The most plausible as well as conspiratorial is HAARP, which is designed to bounce radio waves into the upper atmosphere.
More likely it is an earth phenomenon that we just don't get. Historically these are very likely the sources for Biblical references for the Angels Trumpets.
A gentleman that I know is a PhD in geography, etc and said there is a hot spot in Northern California where the ground is over 140 degrees. No magma chamber underneath, not earth activities, nothing...zero explanation for it. Lots going on science still has no idea how to explain. Thanks for posting!
boo