The coast, and wider littoral zone, has distinctive features and landscapes
Stand on the corniche at Khasab in Musandam, the northern tip of Oman, and the coast looks nothing like the coast of Abu Dhabi, about 270 km to the south-west.
At Khasab, bare limestone mountains drop straight into deep, narrow inlets called khors.
Along most of Abu Dhabi's shore, the land is so flat that the sea at high tide spreads for kilometres across salt flats.
Both are coasts, but they are built of different rocks, receive different amounts of wave energy and have a different history of sea-level change.
This section gives you the vocabulary to describe any coast you are shown, which is exactly what the short resource items that open Question 1 of the Unit 2 paper (Section A, Crowded Coasts) test.
The littoral zone
The coast is the narrow strip where land meets sea.
Geographers widen it to the littoral zone: everything from the highest reach of storm waves on land to the depth offshore where waves no longer move sediment on the seabed.
The littoral zone is divided into three parts, shown in Figure 1.
- The backshore lies above the normal high tide level. Waves reach it only in storms, so it holds the cliff foot, dunes and the upper beach that waves rarely touch.
- The nearshore runs from the high tide level out to where waves break. This is where most sediment moves: swash and backwash, longshore drift and the building and removal of beaches.
- The offshore lies beyond the breaker line. Waves here move sediment only gently, but offshore bars and the sand that feeds beaches sit in this zone.
Why is it called a dynamic zone of rapid change?
Because three systems meet there: the land, the sea and the atmosphere.
Energy from waves, tides, currents and wind is concentrated in a very narrow strip, and the sediment that energy moves is loose.
A single storm can strip metres of sand from a beach in a night; a cliff in soft glacial till can lose several metres in a winter.
Compare a river valley, where the same amount of change may take centuries.
That speed is why coasts are hazardous places to build on, and why people try so hard to manage them (the last enquiry question of this unit).
Classifying coasts
You need to know the criteria coasts can be classified by, in this order: geology (resistant/less resistant), high or low energy, changes of sea level, relief (cliffed or coastal plains) and sediment type.
Each criterion is a question you can ask of any coast.
Criterion
The question it asks
Musandam khors, Oman
Abu Dhabi sabkha coast, UAE
Geology
Is the rock resistant or less resistant?
resistant limestone and dolomite
less resistant: loose carbonate sand and mud
Energy
Are waves powerful (high energy) or weak (low energy)?
sheltered inlets, low energy inside the khors
low energy: shallow Gulf water, short fetch
Changes of sea level
Has the land sunk (submergent) or risen relative to the sea (emergent)?
submergent: drowned river valleys
slightly emergent: sea level stood a little higher several thousand years ago, and the shoreline has since built seaward
Relief
Is it cliffed or a coastal plain?
cliffed, mountains up to the water
coastal plain, almost flat
Sediment type
Rocky, sand, shingle or mud?
rocky shores, small pocket beaches
fine sand and mud, salt crusts
Musandam: a submergent, cliffed coast. The khors are drowned river valleys (rias), not glacial fjords: Arabia has not been glaciated for more than 250 million years.
They exist because the northern edge of the Arabian Plate is being bent down as it pushes beneath Eurasia, so the peninsula is sinking.
Estimates of the subsidence are of the order of a few millimetres a year; one geological review in GEO ExPro puts it at about 6 mm a year.
Over many thousands of years, the sea has flooded valleys that rivers once cut.
Khor Ash Sham, the longest, runs for roughly 16 km between cliffs that rise hundreds of metres from the water.
Abu Dhabi: a low-energy coastal plain. Along much of the emirate, a sabkha (a salt flat just above high tide) stretches inland for kilometres.
The Gulf is shallow and enclosed, so waves have a short fetch and little energy.
Fine carbonate sediment settles, tidal flats and lagoons form behind sand barriers, and in the heat, seawater that soaks into the flats evaporates, leaving gypsum and salt.
Here the coast is built by deposition, not shaped by erosion.
The same criteria explain the contrast in one chain: resistant rock plus sinking land gives steep, rocky, drowned valleys; loose sediment plus shallow water plus low energy gives flat, muddy shores that grow seaward.
Unit 1 link: sea-level change appears again in World at Risk, where rising seas threaten low coastal plains like Abu Dhabi's far more than cliffed coasts like Musandam's.
- Littoral zone: The littoral zone consists of backshore, nearshore and offshore zones and is a dynamic zone of rapid change.
- Backshore: the part of the littoral zone above normal high tide, reached by waves only during storms.
- Nearshore: the part of the littoral zone between the high tide level and the line where waves break, where most sediment is moved.
- Offshore: the part of the littoral zone beyond the breaker line, where waves have little effect on the seabed.
- Submergent coast: a coast where the sea has risen relative to the land, flooding valleys and lowland.
A coast is described as "low sandy shores backed by salt flats, sheltered from large waves, with wide tidal mud flats".
Identify two criteria that could be used to classify this coast and say how it would be classified by each.
1. Pick criteria from the list, not general words: relief and energy are both clear in the description.
2. Relief: low shores and salt flats mean a coastal plain, not a cliffed coast.
3. Energy: "sheltered from large waves" means a low-energy coast.
Answer: relief, a coastal plain (1); energy, a low-energy coast (1).
Sediment type (sand and mud) would also score.
Question: Explain one reason why the littoral zone is a dynamic zone of rapid change.
(2)
Stronger answer: "Wave, tide and wind energy are concentrated in a narrow strip where sediment is loose (1), so a single storm can remove metres of beach sand or cut back a cliff in a few hours (+1)."
Weaker answer: "Because it changes a lot and there are waves."
This repeats the question and gives no mechanism: 0 or 1 at most.
Question: Assess the importance of changes of sea level in explaining the character of different coasts.
(8)
1. Frame (AO1): name the classification criteria; say sea-level change is one of five and that you will judge how far it explains what a coast looks like.
2. Where it matters most (AO1 detail, AO2 link): Musandam, subsidence of a few millimetres a year has drowned river valleys, so the whole coastline of steep khors exists because of submergence.
3. Where other factors matter more (AO1 range): Abu Dhabi's sabkha coast is explained mainly by low energy and loose sediment, which let deposition dominate.
4. Interaction (AO2): sea level sets where waves attack, but geology decides how fast the coast responds; a sinking coast of soft rock would not keep steep khors.
5. Judgement: sea-level change is the main cause on drowned coasts, but across most coasts geology and energy explain more of the day-to-day character, so it is important but not usually the most important factor.
Outcome: a Level 3 answer (7 to 8) because it uses accurate, located detail on two contrasting coasts and weighs sea level against the other criteria to reach a judgement.
An answer describing Musandam alone, with no weighing, sits in Level 2.
When a resource item asks you to identify features or classify a coast from a photo, use the exact terms from the classification list (resistant or less resistant, high or low energy, cliffed or coastal plain).
One precise word or phrase per mark is all that is needed; examiners report that long answers to 2-mark items waste time and earn nothing extra.
- Calling the nearshore "the sea" and the backshore "the beach". The beach can stretch across both: the zones are defined by tide levels and the breaker line, not by what you see on the surface.
- Describing Musandam's khors as fjords cut by glaciers. They look like fjords, but they are river valleys drowned by a sinking coast, because no ice sheet has covered Arabia in the time it took to carve them.
- Treating "high energy" as the same as "eroding". A high-energy coast can still be building beaches if sediment supply is large; energy describes the waves, not the outcome.
Check your understanding
1. Study Figure 1. Identify the zone of the littoral zone that lies between the high tide level and the line where waves break. (1) Total [1]
2. Identify two criteria used to classify coasts. (2) Total [2]
3. Explain one reason why a low-energy coast such as the Abu Dhabi shoreline is dominated by deposition. (2) Total [2]
4. A student says: "All steep coasts with deep inlets were carved by glaciers." Explain why this is not true of the Musandam peninsula. (2) Total [2]
5. Explain why the littoral zone includes the offshore zone as well as the beach. (2) Total [2]
6. Examine the extent to which geology explains the differences between two coastlines you have studied. (8) Total [8]
Answers
1. The nearshore (1).
2. Any two of: geology (resistant/less resistant); high or low energy; changes of sea level; relief (cliffed or coastal plains); sediment type (1 each).
3. Waves in the shallow, enclosed Gulf have a short fetch and little energy (1), so they cannot carry fine sand and mud away, and sediment settles to form tidal flats and sabkha (+1).
4. Arabia has not been glaciated in the time the inlets formed (1); the khors are river valleys flooded as the peninsula sinks by a few millimetres a year, as the Arabian Plate is bent down (+1).
5. Sediment that feeds beaches and builds bars moves on the offshore seabed (1), so changes offshore, such as dredging or a bar forming, alter waves and sediment supply at the shore (+1).
6. Levels-marked (AO1 6, AO2 2). Level 3 (7 to 8): accurate, located detail on two coasts (for example Musandam's resistant limestone and the Abu Dhabi sabkha's loose carbonate sediment), explains how rock resistance shapes relief and sediment, then weighs geology against energy and sea-level change, and reaches a judgement (geology explains relief and erosion rates, but sea-level change explains why Musandam's valleys are drowned). Level 2 (4 to 6): relevant knowledge of two coasts, some links to geology, little weighing. Level 1 (1 to 3): generic points about hard and soft rock with no located coasts.