“Do you know why we have white sand in Kutch in Gujarat (India)?” a Professor asked during my Graduation.
All the Students started Murmuring and thinking about it. Suddenly a topper, not me said that it is not sand but just salt!
Then, the Professor went on explaining certain things and finally concluded the class by explaining about sea level rise (transgression) and regression.
Today, we will talk about the sea level rise or transgression.
Why should we bother about it?
Human civilization needs water to flourish. We are obligated for the settlement near coastal areas and river banks. Almost 40% of the world’s population lives within 100 kms of coast. That is a big number!
Thus, it will be worrisome in the near future if sea level rises.
What does a rise in sea level mean?
To a normal man, it is nothing more than an increase in the amount of water in the Seas or Oceans. But that’s not the complete situation. There are several consequences and various factors that need to be completely understood.
Sea level monitoring is important to predict future changes. The pattern of sea level change is accompanied with many factors like the rate of global warming, changes in the oceans and level of CO2. All these are considered as crucial factors for the rise in sea level.
Sea level rise rate
From the very beginning of the 20th century, sea level has risen at a much faster pace. In 2014 the highest annual average was recorded through satellites. It was about 2.6 inches more than the 1993 average.
|Data source: Satellite sea level observations
.Credit: NASA Goddard Space Flight Center
What causes sea level rise?
The main culprit is “Global warming”. It is responsible for two processes that ultimately leads to sea level rise. The first process is the thermal expansion of ocean water. Oceans store heat and also water expands on heating or through increase in the temperature.
Another process is melting of land based ice sheets and glaciers. The melting of floating ice sheets or floating ice shelves do not contribute to sea level rise.
Some minor reasons:
Greenhouse gases such as CO2 are also responsible for sea level rise. It can raise the sea level by 2% to 3%.
A study has revealed that freshwater storage reservoirs also impact sea level rise. Decline in the freshwater storage makes a space for the ocean water to inhabit.
If temperature rises only by 1℃ it fastens the sea level rise by 2.3 metres over 2000 years.
Is sea level rise uniform everywhere?
No, it is not an uniform occurrence. It depends on several local factors such as tides, currents, storms, tectonic motions, subsidence of the land and many more factors that contribute to it.
Now… Let us talk about effects of sea level rise
There are a number of impacts which can be sometimes devastating. The first visible impact of the sea level rise on human settlement is loss of land. The agricultural or even habitats of people are lost due to sea level rise. They are powerless in front of nature and ultimately they have to displace.
The other dominant impact is coastal flooding which is also regarded as “Nuisance flooding”. Such coastal floods are also experienced earlier. It has a devastating effect on Human life. Losses of lives, properties, infrastructures and what not.
Tsunami is another destructive impact. Tsunamis carry the complete water mass of the ocean and erodes the sediments along its pathway. There are several factors responsible for Tsunami.
.Disturbance in the ocean because of Seismic activities- the most suitable example here is that of Indian Ocean Tsunami of 2004. The disturbance was caused 1000 kms away still it has a great impact. Earthquake of magnitude 8.9 had struck the west coast of Northern Sumatra. The shift of plate was about 130 kms.
Submarine Landslides- submarine landslides get triggered due to seismic activity at the plate boundary. Accretionary wedges formed due to the convergence of lithospheric plates also contribute for Submarine Landslides. The well-known example is “Makrand Fracture Zone”.
Submarine Volcanic Eruption– Krakatau, an island group in the Sunda strait is a classic example for this category. In 1883, Krakatau exploded in a devastating way. It triggered a tsunami which took off 30,000 lives. The noise of eruption was heard for several seconds and upto miles away.
Saltwater intrusion is the other problem. It is a phenomenon wherein the saline water from the sea intrudes into the fresh water aquifer.
As the fresh water is less dense it floats above the saline water. When freshwater is completely consumed by pumping, the saline water fills up the space and mixes with the freshwater.
Hurricanes are the consequences of warm water. Because of Global warming, the surface temperature of ocean water has increased in such a way that the rate of evaporation has gone up. All this, triggers the hurricanes.
Some study shows that the most devastating and energetic storms of Category 4 or Category 5, particularly in the North Atlantic and North Indian ocean is due to the rising warmness.
Marine ecosystem is also greatly affected by sea level rise. Also shoreline retreating is the result of sea level rise.
Predictions for sea level rise
Many scientists are working on predicting the future sea level rise. A report by IPCC i.e. The Intergovernmental Panel on climate change has indicated 10 to 30 inches sea level rise by 2100. Such a rise will severely affect the U.S. East coast.
NASA and European studies have revealed that there will be a 26 inches rise in the sea level by the end of the century.
Sea level rise by 2050 will affect the lives of 300 million people. Six Asian countries having large coastal density will get affected. The countries are India, Bangladesh, Vietnam, Indonesia, Thailand and China.
If all the ice present on the Earth in the form of glaciers melts, there will be a rise of about 216 feet. That would be scary! However, it will take a lot and lots of time.
Solutions for sea level rise
The solutions that can be used are either natural or manmade. Sometimes, both are used simultaneously. The only trick to be used here is by creating a barrier for the water.
Humans can respond to the increasing sea level by three ways:
Natural ways include the usage of Natural communities to combat the problem of sea level rise. Plants such as Mangroves are utilized which helps in absorbing the moisture. Moreover, barrier islands, coral reefs, salt marshes, oysters and sea grass acts as safeguard against storms and coastal flooding.
|Some man made structures.|
There are various man made barriers utilized against the sea level rise.
Beach : Beach and Sand dunes can serve as barriers. For that the area occupied by the beach should be large and also it should contain a great amount of sand. It is done by what is known as “beach nourishment”. Beach nourishment is the artificial dispersion of sand on the beach.
Used in- Norfolk
Sea wall : constant striking of the sea can be reduced by the construction of sea walls. Such walls are built at a height of 5 to 6 feet above sea level. As the water is constantly striking the wall, it needs timely maintenance.
Used in- New York
Raising Roads : raising of roads could be the other solution. Such roads should be at a height greater than sea level so that the settlement can be prevented by the coastal flooding. Storm pumps also need to be installed to drain out storm water.
Used in- Miami Beach
Also, Sewage systems should be upgraded and groundwater pumping should be reduced to the issue of land sinking.
In India, particularly in Bombay tetrapods are used. Tetrapods are embankments by boulders. Such tetrapods are bound with each other to increase the efficiency.