Based on this calculation. Let's refer to this scan here. Reading from this, we know that...
- Everything within a 10km radius would have been completely turned into ashes
- A volcanic eruption would occur, turning the entire demon world into Darkness
Let's do two ends for this calculation. One with just the explosion, and the other with a volcanic eruption.
Explosion[]
If everything within a 10km radius has been destroyed, we do this step.
- Y (in megatons) = ((Radius in km/0.27)^3)/1000 and divide that by 2, since only 50% of the energy is from *the actual blast.
Y = ((10/0.27)^3)/(1000*2) = 25.4 megatons. City level
It seems that the aftermath of said explosion caused everything inside the radius of the explosion to completely turn into ashes, meaning heat energy was involved in this". Since up to 50% of the energy from an explosion involves thermal radiation/heat (up to 50% of the energy from an explosion is from the actual blast), the initial answer for this calculation is doubled.
Y = 50.8 Megatons. City level
Volcanic Eruption[]
Now here is the part where it gets tricky.
Reading from this article here, it states that when the Krakatoa eruption occured, we have a quote that states...
| “ | The explosions hurled an estimated 11 cubic miles (45 cubic km) of debris into the atmosphere darkening skies up to 275 miles (442 km) from the volcano. | „ |
So I guess this means that we have a possible radius for said volcanic cloud here? Basically, the above quote tells us that the radius of the volcanic cloud here is about 442km.
Now Satan's statement did say that the volcanic eruption from said volcano has completely covered the entire world in darkness, meaning that the radius of the volcanic cloud well, covers the entire Earth. Since the radius of the circumference of the Earth (This is the radius needed to cover the entire surface of the Earth) is about 20012km
- (2)*(Pi)*(radius = 6370km) = 40024km (Circumference of Earth)
- 40024/2 = 20012km
As for how much larger said cloud would have to be to cover the entire Earth compared to the cloud that occured in Krakatoa, we can actually find it right now.
- Circular area of volcanic cloud (Krakatoa) = (Pi)*(radius^2) = (3.1416)*(442^2) = 6.138e5 km^2
- Circular area of volcanic cloud (The one that covered the entire world) = (3.1416)*(20012^2) = 1.258e9 km^2
Finding the ratio between the top and bottom ((1.258e9 km^2)/(6.138e5 km^2)), we get a result of ~2050 times the size of the cloud compared to that of Krakatoa.
Since the eruption that occurred at Krakatoa had released about 200 megatons of TNT
| “ | The energy released from the explosion has been estimated to be equal to about 200 megatons of TNT | „ |
Since the volcanic cloud that covered the wolrd is about 2050 times the size of Krakatoa, we can infer that said volcanic explosion would have at least been 2050 times stronger as well. Thus, we multiply the yield of Krakatoa by 2050.
- Y (Krakatoa) = 200 Megatons or 2e8 Tons of TNT
- Y (Satan's Volcano) = (2e8 x 2050) = 4.1e11 Tons of TNT, or 410 Gigatons. Large Island level
As for the size of the crater, I don't think the author thought too much about volcanic sciences, so we'll ignore this issue for now.