Sudden annihilation
Most Life forms in the target zone are immediately annihilated. In Hiroshima, everything within a 4.4 square mile radius of detonation was decimated. Surviving humans and animals in Hiroshima sustained radiation poisoning, severe burns and injuries from flying shrapnel. Similar casualties occurred in Nagasaki after it was bombed. In nearby area, trees were uprooted, snapped off, scorched and stripped of leaves.
Firestorm
The blast created a fireball 1200ft in diameter which rapidly spread. This drew in a lot of air and a strong wind formed around the fire causing it to surge forward. As the draft increases more oxygen will be drawn in and this increases combustion and also feeds the flame. The heat created by the firestorm resulted in a lot of radiated heat which also caused things ahead of the firestorm to catch fire. A lot of buildings in Hiroshima were also made of wood which caught fire easily resulting in the fire spreading very quickly. While there were small fires in Nagasaki after Fat Man was dropped, there was no firestorm and this was due to the difference in terrain between Hiroshima and Nagasaki. Hiroshima is relatively flat while Nagasaki has uneven terrain and this prevented the fire from spreading to the extent it did in Hiroshima.
nuclear FAllout
The detonation of a nuclear bomb injects radioactive particles into the atmosphere that eventually fall to Earth. A wide range of biological changes may follow the irradiation of animals. This varies from rapid death due to high doses of penetrating whole body radiation to people leading normal lives for a variable period of time until the development of delayed radiation effects.