Friday, September 6, 2013

Geo 365: Sept. 6, Day 249: Lupines!

Lupines are very common "spring" wild flowers at mid- to higher elevations in the Cascades, especially on recent fragmental volcanic deposits. That was certainly the case here, as we approached the rim of Crater Lake. They are legumes, like peas and beans, and have similar flowers and seed pods. Also, like many (most? all?) members of that group, they're "nitrogen fixers," which is a somewhat inaccurate shorthand of saying they have root structures, or nodules, that host commensal symbiotic bacteria. It's those bacteria that take atmospheric N2, and convert it to biologically useful nitrogen compounds like ammonium and nitrate. This gives lupine a competitive advantage in colonizing nitrogen-poor soils. I vaguely recall that there was one nitrate mineral listed in one of my texts, but for practical purposes, rocks contain no biologically useful nitrogen. Young tephra deposits may have available phosphorus and potassium as they weather, but there will be no available N until something like this lupine puts it there (there is also a small contribution by lightning). So while these pretty little flowers aren't geology directly, they're a huge part of the story of this area's recovery from a catastrophic volcanic eruption.

Photo unmodified. August 18, 2011. FlashEarth location.

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