2B.6C: Landforms produced by Mass Movement
Mass movement creates distinctive landforms (rotational scars, talus scree slopes, terraced cliff profiles)
Blockfall
Rotational Slumping
Blockfall
- The angular blockfall debris accumulates at the cliff foot to form a talus scree slope, a fan shaped mound of material.
- Undercutting of cliffs by the creation of wave-cut notches can lead to large falls and talus scree slopes at their base.
- A talus scree slope has a slope angle of 34-40' (larger fragments maintain a steeper angle of rest)
- In April 2013 there was a large blockfall in St Oswald's Bay on the South Dorset Coast where an 80 m section of chalk cliff was detached overnight.
- A large fan shaped talus scree slope was created at the slope foot, extending 30 m into the sea that will protect the cliff from further erosion for a decade or more.
Rotational Slumping
- Rotational slumping exposes a rotational scar
- A rotational scar is a fresh, curved, unweathered and unvegetated rock surface on the cliff face.
- The detached slope section, often with vegetation intact on top of the slump, forms a beach or terraced cliff profile.