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MARGINALIA

Thermophiles in Kamchatka

Roald Hoffmann

Into the Volcano

Workhorse Russian troop-carrier helicopters flew us into the Uzon Caldera. Two hundred thousand years ago a volcano erupted here. The frequent earthquakes fragmented the deposits in the caldera. But around was hard rock, sealing in a kind of giant chemical reactor. Several kilometers below the surface, a magma chamber is buried. Surface water seeps down to it, is sent up as hot steam, corrosive, mixed with volcanic gases. There's dissolution and redeposition of ions under conditions of varying acidity and lots of time—it's a veritable hotbed of geochemistry. Beneath the surface lie layers rich in arsenic, phosphorus, copper, lead, antimony, even gold. Hydrogen sulfide (H2S) and sulfur are never far away. We saw a little pool, a meter across, bubbling merrily away at 95 degrees Celsius and depositing at the surface a beautiful yellow-orange layer of As2S3.

From far away, Uzon is nondescript. Thin "smoke" is the first thing one notices, rising from some shallow lakes. Closer up the lakes and surrounding hills seem a Monet-like landscape of blues, grays, greens and yellows blending into each other. The smoke turns out to be condensing steam; it does the blending. Krasheninnikov saw those marvelous colors too, in the microcosm of a rock; he wrote "the clay in taste is sour and astringent; and if a piece of it, or a stone, is broken, there appears an efflorescence of alum, like a moss, with the colors blue, white, red, yellow, green, and black, which are so mixed as to resemble marble; and when the day is not quite dry, the colors are pretty bright."

Still closer, the pastel landscape breaks up into pools. Some are crystal clear, some muddy, filled with clay. Except suddenly a bubble pops in the clay, more burst explosively, and soon, especially as we smell the hydrogen sulfide, it looks like a nook reserved for some of Dante's less favorite people. The subtle color around the pools comes from mats of bacteria and Archaea. Sometimes we see several rings of slightly different color, each a species flourishing in a different temperature range.




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