Well, I've just sat down to relax after a long day of work, and find out there's a kind of geological meme going around about death-defying geological experiences. Geotripper, what have you started?!
As a rule, I personally try to avoid death-defying experiences, and consider things like downhill skiing and white-water rafting to be extreme enough, and I haven't done either of those things in a good number of years. Many of the stories I could tell, would really be of other people, or would be about getting stuck in 4WD a long way from anywhere.
So here goes: Flying around in a helicopter 50 feet off the ground while contouring around the hills and mountains of the Great Basin -- rather than flying a grid so that the U-Th-K spectrometer wouldn’t need any elevation correction -- was death defying enough for me. And then when our end-of-field-season replacement pilot forgot to pick me up one night, and then when he simultaneously forgot where he was supposed to pick me up, well, that isn’t really death-defying, I don't think. It's merely very inconvenient. I stayed out overnight with water-proof matches, one wool sweater, a small snack, less than a cup of water, and one so-called helicopter blanket (kind of like those thin, reflective “space blankets” but bright orange on one side, so you might be able to flag down a wayward or lost helicopter). It was early October in central Nevada, in the high country, in a not particularly warm year.
I learned that it takes about a half hour to collect enough sagebrush to keep a fire going for about a half an hour, and that sleeping wrapped in a space blanket, in amongst the low branches of a juniper tree, with a few bushes stuffed around for “insulation” is downright ridiculous. I walked out the next day, and met the only other geologist in camp -- he knew right where I was and brought a candy bar for my breakfast -- while the rest of our crew and the pilot searched diligently for me three miles to the south in a different drainage area.
But, like many geologists, I too have stood on barely cooled basaltic lava (non-explosive, definitely not pyroclastic).
Update: Check out Highly Allochthonous for a lot of stories, many in the comments.
Update-Update: Geotripper is keeping a list of all posts for this impromptu carnival.