It's what we gearheads call a "blow-off." The turbocharger gets loaded too much; there's a backfire; and poof, a big flame. Race cars do it all the time, except it's much smaller. A "pop-off valve" is supposed to prevent this build-up; it doesn't always work.
Also happens in D-9 & AC4400's. I have a great video of an SP lashup of units at Minturn as the start out heading up Tennessee Pass at just about dusk. The flames went at least as high as the photo above but you get the motion and the NOISE. Awesome.
This flaming situation is also why this building on my layout (to the right side of the image) is "The Alco Turbo Division," as Alco turbos were infamous for blowing their stacks.
That wouldn't go well in my trainroom considering all the foam I used on the JJJ&E. Stay cool and run steam......