Title says it all.
610 meters is the minimum for it to be considered a mountain, so 1p = 5.9177 meters. First let's try the explosion calc, then the actual damage calc.
W = R^3*((27136*P + 8649)^(1/2)/13568 - 93/13568)^2
That's the formula, using this blog for reference 20psi should be alright since it caused near-pulverization of a rocky structure.
W = 127.375^3*((27136*1.37 + 8649)^(1/2)/13568 - 93/13568)^2
W = 164.54 Tons, 8-A
If we were to calc the actual damages, it seems like a spherical cap. Putting the info into this gets us 3695425.34 cubic meters or 3695425340000cc. V.Frag values for rocky structure gets us 254984348460000J or 60.94 Kilotons, 7-C+.
The results of the destruction on the second mountaintop in the background yielded 52972 Tons, added to the 60940 Tons on the first mountain top here gets you 113.9 Kilotons, High 7-C