A little room to wonder

Landforms & Processes

Weathering breaks down material in place, erosion removes or carries material, and deposition leaves transported sediment somewhere new. A landform can record several processes acting at different times.

How could material disappear from one part of a model while the total amount remains unchanged?

An aerial photograph shows a river bend among fields and trees.
The River Towy photograph offers a real bend to notice. It does not measure sediment transfer; the twelve-unit account is a separate fictional model.Anthony Stevenson / River Towy Meander and Oxbow Lake / Geograph, via Wikimedia Commons. CC BY-SA 2.0. · Source · CC BY-SA 2.0

Separate the jobs of three processes

Weathering changes rock where it is situated. Erosion involves removal and transport, while deposition occurs when transported sediment is laid down. A cracked rock has not necessarily been carried anywhere. A deposit tells you material arrived, but not by itself where every grain began.

These terms describe processes rather than permanent labels for places. A river bend can have material removed at one location and accumulated at another. The visible landform is an outcome of interacting processes over time; one photograph does not show the whole history.

Worked example: follow twelve fictional units

Imagine twelve labelled units of loose material beside a paper channel. During an invented interval, eight are transported away from the starting patch and four remain. Of the eight moved units, five are deposited at bend B and three stay in transport beyond B.

The account balances: four at the start, five at B and three still moving total twelve. The starting patch has lost eight without the model losing any material overall. The five at B are not newly created matter. Weathering could have supplied loose fragments before this interval, but this account does not measure a weathering rate.

A shape does not identify only one cause

Similar-looking hollows or piles can have different origins. To test a proposed explanation, look for evidence suited to the process: repeated positions, material characteristics, changes over an interval or a broader landscape setting. Colour or neatness alone does not establish whether water, wind or another agent moved material.

The model omits grain sizes, water speed and exchanges with places beyond its boundary. Those omissions are acceptable when the question is bookkeeping, but important if the question changes to predicting the shape of a real river. Keep your explanation proportional to the evidence.

Use boundaries and time explicitly

An amount needs an area and an interval before it becomes a meaningful change record. Five deposited units during one model turn cannot be compared directly with five over ten turns as though the rates were equal. Likewise, a whole-catchment account differs from a single bend.

A diagram with labelled arrows can make these distinctions visible. You can revise the invented transfers and preserve the earlier account for comparison. No breaking rocks, making channels, collecting sediment or entering waterways is necessary.

Only if you feel like trying

Balance a fictional sediment account

  1. Draw the start, bend B and an in-transport box. Place the twelve supplied model units among them after the interval.
  2. Check that the total remains twelve. Label which changes describe transport and deposition rather than creation of material.
  3. Change the deposit at B to six while keeping eight transported. Work out the revised in-transport amount and identify a missing real-world variable.

Optional paper accounting model. Do not disturb a landscape, crush material or perform a water-flow experiment.