Tuesday, January 26, 2016

Hiking Down Glass Mountain

A few weeks ago, we were about to hike back down Glass Mountain after our short hike part way up the glassy rhyolite flow dome. We had taken some overview photos and had stopped at the old working in the foreground (above) to collect some scouring stones. (And then we went off on a float-testing tangent.)

I had vowed to myself, and to MOH, to keep my eye out for some reddish, oxidized glass on the way down...
...and indeed, I found some.
The pile of obsidian and pumice rubble is eroding from a part of the rhyolite flow that includes dense, black obsidian, white to tan-colored pumiceous rhyolite, and reddish brown to reddish orange oxidized rhyolite glass.
I've zoomed in a little here. The black glass looks a little bluish because it's reflecting the sky (what little of it was showing through the clouds).
The oxidized and probably partly devitrified (?) obsidian always seemed to be perched on the treacherously glassy scree slopes above the road we were hiking on. I didn't find any good examples of the orangey rock along the road, and I wasn't about to go climbing over the glassy talus, without sturdy boots and leather gloves.
This rock from in an earlier post shows thin, oxidized bands and streaks, and I'll have to let it stand for a closeup example, although the reddish orange color is not as intense as in some smaller pieces or in the outcrops above the road.
Looking out over the northern dacite flow, and beyond to Timber Mountain.
The photo really captures the blocky and jagged nature of the surface of the dacite flow. It wouldn't be easy to walk across that terrain; one should have very sturdy boots and equally sturdy leather or work gloves. And please don't even consider shorts!

The northern dacite flow is the darker flow area in the upper part of this Google Earth image. The rhyolite flow is the long, almost cylindrical-shaped area emanating from Glass Mountain itself, the small, grayish, round area west and a little south of center.
Read more about the geology in this post.
An old tree grew around a large obsidian boulder (and is therefore younger than the flow). Trees are fairly sparse. 
A geo-type walks down the trail.
Pine trees grow on the angle-of-repose slope, their trunks bent from downhill creep of the colluvium.
I've zoomed in here to take a closer look at a mass of oxidized, reddish brown obsidian near the base of a large, conchoidally fractured obsidian outcrop.
Finally! Down the trail just in time for lunch.
An unreadable metal sign in front of the dacite flow. Maybe it said "Keep Out," once upon a time.

Related Posts:
A Hike Up Glass Mountain
Views from Glass Mountain (and some geology)
Which of These Rocks, Mostly from Glass Mountain, CA, Will Float
The Conclusion of Our Float Test
Hiking Down Glass Mountain (this post)
Links: Pumice and Pumicite

No comments: