[ROLF of the HILL COUNTRY]

"...what a 100 megaton device can do..."

For the record: We don't have a 100MT bomb; never have.
In fact the largest known nuke was an estimated 60MT the soviets detonated back in the 60s. They claimed to have a 100MT, but we doubted it. Why don't we have such monsters?
Simple. They don't do as much damage as more numerous smaller bombs, they just make a big hole in the ground.

About the only thing they might be useful for would be a high-altitude burst to create an EMP to knock out electronics. Or remove about a quarter of a mountain somewhere (but the fallout would be bad from that; worldwide that is.)

[BlueDragon]

Ivan might have been "only" 50 megatons. In comparison, the biggest the U.S. has detonated (or at admitted to, anyway) was only 15 megatons.

Ivan could have concievedly been a 100 megaton device, if the Soviets had not chosen to use a non-functioning "tamper"(lead, in this case). Had they used U-238 (depleted Uranium) instead, that would have been the 3rd stage of the fission-fusion-fission thermonuclear "hydrogen bomb" 3 stage reaction/detonation.

Here's an old pic, pre-detonation, of course ;)