I'm not sure how to calculate it, since this is a chain reaction and the size is
insanely inconsistent (for example, the column takes up a
huge portion of the cascade, yet Re is
very visible next to it). Maybe we could divide
this (29 gigatons) by time, since it's the minimum energy to cause a
chain reaction that'd ignite the atmosphere.
Usually, I'd be against such things, but the cascade was reaching a level where it had the energy to ignite the atmosphere, not gaining more energy than causing the chain reaction by reaching that level.
Edit: It's about 4 minutes in episode time. 29 gigatons / 4 minutes is just over baseline
Mountain level.