lonar lake: Martian crater on the earth

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lonar lake: Martian crater on the earth

Tuesday, 27 February 2018 | GYANENDRA NATH MITRA

The lonar lake is located in Buldhana district of Maharashtra. lakes generally have saline or sweet water. lonar is a salt and soda lake. Apart from sodium chloride (salt), it also contains soda (carbonates of sodium).

The lake has been a subject matter of investigation by many famous institutions around the world. To name a few, these include Smithsonian Institution, the Geological Survey of USA, Harvard University, Massachusetts Institute of Technology, Woods Hole Oceanographic Institution, Geological Society of India and Physical Research laboratory, apart from a number of universities in India. What is unique in this lake to gain such prominenceIJ

The oval lake at the base has a mean diameter of 1.2 km and circumference of 4.8 km, surrounded by an oval basin consisting of small hills with a circumference of 8 km. The sides of the basin rise abruptly at an angle of 75IJ. Two small streams Purna and Pen Ganga drain into this lake. A well in the southern side adjacent to the water edge has sweet water.

There is small circular depression about 700 m from the main lake called Ambar lake, also called Chhota(small) lonar. A number of temples are located around the lake such as, Daitya Sudan Temple, a Vishnu temple dated to the Chalukya Dynasty, which ruled the Central and Southern India between the 6th and 12th centuries AD. Other temples include Kamala Devi, Gomukh, Shankar Ganesh, Ram Gaya and Mota Maruti etc. some of them in ruins. There is a Hanuman temple near the Ambar lake. The idol inside the temple is made of rocks, which are believed to be highly magnetic.

The lake is mentioned in the Ain-i. Akbari (1600 AD), besides in the Skanda Purana and the Padma Purana with usual puranic stories. A British officer first visited the place in 1860. The chemical composition of water was reported by agricultural chemist Plymen. According to him, unlike the famous salt-lake, Sambhar of Rajasthan which contains only salt (sodium chloride), lonar water contains salt and soda (carbonates of sodium). These chemicals are found as crystals on the shore of the lake as water dries out. The local people distinguish the products from their crystal shape and colour and separate them for use.

The unlikely presence of soda in the water led to a number of investigations to find out its origin since its presence could not be explained in the basaltic Deccan Traps. Minerals such as Gaylussite, a hydrated sodium calcium carbonate with the formula Na2Ca(CO3)2.5H2O, was detected in the core samples drawn from the bottom of the lake. It is an unstable mineral, which dehydrates in the air and decomposes in water.

The water of the lake is neutral on the shore but alkaline inside, each of them with their unique flora and fauna, studied by several universities. Theory of volcanic eruptions leading to creation of the lake was ruled out after the discovery of the mineral plagioclase, which had been converted to maskelynite. The presence of planar deformation features pointed to an impact origin of the lake. Maskelynite is a glassy phase found in some meteorites and craters created by meteorite impact.

Scientific studies conducted on lonar(Misra and co-researchers, 2008, 2009) indicate that its crater was created by a hypervelocity comet or asteroid coming from the east, which crashed on the earth at an angle of 30-45 degrees about 52,000 years ago. A still ancient date of 570,000 ±47000 years is more probable. The crater floor lies 90 meters below the preimpact surface. Chota lonar is believed to have been created by impact of a splinter of the asteroid, which hit the ground at this location. Its scientific origin is yet to be reported. Recently Maloof and co-researchers from Princeton, Harvard and Stanford (MIT) Universities, made field studies of lonar lake and presented results of their research at the 42nd lunar and Planetary Science Conference, Texas, USA in 2011. According to them, lonar is a unique Martian analog for studies of ejecta flow dynamics, paleo-magnetism, and impact glasses, as it is the only terrestrial crater formed entirely within basalt. The ejecta (material ejected due to impact of asteroid) topography of lonar,with a circum-rim-syncline (folds of rock layers that slope upwards) and accumulation of material at the flow terminus, is similar to layered ejecta structures on the Mars. The properties of the ejecta blanket demonstrate significant radial mass movement following ballistic (aerial) emplacement and final structures similar to Martial layered ejecta form of Martial craters.

(Dr Mitra is a former Dean, College of Agriculture, OUAT and Professor of Soil Science and Agricultural Chemistry. email: gnmitra@gmail.com)

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