LONAR - A Natural Wonder

METEORITES

The word meteor comes from the Greek word ‘meteoron’, which means phenomenon in the sky. This phenomenon is a bright streak of light suddenly appearing in the sky and vanishing in a few moments. Whenever a small rock or a grain of cosmic dust gets nearer the Earth the gravity pulls it to Earth and upon entering the atmosphere it burns due to friction with air and produces temporary incandescence. There are billions of such small rocks and dust-grains in the Solar system revolving around the Sun. The rocks are called meteoroids and the smallerdust particles are called micrometeoroids. The meteoroid enters the atmosphere at a speed of about 10 to 30 Km per second, it’s temperature rises due to friction with air and it slows down. At about 80 to 110 km above the Earth’s surface the meteoroid starts burning as the temperature increases rapidly.

CRATERS

A crater is formed when two objects collide at high velocity. The smaller colliding object is usually destroyed by the impact and a crater is created on the larger object. During the impact, target material is ejected out of the crater forming ejecta. Ejecta then contains vaporized, molten material, some from the impactor but mostly from the target, which is now solidified and settled around the crater rim. When an impactor hits the target tremendous amount of energy is released in the form of heat and pressure. This melts and shatters the surface of the target at impact site.

THE GEOLOGICAL THEORY

Lonar crater is located in the Buldhana district of Maharashtra State, India (19058’N, 760 31’N ). It is an important geological structure. This crater formed in basalt rock of the Deccan plateau some 35 to 50 thousand years is only of its kind.

WEATHER

The region is reputed for its extreme climatic conditions. It’s scorching hot during the day, and pleasant as one progresses towards the night. So, one can safely state that winter is the best time to visit the destination, while the same definitely does not hold true in the summers.

50,000 YEARS AGO
If you were there during the impact.........

Well actually you would have been there in the middle of the Ice Age. There were dense forests and large animals the vegetation was lush. It was cold and wet most times and you had to thrive in varied climatic conditions, humans were still in their formative years. You relied on animal food during certain parts of the year and hunted small game. Dr. Richard G. Klein of Stanford University believes that major genetic changes in humans took place about 50,000 years ago, like the development of language, advanced stone implements and first forms of art. The route of human migration was out of Africa from east along the coast toward Southeast Asia and Australia. So perhaps some of your ancestors were from the African subcontinent. You probably watched the sky grow dark as the huge meteor approached the earth. When the impact occurred it must have produced an explosion that rocketed through central India and destroyed everything up to 15 kms radius! Much has been done to know the exact nature of the destruction, how it happened and what the meteorite was made of. The newly formed bowl shaped hole-in-the-earth was soon filled with water, producing a saline lake where new vegetation was found.

LONAR CRATER

A Meteor falling onto the surface of the earth with an impact so intense that it creates a huge crater (depression) on the surface of the earth much like those found on the moon! Well, that is what happened at Lonar, nearly half a million years ago, generating a huge meteoritic crater, 2km in diameter and several hundred meters deep. Eventually, a shallow saline lake formed at the bottom of this crater. At 60 meters long and weighing 20 lac tons it was racing at a speed of 25 km per second towards the planet. The impact was so severe that it left a massive crater 170 meters deep and with 1800 meters diameter. The world's largest impact crater in basaltic rock lies in the Lonar Village of Buldana district near Aurangabad, Maharashtra. 1. The lake has two distinct regions that never mix - an outer neutral (pH7) and an inner alkaline (pH12) each with its own flora and fauna. 2. There is a perennial stream feeding the lake with sweet water, but there seems to be no apparent outlet for the lake's water. And it is also a big unsolved mystery where the water for the perennial stream comes from, in a relatively dry region like Buldhana. Even during the height of the summer months of May and June, the stream is perpetually flowing. Lonar Crater is a young meteorite impact crater emplaced in Deccan basalt. The estimates of the pre-erosion dimensions are; average diameter of 1710m: average rim height of 40 m (30-35 m of rim rock uplift, 5-10 m of ejected debris); depth of 230-245 m (from rim crest to crater floor). A continuous ejecta blanket extends over an average of 1410 m beyond the pre-erosion rim crest. The target rock column at Lonar consists of one or more layers of weathered, soft basalt capped by fresh, dense flows. Plastic deformation and/or compaction of this lower, incompetent material probably absorbed much of the energy normally available in the cratering process for rim rock uplift. A fluidized debris surge was the dominant mechanism of ejecta transportation and deposition at Lonar. In this aspect, Lonar should be a good analog for the ‘fluidized craters’ of Mars.

GEOLOGIC SETTING AND PRESENT CRATER MORPHOLOGY

Preliminary descriptions of the Lonar Crater and rather detailed descriptions of its associated shock metamorphic features have been published previously (Fredriksson et al. 1973: Milton et al. 1975; Kieffer et al. 1976; Milton and Dube, 1977; Frediksson et al. 1979). In the Lonar area an estimated 600-700 m of sub horizontal Deccan basalt flows overlie the Precambrian basement. At least in the upper part of this sequence the individual flows range from 5 to 30 m in thickness. The flows are massive except near their tops where they become somewhat vesicular, with the vesicles now largely filled by secondary minerals. Each flow was subjected to weathering before eruption of the next flow, with effects ranging from minor to extensive. Five such flows are exposed on the inner slopes of the crater’s rim. In the upper 50 m these are composed of fresh, dense basalt. Below this level the flows are heavily weathered and friable. All five flows are separated by paleosols of red bole. The present surface is a sub horizontal plain with a few meters of rolling relief cut by gullies 1-2 m deep. The uppermost basalt flow is overlain in most places by a dense, structure less, black, clayey soil up to 2m thick. This soil is also exposed beneath the outer portions of the ejecta blanket in several gullies south of the crater. Thus it definitely predates the crater, demonstrating that the surface configuration has not changed significantly since the cratering event. A much weaker, post-cratering soil profile has developed on the ejecta blanket. A continuous blanket of ejecta extends outward to an average of 1350 m from the crater’s rim. Beyond this, discontinuous patches of ejecta and large secondary craters can be found as far out as three kilometers. The continuous ejecta blanket slopes very gently (2-60) away from the crater and has a somewhat hummocky surface that appears to be an original characteristic rather than an erosional modification. In fact, there has been remarkably little post-cratering erosion of the ejecta, presumably due to the very gentle slopes and stabilizing cover of vegetation. The uppermost layer of ejecta, containing shock-melted fragments, is preserved as a thin discontinuous deposit and the present edge of the blanket is in, approximately, its original location.
The present crater floor is occupied by unconsolidated sediments and is almost flat, ranging in elevation (above sea level) from 475m near the base of the inner rim wall to 468 m in the central area. A broad, shallow, saline lake, which contracts and expands with the seasonal precipitation, overlies the sediments. This lake is also fed by several permanent springs issuing from the floor and rim of the crater.
The maximum elevation of the rim crest is somewhat more than 600 m but almost all the crest is much closer to 590m. the slope of the inner rim wall averages 26o and there is a thick layer of debris covering much of it, especially the lower portions. However, gullying is only modestly developed except where a large spring issues in the village of Lonar. Here the rim crest has been cut back sharply and a deep gully leads into the crater. Ignoring this erosional feature, the rim crest diameter varies from a maximum of 1875 m to a minimum of 1787 m – the average value being close to 1830 m. The circularity index (“…the ratio of the area of an inscribed circle to the area of an circumscribed circle fitted to the outline of the crater rim crest” [Pike, 1974a] of the crater is 0.90. This index was derived from the latest topographic map of the crater (scale 1:5000). It is among the highest thus far measured for impact crater on both the Earth and Moon (Pike, 1976, 1977). In most of the rim wall, bedrock dips away from the crater at low angles (8-20o). there are, however, sharply bounded patches in which bedrock is overturned to attitudes approximately parallel to the rim wall slope. Similarly, although most of the debris on the rim crest is fragmentary and chaotic, coherent, overturned units of ejecta present an inverted stratigraphy in certain areas. The black, clayey, pre-crater soil caps the upturned top of the basalt sequence at about the 585 m level in the northeastern segment of the rim wall. Debris overlying this soil averages 5 m in thickness at the crest. The same horizon, exposed in the gullies south of the crater at the 560 m level, is too far out(>1 crater radius) to be uplifted and must delineate the approximate level of the pre-impact surface. The present rim, them, averages 30 m in height, of which about 25 m is uplifted bedrock and about 5 m is ejected debris. The crater floor now lies – 120 m below the present rim crest. A new theory of formation which was proposed was of vertical subsidence of the ground . The LONAR crater has water in it is the biggest meteoric crater which has BASALT in it and has water in it. The lake is deep and one cannot make out whether it is a crater until one comes to the edge of crater . The crater has a large slope and there is a dense forest in this region. The two slopes within the crater out of that one is of 15 to 18 degrees while the other one measures of 30 degrees. This shows that it is a Meteor crater e.g. when a metal ball is thrown in sand in a certain direction in which the ball hits the sand gets little small while the opposite side to it increases. The slope measuring 15-18° has a notch through which the meteor came. The opposite side of slope increases due to the pressure created by the meteor and by the remains of the notch side blown away . The water in the crater is very salty. It is 10 times saltier than drinking water (pH = 10.5 ). Salts and Minerals like sodium, chloride, carbonates, flourides and bicarbonates are found. These are found by the small streams of water joining the crater. Then streams bring water as well as salts and minerals with them. But as this water does not drain away these substances get collected beneath the surface. Some 4 years back , water from the Lonar lake had evaporated . The villagers witnessed some crystalline form of these salts and minerals. In such conditions one cannot think of any living organisms.

MICROBIOLOGY OF LONAR LAKE

Microorganisms like Arthorospira and algae are found abundant. We also found Spirullina, Closterium, Chlorella, Eudorina and Ankistrodesmus in the water. Various bacteria’s are also presnt.Algaes are found in abundant near the sides of lake.Distinct layers of Dried Algae, Green Algae and Newly forming Algae are seen. Spirulina sp., growing in high alkaline conditions is an interesting area which has been studied. We have successfully studied various microbiological interactions at extreme conditions. The organisms isolated included Bacillus sp., Pseudomonas sp., Serratia sp., Azatobacter sp., etc. All the microorganisms found in the garden flora are found in the Lonar lake water as well as soil samples. The Lonar lake microorganisms interestingly are categorized as alkalophiles (microorganisms growing in high alkaline conditions). Though the temperature optima for these bacteria essentially have been in the mesophillic range some isolates have shown the thermo tolerant character. One interesting study revealed that phosphate solublisation (rock phosphate) took place at an high alkaline range. The microorganisms have exhibited a dual character, especially with the fungal isolates. Till now we have isolated and characterized fungi like Aspergillus oryzae, A. niger, Penicillium notaum, Mucor, Rhizopus, etc. Though these fungi grow in an alkaline conditions (normally fungi love to grow in acidic conditions) most of their biochemical activities have been in the near neutral to alkaline conditions. Biochemical activities of all the fungi and the bacteria seem to be come to an end in the acidic conditions of their growth.