I'll be trying to calc that old feat from chapter 589, when Madara's Perfect Susanoo was first introduced and destroyed a couple mountains in a slash.
Of note, this calc has encountered a large amount of scaling issues in the past when attempted so I will at least attempt to get a good size for the mountains this time.
1. The dust "explosions" in front are of the same size as the ones in the back
Also, some additional proof that the two meteors (of equal size) is the object your can see in the scan, one of which retained its full height from the collision.
Picture 1: Madara's Slash
Perfect Susanoo Midface Height = 1780m = 181 pixels
Top of dust explosion near = 108 pixels = 1062m
[size assumption change due to depth]
Top of dust explosion far = 33 pixels = 1062m
Radius mountain 1 = 91 pixels = 2928.8m
Height of fragment mountain 1 = 61 pixels = 1963.3m
Airheight of fragment mountain 1 = 22 pixels = 708.1m
Radius mountain 2 = 58 pixels = 1866.7m
Height of fragment mountain 2 = 36 pixels = 1158.7m
Airheight of fragment mountain 2 = 30 pixels = 965.5m
From here, we just need to find the gravitational potential energy of those mountain tops and cutting force required to cleave through them.
I'll treat each mountaintop slice area as a circle (a=pi(r)^2) and the mountaintops as cones (v=(pi)r^2(h/3)).
Mountain 1 area: 2.6948 x 10^7 m^2
Mountain 2 area: 1.0947 x 10^7 m^2
Mountaintop 1 volume: 1.7636 x 10^10 m^3
Mountaintop 2 volume: 4.22981 x 10^9 m^3
This link says the tensile strength for rock is between 8-20 MPa so I will use 10 MPa (aka 1 x 10^7 N/m^2). Shear force = 0.6 x tensile strength times shear area; work = force x distance (2r), so the shear energy required is:
Mountain 1 SE: 9.4710 x 10^17 Joules
Mountain 2 SE: 2.4522 x 10^17 Joules
Then we get mass for MGH (density of rock = 2700kg/m^3)
Mass Mountain 1: 4.6872 x 10^13 kg
Mass Mountain 2: 1.1420 x 10^13 kg
Thus, GPE for the mountains is:
GPE Mountain 1: 3.253 x 10^17 Joules
GPE Mountain 2: 1.081 x 10^17 Joules
Adding up the energies, we get a total energy of 1.626 x 10^18 Joules = 388.6 megatons of TNT = Mountain Level
Keep in mind, this is a low end because a) the attack was a shockwave and b) the rubble near Madara is easily comparable in size to each mountaintop by the size of Perfect Susanoo alone. I just don't want to bother with all those GPEs.