North Korea: Putin In 'Chernobyl' Warning

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9. Doesn't happen with air bursts, only with ground bursts.

If the nuclear fireball touches the earth, then there will be many tons of fallout. If the nuclear fireball stays in the air, then there will be very little fallout.

Your picture is of a ground burst.

Air busts are militarily more useful as the blast effect is magnified by blast being reflect from the earth and being combined with the direct blast wave, causing more destruction one the ground and at a greater distance of about 40%. Since the fireball doesn't touch the ground, troops can quickly move into the area. However, if the target is underground then a ground burst sends a shock wave through the ground, but greatly contaminates the place.