A2GEOGRAPHYREVISIONCOASTALENVIRONMENTS

8.2 COASTALLANDFORMSOFCLIFFEDANDCONSTRUCTIVECOASTS

KEYTERMSANDDEFINITIONSArch is a natural bridge-like feature formed by erosion. Arches are formed from the erosion of a headland where two caves meet and break through the headland.

Bar is a depositional feature: a long sandy ridge running parallel to a coastline that is submerged at high tide. Some bars develop as offshore bars whilst others form from the development of a spit across the whole of a small bay.

Bay is a wide, open, curving indentation of the sea.

Beach is a feature of coastal deposition, consisting of pebbles on exposed coasts or sand on sheltered coasts. It is usually defined by the high- and low-water marks.

KEYTERMSANDDEFINITIONSCoastal cave is formed where relatively resistant rock containing lines of weakness is exposed to severe wave action.

Cliff is a rock-face along the coast, where coastal erosion, weathering and mass movements are active and the slope rises steeply (over 45 º) and for some distance.

The nature of the cliff depends on the nature of the rocks and their hardness and jointing pattern.

Headland is a coastal promontory with a steep cliff-face projecting into the sea, also known as a cape.

Offshore bar is a linear ridge of sand or pebbles parallel to the shoreline. Offshore bars are formed when waves disturb sediments on the seabed and form them into a submarine ridge or bar.

KEYTERMSANDDEFINITIONSSalt marshes are low-lying areas with salt-tolerant (halophytic) vegetation. Salt marshes develop around estuaries and on the sheltered side of spits. Salt marshes usually have a network of creeks and channels by which sea water enters and leaves the marsh.

Sand dune is a mound or ridge of wind-drifted sand common on coasts and in deserts. In coastal areas, sand is trapped by vegetation, notably sea couch grass and marram grass, to form stable dunes.

Spit is a ridge of sand or shingle connected to the land at one end and in the open sea at the other end. It is formed by the interruption of longshore drift due to wave refraction, river currents, secondary winds and/or changes in the shape of the coastline.

KEYTERMSANDDEFINITIONSStack is an isolated upstanding pillar of rock that has become separated from a headland by coastal erosion. It is usually formed by the collapse of an arch.

Stump is an eroded stack, which is exposed only at low tide.

Swash is the movement of material up the beach in the direction of the prevailing wind.

Tombolo is a bar that links an island to the mainland.

Wave-cut platform (abrasion platform / shore platform) is a gently sloping rock surface found at the base of a coastal cliff. It is covered by water at high tide but exposed at low tide. It is formed by the erosion (by waves) of a former cliff face.

TOPICSUMMARYCliff profiles are very variable and depend on a number of controlling factors. One major factor is the influence of bedding and jointing.

● Rocky shores can be divided into three main types: sloping shore platforms, sub-horizontal shore platforms and plunging cliffs.

● As a result of cliff retreat, a platform along the coast is normally created.

● Beach form is affected by the size, shape and composition of materials, tidal range and wave characteristics.

● A whole variety of materials can be drifted along the coast by waves, fed by longshore drift.

● A typical beach will have three zones: backshore, foreshore and offshore.

TOPICSUMMARYA berm or shingle ridge is often referred to as a storm beach.

● Swash-aligned coasts are orientated parallel to the crests of the prevailing waves.

● Drift-aligned coasts are orientated obliquely to the crest of the prevailing waves.

● A spit is a long, narrow ridge of sand and shingle that is joined at one end to the mainland.

● If a spit continues to grow lengthwise, it may ultimately link two headlands to form a bay bar.

● A tombolo is a ridge of material that links an island with the mainland.

TOPICSUMMARYCuspate forelands consist of shingle ridges deposited in a triangular shape, and are the result of two separate spits joining or of the combined effects of two distinct sets of regular storm waves.

● Sand dunes occur where there are strong on-shore winds, a large tidal range and a good supply of sand.

● Salt marshes are typically found in three locations: low energy coastlines, behind spits and barrier islands and in estuaries and harbours.

● Vegetation succession can be observed on sand dunes and in salt marshes.

ADDITIONALWORK1. Describe and explain variations in cliff profiles.

2. Outline the conditions that lead to the formation of depositional landforms.

3. Account for the formation of barrier islands and tombolos.

4. Briefly explain the succession associated either with sand dunes or salt marshes.

5. Outline the main ways in which waves may erode cliffs.

6. Explain the formation of spits and bars.

SUGGESTEDWEBSITEShttp://pubs.usgs.gov/pp/pp1693/ for the formation, evolution and stability of cliffs download the pdf.

www.beachcalifornia.com/beach2.html for information on beaches, with a slant towards California.

www.csc.noaa.gov/beachnourishment/html/geo/barrier.htm is a very good site for barrier islands.

www.jurassiccoast.com/278/category/coastalprocesses-142.html contains links to information on cliffs, bays, headlands and beaches of the Jurassic Coast, UK.

www.chesilbeach.org/FSG/MBfrmtn.pdf for a detailed review of the formation of Chesil Beach.

http://homepages.ihug.co.nz/~sissons/Beachhistory.html for a brief history of the development of Tahuna Beach, New Zealand.