One of the most fascinating topics in the National Park System is Yellowstone National Park and its geothermal basement.

Sometimes, as you're watching Old Faithful erupt or walking through the Upper Geyser Basin, it's hard to remember that the park is set atop a living and breathing volcano. Actually, a super volcano. Who in their right mind would walk atop such a thing, let alone spend the night?

Earlier this year the park generated quite some attention with swarm after swarm after swarm of earthquakes. What was causing them? What was going on? Were they indicative of anything? While swarms are not entirely unusual in Yellowstone, the duration and vigor of these swarms raised some eyebrows.

In this, the first of three USGS videos, Jake Lowenstern, the scientist-in-charge of the Yellowstone Volcano Observatory, explains the volcanics at work in Yellowstone. (Click the second button from the right on the toolbar and you can enlarge the video to full screen.)

Tomorrow: The Yellowstone Volcano Observatory