Regional Coastlines: Submergence, Emergence and Rising Sea Level

What Regional Coastlines: Submergence, Emergence and Rising Sea Level covers

Regional coastlines: submergence, emergence and rising sea level is examined in Unit A2 1, Physical Processes, Landforms and Management. It covers eustatic and isostatic change, coastlines of submergence, coastlines of emergence and rising sea level and the threat of climate change.

The 4 subtopics

Each one has its own page.

• Eustatic and isostatic changeEustatic change, isostatic change and relative sea level.Open →
• Coastlines of submergenceCoastline of submergence, ria and how does it form and shape and depth characteristics of a ria.Open →
• Coastlines of emergenceCoastline of emergence, raised beach and relict cliff.Open →
• Rising sea level and the threat of climate changePhysical effects of rising sea level on a coastline and effects of rising sea level on people and their property.Open →

What you need to know

Answer each one before you reveal it.

Take Regional Coastlines: Submergence, Emergence and Rising Sea Level further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Submergence vs Emergence

  Submergence: a relative rise in sea level that drowns a coastline. Emergence: a relative fall that lifts a former shoreline clear of the water.

• Ria vs Fjord

  Ria: a drowned river valley, shallowing gradually seaward. Fjord: a drowned glacial trough, deep inland with a shallow entrance sill.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What is eustatic change?

   Model answer

   A change in the volume of water in the world's oceans, or in the capacity of the ocean basins that hold it, which alters sea level. Because the oceans are connected, a eustatic change affects sea level everywhere on Earth at broadly the same time, so it is global in extent. The word to attach to it is water: eustatic change is a change in the amount of water, and it is worldwide.

2. 2

   What is isostatic change?

   Model answer

   A change in the level of the land relative to the sea, caused by the crust rising or sinking rather than by any change in the amount of water. Because the cause is local, the loading or unloading of a particular piece of crust, the effect is local or regional and different areas can move in different directions at the same time. The word to attach to it is land: isostatic change is a change in the height of the land, and it is local.

3. 3

   Distinguish between eustatic and isostatic change.

   Model answer

   Eustatic change is a change in the volume of water in the oceans and is therefore worldwide and simultaneous everywhere. Isostatic change is a change in the level of the land, caused by crustal loading or unloading, and is therefore local or regional and can differ from one coast to another. A useful check is to ask what moved. If the water moved, it is eustatic and every coast is affected. If the ground moved, it is isostatic and only that region is affected. Both produce the same visible result, a change in relative sea level, which is why the features they create look alike and the cause has to be reasoned out rather than read off.

4. 4

   What causes eustatic sea level to fall, and what causes it to rise?

   Model answer

   Sea level falls eustatically when water is removed from the oceans and stored on land, which happens during a glacial period as precipitation is locked up in growing ice sheets and glaciers, and when cooling causes sea water to contract in volume. At the height of the last glacial, world sea level was of the order of 100-130 m lower than today. Sea level rises eustatically when that ice melts and returns water to the oceans during an interglacial or a period of warming, and when warming causes the water already in the oceans to expand thermally. Longer-term changes in the shape and capacity of the ocean basins through tectonic activity also alter eustatic sea level, but over much longer timescales.

5. 5

   Explain how the growth and melting of an ice sheet causes isostatic change.

   Model answer

   An ice sheet several kilometres thick is enormously heavy, and its weight presses the crust beneath it downwards into the more plastic mantle below, which flows slowly outwards to accommodate it. This is isostatic depression, and it lowers the land relative to the sea. When the ice melts, the load is removed and the crust slowly rises again as the mantle flows back beneath it. This is isostatic recovery, uplift or rebound, and it raises the land relative to the sea. The response is very slow because mantle flow is viscous, so recovery continues for thousands of years after the ice has gone and in formerly glaciated regions it is still measurable today.

6. 6

   Why does a formerly glaciated coast often show evidence of submergence and then of emergence?

   Model answer

   Because the two processes operate on different timescales. When the ice melts, meltwater returns to the oceans quickly, so eustatic sea level rises rapidly and drowns the coast, producing features of submergence. Isostatic recovery of the unloaded crust is far slower, because it depends on the viscous flow of mantle material, and it continues long after the eustatic rise has finished. So in the later stage the land is still rising while sea level has stabilised, relative sea level falls, and features of emergence are produced. The result is a coast that carries both sets of features, with the emergent evidence superimposed on the drowned outline.

What is inside Levo

Six ways to work the same material.

Regional Coastlines: Submergence, Emergence and Rising Sea Level revision questions

What does Regional Coastlines: Submergence, Emergence and Rising Sea Level cover in CCEA A-Level Geography?

4 subtopics: eustatic and isostatic change, coastlines of submergence, coastlines of emergence and rising sea level and the threat of climate change. Each one has its own page with questions and model answers.

How is Regional Coastlines: Submergence, Emergence and Rising Sea Level organised?

By the CCEA 3910 specification, subtopic by subtopic, so it matches the order you are taught it in.