Question 1 Report
Fig. 1 shows part of a field sketch made beside an ephemeral river in the Namib Desert. After a rare storm, water crossed the flat channel floor and left a fan of sediment at the foot of a rocky slope. The study group measured the size of stones at three places. Table 1 shows their results.
| Location | Mean sediment size (mm) |
|---|---|
| Upper channel | 68 |
| Channel mouth | 31 |
| Outer fan | 9 |
(a) Which location in Table 1 has the smallest mean sediment size? [1]
(b) Outline one reason why sediment becomes smaller towards the outer part of the fan. [2]
(c) Draw a labelled arrow on Fig. 1 to show the direction in which water flows from the rocky slope. [1]
(a) Outer fan [1] (b) Any two: water loses energy as it spreads across the fan [1]; large/heavy particles are deposited first [1]; smaller particles are carried farther [1]. (c) Arrow from rocky slope/wadi mouth outwards across the fan towards the plain [1]
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