Geological Structure and Cliff Profiles

Question 1

what are joints

Answer 1

Joints are fractures in rocks created without displacement.
They occur in most rocks, often in regular patterns, dividing rock strata up into blocks with a regular shape.

Question 2

How does jointing increase erosion?

Answer 2

Jointing increases erosion rates by creating fissures which marine erosion processes such as hydraulic action can exploit.

Question 3

Stair Hole (a small cove adjacent to Lulworth cove)

Answer 3

Purbeck Limestone is intensely folded, known as the Lulworth Crumple. The folding created heavy jointing making the Purbeck Limestone erode much more rapidly that the adjacent Portland Limestone.

Question 4

folds

Answer 4

Folds
Folds are bends in rocks. They are produced by sedimentary rock layers being squeezed by tectonic forces. The two main types are anticlines and synclines.
Folded rock is often more heavily fissured and jointed, meaning they are more easily eroded.

It also increases erosion rates by increasing angle of dip, and by causing joint formation as rock is stretched along anticline crests and compressed in syncline troughs.

Question 5

Dip

Answer 5

Dip is the angle of inclination of the rock strata from the horizontal. It’s a tectonic feature. Sedimentary rocks are deposited horizontally, but can be tilted by folding and faulting by tectonic forces. It can have dramatic effects on cliff profiles.

Question 6

Horizontal dip

Answer 6

produces a vertical, or near-vertical profile, with notches reflecting weathering and small scale mass movement of strata that are jointed or more easily eroded.