1) Lower Tunguska
(Russian: Nizhnyaya Tunguska)
River in Siberia, a tributary of the Yenisei; 2989 km long. The Lower Tunguska cuts through the Central Siberian Mountains. In its upper course, it runs through deep valleys with many waterfalls. In its lower course, it expands into large lakes.
Frozen from October to May, the Lower Tunguska is navigable during the spring up to the settlement of Tura.
2) Stony Tunguska
(Russian: Podkamennaya Tunguska)
River in Siberia, a tributary of the Yenisei; 1865 km long. The Stony Tunguska, like its namesake above, cuts through the Central Siberian Mountains, running in deep valleys with many waterfalls. Frozen, too, from October to May, the Stony Tunguska is navigable for over 1145 km during spring.
3) The Tunguska Incident
Explosion in the atmosphere above the Siberian tundra, near the Stony Tunguska river, on June 30, 1908.
Although a number of wacky theories have been presented to account for the explosion, and much myth surrounds it, the consensus among serious scientists is that the explosion was astronomical in origin. It is generally considered likely that an astronomical object (probably made of ice, possibly a cometary fragment), observed over China and Lake Baikal, exploded at an altitude of about 8 km.
The Tunguska explosion released energy corresponding to approximately 13 megatons, devastating an area of about 2000 km2. Trees were knocked over at up to 52 km from the epicenter, and the pressure wave from the impact travelled twice around the globe.
The first scientific expedition to Tunguska, led by L. Kulik, arrived at the remote area in 1927. Attempts at that time (and since) to locate a crater have been fruitless. Likewise, examining core samples from Greenland's ice cap has not produced any traces of iridium, generally considered a reliable indicator of cosmic impacts, for the years 1908 to 1910. A Danish/Russian team, working in 1999, determined that the traces of iridium and carbon in samples from the site indicated that the object had to have been composed of very pure ice, which would also account for the lack of a crater - since such an object would have disintegrated entirely through atmospheric friction. | 
