Friday, May 1, 2015

Geo 1095: May 1, Day 851: Lichen the Joints

As I indicated yesterday, joints cutting through more or less solid, blocky rock are crucial to understanding how the enormous amounts of precipitation that falls in the High Cascades as rain and snow simply disappear over the many square miles that comprise this plateau. This is a surficial feature, and I'd guess the deeper buried joints don't tend to be as wide, but clearly, even at a fraction of this width, such fractures would allow rain and snow melt to easily trickle down to the water table. There's a bit of a mystery here, as it has become clear that the hydrologic divide in this area is not congruent with the topographic divide. In most environments, ridge crests mark the boundary from which water flows into one basin or another, but this is not the case here. Water is clearly flowing, hidden underground, across the Cascade crest, predominantly from west to east. I'll clarify and expand on that later.

Another interesting thing I notice in this photo is that lichens seem to be present in the shaded portions of the shot, but absent in the areas that are fully sunlit. On one hand, that may be just a fluke of this shot and the time of day I took it. On the other, it makes sense to me that the scorching heat of dry basalt in full sunlight would make it much more difficult for lichens and other colonizing organisms to become established. So areas that are shaded, at least sometimes, during the warm and dry season are easier for the lichens to live upon.

Photo unmodified. July 6, 2013. FlashEarth location.


Hollis said...

Several neat stories here!

Lockwood said...

Such apparent simplicity, but so much going on. Gotta love sciencing!