Different Coastlines

1. Different Coastlines • What do these photos show? • What are the similarities and differences between them? • What produced these differences? Waves Geology

2. There Goes Concord AgainThe Native Hipsters Concordant and Discordant Coasts Investigate concordant and discordant coasts and the influence of joints and faults.

3. Introducing Dorset’s Jurassic Coast

4. Rock Structure Rock structure simply means the way different rock types are arranged. Rocks are generally found in layers, called strata. This means there may be several types of rock in one cliff. The cliff will only be as resistant as its weakest layers. • Rock strata can be arranged in two ways along coastlines: • If the layers are parallel to the coastline, the coast is concordant. • If the layers are perpendicular (at 90o) to the coast, the coast is discordant. • Concordant coasts have the same type of rock all along the coastline. • Discordant coasts have lots of different rock types. When these two types of coast erode, different landforms are produced, as the diagram shows.

5. Concordant and Discordant Coasts • Use three colours to shade the layers of rock on your map. • Complete the key. • Identify the hard and soft rock. • Read the definitions of a concordant and discordant coastline. Label a concordant coast and a discordant coast on your map.

6. Discordant coastline. Concordant coastline

7. Landforms on a Discordant Coast Headlands and Bays The harder rocks (e.g. chalk and limestone) are more difficult for the waves to erode, so they stand out as headlands. The softer rocks, which are clay and sand in Dorset, are more easily eroded and so form bays. In the Swanage area, the alternating hard and soft rocks are at right angles to the coast. Label a bay on your map. Label a headland. What other land forms might we expect to find on a discordant coast? harder rock

8. Bay Headland The Old Harry Rocks are here. Discordant coastline. Bay Concordant coastline

9. Landforms on a Concordant Coast Coves A cove is an oval-shaped bay with a narrow opening to the sea. Did you know? Because coves have narrow entrances from the sea, but shelered beaches hidden by steep cliffs, they were often used by smugglers in the past. Layers (strata) parallel to the sea

10. Concordant Coasts: Coves and Cliffs • Study the photo of Lulworth Cove and put these changes into a correct sequence: • Erosion by sea • Less resistant sand and clays are eroded • Cuts through resistant limestone • Cove forms • Cliffs of resistant limestone • Sea can’t erode resistant chalk so widens cove • Forms a break in the cliff • Sea reaches resistant chalk • Describe how Stair Hole will change in the future as it continues to erode. • Draw a sketch of the photo A. Shade it so show the different rock strata (layers). Label them. Photo A

11. Joints and Faults • Weaknesses in the rock forming cliffs influences erosion. There are two types of weakness: • Joints are small, natural cracks, found in many rocks. • Faults are larger cracks caused in the past by tectonic movements. • The more joints and faults there are in a cliff, the weaker the cliff will be. Hydraulic action attacks faults and joints, causing erosion. Joints in limestone Faults at Stair Hole

12. Different Coastlines Find the photos showing a: • bay; • cove.

13. Bays and Coves 1. a) Find the photos showing a: • bay; • cove. b) Split your page into two columns. c) Stick a photo at the top of each column. d) Complete the table to show the differences between the two landforms. Now add any similarities you can think of. 2. Annotate the photos to show what you know about them. E.g. identify the layers of hard and soft rock.