Coasts: Headlands and Bays

Sitges, Barcelona

What's expected for today

By the end of this lesson, you should be able to:

Explain how headlands and bays are formed with the help of well-labelled diagrams

Draw clear diagrams in boxes with: Labels Title

Headlands and bays

Headlands and bays form along a coast that is made up of bands of rock with

v a r y ing r e s i s t a n c e to erosion.

This means that, the rate at which a coast is eroded depends partly on rock

resistance.

Textbook p. 144

Headlands and bays

More resistance rock → the faster/slower it takes for waves to erode it

Less resistant rock → the faster/slower it takes for waves to erode it

Textbook p. 144

1.3 Formation

Wave energy is concentrated at the headlands because the waves bend as they approach the protruding headlands.

This is due to the waves slowing down as they reach the shallower waters in front of the headlands while other waves not affected by the headlands continue ahead at the same speed. [1]

1.3 Formation

different rate of erosion of rocks along the coast produces an uneven coastline

- less resistant rocks curve inwards, forming bays (Y)

- while the more resistant rocks will protrude out from the coastline, forming headlands (X)

1.1 Some specifics

Granite and basalt are examples of more resistant rock.

Textbook p. 144

1.1 Some specifics

Chalk, sandstone, and shale examples of less resistant rocks.

Textbook p. 144

1.1 Some specifics

What are some of the places where headlands and bays can be found?

This is Homework Part 1: due tomorrow (April 3, Tuesday).

Textbook p. 144

1.2 Wave refraction

Wave refraction refers to the bending of waves because of differences in wave speeds.

Textbook p. 145

1.2 Wave refraction

Waves bend and slow down as they approach the protruding headlands.

Because they encounter friction with the increasingly shallow seabeds in front of these headlands

Textbook p. 145

1.2 Wave refraction

Wave refraction causes headlands to be the focus of wave energy and thus the focus of erosion.

Wave energy is weakened along the wider stretches in the bays, so waves deposit sediments at bays.

Textbook p. 145

1.3 Formation

At a coast where resistant rocks alternate with less resistant rocks,

the less resistant rocks are eroded at a faster rate than the resistant rocks.

Textbook p. 144

Figure 1: Formation of headlands and bays

Headland

More resistant rock

Less resistant rock

More resistant rock

Bay

Headland

1.3 Formation

The different rates of erosion along the coast produces an uneven coastline.

Textbook p. 144

1.3 Formation

The less resistant rocks curve inwards, forming bays,

while the more resistant rocks protrude from the coastline, forming headlands.

Textbook p. 144

Homework

Part 1 Complete asterisked (*) question under

1.2 Some specifics

Part 2 Read textbook pages 146-148 for

tomorrow's lesson on beaches, spits and tombolos.

Looking back and ahead...

1. Coastal processes

Erosion ✔

Deposition ✔

Longshore drift ✔

2. Coastal landforms

Cliff & shore platform ✔

Headland and bay ✔

Beach

Spit

Tombolo

3. Coastal engineering

What's expected for today

By the end of this lesson, you should be able to:

Explain how a coastal SPIT is form with the help of well-labelled diagrams

Predict what a spit would turn into if there is an offshore island nearby - TOMBOLO

Draw clear diagrams in boxes with: Labels Title

Depositional Landforms

In addition to shore platforms there are three other types of depositional landforms. Beach Tombolo Spit

Beach

A beach is the result of constructive waves depositing material on the coast.

Swash is stronger than backwash

Waves have energy to bring material upshore but not back into the sea

The coarser the sediment, the steeper the beach gradient

Pebble Beach, California

The finer the sediment, the gentler the beach gradient

Moonlight Cove, California

Tombolo

Homework

Complete Worksheet _____ in the Workbook.