What an interesting article. I knew about Krakatoa but I never imagined it was that loud.
You need 51 active LFRs each fed with 4100 peak Watts.
172dB at 100 miles is 277dB at 3 feet. I made the simplifying assumption that SPL would attenuate by 6dB for each doubling of distance.
One active can produce 126dB at 3 feet given 1 peak Watt.
The SPL at 3 feet produced by n actives is given by:
SPL = 126 + 3*(n-1)
For an SPL of 277dB at 3 feet, solving for n gives 51.
Since each active requires 4100 peak Watts to produce that SPL, over 200KW are required.
I think Ian ought to try it. If he immerses them in Lake Muskoka, he can produce a tsunami.
