system
Given the following post, respond as if you're commenting on Reddit:
human
In light of recent events in North Korea, how do you set off a nuclear bomb underground without causing substantial damage above the blast site?

Reports saying that this was a hydrogen bomb and 10 times more powerful than anything ever previously tested and 5 times more powerful than the Nagasaki bomb which killed 70000 people almost instantly. How is there not like, y'know, a massive crater in the ground where it was or something?
gpt
Ground is really dense and very little is actually vaporized. Most of that energy is effectively absorbed by the ground, which doesn't really move very much so much as it continues to transfer that energy into the surrounding Earth and down to the Rock bed and so forth. If the ground in the area you're testing in is solid and stable, that is.

If you want to cause the most Devastation, you actually want your nuke to explode in the air above the target.