Mass Movement

1. Mass Movement Mudflow

2. Diagram of Mudflow Start of Mudflow Toe marks final resting place Angle of slope > 10° • Input of precipitation above the hollow increases weight and lubrication of topsoil Downslope movement of saturated soil lobe

3. Description of Mudflow Flows take place gradually, possibly faster at one time in the year than another Encouraged by wet winters mudflows emerge from the base of a rotational slip and slowly spread and pour over earlier, lower slips and flows into the sea. Mudflow can travel extremely fast at more than 10ft/s.

4. An example of mudflow • ‘I saw a great mass of upper Greensand densely covered with bushes and trees slowly crawling downwards from the highest terrace, while below a river of liquid mud was slipping over the low cliff above the beach…the main movement in the night must have been very rapid, as by daylight a huge fan of debris, crested with uprooted trees, had pushed across the beach to beyond the low water neap tides.’ Source: Quoted in D. Brunsden and A. Goudie: Classic Coastal Landforms of Dorset

5. Conditions for mudflow • Materials involved: • A mixture of mud and water • Soil and rock • Vegetation and human factors: • There are no human factors • Soil becomes saturated • Conditions needed: • Heavy rainfall for long period of time • Both gravity and slope angle play a part • Slope angle must be greater than 10°

6. Mudflow

8. Cows