What is isostatic change?

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.

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

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.

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

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.

CCEA A-Level Geography 3910

Processes That Shape Fluvial Environments

Topic overview The drainage basin as an open system Storm hydrographs Factors influencing storm hydrographs Annual hydrographs and river regimes River erosion and transportation Deposition and the Hjulstrom curve Erosional and mixed river landforms Depositional river landforms

Human Interaction in Fluvial Environments

Topic overview Why rivers are channelised, and the methods used Environmentally sensitive and sustainable river management The causes of river flooding The effects of flooding on people, property and land

Global Biomes

Topic overview The global distribution of biomes The tundra biome: climate and soils The temperate grassland biome: climate and soils Climate change and tundra ecosystems

Small-Scale Ecosystems

Topic overview Biotic and abiotic components Ecosystems as open systems Trophic structure and ecological pyramids Nutrient cycling and the nutrient cycling model Plant succession and seral stages Climatic climax and plagioclimax vegetation

The Processes That Shape Our Weather and Climate

Topic overview The global energy balance Vertical and horizontal heat transfer in the atmosphere Ocean currents and the transfer of heat Pressure belts, the Coriolis effect and the pressure gradient The tri-cellular model, the global winds, and where it breaks down Jet streams and the upper westerly winds Global patterns of temperature, pressure, wind and precipitation Factors influencing air temperature

Weather in the British Isles

Topic overview How precipitation forms Air masses affecting the British Isles The polar front and the birth of a depression The life cycle of a depression, and its fronts The sequence of weather as a depression passes Anticyclones in summer and winter Isobars, wind, and the front symbols on a synoptic chart Station circles, recognising systems, and satellite images

Global Weather Issues

Topic overview The Pacific in a normal year: the Walker circulation El Niño events and their global consequences La Niña events and their global consequences How tropical cyclones form The structure of a tropical cyclone The impacts of a tropical cyclone on people and property Managing tropical cyclones: prediction, preparation and response

Population Data

Topic overview Census taking, vital registration, and how the data is collected The reliability of the data, and the use made of it

Population Change

Topic overview Fertility and mortality measures, and why crude rates are crude The demographic transition model The epidemiological transition

Population and Resources

Topic overview Overpopulation, underpopulation and optimum population Malthus and Boserup, and how they hold up Fertility policies, and evaluating one

Settlement Change and the Rural-Urban Fringe

Topic overview Defining rural and urban settlement The rural-urban continuum Issues affecting the rural-urban fringe Greenfield and brownfield development Suburbanisation Counterurbanisation

Planning in Rural Environments

Topic overview Why the countryside needs planning protection ASSIs and SSSIs Areas of Outstanding Natural Beauty National parks A national park for Northern Ireland: the case for, the case against, and the verdict

Urban Challenges in MEDC and LEDC Cities

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Measuring Development

Topic overview Why 'development' resists definition Two economic measures: GDP and GNI per capita Two social measures: infant mortality and adult literacy Two composite measures: the HDI and the Gender Inequality Index Using the measures together to describe global contrasts

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Topic overview Magma composition, viscosity and eruption style Volcanic activity at constructive margins Volcanic activity at destructive margins Hot spots and intraplate volcanic activity Hazards of volcanic activity Benefits of volcanic activity Preparing for volcanic activity: monitoring, planning and protection Responding to volcanic activity and evaluating the response

Seismic Activity and Its ManagementTectonics

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Topic overview The Hadley cell and the ITCZ Tropical forest: distribution, climate and biomass Tropical grassland: distribution, climate and biomass Hot desert, and the tropical biomes compared

Management and Sustainability in Arid and Semi-Arid Tropical EcosystemsTropical

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Management and Sustainability in the Tropical Forest EnvironmentTropical

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Coastal Processes and FeaturesCoastal

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Regional Coastlines: Submergence, Emergence and Rising Sea LevelCoastal

Topic overview Eustatic and isostatic change Coastlines of submergence Coastlines of emergence Rising sea level and the threat of climate change

Coastal Management and SustainabilityCoastal

Topic overview Environmental Impact Assessment and Cost-Benefit Analysis Sediment cells and Shoreline Management Plans Hard engineering strategies Soft engineering strategies Choosing and evaluating a management strategy

Natural Climate Change: Evidence, Causes and the Arrival of the HoloceneClimate

Topic overview Evidence for past climate change: ice cores, pollen and ocean-floor deposits Causes of long- and medium-term climate change The end of the last glaciation and the arrival of the Holocene

Lowland Glacial LandscapesClimate

Topic overview Ice sheet formation and glacial and fluvioglacial processes Landforms of glacial deposition: till, drumlins, moraines and erratics Landforms of fluvioglacial deposition: eskers and outwash plains Socio-economic development in lowland post-glacial environments

Current Global Climate Change: Human Causes and ImpactsClimate

Topic overview The greenhouse effect and the enhanced greenhouse effect Evidence for recent climate change and its links to human activity Present and potential impacts of climate change

Managing Global Climate ChangeClimate

Topic overview Mitigation: reducing greenhouse gas emissions and capturing carbon Adaptation: reducing vulnerability to climate change International action: the Kyoto Protocol, the IPCC and progress so far

Cultural Groups, Social Inequality and LandscapeCultural

Topic overview Why cultural groups exist Differences between cultural groups Cultural nationalism and its expression Social inequality: exclusion and discrimination as distinct mechanisms Inequality by ethnicity, race, religion, gender, sexuality and class Social constructions of nature and landscape

MigrationCultural

Topic overview Push and pull factors: economic, social, political, cultural and environmental Barriers to migration, and its implications for services, the economy and stability Voluntary and forced migration, and immigration as a political issue

The Geographies of CyberspaceCultural

Topic overview Cyberspace, economic change and cultural globalisation Minority cultures, virtual communities and the digital divide

Sustainable Development in SettlementsPlanning

Topic overview Sustainability, and the urban ecological footprint Carbon footprints and waste management Energy consumption and water supply

Urban Design, Planning and Management for SustainabilityPlanning

Topic overview Eco-towns, eco-cities, residential space and defensible space How greenfield and brownfield development relate to sustainability Retail parks, leisure facilities and open space

Traffic and TransportPlanning

Topic overview The sustainability of transport by sea, air and land Public transport, integrated networks, and restrictions on car use Pedestrian and cycling policies, and judging a traffic management strategy

Defining EthnicityEthnic

Topic overview Race, nationality, language and religion as defining factors Ethnicity as socially constructed and self-ascribed Role, residential concentration, age and gender in perceived identity

Processes That Create and Maintain Ethnic DiversityEthnic

Topic overview Colonisation, annexation and international migration Segregation as a process maintaining diversity Multiculturalism as a process maintaining diversity Economic, social and spatial outcomes of ethnic diversity

Ethnic ConflictEthnic

Topic overview The causes of ethnic conflict The nature of ethnic conflict Social, economic and territorial outcomes of ethnic conflict Ethnic cleansing, international intervention and peace processes

The Changing Nature of TourismTourism

Topic overview The growth of mass tourism as a global industry Positive social and economic impacts of tourism The pleasure periphery and the Butler model of resort development

Challenges and Management of Mass TourismTourism

Topic overview The challenges arising from mass tourism Strategies to reduce the negative impacts of mass tourism

Ecotourism: Opportunities, Challenges and RegulationTourism

Topic overview Defining ecotourism The benefits of ecotourism The negative impacts of ecotourism Regulating ecotourism internationally

Decision Making in Geography

Topic overview What a decision-making exercise asks of you Adopting and maintaining a role Reading maps as evidence Reading photographs as evidence Reading statistics and data as evidence Reading reports and written sources as evidence Reading infographics and diagrams as evidence Processing and presenting supplied quantitative data Interpreting and evaluating the information provided Examining conflicting values Considering alternative choices Making and justifying a recommendation on greater overall benefits Structuring and supporting the decision

Regional Coastlines: Submergence, Emergence and Rising Sea Level

Eustatic and isostatic change

3 things to know
Unit A2 1

Overview

Eustatic change, isostatic change and relative sea level.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is eustatic change?

Key term

Distinguish between eustatic and isostatic change.

Key term

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

Questions from this subtopic

Each one with the model answer underneath.

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
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
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
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
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
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.

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