In February, a meteor entered the Earth's atmosphere over Chelyabinsk, Russia and exploded, producing a shockwave blast that damaged hundreds of buildings around the explosion site in Russia.
But why did it explode? Why didn't it simply burn instead?
Same reason as the explosion at the Tunguska event years ago: Pressure, due to boiling water.
Meteors usually cme into our atmosphere at incredible speeds. At these speeds, the meteor is highly affected by the viscosity of air and is heated by compression (and a little bit of friction).
This starts boiling the ice present in the meteor, leading to a pressure buildup. If the conditions are right, it can just explode.
See also: http://www.nature.com/nature/journal/v361/n6407/abs/361040a0.html , https://physics.stackexchange.com/q/76045/7433
The meteorite decelerated from perhaps 30000 mph through friction and impact with the atmosphere, and this made it heat up to an incredible temperature. At this point the rock was boiling and burning, and liquids within it , such as water, became gaseous.
Some small explosions cast off burning pieces of the meteorite, and the major explosion was from the larger chunk being stressed beyond breaking point through pressure from the gases within.
