One obvious-ish lower bound estimate would be an estimate of the energy required to pulverize a Hunga Tonga-Hunga Ha'apai-sized rock into a troposphere-height c

One obvious-ish lower bound estimate would be an estimate of the energy required to pulverize a Hunga Tonga-Hunga Ha'apai-sized rock into a troposphere-height cloud. Edit: It's not any kind of estimate but the before and after pictures of the first thermonuclear weapon test site look quite a bit like the images from Tonga: https://en.wikipedia.org/wiki/Ivy_Mike#Detonation https://en.wikipedia.org/wiki/Ivy_Mike#Detonation That was coincidentally (and somewhat accidentally), a 10 megaton explosion.