Type: Prelims Only

The colour of water in Maharashtra’s Lonar Lake, formed after a meteorite hit the Earth some 50,000 years ago, has changed to glaring.

Make a note of all saltwater lakes in India. Few of them are Pulicat, Pangong Tso, Chilika, and Sambhar Lakes etc.

About Lonar Lake

• Lonar Lake, also known as Lonar crater, is a notified National Geo-heritage Monument, saline (pH of 10.5), Soda Lake, located at Lonar in Buldhana district, Maharashtra.
• It was created by an asteroid collision with earth impact during the Pleistocene Epoch.
• It is one of the four known, hyper-velocity, impact craters in basaltic rock anywhere on Earth.
• It sits inside the Deccan Plateau—a massive plain of volcanic basalt rock created by eruptions some 65 million years ago.
• Its location in this basalt field suggested to some geologists that it was a volcanic crater.

Why there’s a color change?

• The salinity and algae can be responsible for this change.
• There is no oxygen below one meter of the lake’s water surface.
• There is an example of a lake in Iran, where water becomes reddish due to increase in salinity.
• The level of water in the Lonar Lake is currently low as compared to the few past years and there is no rain to pour fresh water in it.
• The low level of water may lead to increased salinity and change in the behaviour of algae because of atmospheric changes.

On June 7, astronaut and oceanographer Kathy Sullivan, who was the first American woman to walk in space in 1984, became the first woman and the fifth person in history to descend to the deepest known spot in the world’s oceans, called the Challenger Deep in the Mariana Trench.

The ocean relief can be divided into various parts such as Continental Shelf, Continental Slope, Continental Rise or Foot, Deep Ocean basins, Abyssal plains & Abyssal Hills, Oceanic Trenches, Seamounts and Guyots.

Revise these ocean bottom relief  features from your basic references.

Also revise India’s Deep Ocean Mission.

What is Challenger Deep?

• The Challenger Deep is the deepest known point in the Earth’s seabed hydrosphere (the oceans), with a depth of 10,902 to 10,929 m.
• The deepest part is called the Challenger Deep, which is located below the surface of the western Pacific Ocean.
• The first dive at Challenger Deep was made in 1960 by Lieutenant Don Walsh and Swiss scientist Jacques Piccard on a submersible called ‘Trieste’.
• The British Ship HMS Challenger discovered Challenger Deep between 1872-1876.
• In 2012, film director James Cameron reached the bottom of the Mariana trench after a descent that lasted 2 hours and 36 minutes.
• Cameron reached a depth of about 10,908 metres on a dive in his submersible called the ‘Deepsea Challenger’ and became the first to complete a solo submarine dive to this spot.

Why explore deep oceans?

• Ocean exploration, however, is not randomly wandering in hopes of finding something new.
• It is disciplined and organized and includes rigorous observations and documentation of biological, chemical, physical, geological, and archaeological aspects of the ocean.
• Most of the existing knowledge of the oceans comes from shallower waters, while deeper waters remain relatively unexplored, even as humans are relying more on these areas for food, energy and other resources.
• Further, finding out more about the deep ocean areas can potentially reveal new sources for medical drugs, food, energy resources and other products.
• Significantly, information from the deep oceans can also help to predict earthquakes and tsunamis, and help us understand how we are affecting and getting affected by the Earth’s environment.

What does it take to reach the deep ocean?

• Vehicles called Human Occupied Vehicles (HOVs) may be used that carry scientists to the deep sea.
• Alternatively, there are unmanned Remotely Operated Vehicles (ROVs) that are linked to ships using cables and can be steered by scientists remotely.
• Even so, it is difficult for most private citizens to travel more than 100 feet below the surface of the ocean.
• Further, technical divers can go as deep as 500 feet or more, but with an array of tanks filled with different gas blends.

Why is it so difficult to explore deep oceans?

• Most recreational divers can’t explore more than about 120 feet down due to the amount of air needed to keep lungs pressurized at depth.
• Such depths could lead to nitrogen narcosis, the intoxication by nitrogen that starts to set in around that depth (most of our atmosphere is nitrogen, not oxygen).
• Waters at such depths of several kilometres exert tremendous pressure which human bodies cannot sustain.