weBLOGic

It is the world’s biggest crater in basaltic rock. Located in Buldhana district of Maharashtra, India. Co-ordinates: 19 degrees 87 minutes longitude (N) and 76 degrees 43 minutes latitude (E). Scientists estimate its age to be ~50000 years. The meteorite hit the Deccan basaltic trap near Buldhana. The thickness of basaltic rock around this region is believed to be between 30 to 1000 meters. The basaltic rock is in many layers or flows in this region[1]. These flows were created by volcanic activities over several million years.

The meteorite hit created the crater which is about 165 meters deep and 1830 meters in average diameter. This meteorite hit exposed a few basaltic layers at the rim of crater. The elevated rim around the crater is 12 to 15 meter in height. It is covered with 5 meter ejecta over it. The rim can be clearly seen in the satellite image[3]. The rim is mostly made of ejecta blanket spread over the distance of 1.5 kilometers around the crater with slope of 4-7 degrees and approx 15-30 degrees inclination at the inner edge of the rim.

Early in the 19th century, when a scientist pointed out this crater, it was believed to be a volcanic crater. Almost one and a half century this belief was intact. In 1961 two scientists named N. C. Nandy and V. B. Deo. They found breccia in drilling done at site. Breccia is another feature of shocked rocks found in impact craters.

This inference was reasserted by the studies conducted by Eugene C Lafond and Robert S Dietz in 1964. They conducted a survey and studied the crater. Based on their study they concluded that the crater is not of volcanic origin but it is of impact origin.

For the support of their conclusion they provided several reasons.
1 The crater is highly circular in diameter and has a characteristic depth-to diameter ratio of an impact crater.
2 The crater has a raised rim, about 20 m above the surrounding.
3 The surrounding rock dips away from the crater edge at inclinations of 15-30 degrees.

The theory of impact crater was further affirmed when V. K. Nayak of Center for Advanced Studies in Geology, University of Sagar, M.P., India, found glass like objects near the site. In drilling he also found breccia with shocked features, broken and twisted, highly oxidised. All these features indicated towards high velocity impact.

In 1973, some US scientists along with India scientist from GSI worked together to establish its impact origin. They discovered breccia with shatter cones and material containing maskelynite. Maskelynite formation requires very high pressure almost 4 lakh times the average atmospheric pressure on the Earth. And this is created only during hypervelocity impact. No volcanic process can form maskelynite. Thus impact origin of Lonar crater was proved. Three other scientists estimated its age to be about 52000 years.[4]

[1] http://www.virtualexplorer.com.au/journal/2003/12/tewari/
[2] http://www.mantleplumes.org/Deccan.html
[3] http://www.whoi.edu/hpb/viewImage.do?id=20170&ppid=153&sid=67&cl=2&isProj=1
[4] http://www.khagolmandal.com/index2.php?option=com_content&do_pdf=1&id=4