Monday, August 4, 2014

Geo 730: August 4, Day 581: Calcite-Filled Fault

This stop has been badly weathered over the years, but it's an interesting one in that it shows a gradient from a more or less unaltered lahar deposit(s) to highly altered near the vein showing above. The vein doesn't stand out well from the surrounding clay-rich material, but it's the diagonal slash in the rock face below the alder tree at the top. This is another stop that rewarded multiple visits; the weathered surface of the unaltered (by hot water) lahar material looks almost indistinguishable from basalt at a cursory glance. However, if you break open a fresh surface, it's pretty easy to tell it's volcaniclastic, not directly volcanic. For years I had told kids it was basalt, and had to change my story when an adult assistant found a bit of petrified wood.

Photo run through Paint.Net's auto-level routine for saturation and contrast. June 19, 2014. FlashEarth location.

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