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Stage 2: Fieldwork

The yellow lines in the photograph (right) indicate a band of fluvio-glacial deposits which have been exposed by coastal erosion. The main fieldwork techniques for investigating fluvio-glacial landscapes are sorting analysis, roundness analysis and mapwork. Before you start, you need a trowel, plastic bags for samples, and enough labels for each plastic bag.

Stone orientation

Sample 50-100 pebbles - but do not disturb them from their resting place on the face. Decide whch is the longest axis of each stone, then measure the orientation using a compass of each long axis. It may also be useful to measure the angle of dip or of rise of each one using a clinometer or Abney level.

Stone roundness

Select at least 50 pebbles / cobbles / stones from the deposit. For each stone, the simplest way to measure its shape is to classify the stone as very angular, angular, sub-angular, sub-rounded, rounded or very rounded. Decide which shape is the best fit for each stone.

Power's scale of roundness

3d pebbleFor an estimate of pebble size, measure the longest axis of each pebble.

For more precise shape data, use Cailleux's Flatness Index to measure the degree of roundness. The raw data needed for each pebble is as follows.

  1. The length of the longest axis (called l)
  2. The radius of the sharpest angle (called r)

To calculate the Cailleux Index see Stage 4.

For more precise size data, measure the a, b and c axes of each pebble. For pebbles where it is difficult to pick out the axes, allow the pebble to rest on a flat surface. The length of the longest axis is the a axis.

The a, b and c axes can also be used to calculate Krumbein's Index of Sphericity and for Zingg's shape classes (see Stage 4).

Stone sorting

Use a trowel / soil augur to take sediment samples from below the soil. Take a stratified samples (e.g. across the length and width of a drumlin).

Each sample needs to be dried in the lab, then broken down with a pestle and mortar. Find the total mass of the sample. Then shake through a series of sieves, each decreasing in mesh size. Find the mass of material at each level.

GO TO NEXT STAGE: Finding more data

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