any of three rivers in Russia, in central Siberia, all tributaries of the Yenisey: the Lower (Nizhnyaya) Tunguska 2690 km (1670 miles) long; the Stony (Podkamennaya) Tunguska 1550 km (960 miles) long; the Upper (Verkhnyaya) Tunguska which is the lower course of the Angara. The area was the scene in 1908 of a massive explosion believed to have been the result of the disintegration in the atmosphere of a small comet or meteorite