Sometimes a question gives you observations and asks for the process behind them. Find the pattern in the observations first, then name the process that would produce it.
This lesson is part of physical geography. It reverses the chain taught in explaining how a landform forms.
Which observation points to which process?
| Observation | Likely process |
|---|---|
| Pebbles smaller and rounder downstream | Attrition during transport |
| Cracked rock surface with small fragments at its base | Physical weathering |
| Steep outer bank, sandy inner bank at a bend | Erosion on the outside, deposition on the inside |
| Soil and rock in a heap at the foot of a slope | Mass movement |
| Sand ridge growing into a bay | Deposition from longshore drift |
Worked example: an original river survey
An original survey measures the longest axis of pebbles at four points along one river, upstream to downstream. The mean sizes are 18 cm, 11 cm, 6 cm and 3 cm. The upstream pebbles are angular, and the downstream ones are rounded.
Find the pattern. Size falls from 18 cm to 3 cm, a drop of 18 − 3 = 15 cm. Shape changes from angular to rounded.
Name the process. Pebbles are worn by hitting each other and the riverbed as they are carried. This is attrition, which reduces size and rounds the edges.
Write the link. “Pebble size falls steadily downstream and the pebbles become rounded, which suggests attrition as they are carried along the river.”
The mistake: naming a process with no observation
A common slip is to write “attrition wears the pebbles” with no reference to the survey. The sentence is correct, but it could be written without seeing the data.
| Answer | Problem |
|---|---|
| “Attrition makes pebbles smaller” | No figure from the survey |
| “The river has less energy downstream, so pebbles are smaller” | A different process, not supported by the data given |
| “Size falls from 18 cm to 3 cm and pebbles are rounded, suggesting attrition” | Quotes evidence, names the process |
A second slip is to claim too much. Four points on one day support a pattern, not a proof.
Check yourself
An original survey of a hillside finds a pile of loose rock fragments at the base of a bare cliff. The cliff face is full of small cracks, and the pile has grown in the last wet season. Name the two processes that best fit and link each to an observation.
Answer
Physical weathering fits the small cracks in the cliff face, because rock that cracks breaks into fragments.
Mass movement fits the pile at the base, because loose fragments have moved down the slope under gravity, especially after a wet season when water adds weight.
What to study next
Test your reasoning on the physical geography practice set. You can also return to interpreting weather and climate graphs to see how data sets the pace of these processes.
If you want a teacher to hand you fresh observation sets to work through, see online one-to-one Geography tuition.