Hollywood disaster movie-makers don't have much in the way of imagination...a movie like 2012, with pieces of California sundering into the sea, explosive chunks of lava chasing recreational vehicles, continents moving thousands of miles, and arks taking a remnant of the human race to a brighter and more hopeful future...nothing of this can compare to real life adventure that took place here 760,000 years ago. I'm gonna go screenwriter on you and compose a movie idea...Imagine the group of unlikely compatriots thrown together east of the Sierra Nevada, a giant wall of rock rising thousands of feet above the valley floor, which despite the relative aridity of the region is well-watered by streams coming off the mountains. We can ignore the fact that nobody actually lived in North America 760,000 years ago; this is Hollywood after all, and we can make things up. There's the plucky child, the quiet guy who seems to be hiding something, the excitable guy who complains a lot, the hero type leader, the beautiful woman, the other woman with suspicious moral character, the slightly addled drunk, the old couple who love each other, even after 50 years...you can add some other stereotypes as you wish. Thrown together, they argue, but then up the hill the first eruption begins, throwing a shower of fine ash particles across the landscape. The unlikely band pulls together and starts their quest to redemption.
Every so often, as they make their way across the ash covered landscape, someone dies, either being picked off by hungry predators, or falling off a cliff, or falling into a muddy river while making a desperate crossing. The survivors hold together, finding new truths about themselves and each other, and in general growing in admiration for the pluckiness of the human race.
The ash eruptions continue over the next few days or weeks, leaving behind a layer after layer of cinders and ash particles amounting to several feet in thickness. Our band of people carry on, seeking that redemption that lies just over the next hill.
Then, the paroxysmal eruption begins. The ground shakes violently as a vast plume of ash rises on the horizon. The wall of ash is 18 miles across, and 10 miles wide, and rises into the stratosphere, far higher than any airliner can fly. The amount of ash exceeds 120 cubic miles. It is incandescent, so hot it glows in the night. The hot ash spreads rapidly across the landscape, instantly incinerating anyone and anything in its path. The layer is hundreds of feet deep, and covers thousands of square miles. Areas as distant as Kansas and Nebraska are covered in several inches of ash. World climate changes to the cool side for decades, at least. In the aftermath of the explosion, the land collapses into a giant hole 10 by 18 miles wide, and two miles deep.
Needless to say, our plucky band was incinerated in the first moments of the giant pyroclastic surge, and everyone was dead. But they were plucky and all, and we recall their memory while the screen credits roll...
OK, there's a reason I never went to work in Hollywood as a script writer. But, isn't it cool that you can lay your hand across a moment of catastrophe? That's what is happening in the picture below. There are many such thrilling moments of imagination in geology (and not always catastrophe, either). When you know something about the rocks, you can visualize a practically infinite number of worlds that have passed away, worlds with strange life forms and moving continents and giant earthquakes, and mountains rising and being eroded away.
This was the first stop of our geotour through the Long Valley Caldera this last weekend, courtesy of the National Association of Geoscience Teachers, and the National Earth Science Teachers Association. The site is a pumice quarry in the Chalfant Valley northeast of Bishop.
I took lots of pictures, so more soon...
For a more detailed look at aspects of this incredible eruption, check out this post from Callan Bentley at NOVA Geoblog (now Mountain Beltway)
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