Specifically, when you detonate a nuclear bomb underground deep enough that it doesn’t open to the surface, what is left inside that hole?
Rock vaporizes, but how long will it remain so? Will it eventually cool down and condense/solidify back? Then there is no hole left.
While in gas, It should be a lot of gas, right? What orders of pressure are we talking about?
Anyways, please walk me through the basic physical changes that happen in such detonation.
What’s left afterwards depends on lots of factors, but in the case of 1964 Salmon test in Mississippi the deliberate result was a spherical cavity deep underground. This was then used to contain a second test, Sterling, two years later.
In between a camera was lowered down the narrow shaft originally dug to put the bomb in place and into the new cavity. There’s not that much to see, but the rather eerie resulting footage is included in this extract from Peter Kuran’s documentary Atomic Journeys.
This article has more about these tests.
Depending on the nature of the ground where the explosion occurs, the hole either fills in, leaving a crater, or it stays expanded a little, leaving what’s called a “retarc”, or reversed crater (hence the clever name).
Take a look at the Nevada Test Site to get an idea of what the craters look like.
More detailed info, including the retarc explanation:
http://nuclearweaponarchive.org/Library/Effects/UndergroundEffects.html
Thanks for the responses. I had wikied it before posting and seen some other sites. My question is more about the physics of what’s happening. A lot of solid earth is being turned to gas. Where does that gas go in a contained explosion that doesn’t vent to the surface? Does it eventually cool back to liquid and then solid? Why or why not? Clearly the problem here is a big gap in my understanding of the physics surrounding the event. Anyone?
Hilarious!
Not really. You’ll compress and liquify some rocket but very little will become gas, and most of it will condense back down pretty quickly. Underground nuclear explosions are also substantially different in character than airburst or even ground burst; because there is only a small mass of air to absorb x-rays and neutrons the blast is significantly attenuated, and most of the energy becomes direct thermal heating of the rock. And most underground explosions are not typically full-scale tests but rather subscale tests to validate aspects of the design (hydrocode simulation, practical yield for a given thickness and compression, one point safe criteria). The big billowing mushroom cloud you see in above ground surface explosions and the resulting pressure wave is due to thermal expansion of the atmosphere and differences in atmospheric density at altitude.
Stranger
One of the posted links goes into great detail about this. In summary form, you have a small amount of rock vaporized, a small amount melted, and mostly a lot of it compressed and/or moved around. The “retarc” is the perfect example, resulting when the blast is deep enough that it can’t erupt through the surface, but shallow enough that it still thrusts the rock up in a visible manner. Part of what happens illustrates the fact that rock is more plastic than we usually give it credit for.
Ok, I just found that the hole is a lot smaller than I thought (around 100 feet). The mass displaced to make that hole simply goes into compressing the rock around it. Very cool.
