One second after detonation, the fireball was over 4 miles wide. Despite the high altitude of the test, the fireball swelled down to the Earth’s surface almost licking the ground. The shockwave of the blast almost killed the crew of the Tu-95 that dropped the plane as the fireball almost reached the height of the release plane. Despite cloudy skies,
the flash of light was clearly visible 1,600 miles away. The shockwave destroyed buildings and tore roofs off of homes
hundreds of miles from ground zero. Windows
in Norway and Finland were
shattered. The scientific settelment on the Matochkin Strait called Severney, some 35 miles south of the explosion, was devastated. The thermal pulse of the blast was felt
500 miles from the epicenter....
http://www.atomicforum.org/russia/tsarbomba.html