Lonar Crater Is 1.88 km Wide and Cut Into 66-Million-Year-Old Deccan Basalt, and Two Peer-Reviewed Ages Put Its Impact at 37,500 and 570,000 Years Ago

Lonar Crater, in Buldhana district of Maharashtra, is a bowl 1.88 km across and about 150 m deep that an impact punched into Deccan lava flows, and a salt lake now fills its floor. Nobody has settled when it happened. A 2011 argon study dated the impact to 570,000 years ago, and a 2014 study based on cosmogenic nuclides dated it to 37,500 years ago.

A 2023 review in the journal Earth-Science Reviews describes it as the best-preserved terrestrial hypervelocity impact crater in basaltic terrain. Jourdan and colleagues note that most impacts in the inner solar system hit bodies covered by primitive igneous rocks like basalt, while most craters on Earth sit in other rock types, which makes Lonar a closer model for craters on the Moon and Mars.

A bowl cut into 66-million-year-old lava

Jourdan and colleagues, writing in Geology in 2011, give the diameter as 1.88 km and say the crater sits on the Deccan basaltic traps, lava flows about 66 million years old. They call it one of the very few craters on Earth emplaced directly on basaltic lava flows. NASA’s Earth Observatory gives an average diameter of almost 1,830 m, a depth of about 150 m and a rim that rises roughly 20 m above the surrounding land. NASA dates the basalt to some 65 million years ago.

The Deccan flows are the same family of rock that the masons of Ellora carved. The Kailasa temple at Ellora was cut downward out of a basalt slope, and the caves described in Ajanta and Ellora, carved from rock lie in the same Deccan lava country.

How a volcano suspect became a confirmed impact

NASA says a British officer, C. J. E. Alexander, identified the crater in 1823. Because it lies in a volcanic basalt field, some geologists took it for a volcanic crater.

The case for impact rests on shocked rock. In a 1973 paper in Science, K. Fredriksson and co-authors reported drill holes through the crater floor that struck coarse breccia (rock broken and recemented) showing shatter coning, the cone-shaped fractures a shock wave leaves, and microbreccia containing maskelynite. Trenches on the rim yielded strongly shocked fragments in which the mineral plagioclase had melted and bubbled, along with bombs and spherules of rock melt. NASA describes maskelynite as a natural glass formed only by extremely high-velocity impacts, and calls it perhaps the most compelling evidence. The 1973 authors added that Lonar was the only known terrestrial impact crater in basalt and that its microbreccias and glass spherules had close analogues among the Apollo samples.

What the rim and the ejecta kept

A team led by Adam Maloof of Princeton published a one-metre-resolution elevation model and geological map of the crater in the Geological Society of America Bulletin in 2010. They found upturned basalt flows in the upper crater walls and rim folds that lie over on themselves, with the fold hinge still preserved around 10 to 15 per cent of the rim. The continuous blanket of ejecta, the debris thrown out of the crater, shows little stream erosion. The authors liken its emplacement to a ground-hugging debris flow and note that its thickened outer edge resembles fluidised ejecta on Mars.

The 2023 review adds details from later work. Spherules from the ejecta carry a chemical signature that points to a chondritic impactor, a stony asteroid. A few zircon grains of about 3.0 to 3.1 billion years in an impact breccia, together with quartz grains showing impact damage, show that the blast reached down into the ancient Peninsular gneiss beneath the lava, which the review puts at a penetration of 522 to 570 m. It also cites a study that put the crater’s cumulative rim erosion at 30 m.

Six dates for one impact

The sources lay out the dating attempts as follows, in the summary given by Ray and Misra in 2014 unless another paper is named.

• Thermoluminescence, a method that estimates when minerals were last heated, on three impact-melt bombs from the rim: a mean of 52,000 years with an error of 6,000 (Sengupta and colleagues, 1997).
• Fission tracks in three impact-glass samples: 15,300 years with an error of 13,300, a spread Ray and Misra attribute to the small number of tracks counted (Storzer and Koeberl, 2004).
• Radiocarbon on soil buried under the ejecta: a minimum age of 11,650 years (Maloof and colleagues, 2010). Radiocarbon on lake sediment gave 15,000 to 30,000 years, but the sediment carried modern carbon, so those dates are read as minimums.
• Argon dating of four melt-rock samples: 570,000 years with an error of 47,000 (Jourdan and colleagues, 2011).
• Cosmogenic beryllium-10 and aluminium-26, produced when cosmic rays hit surface rock, on quartz pebbles from the rim and ejecta: one pebble gave about 37,500 years, read as a minimum.
• Radiocarbon on soil from before the impact, west of the crater: a maximum of 40,700 years with an error of 700 (Nakamura and colleagues, 2014).

Jourdan’s team ran 12 step-heating experiments on four melt-rock samples and combined them into a global inverse isochron, a way of separating trapped argon from argon made by decay since the rock cooled. Their abstract notes that earlier non-isotopic work gave much younger ages of roughly 12,000 to 62,000 years, on rocks they considered affected by secondary processes. They also report an argon-40 to argon-36 ratio of 296.5 with an error of 1.7, indistinguishable from air, which they take to mean the melt rock holds no inherited argon from before the impact.

Nakamura’s group combined the exposure ages with the pre-impact soil date to estimate 37,500 years with an error of 5,000. Their abstract says this conflicts with the 570,000-year argon age and suggests that argon inherited by the impact glass may have skewed it. The authors also report that the pattern of exposure ages differs from that at Barringer Crater in Arizona, which indicates that Lonar’s rim is actively eroding.

Published summaries do not agree on where this stands. Ray and Misra wrote that the age is not yet conclusively known. The 2023 review says that, based on the cosmogenic dating, the age is determined as 37,500 years with an error of 5,000. NASA’s page gives 35,000 to 50,000 years, and the Ministry of Tourism’s Incredible India page gives about 52,000 years.

A soda lake and a Ramsar listing

The Ramsar Sites Information Service lists Lonar Lake as site 2441, designated on 22 July 2020, with an area of 427 hectares. Its description calls the wetland an endorheic basin, meaning a closed one with no outlet, almost circular and formed by a meteorite impact onto basalt. The site includes the lake, the escarpments that form the crater walls and forested zones. The lake is high in salinity and alkalinity because water leaves only by evaporation, and the sheet names anaerobes, cyanobacteria and phytoplankton among the organisms that survive in it.

The same record counts 160 bird species, among them the vulnerable Asian woollyneck and the common pochard, 46 reptile species and 12 mammal species, including the grey wolf. It lists household sewage, urban wastewater and unsustainable tourism as threats. The Indian Wetlands Portal factsheet names the Maharashtra Forest Department as the managing authority and records protection as a national geo-heritage site and the Lonar Wildlife Sanctuary. The Free Press Journal reported the listing on 13 November 2020.

For another Indian wetland with a long Ramsar record, see Chilika Lake, and for the list’s growth since 2020, see India’s October 2026 Ramsar additions.

The 2020 pink water

In 2020 the lake water turned pink. On 22 July 2020 PTI reported, in The Tribune, that a probe by the Agharkar Research Institute in Pune had traced it to a large population of haloarchaea, salt-loving microbes that make a pink pigment. The state forest department had told the Bombay High Court that it sent samples to the National Environmental Engineering Research Institute in Nagpur and to Agharkar. The institute’s director, Prashant Dhakephalkar, said the team first suspected red-pigmented Dunaliella algae.

He said higher salinity and pH favoured the microbes, that a settled sample cleared as the biomass sank, and that the colour was fading as the monsoon diluted the lake and green algae returned. He also noted that flamingos visiting the lake take up carotenoid pigments from such food.

A 2016 survey of the lake’s microbes in Frontiers in Microbiology, by Dhiraj Paul and colleagues of the National Centre for Cell Science in Pune, found Proteobacteria at 30 per cent, Actinobacteria at 24 per cent and Firmicutes at 11 per cent of the community. The authors call Lonar a hypersaline and hyperalkaline soda lake and the only meteorite impact crater in the world situated in basalt rocks.

Heritage status and visiting

A Ministry of Mines reply in the Rajya Sabha on 9 March 2016, published by the Press Information Bureau, says the Geological Survey of India declares geo-heritage sites and national geological monuments for protection and maintenance. Its annexure of 32 sites lists Lonar Lake, Buldana district, under Maharashtra. The reply says the Geological Survey or the state governments take measures to protect them.

The Incredible India page, checked on 28 October 2026, gives the site’s hours as 6 am to 6 pm. It says temples around the rim date to the sixth century CE and that the nearby Daitya Sudan Temple is in the Hemadpanti style. It adds that local people regard the lake as sacred and associate it with Lord Vishnu.