Lesson 5:

Sandspit, Sandbar and Tombolo

What you should know by the end of this lesson:

What is the process of Longshore Drift
How a Sandspit forms
How a Sandbar forms
How a Tombolo forms

(Sandbar and Tombolo are continuations of a Sandspit)

Longshore Drift

Longshore drift is the one process we need to understand in this topic that is not an erosional process.

While it relates to depositional features, Long Shore Drift is actually a process of transportation Depositional processes are all to do with the removal of energy from the transportation processes.

When the energy is removed, the water can no longer carry material and will put it down or deposit it.

Remember these 2?

Swash the movement of the wave up the beach. The angle of the swash is controlled by the wind.

Backwash the movement of the wave down the beach. This follows gravity and

will flow straight down the beach.

Try this...

Try and roll a ball up a slope at an angle, move along and see if you can catch it. Do it again and you will see yourself slowly move along the base of the slope with the ball but never move with the ball.

Longshore drift is the movement of material along the beach due to the work of Swash and Backwash. This process is essential for the formation of a Sandspit

Digital Workbook and Paper Jotter

Copy the diagram into your jotter
Write the full explanation to your notes below your diagram

Longshore drift is the method by which sand and pebbles are transported along a coastline
When waves approach the coastline at an angle the sand and pebbles will be carried up the beach (swash) at the same angle; it then moves back down (backwash) at right angles.
The angle of the swash is determined by the angle of the wind to the coastline
The result is a zig zag motion along the beach which moves sand and pebbles along a coastline.

Sandspit

Background

Beaches form in sheltered environments, such as bays. When the swash is stronger than the backwash, deposition occurs. When a beach becomes big enough and doesn't get fully submerged by the tide, grasses start to grow such as marram grass.

The roots of these plants hold the sand together and In such cases, dunes may form – such as at Studland on the Dorset Coast.

REMEMBER!

When answering these as a full Higher Question you need to explain the processes which are involved in these formations. A well-explained process can gain you 2 marks, 1 mark for naming the process and 1 mark for explaining the process, but you need to have both to gain both marks.

The same goes for every process term you say

These features are straight forward and your task is simply to try and understand the processes which explain how they form

Digital Workbook and Paper Jotter

Copy the diagram into your jotter
Write the full explanation to your notes below your diagram

Farewell Spit, New Zealand

Diagram

Explanation

A sand spit is formed when there is a change in direction on a coastline (1). They are formed through the process of longshore drift (1). Longshore drift is where, swash (1), waves driven by prevailing winds push material up the beach at an angle (1) then the returning backwash (1) is dragging the material back down the beach at right angles due to gravity (1).

The change in coastline direction allows for a sheltered area for deposition (1), the material slowly builds up appearing above the water level (1). A spit is formed when the level of deposition is greater than the amount of erosion (1). Changes in wind direction can make the sand spit hooked shaped (1). The sheltered area behind a sand spit may encourage a salt marsh to form (1).

A famous sand spit is the Farewell Spit in New Zealand. (1)

Sandbar

Add this to a Sandspit Explanation

If the sandspit reaches the other side of the break in the coastline it forms a sandbar. The blocked-off water will form a saltmarsh or a lagoon.