Coastal Landforms and Sea Level Changes Flashcards Preview

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Flashcards in Coastal Landforms and Sea Level Changes Deck (32)
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How do Cliffs and Wave-cut platforms form?


Cliffs are common coastal landforms - they form as the sea erodes the land. Overtime, cliffs retreat due to the action of waves and weathering.
Weathering and wave erosion cause a notch to form between the high and low water mark. This eventually develops into a cave.
Rock above the caves becomes unstable with nothing to support it, and it collapses.
Wave cut platforms are flat surfaces left behind when a cliff is eroded.


How do headlands and bays form


Headlands and bays form where there are bands of alternating hard rock and soft rock at right angles to the shoreline, discordant coastline.

The soft rock is eroded quickly, forming a bay. The harder rock is eroded less and sticks out as a headland.


What’s a discordant coastline


Discordant coastline occurs where bands of differing rock type run perpendicular to the coast.


What is a concordant coastline


A concordant coastline occurs where the bands of differing rock types run parallel to the coast.

The outer hard provides a protective barrier to erosion of the softer rocks further inland.


How are caves, arches and stacks formed


Some landforms are found in cliffs - these are called cliff profile features

Weak areas in rock (eg joints) are eroded to form caves.
Caves on the opposite sides of a narrow headland may eventually join up to form an arch
When an arch collapses it forms a stack.

Cracks in the cliff appear, small cave forms, arch forms, stack forms and then stump.


What are cliff profile features


landforms found in cliffs


How are beaches formed


They are landforms of deposition
Beaches form when constructive waves deposit sediment on the shore - they are a store in the coastal system.
Shingle beaches are steep and narrow. They’re made up of larger particles, which pile up at steep angles.
Sand beaches, formed from smaller particles, are wide and flat.

Beaches have distinctive features. Berms are ridges of sand and pebbles (about 1 to 2 metres high) found at high tide marks.
Runnels are grooves in the sand running parallel to the shore, formed by the backwash draining to the sea.
Cusps are crescent shaped indentations that form on beaches of mixed sand and shingle


What are berms


Berms are ridges of sand and pebbles (about 1-2 metres high) found at high tide marks.


What are runnels


Runnels are grooves in the sand running parallel to the shore, formed by backwash draining to the sea.


What are cusps


Crescent shaped indentations that form on beaches of mixed sand and shingle.


How do spits form


Spits tend to form where the coast suddenly changes direction eg across river mouths.

Longshore drift continues to deposit material across the river mouth, leaving a bank of sand and shingle sticking out into the sea. A straight spit that grows out roughly parallel to the coast is called a simple spit.

Occasional changes to the dominant wind and wave direction may lead to a spit having a curved end, also known as recurved end.
Over time, several recurved ends may be abandoned as the waves return to their original direction.
A spit that has multiple recurved ends resulting from several periods of growth is called a compound spit.
the area behind the spit is sheltered from the waves and often develops into mudflats and salt marshes.


How do offshore bars and tombolos form


Bars are formed when a spit joins two headlands together. This can occur across a bay or across a river mouth.
A lagoon forms behind the bar.
Bars can also form off the coast when material moves towards the coast (normally as sea level rises). These may remain partly submerged by the sea - in this case they’re called offshore bars.

A bar that connects the shore to an island (often a stack) is called a tombolo.


How do Barrier islands form


Barrier islands (also called barrier beaches) are long narrow islands of sand or gravel that run parallel to the shore and are detached from it. They tend to form in areas where there’s a good supply of sediment, a gentle slope offshore, fairly powerful waves and a small tidal range.

It’s not exactly clear how barrier islands form, but scientists think that they probably formed after the last ice age needed, when ice melt caused rapid sea level rise. The rising waters flooded the land behind the beaches and transported sand offshore,where it was deposited in shallow water, forming islands.

Another theory is that the islands were originally bars, attached to the coast, which were eroded in sections, causing breaches in the bar.

A lagoon or marsh often forms behind the barrier island, where the coast is sheltered from wave action.


Tell me how sand dunes form


Sand dunes are formed when sand deposited by longshore drift is moved up the beach by the wind. Sand trapped by driftwood or berms is colonised by plants and grasses, eg marram grass. The vegetation stabilises the sand and encourages more sand to accumulate there, forming embryo dunes.

Over time, the oldest dunes migrate inland as newer embryo dunes are formed. These mature dunes can reach heights of up to 10m.


Tell me about the formation of estuarine mudflats and salt marshes


Mudflats and salt marshes form in sheltered, low energy environments eg river estuaries or behind spits.

As silt and mud are deposited by the river or the tide, mudflats develop.
The mudflats are colonised by vegetation that can survive the high salt levels and long periods of submergence by the tide.
The plants trap more mud and silt, and gradually they build upwards to create an area of saltmarsh that remains exposed for longer and longer between tides.
Erosion by tidal currents or streams forms channels in the surface of mudflats and salt marshes. These may be permanently flooded or dry at low tide.


What is eustatic sea level change


Eustatic sea level change is caused by a change in the volume of water in the sea, or by a change in the shape of the ocean basins.

The effects are always global.


What are the main causes of eustatic sea level change


Changes in climate. An increase in temperature causes melting of ice sheets, which increases sea level. It also causes water to expand, which increases sea level further. A decrease in temperature causes more precipitation to fall as snow. This increases the volume of water stored in glaciers and so reduced the volume of the sea, which decreases sea level.

Tectonic movements of the earths crust that alter the shape (and so the volume) of ocean basins. Eg, sea floor spreading increases the volume of the basin and so decreases sea level.


What is isostatic sea level change


Isostatic sea level change is caused by vertical movements of the land relative to the sea. Any downward movement of the land causes sea level to rise locally, while uplift of land causes sea levels to fall locally.

Effects are always local


What are the main causes of isostatic sea level change


Uplift or depression of the earths crust due to accumulation or melting of ice sheets. Slow uplift of land can continue for thousands of years after the weight of a retreating glacier has gone. Accumulation of sediment, mostly at the mouths of major rivers, can also cause depression.

Subsidence of land due to shrinkage after abstraction of groundwater eg. Drainage of Marshland

Tectonic processes, eg as one plate is forced beneath another at a plate margin.


How does sea level vary in the short term


Sea level varies on a daily basis with the tidal cycle. Onshore winds and low atmospheric pressure systems also cause the sea surface to rise temporarily.


In the long term, how has sea level changed


During the last glacial period (from roughly 110000 to 12000 years ago), water was stored in ice sheets, so sea level was lower than present. At the last glacial maximum (around 21000 years ago) sea level was about 130 m lower than present.

As temperatures started to increase (about 12000 years ago), ice sheets melted and sea level rose rapidly. It reached its present level about 4000 years ago.

Over the last 4000 years, sea level has fluctuated around its present value.

Since about 1930, sea level has been rising.


Tell me about climate change causing changes in sea level


Over the last century, global temperature has increased rapidly. This is called global warming. There’s been a sharp rise in average temperature.

The temperature increase over the last century has been very fast. There is a consensus among scientists that the changes in climate over the last century are as a result of human activities, such as deforestation and burning fossil fuels.

These activities increase the concentration of greenhouse gases in the atmosphere- greenhouse gases absorb outgoing long wave radiation, so less is lost to space. As their concentration increases, more energy is trapped and the planet warms up.

Increases in temperature are likely to cause increases in sea level, through melting of ice sheets and thermal expansion of water in oceans.
Global sea level is currently rising at almost 2mm each year. If greenhouse gas emissions remain very high during the 21st century, this could increase to as much as 16mm a year.


How will climate change impact storms


Storms are likely to become more frequent and more intense due to changes in ocean circulation and wind patterns. This would cause damage to coastal ecosystems and settlements.


If sea level continues to rise as predicted, what impacts will it have on coastal areas


More frequent and more severe coastal flooding.

For example In 1995 to 2004, kings point in New York flooded around 80 times, but from 2005 to 2014 it flooded nearly 160 times.

Submergence of low lying islands - if sea level rises by just 0.5m, most of the Maldives will be submerged

Changes in coastline. As sea levels rise the coastline changes - islands are created and the area of land is decreased.

Contamination of water sources and farmland. Salt water may enter bodies of fresh water near the coast, damaging ecosystems and making the water unsuitable for lots of uses. Salt water entering soils may damage crops and make land impossible to farm.

Sea level rise and increased storminess will increase coastal erosion, putting ecosystems, homes and businesses at risk.


What does sea level fall result in


Coastlines of emergence

When sea level falls relative to the coast, new coastline emerges from the sea


What landforms may be created from an emergent coastline


Raised beaches are formed when the fall in sea level leaves beaches above the high tide mark. Overtime, beach sediment becomes vegetated and develops into soil.

Sea level fall also exposes wave cut platforms (marine platforms), leaving them raised above their former level.

The cliffs above raised beaches are no longer eroded by the sea, and slowly get covered by vegetation. They’re called relict cliffs.

It’s not uncommon to sea wave cut notches, caves, arches and stacks within relict cliffs. These raised features are gradually degraded (weathered) over time.


Coastlines of submergence are a result of…


Sea level rise.

When sea level rises relative to the coast, the sea submerges (drowns) the existing coastline.


List the different landforms of submergence


Dalmatian coastlines


How do rias form


Rias are formed where river valleys are partially submerged. Rias have a gentle long and cross profile. They’re wide and deep at their mouth, becoming narrower and shallower the further inland they reach.


How do fjords form


Fjords are a lot like rias, but they’re drowned glacial valleys rather than drowned river valleys. They’re relatively straight and narrow, with very steep sides. They have a shallow mouth caused by a raised big of ground (called the threshold) formed by deposition of material by the glacier. They’re very deep further inland.


How are Dalmatian coasts form


In areas where valleys lie parallel to the coast, an increase in sea level can form a Dalmatian coastline. Valleys are flooded, leaving islands parallel to the coastline.


Explain how processes can create and alter landforms and landscapes over time


Individual landforms combine to form landscapes - coastal landscapes can be dominated by processes of erosion or deposition, but most are formed by both.

A change in one factor can lead to changes in others, eg a change in wave direction might increase deposition and change a landscape do,image by erosive landforms to one dominated by depositional landforms.

Relict landforms can still experience coastal processes eg weathering.

Coastal landscapes are often made up of a mixture of active and relict landforms that reflect different periods of change.

Changes occur over a range of spatial scales and temporal scales.