Sea levels change daily according to the tide. However, over a longer time scale, sea-level changes are affected by changes in how much landmasses are uplifted or submerged (isostatic changes) and water levels (eustatic) changes. Let's take a look.
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Jetzt kostenlos anmeldenSea levels change daily according to the tide. However, over a longer time scale, sea-level changes are affected by changes in how much landmasses are uplifted or submerged (isostatic changes) and water levels (eustatic) changes. Let's take a look.
The land can rise or fall over:
Similarly, sea levels can rise or fall:
Sea level changes are influenced by various factors, and it's important to understand the difference between eustatic and isostatic sea level change. Let's take a look.
A coastal region experiencing seismicity (earthquakes) can encounter land being shifted upwards (uplift) or downwards (downthrust) as geological pressures are released, and the adjacent rocks adjust at fault lines. Consequently, there can be a rapid change in relative sea level depending on whether the land has been shifted up or down. Some notable land/sea-level changes are:
On coastlines not affected by glacial ice cover, the post-glacial sea-level rise caused drowned, submergent coasts. Examples of these can be found along the south coast of England and the east coast of America. The most common feature is a ria.
Emergent landforms were produced towards the end of an ice age when isostatic rebound occurred faster than the eustatic rise in sea level. In other words, the land's height rose more quickly than the sea's. An example of this is the eastern Scottish coastline, near Earlsferry in Fife.
Previous sea levels are reflected in their landforms:
Isostasy is where one layer of the earth's crust floats on top of another more pliable layer beneath. As a result, the natural buoyancy of crustal rocks gets depressed when land-based ice sheets are formed due to the weight of the ice sheets. However, when the ice sheet melts, the weight reduces, resulting in the land surface being released and slowly rebounding upwards over thousands of years. This is known as post-glacial isostatic adjustment. Isostatic sea-level change can also be caused by tectonic uplift or depression; however, as this only takes place along plate boundaries, this isostatic change only occurs in particular areas of the world.
Two different isostatic changes have occurred in the UK since the last ice age.
When the ice age began, the temperature fell. Water froze into glaciers, meaning that it was removed from the sea but not put back in. This led to a fall in sea level. Conversely, when the ice age ended, the temperature rise and the melting ice returned the water to the sea, causing it to increase globally. Global temperature increases cause the volume of ocean water to increase (thermal expansion), leading to sea level changes.
Key points:
The scale of isostatic and eustatic changes during and after the last glacial period are linked but are happening at very different rates.
As a result, some coastlines may be emerging while at the same time some are submerging, and others will be achieving a state of dynamic equilibrium with the changing sea level.
We constantly hear that sea levels are still rising. The reasons are widely debated and two of the most common answers are:
We know that sea levels rise due to climate change, it causes the melting of ice sheets, and because of thermal expansions, the sea expands as it gets warmer.
The tectonic activity that affected Aceh province's coastline in Sumatra also created tectonic subsidence resulting in a ria. At the same time, in some locations, coral reefs were raised and then subsequently eroded by wave action. This type of change is rare, localised, and limited to tectonically active zones, but it causes significant instant changes to the coastline when it happens.
The effects of changing sea levels are already being felt globally. Millions of euros have already been invested in the Delta works in the Netherlands, and substantial public funds are earmarked for their continuing maintenance and improvements to safeguard this densely populated region of northern Europe. The Sundarbans region of West Bengal and the low-lying delta of Bangladesh are amongst the fastest eroding coastlines globally, with some places experiencing more than 20 meters of erosion each year. In addition, there appears to be an increasing frequency of cyclones with their associated tidal surges. In the Pacific Ocean, low-lying island states are already suffering the worst effect of sea-level rise, with increased rates of salinisation, coastal erosion, and storm surges forcing many to consider migration, and environmental refugees.
In the UK, as mentioned earlier, the east coast has a high risk of being flooded and destroyed. Lots of people inhabit the east coast. As a result, their homes and livelihoods are at risk. There is also some critical infrastructure present in the area, including several power stations. Six of them are nuclear power plants, two of which have been deactivated.
Changes in sea level are part of ongoing concerns regarding coastal risks. Other coastal risks include coastal retreat and coastal flooding. There are management approaches that we can take to prevent coastal risk and be prepared for any natural hazards that may occur. It is also important to be aware of the risks worsened by human activities.
Sea level changes are a massive problem as a result of flooding in coastal areas. For example, although millions have already been invested in the Delta works in the Netherlands as this is a hugely populated area in the Pacific Ocean, low lying island states are already suffering the worst effect of sea-level rise, with increased rates of salinization, coastal erosion and storm surge.
Sea levels are changing due to the melting of the ice sheets, the world is getting warmer, causing the thermal expansion of the sea, and the land is sinking.
Sea levels are changing because of thermal expansion, caused partly due to climatic conditions. It's getting warmer. Melting of the ice sheet and tectonic readjustment
Changes in sea levels are linked to three factors, all affected by the ongoing global climate change: Thermal expansion - when water heats up, it expands. Melting glaciers: Through persistently higher temperatures, caused by global warming, have led to greater-than-average summer melting which has been compounded by
diminished snowfall due to later winters and earlier springs. That creates an imbalance between runoff and ocean evaporation, causing sea levels to rise. And Loss of Greenland and Antarctica's ice sheets: As with mountain glaciers, increased heat is causing the massive ice sheets that cover Greenland and Antarctica to melt more quickly.
What is a tectonic factor which can influence sea-level change at the coast?
A coastal region experiencing seismicity (earthquakes) can encounter land being shifted upwards (uplift) or downwards (downthrust) as the geological pressures are released and the adjacent rocks adjust at fault lines. This will cause a rapid change in the sea levels.
Give an example of tectonic activity which has affected sea-level changes?
Following the Tohoku earthquake in 2011, more than 200miles of the eastern coastline of Honshu, norther Japan, fell by 0.6 m. A destructive tsunami then followed.
What do you understand by the term Isostatic?
A change in the local coastline of land height relative to the sea level.
What is a post-glacial adjustment?
It is when the ice sheet melts, the land surface is released and slowly rebounds upwards over thousands of years.
In the UK, two different isostatic changes have occurred since the last ice age. What were they?
What do you understand by the term Eustatic?
Global changes to sea levels.
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