Sea Level Change in the UK

Sea Level Change in the UK

http://www.discoverysoftware.co.uk/GallerySeaLevel.htm

KEY TERMS – SEA LEVEL CHANGE

EUSTATIC – Global-scale sea level change caused by a change in the volume of water in the ocean store

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

EMERGENCE – the impact of a fall in Sea-Level (Marine REGRESSION)

SUBMERGENCE – the impact of a rise in Sea-Level (Marine TRANSGRESSION)

Source: http://www.gly.uga.edu/railsback/1122/1122SeaLevelChange.jpeg

EUSTATIC CHANGES (Global scale - change volume of water in ocean – due to physical factors such as Climate Change)

• Decrease in temp – result in growth of ice caps and global fall in sea-level

• Rise in temp – causes retreat of glaciers / thawing of ice-capes – global rise in sea-level

NB. THERMAL EXPANSION of water is also a significant components of sea-level change – as atmospheric temperatures rise – this causes thermal expansion of the water, and further sea-level rise.

ISOSTATIC CHANGES (Local scale – caused by change in height of land leading to a relative sea-level change – due to physical factors – e.g. readjustment as glaciers form / melt and during the processes of orogeny)

• During glacial period – mass of ice – adds weight to earths crust causing it to sink lower into the mantle (relative rise in the sea-level)

• End of glacial period – mass of ice melts – weight is lost from crust – which then rises (isostatic re-adjustment) – results in a relative fall in sea-level.

(some places in Scotland still undergoing isostatic re-adjustment – up to 7mm per year in some areas)

* Uplift / Mountain building due to plate movements may also result in a relative fall in sea-level as land rises up.

LANDFORMS OF SUBMERGENCE

These are caused by a relative rise in sea level – the sea spreads over the land (marine transgression) and the coastline retreats

1. RIAS

e.g. Kingsbridge Ria – South Devon

Rias are submerged RIVER VALLEYS.

The lowest part of the River’s course and the floodplains alongside the river may be

completely drowned, but the higher land forming the tops of the valley sides and the

middle and upper part of the river’s course remain

exposed.

Photo Source: http://www.devon-online.com/towns/salcombe/historyofsalcombe.html

PLAN VIEW

Show a winding profile, reflecting the original

route of the river and its valley.

CROSS SECTION

Relatively shallow water – becomes increasingly deep

towards the centre (representing the lowest

point of the flooded valley / old river channel). Exposed

valley sides – gently sloping.

LONG PROFILE

Have a quite even and smooth profile with

water of a fairly uniform depth – although

deepest water is at the mouth.

CHARACTERISTICS OF A RIA:

LANDFORMS OF SUBMERGENCE

2. FJORDS

Examples: Sognefiordan, (Norway) and Milford Sound Fjord (New Zealand)

Fjords are submerged GLACIAL VALLEYS

Due to the effects of the glacial erosion which shaped the original landscapes, these features have very steep sides and the water in Fjords is very deep (can reach over 1000m in depth.

CHARACTERISTICS OF A FJORD

PLAN VIEW

Straighter profile than a ria – as the glacier has

truncated any interlocking spurs.

CROSS SECTION

Steep, almost cliff like valley sides – water is

uniformly deep – often over 1000m in depth – the cross section is u-shaped which reflects the original shape

of the glacial valley.

LONG PROFILE

Fjords are not deepest at their mouth – they

have a shallower section at the seaward end

known as a threshold (various theories as to

how this ‘rock lip’ forms)

Photo Source: http://www.sce.carleton.ca/faculty/wainer/Favo/sognefjorden2_8772.jpg

SOGNEFJORDEN

Source: http://www.petergknight.com/photos/b01.jpg

Raised Beaches – at Little Gruinard – near Ullapool

(Far NW of Scotland)

What are Raised Beaches?

Areas of former wave-cut platforms and their beaches left at a higher level than present

sea level due to sea level change. They are found at a

distance inland from the present coastline.

What are Abandoned Clifflines?

Commonly find abandoned (relict cliffs) with wave-cut

notches, caves and arches and stacks behind the raised

beaches which were formed due to marine erosion when sea-

levels were higher.

LANDFORMS OF EMERGENCE

These are caused by relative fall in sea-level (marine regression)

Raised Beaches and Abandoned Clifflines

DOUGARIE – ISLE OF ARRAN

Abandoned Cliff Stack

Raised Beach

Photo Source: Val Vannet

KINGS CAVE – Isle of Arran (Abandoned Cliffline)

Photo Source: Val Vannet

These caves in the sandstone cliffs were originally cut by marine erosion – due to sea-level change along this ‘emerged’ coastline they are now left high and dry and unaffected by marine erosion.

NEWTON POINT, LOCH RANZA (Isle of Arran)

Raised Beach

(no longer affected by wave action)

Photo Source: Val Vannet

“During the 20th century, global sea level rose by around 20 cm, a rate that may be higher than at any time during the past thousand years. Without a reduction in Greenhouse gases, the UK Met Office estimates that sea-levels may rise a further 41cm by 2080, a reflection primarily of the melting of small glaciers and ice sheets and the thermal expansion of sea-water as temperatures continue to rise.” (http://www.benfieldhrc.org/climate_change/sea_level_rise/sea_level_rise.htm)

This figure indicates a sea level rise of

between 18.5 - 20cm between 1900-2000.

SEA LEVEL RISE DURING THE 20th CENTURY

Present sea level rise is approx 2mm/yr.

Estimates suggest a rise of 20cm by 2030 and a rise of 1m over

the next 100 years

But what if?.....

Source: Wikipedia

7m Rise in Sea Level

13m Rise in Sea Level

FUTURE SEA LEVEL RISE IN UK – WHAT IF? SCENARIOS

If combined with other causes of rising sea level rise – if either the Greenland or West Antarctic ice sheets melted – expected sea level rise of 7m (many coastal

towns and cities would be flooded) – if both melted a 13m rise could occur!

Source of Maps: http://www.benfieldhrc.org/climate_change/sea_level_rise/sea_level_rise.htm

84m Rise in Sea Level If the gigantic East Antarctic

ice sheet (EAIS) also melted this could result in a

cataclysmic rise of 84m, which would drown much of

eastern and southern England and separate Scotland from

England and Wales.

Source of Maps: http://www.benfieldhrc.org/climate_change/sea_level_rise/sea_level_rise.htm

IMPACT OF RISING SEA-LEVELS ON HUMAN USE OF THE COASTLINE:

RESIDENTIAL PROPERTY / AGRICULTURE

• Many major conurbations and high grade agricultural land are threatened – they are low lying and at risk of flooding;

• In the UK 26 million+ live in major urban areas in the coastal zone

• 57% of the most productive agricultural land is below the 5m contour line

• Cities at risk include Tokyo, Shanghai, London and Calcutta;

• Major road and railway links near the coast are being threatened;

• Relocation is expensive

• Sea Level likely to increase coastal erosion (greater threat to property / farmland – e.g. Dunwich / Holderness Coast)

2. RESIDENTIAL PROPERTY / AGRICULTURE

• Several power stations are located on low lying land

• Coastal nuclear reactors are at risk;

• Significant loss of income / economic loss if agricultural areas are flooded;

3. TOURISM

• The impact of rising sea-level on the scenic value of coastlines affects tourist revenue;

• As the tide becomes higher, beaches are smaller;

• More hard defences necessary to reduce flooding are unattractive;

• Economic loses (tourism is an important economic sector)

4. Wildlife habitats:

• Coastal ecosystems (e.g. Sand dunes and Salt Marshes) are at risk – see previous notes;

• These areas are important for coastal protection and they are home to some of the most important / spectacular wildlife.

CASE STUDIES:

(MEDC – UK) CHICHESTER AND SELSEY (SUSSEX) – learn some specific locational detail;

(LEDC – Bangladesh or Egypt)

Potential Impact of Sea Level Rise on Bangladesh:

Source: http://www.sdnbd.org/sdi/issues/climate_change/Sea-level%20rise%20on%20Bangladesh.htm

Bangladesh, one of the world's poorest nations is also the country most vulnerable to sea-level rise. The population is already severely affected by storm surges. Catastrophic events in the past have caused damage up to 100 km inland. It is hard to imagine to what extent these catastrophes would be with accelerated sea-level rise.