Tuesday, August 25, 2015

Of Tuffs and Tufas

On Tuesday, I (Reena) was feeling pretty darn great. This may have had something to do with two cups of unexpectedly good coffee at breakfast, or having gotten to take a bath in a river the night before. Anyway, in the morning we drove to Mono Lake to see its iconic tufa towers: tall, lumpy buildups of chemically precipitated calcium carbonate. All lakes are natural aqueous chemistry labs, each one with a unique mix of dissolved ions. At present, Mono Lake is very very alkaline, very very salty, and very very rich in dissolved inorganic carbon – much more so than sea water. The otherworldly-looking tufa towers grow where calcium-containing groundwater seeps in beneath the surface of the unusually carbonate-rich lake (Ca levels in the lake itself, meanwhile, are really low, as any entering calcium is quickly precipitated out with the tufa).

Mono Lake tufa. Photo by Kelly K. '15, with what is presumably her Brass Rat.
Once I'd adequately recalled how sad I am that I never had time to take Course 1's limnology class, a park ranger demonstrated the tufa-forming reaction for us by adding dissolved calcium chloride to a flask of lake water. Here's Madison D. '16 being excited about it:

We also learned that, since the tufa forms beneath the water surface, the exhumed towers provide a lower bound on the paleo-depth of the lake, and can be radioisotopically dated to help track how its hydrology has changed through time.

Then Kelly and I got distracted by the flies. Zillions of flies, for once not wanting anything to do with us, just sitting atop the salty sand and detritus along the shore. You see, when you run through them, they scatter, and unfortunately, terrorizing them like such is absurdly fun. Until I have our video of it, here's a random stranger's...
Thanks YouTube.
To be honest, I'd been expecting Mono Lake would be my personal favorite stop on this trip. But by the end of the day, it was surpassd by the Bishop Tuff, the humungous mass of rhyolitic lava that erupted at the Long Valley Caldera ~760,000 years ago. We'd read about the Bishop Tuff in our spring seminar, and it had been pretty impressive then, but standing within canyons of it was another thing entirely. Complete mind explosion. Allegedly, as far away as Illinois, the tuff layer is still a foot thick.
The rock was surprisingly friable. So basically, the apocalypse happened here 760,000 years ago, and its remains are miles and miles of baby-pink powder?
EAPS undergrads and undergrad-alums in front of the Bishop Tuff.

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