Quasi-Apocalyptic, quasi-scientific theory popular in certain odd and interesting corners of the new counter-culture. Pretty much what the name suggests; to wit, the earth is gonna go through some pretty severe natural disasters, which will cause things we take pretty much for granted, like the location of coastlines and the existence of mountain ranges, to change pretty, well, catastrophically.
Interestingly enough, the reasons for this very from book to book and believer to believer. Some of the most common causes include a shift in the magnetic north pole from north to south, a meteor impact, a massive series of volcanic eruptions, and even concentrated psychic stress from modern civilization.
In the end, maybe it doesn't matter. The idea obviously has a lot in common with its mirror-image on the far right, survivalism, and the general Y2K mania that those of us with particularly long cultural memories may dimly recollect. Now that nuclear annihilation no longer looms large over the collective unconscious, a thousand little heterodox alternatives have sprung up to fill the vacant niche.
And why does that niche exist? Why is there such a massive need to visualize the total destruction of civilization as we know it? Maybe it's a basic human need. Every frustrated serf and burger flipper and Vice President of Marketing at least has the consolation of imagining himself dashing across the endless savannah killing antelope with his teeth and lighting his campfire with his income tax forms before he makes savage love to his woman out in the open and the sleeps as long as he wants.
In short, people need the Apocalypse, they need Catastrophic Earth Changes, need the fire to rain from the sky, and they need it all the more because probably it'll never happen, and that's what they fear the most.