What defines a surface blast in terms of nuclear explosions?

A surface blast is characterized primarily by its devastating impact, making it the most damaging type of nuclear explosion. This type of explosion occurs when a nuclear device is detonated at or near the surface of the earth, leading to significant energy transfer to the ground and the resulting shock wave causing extensive destruction over a wide area.

Surface blasts generate a massive pressure wave combined with the heat and radiation produced by the explosion, which can lead to widespread devastation. The energy is concentrated at the ground level, leading to the creation of a crater and considerable secondary effects, such as fallout from the vaporized soil and debris.

The other aspects, such as altitude (high altitude explosions), crater formation (which could occur but is not exclusive to surface blasts), and a minimal blast radius, do not encapsulate the primary defining characteristic of a surface blast. The destructive capability and the extent of damage it inflicts on structures and the environment are what truly define a surface blast as the most damaging type of nuclear explosion.