Sea Level ChangesSea Level Changes

Sea-Level Sea-Level ChangeChange

Sea-levels are predicted to rise by 1m this century (by 2100).

Why?

Sea-Level Change Key Sea-Level Change Key TermsTerms EustaticEustatic – global-scale sea level – global-scale sea level

change caused by a change in the change caused by a change in the volume of water in the ocean storevolume of water in the ocean store

IsostaticIsostatic – local-scale sea level change – local-scale sea level change caused by a change in the level of the caused by a change in the level of the land relative to the level of the sea.land relative to the level of the sea.

EmergenceEmergence – the impact of a relative – the impact of a relative FALL in sea level FALL in sea level (Marine Regression)(Marine Regression)

SubmergenceSubmergence – the impact of a RISE in – the impact of a RISE in relative sea level relative sea level (Marine Transgression)(Marine Transgression)

Eustatic changeEustatic change– A global sea level change, caused by climatic A global sea level change, caused by climatic

change which causes then size of ice caps to change which causes then size of ice caps to increase or decreaseincrease or decrease

– During a period of glaciation sea level is much During a period of glaciation sea level is much lower because water is stored as ice (during lower because water is stored as ice (during last ice age sea level was 150m below levels last ice age sea level was 150m below levels today)today)

Sea level changes in S. EnglandSea level changes in S. England

The Devensian glacial advance

Flandrian Interglacial (last 10,000 yrs)

Synoptic links with glaciation topic

Isostatic changeIsostatic change

The change in the level of the land compared with The change in the level of the land compared with the seathe sea– During glaciation the ice puts pressure on the During glaciation the ice puts pressure on the

earth’s crust, causing the land to lowerearth’s crust, causing the land to lower– When ice sheets melt the land rises When ice sheets melt the land rises

(“readjustment”)(“readjustment”)

How fast is How fast is isostatic change?isostatic change?

Land rising in NW Scotland by 1mm/yr

Land sinking in SE England by 1.5 mm/yr

Sequence of sea level changeSequence of sea level changeTemperatures decrease. Ice sheets grow. Sea level falls

Ice thickness increases. Land is lowered

Temperatures rise. Ice melts. Sea levels rise

Ice continues to melt. Pressure on land released. Land rises

But how do we know all this?

Accurate measurements can be made of past sea levels and rates of sea advance and retreat by ….

Shoreline deposits such as shells, wood and peat found in marine cores.

Exposed rock outcrops containing marine fossils.

Vegetated tidal flats above the high water mark.

Exposed coral reefs.

Marine rocks displaying evidence of wind-borne erosion.

Radiocarbon and Uranium series dating

Landforms of Landforms of SubmergenceSubmergence RiasRias FjordsFjords Fjards – submerged glacial Fjards – submerged glacial

lowlandslowlands Dalmatian Coasts – submerged Dalmatian Coasts – submerged

valleys running parallel to the valleys running parallel to the coastcoast

RiasRias

Rias are submerged river valleys. The lowest part of Rias are submerged river valleys. The lowest part of the river’s course and the floodplains alongside the the river’s course and the floodplains alongside the river may be completely drowned, but the higher river may be completely drowned, but the higher land remains exposed, e.g. Kingsbridge Estuary, land remains exposed, e.g. Kingsbridge Estuary, DevonDevon

In In cross sectioncross section the ria has relatively the ria has relatively shallow water becoming increasingly deep shallow water becoming increasingly deep towards the centre. The exposed valley towards the centre. The exposed valley sides are quite gently sloping.sides are quite gently sloping.

In In long sectionlong section rias are quite even with a rias are quite even with a smooth profile and water of uniform depth.smooth profile and water of uniform depth.

In In plan viewplan view they tend to be winding, they tend to be winding, reflecting the original route of the river reflecting the original route of the river and its valley.and its valley.

FjordsFjords

Fjords are submerged glacial valleys. They have Fjords are submerged glacial valleys. They have steep, cliff-like valley sides and the water is uniformly steep, cliff-like valley sides and the water is uniformly deep (often 1000m in depth). These were formed deep (often 1000m in depth). These were formed when glaciers eroded below sea-level. When the ice when glaciers eroded below sea-level. When the ice melted the valleys were flooded, e.g. Milford Sound melted the valleys were flooded, e.g. Milford Sound fjord, New Zealandfjord, New Zealand

The u-shaped cross-section reflects the The u-shaped cross-section reflects the original shape of the glacial valley.original shape of the glacial valley.

Unlike rias, fjords are not deepest at their Unlike rias, fjords are not deepest at their mouths, but have a shallow section at the mouths, but have a shallow section at the seaward end known as the threshold.seaward end known as the threshold.

Fjords have much straighter routes, due to Fjords have much straighter routes, due to the erosive power of the glacier.the erosive power of the glacier.

Landforms of Landforms of EmergenceEmergence Raised BeachesRaised Beaches Abandoned CoastlinesAbandoned Coastlines

Raised BeachesRaised Beaches

Raised beaches, e.g. Little Gruinard, Ullapool are Raised beaches, e.g. Little Gruinard, Ullapool are areas of former wave-cut platforms and their areas of former wave-cut platforms and their beaches which are left at a higher level than the beaches which are left at a higher level than the present coastline. Abandoned cliffs, caves and stacks present coastline. Abandoned cliffs, caves and stacks can also be found.can also be found.

Landforms resulting from net sea Landforms resulting from net sea level rise – submerged coastslevel rise – submerged coasts

RiasRias– Drowned river valleys caused by rising sea levels Drowned river valleys caused by rising sea levels

during Flandarin Transgression (ice melt)during Flandarin Transgression (ice melt)– Eg Rivers Fal & Camel in CornwallEg Rivers Fal & Camel in Cornwall

FjordsFjords– Drowned U shaped glacial valleysDrowned U shaped glacial valleys– Eg Loch Torridan in Scotland, Oslo FjordEg Loch Torridan in Scotland, Oslo Fjord

FjardsFjards– Drowned glacial lowlandsDrowned glacial lowlands

Landforms resulting from net fall in Landforms resulting from net fall in sea level – emerged coastlinessea level – emerged coastlines

Raised beachRaised beach– e.g Portland raised beache.g Portland raised beach

Relict cliffsRelict cliffs– Previous coastal cliffs that are raised above current sea Previous coastal cliffs that are raised above current sea

levellevel

Raised mudflatsRaised mudflats– e.g Carselands of River Forthe.g Carselands of River Forth

What will the effects of sea level rise be in the future?

More than 60% of the world’s population lives on or within 60km of the coast.

Synoptic link to AS climate change – find your notes!!

You need to know causes, effects and responses.

Effects in the UKEffects in the UK

Environmental:Environmental:

The threat of nuclear accidents will be higher at Sizewell The threat of nuclear accidents will be higher at Sizewell and Dungeness as they are built on low lying land. and Dungeness as they are built on low lying land. Dungeness is built on a shingle spit which is moving Dungeness is built on a shingle spit which is moving eastwards.eastwards.

62 coastal SSSIs will be at risk from sea level rise.62 coastal SSSIs will be at risk from sea level rise. Habitats will be lost - 10% of saline lagoons and 8% of salt Habitats will be lost - 10% of saline lagoons and 8% of salt

marsh is at risk.marsh is at risk. Coastal squeeze may result in more coastal ecosystems lost Coastal squeeze may result in more coastal ecosystems lost

as they cannot migrate inland as the sea level rises.as they cannot migrate inland as the sea level rises. Migratory birds such as the Grey Plover and Avocet over-Migratory birds such as the Grey Plover and Avocet over-

wintering in The Wash, Thames and Humber estuaries will wintering in The Wash, Thames and Humber estuaries will lose their habitat.lose their habitat.

Of the 106 internationally important sites for wintering Of the 106 internationally important sites for wintering wildfowl, 16 are at risk and 11 are vulnerable.wildfowl, 16 are at risk and 11 are vulnerable.

SocialSocial

26 million people live in 26 million people live in major urban areas in the major urban areas in the coastal zones.coastal zones.

People continue to build on People continue to build on low lying coastline despite low lying coastline despite the threat of increased the threat of increased flooding.flooding.

EconomicEconomic

40% of manufacturing and 40% of manufacturing and 57% of productive 57% of productive agricultural land is in the agricultural land is in the coastal zone.coastal zone.

Coastal zone along the Coastal zone along the South coast is valued at South coast is valued at £5745 million.£5745 million.

Cost of protecting these Cost of protecting these areas will be high.areas will be high.

Cost of insurance claims Cost of insurance claims and repairs if storms to and repairs if storms to breach sea walls. Towyn in breach sea walls. Towyn in 1990 cost £35 million.1990 cost £35 million.

Loss of tourist areas would Loss of tourist areas would result in a loss of income. result in a loss of income. Norfolk Broads are Norfolk Broads are estimated to earn £15.5 estimated to earn £15.5 million per year.million per year.

Homes will be uninsurable.Homes will be uninsurable.

Effects on the MaldivesEffects on the Maldives

The islands of Tebua The islands of Tebua Tarawa and Abanuea (both Tarawa and Abanuea (both uninhabited) have uninhabited) have disappeared underwater.disappeared underwater.

Most of the 29 atolls are Most of the 29 atolls are suffering from increased suffering from increased erosion.erosion.

Severe flooding both Severe flooding both storms and high tides have storms and high tides have occurred.occurred.

Salt is poisoning the soil.Salt is poisoning the soil.

Beaches of a third of the Beaches of a third of the 200 Maldives islands are 200 Maldives islands are being washed away being washed away affecting both erosion rates affecting both erosion rates and tourism.and tourism.