Mushroom cloud is formed only a split second after the bomb explodes and can travel very fast. The small 20-kiloton nuclear weapon dropped at Hiroshima took in a split second 70, 000 lives. Another 70,000 were injured and many died later and continued to die for years after as a result of radiation exposure.
 Why should I be aware of this?
Thermal radiation can cause eye injuries and severe "flash burns which were the cause of twenty to thirty percent of the deaths in Hiroshima and Nagasaki. Many fires that destroyed much of Nagasaki and Hiroshima were also caused by thermal radiation.
 Mushroom cloud and health
The effects of radiation may not be seen for many years. Health effects can be mild (such as skin reddening) or serious (such as cancer and death). The severity of the effects depends on --
- The dose of radiation absorbed by the body
- The type of radiation
- The route of exposure
- The duration of exposure
- Exposure to very large doses of radiation may cause death within a few days or months.
- Exposure to lower doses of radiation may lead to an increased risk of developing cancer or other adverse health effects.
 All about mushroom cloud
Mushroom clouds are created as a result of the sudden formation of a large mass of hot low-density gases near the ground. The mass of gas rises rapidly, and turbulent vortices curl downward around its edges and draw up a column of additional smoke and debris in the center to form its "stem". The largest mushroom clouds to be photographed resulted from the impact of fragments of Comet Shoemaker-Levy 9 on planet Jupiter, some of which rose hundreds of kilometers above the cloud layers.
On release of a significant amount of explosive energy and heat, a mushroom cloud is generally formed. An Atomic Bomb is detonated several thousand feet in the air over its target and does not hit the ground and explode. Ground detonation would force much of the bomb's destructive force into the earth and not through the buildings above it. The force of this blast instantly pulverizes anything in the blast area into dust and debris. Meanwhile, a ball of super hot gases forms instantly in the sky, which destabilizes the surrounding air and creates powerful currents.
 Fireball rises very quickly
The fireball rises very quickly as it is very hot and thus less dense than the surrounding air. While it is rising the fireball leaves a column of low-pressure which acts as a chimney, sucking in smoke, dust and debris from the surroundings. This forms the stem of the mushroom.
In the beginning the hot air and dust mixture rises vertically, forming the column of the cloud. It gradually cools when hot cloud meets the colder air at higher altitudes. On reaching the temperature of the surrounding air, the cloud ceases to rise, but spreads horizontally along air levels at the same altitude, which are at the same temperature. This forms the cap of the mushroom.
Under the right conditions, a few large conventional bombs can create small mushroom clouds. But nuclear explosions and major volcanic eruptions are capable of creating large and visible mushroom clouds.
 Effects of radioactive fallout
Radioactive material from the nuclear device mixes with the vaporized material in the mushroom cloud. As the vaporized radioactive material cools, it forms particles, such as dust. The radioactive material then falls back to the earth, a process known as fallout. Because fallout is in the form of small particles, it can be carried long distances by the wind and end up miles from the site of the explosion. Fallout is radioactive and can cause contamination of anything on which it lands, including food and water supplies.
 What can I do?
Some basic ways to reduce exposure to radiation include the following:
- Spend as less time as possible near the source of radiation
- Stay as far away as possible from the radiation source
- Create more barriers between you and the radiation source. The type of barriers you need will depend on the type of radiation.
- People staying in the vicinity of the radiation event are advised to stay home and take shelter to protect themselves from exposure to the radiation outside.
- Mushroom cloud
- What is radiation?
- How the Atom Bomb Works
 Additional Information
- See pictures of Atomic Bomb Cloud over Hiroshima and pictures of other destruction caused by the explosion.
- See animation of a mushroom cloud and take a Tutorial on how to make such animation
- See Effects of Nuclear Weapons