According to RT.com:
More than 4,000 tons of shells exploded near a military testing ground some 40 kilometers from the city of Orenburg in Central Russia, prompting the mass evacuation of two nearby towns.
Those 4,000 tons included 1,379 tons of 100mm shells, 400 tons of air bombs and 2,300 tons of 280mm reactive shells, the head of the military investigative committee announced.
Witnesses recorded video of a massive plume of smoke rising into the air shortly after the explosions. Local residents said that the blasts were powerful enough to rattle windows dozens of kilometers away from the epicenter.
All documents from EUCOM [4 Pages, 0.6 MB] – Although mostly blacked out from “non-responsive” expemptions, this shows what is available, along with photos.
All documents from the National Geospatial Intelligence Agency [6 Pages, 0.9 MB]