Lonar crater lake

A meteorite hit the Deccan basalt in Maharashtra and left a crater with a lake in it, and the rock is the reason geologists care: this is one of only four hypervelocity impact craters known in basalt anywhere on Earth, and the other three are in Brazil. Basalt resists cratering, so this is one of the few places you can study what an impact does to the kind of rock that covers much of the inner solar system. The age has moved: it was long put at 52,000 years, and argon-argon dating now says about 576,000. There is no outflow, so evaporation has concentrated the minerals into two layers that do not mix, an outer ring at pH 7 and an inner body at pH 11. In June 2020 the whole lake turned from green to red in a matter of days, which turned out to be Halobacterium and carotenoids blooming as the water dropped and the salinity rose. Temples ring the shore, including Daitya Sudan, built on the story of a giant killed here.