The shock wave of a weapon detonated on the ground will produce, as an effect of the explosion, a crater and the material removed will partly deposit itself on the crater's ridge and in part it will raise itself into the atmosphere giving shape to the characteristic nuclear mushroom; this material will subsequently fall somewhere else on the ground in the form of fallout. The crater generated on a soft soil from an 1-megaton explosion would have an internal diameter of 640 meters, an external diameter of 1,200 meters and a depth of 30 meters. The effects of the shock wave, directly and indirectly, are extremely destructive both for the structures, life forms and vegetation which it meets on the area covered by its action.

Fallout - The overheated gases caused by a nuclear explosion expand externally over ground zero and at the same time rise up into the atmosphere. This motion coincides with the motion of the air which is sucked into the temporary vacuum caused by the shock wave and by the rising of the fireball which will ascend at an initial speed of 111 meters per second,. i.e., 400 kilometers per hour. If the fireball contacts the ground beneath a large quantity of earth, debris and dust are sucked in. If only 5 percent of the fireball contacts the ground beneath, about 20,000 tons of earth are pulverized and raised up into the atmosphere . All this, together with the incandescent gases and smoke generated by the explosion, will form the typical nuclear mushroom resulting from an explosion on the ground or close to it. Explosions below 100 kiloton will not have sufficient energy to raise the resulting mushroom above 12,000 meters in the atmosphere and hence they are confined to the atmospheric region known as troposphere. Explosions in excess of 150 kiloton will penetrate the tropopause, i.e., the region which separates the troposphere from the stratosphere, while the explosion of a 10-megaton weapon will raise the fireball and the mushroom conformation up to 33,000 meters in the atmosphere.
When the materials sucked up due to the explosion reach the center of the fireball, they are completely vaporized and they mix with the highly radioactive, as well vaporized, residues of the weapon; at the same time this atomic cauldron is bombarded by the enormous flux of the electrons emitted within the first seconds of the explosion. As the fireball cools down and the effects of the heat attenuate the vaporized mass re-condenses itself into particles of solid materials which assume the form of dust of diverse dimensions and configurations. This dust may resemble snowflakes, sand or specks of talcum powder in relation to the case and, in the case of high power explosions, it will have microscopic dimensions. This radioactive dust is called fallout. Particles of fallout of considerable size fall rapidly to the ground, others, depending on their size, will fall to the ground within days, weeks, months or years, depending on their size and the weapon's power.
About 300 different radioactive elements have been identified within the radioactive dusts, or fallout. These substances are known as radionuclide, or radioisotopes. Apart from the fact that each of these radionuclide emits nuclear radiations, they have the same chemical conformation of similar non-radioactive elements. Some of them simulate the properties of elements fundamental for the biological life and therefore the inhalation or assimilation of those substances is a serious menace for the health of men and animals.