Everyone knows, by now, about the supervolcano caldera under Yellowstone National Park. A caldera, mind you, that blew a 25 by 50 mile gap in a mountain range the last time it erupted. Think about that. An area 25 miles long, 50 miles wide where the mountains just disappeared, blown to smithereens by a magma charge from deep within the earth.
The magma chamber under Yellowstone is being fed by a hot plume of molten rock that originates 400 miles down in the earth's crust. The floor of the valley is being lifted, tilted, by the magma moving under Yellowstone. The last eruption was 640,000 years ago. The eruption cycle, in the past, has been about every 600,000 years. Yellowstone is overdue. It could, literally, happen any day.
That is not the bad news.
Long Valley caldera, in eastern California, near Bishop and Mammoth Mountain, last erupted 760,000 years ago. When it erupted, blowing its share of mountains into oblivion, it laid down a blanket of ash THOUSANDS of feet thick. It would be, today, far more dangerous than the very dangerous Yellowstone. It, too, is overdue.
Since the middle of November, there has been a sharp upspike in seismic activity in Long Valley. The caldera, it seems, is filling with magma, again. THAT is the bad news.
Personally, I hope these catastrophes happen in a few thousand years - when Man and his technology will be better able to handle and survive the eruptions. The problem is that there is a very real possibility that they could go up - not in the next thousand years - but in the next thousand seconds.