How Nuclear test are done underground

[r.vittalkiran]

Many countries have been found building Nuclear weapons,
I want to know how Nuclear test are done underground, and doesn't it cause any damage?
Many countries do test Missiles(firing them towards sea), are they loaded ones/ unloaded missiles?

WONT NUCLEAR TEST'S CAUSE DAMAGE​

 

[QuantumPion]

If a nuclear test is conducted sufficiently deep underground, only a small amount of radiation is released to the environment. An underground test can create a cavity up to several hundred meters in diameter. Soon after the test, the cavity collapses in on itself which may cause a small surface crater as well, depending on the depth. Nuclear bombs are not powerful enough or detonated deep enough to cause earthquakes or any other significant geological effect.

Ballistic missile tests performed by North Korea and Iran are not loaded with warheads, they are testing the functionality of the launch and guidance system.

 

[K^2]

Do they always collapse? I think I saw a show on TV once where they sent a crew down into one of these cavities, decades after the test, of course.

Maybe I'm thinking of something else.

 

[QuantumPion]

I don't know. A cavity from a low yield device at a relatively shallow depth might remain intact.