Really an excellant documentary, and very well written. I would have appreciated more Geology, but that is just being selfish as I am a geologist. But they totally passed over the significance of what would happen if the volcano errupted (very significant). The consequences for the United States would be devastating. My other comment I never would have expected, but Kevin Costner's narration was flat, monotone, and lacked any feeling. He would have been much better off had he hired someone else. Lastly, the way the script is worded is not quite correct in terms of the earthquake. The geologic shift caused the quake. The quake did not cause the shift. And obsidian is volcanic glass .