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10 Physical Effects of Nuclear Weapons
Mach effect noted above and it increases the force of the blast, making the weapon
more destructive to a greater distance than for a weapon of a comparable detonated
on contact with the surface.
In addition to having a stronger blast wave, an airburst can expose a greater area
to the pulse of thermal radiation, provided the altitude of detonation is greater than
the height of any terrain or structures that might block the line of sight from a lowaltitude or surface burst. Thus, the radius of the mass fire ignited by an air burst is
likely to be larger than that from a surface burst.
While the blast from an air burst is stronger than from a surface burst this is
due in part to the Mach effect. Accordingly, air bursts do not produce a large crater
and, indeed, most produce no crater whatsoever. However, when the blast wave from
an air burst slams into the ground it can transmit that force to the rocks and soil
beneath. This shock will be transmitted through the soil to the underlying bedrock
and to anything buried within the soil, including utility lines, basements, subway
tunnels, and so forth. Shock is transmitted most effectively through rock and tightly
packed soil and least effectively through loose soil, sand, and other less consolidated
materials.
While a high-altitude airburst (greater than about 30 km) produces the most widespread EMP effects, intermediate-level airbursts (from several hundred meters to a
few tens of km) are the least effective at causing EMP [1]. Thus, an airburst intended
to maximize blast and thermal effects will produce little EMP while one designed to
maximize EMP effects will cause only minor blast and thermal damage.
10.2.2 Surface Burst
The fireball from a detonation on the ground is likely to be somewhat smaller than for
an airburst as the ground will absorb much of the weapon’s radiant energy [1]. In a
surface burst, much of the fireball’s thermal energy goes into vaporizing the ground
and structures in close proximity to the site of the detonation and the remaining
energy powers the blast wave and the thermal pulse. The blast wave will be less
powerful than that from an air burst because, without a reflected shock, there is only
the power of the primary shock to cause damage. These are all notable differences,
but the most important differences are in other areas:
• EMP
• Cratering and shock transmitted through the ground
• Radioactive fallout.
The EMP effects of a surface burst are shorter-ranged but more intense than for
an intermediate-altitude air burst. The shorter range is a result of the need to have
a “line of sight” from the site of the detonation to the parts of the atmosphere that
are ionized; the horizon (the part of the Earth’s sphere that we can see) is closer at
lower elevations, as are the parts of the atmosphere that can be exposed to gamma
radiation traveling in a largely straight line. On the other hand, more material—the
10 Physical Effects of Nuclear Weapons
Mach effect noted above and it increases the force of the blast, making the weapon
more destructive to a greater distance than for a weapon of a comparable detonated
on contact with the surface.
In addition to having a stronger blast wave, an airburst can expose a greater area
to the pulse of thermal radiation, provided the altitude of detonation is greater than
the height of any terrain or structures that might block the line of sight from a lowaltitude or surface burst. Thus, the radius of the mass fire ignited by an air burst is
likely to be larger than that from a surface burst.
While the blast from an air burst is stronger than from a surface burst this is
due in part to the Mach effect. Accordingly, air bursts do not produce a large crater
and, indeed, most produce no crater whatsoever. However, when the blast wave from
an air burst slams into the ground it can transmit that force to the rocks and soil
beneath. This shock will be transmitted through the soil to the underlying bedrock
and to anything buried within the soil, including utility lines, basements, subway
tunnels, and so forth. Shock is transmitted most effectively through rock and tightly
packed soil and least effectively through loose soil, sand, and other less consolidated
materials.
While a high-altitude airburst (greater than about 30 km) produces the most widespread EMP effects, intermediate-level airbursts (from several hundred meters to a
few tens of km) are the least effective at causing EMP [1]. Thus, an airburst intended
to maximize blast and thermal effects will produce little EMP while one designed to
maximize EMP effects will cause only minor blast and thermal damage.
10.2.2 Surface Burst
The fireball from a detonation on the ground is likely to be somewhat smaller than for
an airburst as the ground will absorb much of the weapon’s radiant energy [1]. In a
surface burst, much of the fireball’s thermal energy goes into vaporizing the ground
and structures in close proximity to the site of the detonation and the remaining
energy powers the blast wave and the thermal pulse. The blast wave will be less
powerful than that from an air burst because, without a reflected shock, there is only
the power of the primary shock to cause damage. These are all notable differences,
but the most important differences are in other areas:
• EMP
• Cratering and shock transmitted through the ground
• Radioactive fallout.
The EMP effects of a surface burst are shorter-ranged but more intense than for
an intermediate-altitude air burst. The shorter range is a result of the need to have
a “line of sight” from the site of the detonation to the parts of the atmosphere that
are ionized; the horizon (the part of the Earth’s sphere that we can see) is closer at
lower elevations, as are the parts of the atmosphere that can be exposed to gamma
radiation traveling in a largely straight line. On the other hand, more material—the