One of the more fascinating geologic areas on earth is Yellowstone, featured in this month's National Geographic. The reason that Yellowstone is such an interesting area filled with hot pools and geysers is because the land sits on top of a huge volcanic reservoir -- a supervolcano.
Eruptions of supervolcanoes are very rare - so rare that humans have never experienced an eruption of a supervolcano. Yet someday what sits beneath Yellowstone most likely will erupt. If we humans are around when it erupts, what we would see would be truly terrifying.
Volcanoes form mountains; supervolcanoes erase them. Volcanoes kill plants and animals for miles around; supervolcanoes threaten whole species with extinction by changing the climate across the entire planet.
What lies below Yellowstone is not extinct. Indeed, it is a sleeping giant that is biding its time until it erupts once more.
This is a great summer article by Joel Achenbach for those of us who are awed by the tremendous power and incredible mystery of this home which we call planet Earth.