From a little exchange on sci.space.policy (with minor editing)…

Ed Wright suggests:

If one were to set up a large rocket engine at the mouth of the cave complex–or several mouths –and run them, what would the resulting decibel level be inside the caves? To maximize the effect, I suppose you could direct the exhaust into the cave.

I know that sound tends to reflect (echo) inside of caves. How deeply would it travel, and what would the effect be? Would decibel levels be above the threshold of pain? Could they cause internal damage to cave dwellers or structural damage to the caves themselves?

Or would it simply be annoying, like the existing psyops tactic of playing loud rock music throughout the night?

To which Doug Jones responds:

A rocket isn’t necessary- just use a jet engine on afterburner, this would be logistically simpler and much more readily available. If the exhaust is ducted into the cave (and there are other uncovered exits), the breathable air inside would be very quickly displaced. This would be a bit like cave clearance with flame throwers as used in WWII, but much more effective for large tunnel complexes. I dunno if the carbon-monoxide-laden gases could be construed as a Geneva Convention violation, though.

More conventionally, some combination of laser-guided bombs to seal the entrances together with fuel-air explosives forced down ventilation shafts would be more than sufficient. Heck, if water is available nearby, take a page from the prison riot resolution, bring in a bunch of fire pumpers, and flood them out. Undramatic but effective, and perhaps a better psyops tactic by not martyring a lot of enemy troops.

And they said Usenet waren’t good for nuthin’…