CHAPTER 11: MASS MOVEMENT PROCESSES, PATTERNS AND LANDFORMS
Very slow mass movements Soil creep Main processes: freeze-thaw action, wetting, drying This is a very slow but continuous movement of soil downhill. It is common on grassy slopes in Ireland. Soil creep occurs so slowly you cannot see it happening, but it leaves tell-tale evidence behind.
Evidence of soil creep
Once you know what to look for, evidence of soil creep is easy to see and it is quite widespread across Ireland.
1. Terracettes (small steps) in grassy slopes 2. Cracks in roads parallel to the slope 3. Tilted telegraph poles
4. Soil bulging against the upslope side of a wall on a hill
5. Burst stone walls 6. Tilted fence posts
7. Tree trunks curved as they try to grow straight up but their roots are moving downhill.
Fig. 5 Evidence of soil creep
IN DEPTH - Soil creep Soil creep occurs due to the combination of two processes. 1. Alternating wet and dry periods 2. Freeze-thaw action
During rainy weather soil grains expand (hydration) and are pushed up and away from each other. As the soil grains dry out during dry weather they shrink (dehydrate) and as they move closer to each other they roll slowly downhill. Repeated wetting and drying causes the gradual movement of soil downhill. Soil piles up against walls or forms terracettes and may cause fences and poles to tilt. During colder weather frost can cause the upward movement of soil as the ice expands. When the soil thaws, the soil grains move slowly downhill.