COASTAL EROSION AND SEA LEVEL CHANGE

WHAT ARE THE TWO MAIN TYPES OF SEA LEVEL CHANGE?

1. EUSTATIC CHANGE - global changes in the VOLUME OF WATER IN THE OCEANS

2. ISOSTATIC CHANGE - local changes in LAND HEIGHT RELATIVE TO SEA LEVEL

WHAT IS EUSTATIC SEA LEVEL CHANGE?

EUSTATIC change occurs when the VOLUME OF WATER IN THE OCEANS ISOSTATIC BASINS CHANGES, affecting GLOBAL SEA LEVELS

WHAT IS EUSTATIC SEA LEVEL CHANGE MOSTLY CAUSED BY

• MELTING OR FORMATION OF ICE SHEETS

• THERMAL EXPANSION OF WATER

• TECTONIC CHANGES AFFECTING OCEAN BASIN CAPACITY

WHAT IS ISOSTATIC SEA LEVEL CHANGE?

ISOSTATIC change occurs when LAND RISES OR FALLS RELATIVE TO SEA LEVEL.

It is usually LOCAL OR REGIONAL rather than global

WHAT CAUSES ISOSTATIC SEA LEVEL CHANGE?

• POST GLACIAL REBOUND

• SEDIMENT DEPOSITION

• SUBSIDENCE

• TECTONIC ACTIVITY

HOW DO CHANGES IN GOBAL ICE VOLUME AFFECT SEA LEVEL?

During GLACIAL PERIODS:

• Water is stored in ICE SHEETS AND GLACIERS

• Sea level FALLS

During INTERGLACIAL PERIODS:

• Ice melts

• Water returns to oceans

• Sea level RISES

WHAT IS THERMAL EXPANSION AND HOW DOES IT AFFECT SEA LEVEL?

Thermal expansion occurs when WATER WARMS AND EXPANDS, increasing ocean volume.

This is one of the MAJOR CAUSES OF MODERN SEA LEVEL RISE LINKED TO CLIMATE CHANGE

HOW CAN TECTONIC ACTIVITY INFLUENCE SEA LEVEL?

Tectonic processes can alter the CAPACITY OF OCEAN BASINS

E.G.

• Rising magma LIFTS OCEAN CRUST

• Ocean basins become SHALLOWER

• Water is displaced

• SEA LEVEL RISES GLOBALLY

WHAT IS POST - GLACIAL ISOSTATIC RECOVERY?

During glacial periods:

• THICK ICE SHEETS COMPRESS EARTHS CRUST

After ice melts:

• Land REBOUNDS UPWARD

HOW DOES ISOSTATIC CHANGE AFFECT THE UK?

The UK is still adjusting after the LAST ICE AGE

• SCOTLAND IS RISING by about 1.5mm PER YEAR

• SOUTHER ENGLAND IS SINKING by about 1.1mm PER YEAR

HOW CAN ACCRETION CAUSE ISOSTATIC CHANGE?

When LARGE AMOUNTS OF SEDIMENT ARE DEPOSITED, the wight of the sediment can cause the LAND SURFACE TO SINK SLIGHTLY.

This can lead to RELATIVE SEA LEVEL RISE

HOW CAN SUBSIDENCE AFFECT COASTAL SEA LEVEL?

Subsidence occurs when land SINKS DUE TO LOSS OF GROUNDWATER OR SEDIMENT COMPACTION.

This lowers land relative to the sea, increasing FLOOD RISK AND COASTAL RECESSION

WHAT IS AN EMERGENT COASTLINE

WHEN LAND RISES RELATIVE TO SEA LEVEL. EXPOSING FORMER COASTAL LANDFORMS ABOVE THE CURRENT SEA LEVEL.

WHAT ARE RAISED BEACHES?

Raised beaches are FORMER BEACHES NOW LOCATED ABOVE THE PRESENT HIGH - TIDE LEVEL.

CHARACTERISTICS OF RAISED BEACHES

• FLAT SURFACES

• SAND OR PEBBLE DEPOSITS

• VEGETATION SUCCESSION

WHAT IS A FOSSIL CLIFF?

A FOSSIL CLIFF is a FORMER SEA CLIFF THAT IS NO LONGER ERODED BY WAVES because sea level fallen or land has risen

WHAT IS SUBMERGENT COASTLINE?

A SUBMERGENT COASTLINE forms when SEA LEVEL RISES RELATIVE TO THE LAND, flooding coastal landscapes

WHAT IS A RIA?

A RIA is a DROWNED RIVER VALLEY FORMED WHEN RISING SEA LEVEL FLOOD THE LOWER COURSE OF A RIVER

CHARACTERISTICS OF A RIA

• V - SHAPED VALLEY

• BRANCHING STRUCTURE

• COMMON IN ESTUARINE ENVIRONMENTS

WHAT IS A FJORD?

A FJORD forms when RISING SEA LEVELS FLOOD A GLACIAL VALLEY

E.g. MILFORD SOUND, NEW ZEALAND

WHAT IS A DALMATIAN COASTLINE?

A Dalmatian coast forms when PARALLEL RIDGES AND VALLEYS ARE FLOODED BY RISING SEA LEVELS, leaving LONG NARROW ISLANDS PARALLEL TO THE COAST =.

HOW MUCH HAS GLOBAL SEA LEVEL RISEN SINCE THE INDUSTRIAL REVOLUTION?

Approx. 235mm since 19th century

WHAT DOES THE IPCC PREDICT ABOUT SEA LEVEL RISE BY 2100?

The IPCC PREDICTS GLOBAL SEA LEVEL WIL RISE BY 0.26 - 0.77M BY 2100

Impacts of global sea level rise:

• increased coastal flooding

• Erosion

• Salinisation of groundwater

• Displacement of coastal populations

HOW CAN DREDGING INCREASE COASTAL EROSION?

Dredging removes SEDIMENT FROM ROVERS OR THE SEABED, reducing the amount reaching beaches.

This leads to:

• SMALLER BEACHES

• Less protection from waves

• INCREASED COASTAL EROSION

HOW DO DAMS INCREASE COASTAL EROSION?

Dams trap sediment upstream

—> LESS SEDIMENT REACHES THE COAST:

• beach shrinkage

• Increased wave attack

• Faster coastal retreat

E.g. SEDIMENT REACHING SPAIN’S EBRO DELTA HAS FALLN BY AROUND 93%

WHAT IS TERMINAL GROYNE SYNDROME?

When Groynes trap sediment, AREAS FURTHER ALONG THE COAST RECEIVE LESS SEDIMENT.

This causes:

• Reduced beach size

• Increased erosion

E.g. HOLDERNESS COAST

WHY IS THE HOLDERNESS COAST ERODING RAPIDLY?

The HOLDERNESS coast is mainly BOULDER CLAY, which is:

• soft

• Easily weathered

• Vulnerable to slumping

COMBINED WITH DESTRUCTIVE NORTH SEA WAVES, erosion rates reach ABOUT 1.8M PER YEAR, the fastest in EUROPE

WHY DOES WIND DIRECTION AFFECT EROSION RATES?

When winds blow ONSHORE, they generate HIGHER - ENERGY WAVES that increase erosion.

Prevailing winds combined with LONG FETCH can produce very powerful waves.

WHY DOES HIGH TIDE INCREASE COASTAL EROSION?

At high tide, waves reach HIGHER PARTS OF THE CLIFF, including the BACKSHORE, increasing erosion

WHY DOES EROSION INCREASE DURING WINTER?

MORE STORMS = DESTRUCTIVE WAVES & STRONGER WINDS

WHY ARE MANY COASTAL AREAS AT HIGH FLOOD RISK?

Coastal areas are vulnerable because they are:

• LOW LYING

• Densely populated

• Exposed to storm surges

• Affected by rising sea levels

WHY DO PEOPLE LIVE IN HIGH RISK COASTAL AREAS?

• fertile soils

• Trade and ports

• Tourism

• Access to resources

• Attractive landscapes

HOW DO SALT MARSHES AND MANGROVES REDUCE FLOOD RISK?

COASTAL VEGETATION:

• ABSORBS WAVE ENERGY

• REDUCING WAVE HEIGHT

• TRAPPING SEDIMENT

• RAISING LAND LEVELS

WHAT IS A STORM SURGE?

A STORM SURGE is a TEMPORARY RISE IN SEA LEVEL CAUSED BY STORM OR TROPICAL CYCLONES.

It can lead to SEVERE COASTAL FLOODING

WHAT IS THE INVERSE BAROMETER EFFECT?

When AIR PRESSURE DECREASES, sea level rises.

WHERE DO TROPICAL CYCLONES FORM?

They form between 5° and 30° NORTH AND SOUTH OF THE EQUATOR where:

• sea temperatures exceed 27°

• warm moist air rises rapidly

HOW DOES CLIMATE CHANGE INCREASE COASTAL FLOOD RISK?

Climate change increases flood risk through:

1. SEA LEVEL RISE

2. MORE INTENSE STORMS

3. CHANGING WEATHER PATTERNS

HOW FAST IS SEA LEVELS CURRENTLY RISING?

• 1900s average 1.4MM PER YEAR

• SINCE 2006: 3.6 MM PER YEAR

WHAT ARE THE POSSIBLE IMPACTS OF A 50CM SEA LEVEL RISE?

• 800,000,000 PEOPLE AFFECTED GLOBALLY

• Increased coastal flooding

• Infrastrucutre damage

• Agricultural land loss

• Salinisation of groundwater