and widened. The riffle is an area where the energy is dissipated and thus an area normally of deposition. Helicoidal flow is initiated which is a secondary flow on the surface but returning to the other bank at depth which increases the sinuosity of the stream. The helicoidal flow allows the material to be eroded from the outside of the bend and deposited on the inside of the next bend. Little credit should be given for a diagram which shows a corkscrew running down the centre of the channel. Max 3 without a diagram.
(c) Describe the changes over time that are likely to occur at line Z on Photograph A. [3]
The meanders in photograph A could be further exaggerated due to erosion on the outer bank and deposition on the inner. This would further accentuate their already very curved shape. This will mean that eventually the neck of these meanders is broken through, often in a time of flood, leading to the river taking the quicker, straight route across the neck. This leaves behind the cut-off meander loop which becomes an oxbow lake.
MS:
The candidate should note that both end points of the line are at a place of erosion within the river, being on the inside of the meander. Continued erosion would bring both points closer together. Therefore, the candidate needs to refer to line Z shortening (or the “neck” of the meander becoming thinner) and eventually creating the new cut off thus abandoning the part of the channel in the foreground of the picture. The cut off often occurs following several periods of high flow, even with overbank flow. This creates a new straight channel and the previous bend becomes silted up and forms an oxbow lake. A description which uses diagrams should be credited. Suggest 1 mark for the shortening, 1 mark for the eventual cut off and 1 mark for the creation on an oxbow lake.
Atmosphere and weather Fig. 1 shows the global surface air pressure (mb) for one month.