Thursday, September 1, 2011

All I want is mountains!

So, following along with some of the advice I recieved from fellow bloggers, I am going to write about what I love: MOUNTAINS!

A few weeks ago, some friends of mine got hitched in North Lake Tahoe in a beautiful outdoor ceremony. I was lucky to attend this event and get a week off to travel back-up to Oregon with my S.O. (significant other), all the while exploring, camping, hiking, biking, and sampling all the beauty of the Sierra Nevada and Cascade Mountain Range.

We started off by escaping some crazy traffic in North Lake Tahoe on a Sunday afternoon and heading North towards the Tahoe National Forest. I was overjoyed to be (1) getting away from suburban assault vehicles with screaming children and (2) to be going to an area that I had been on a field trip almost 2 years prior. In Fall 2009, I took an 'advanced field' class which was your classic read a lot of papers then go out in the field and arm wave a lot. It was my first real field class I'd had in my undergraduate career and sure, I had a few classes with ONE field trip, but the field was the basis for this whole class. Needless to say, I was a happy geology student.

Our first field trip for the class was exploring the Sierra Nevada crest in the Tahoe National Forest and many different rocks representing a Paleozoic volcanic arc that had been squished, uplifted and eroded by glaciers. A volcanic arc is a series of volcanoes that form in a 'chain' due to their position relative to a subduction zone. A modern day example of a volcanic arc is the Cascade Mountain range, or for an island arc example, the Mariana Islands in the S. Pacific.

So, to simplify, the rocks in the Sierra Buttes represent some very chaotic environments (and one quiet one). Are you excited yet?

Andesite columns formed from rapid cooling. Photo taken in 2009.

Andesite columns are familiar to me and other geoblogers here in Oregon, but I think I can say these are some of the first columns I ever saw as a geologist. I have memories from being a wee one and seeing 'skyscrapers' in the rocks along the Snake River on a family rafting trip. Now when I recreate around Oregon, I see them all the time, and I still want to put my nose on every one of them with my hand-lens. Anyways, Cool! These andesite columns define a volcanic flow, where the surface is perpendicular to the column shape.

Chert with phosphate blebs. Photo from 2009.

Further up the trail from the last photo, we found a dark sedimentary rock with interesting white, lenticular shapes. This is chert*, which was formed in a 'quiet' marine environment, like a continental shelf. On a side note, Brian Romans at Clastic Detritus posted on twitter today that "a sedimentary particle 1 micron in diameter takes about 3 weeks to settle through 1 meter of water." If this rock formed in a deep, quiet marine environment, imagine how long it took the grains to get to the thickness shown in the hand sample in the picture. The white lenses in this rock are phosphate 'blebs,' as I have it written in my field notes. These blebs underwent a process called diagenesis, where sediment chemically and/or physically alters as it's being created into a hard rock. So this is a little quiet compared to what I promised earlier.

2009 photo of some supah slickenlines.

WAIT. What is this I see in this chert? Are those slickenlines!? Yes! These were the first slickenlines I had ever seen in the field. Glad to share them with you, internetz.

Rock hammer for scale. Photo from 2009.

Now we're into the chaos! May I present a MEGABRECCIA! The large and varying sizes of the clasts in this rock, which turn out to be quartz and  plagioclaise, represent a high energy environment.

This next photo is of some volcanostratigraphy in the Taylor formation which, quite frankly, blew my mind. At that time in my young geology career, I had never thought of what would happen when ash from a volcano came in contact with water. I guess I was more infatuated with imagining mountains blowing up (can you blame me?). Well, this is what it might look like when a lot of volcanic ash from a pyroclastic flow hits a lake, or other calm water body. It helps that the sun was hitting this outcrop just right too.

Volcanostratigraphy of the Taylor Formation. Fall 2009.


Well, now since I've talked about the rocks for a bit, I should give some flashy photos of the scenery here at the top o' the Sierras.


Horse Lake or Deer Lake with MEGABRECCIA. Sierra Buttes peepin up in the background. photo taken in 2009.

Sierra Buttes and Deer Lake (for sure on this one). Taken summer 2011.

The scenery was defiantly competing with the rocks for "which one does Emily want to look at more!?" Thankfully, this was not very stressful because, geologists love all different scales of geology, from the nose of the rock to trying to fit it all into your eyeballs. Completely satisfied.


Wonky trees on the Pacific Crest Trail. A question came up on the trail about why the moss is so far up the trees and is not uniform on the tree. My theory was the snowpack stops at the bottom of the moss, and the moss grows on the side of the tree getting hit by wind (and sticky snow). Any other ideas?

Geologist loves playing with scale...

I'm not sure if this shows up in this photo, but from this view I could see the Sutter Buttes in the Great Valley and even a very faint horizon of the far far distant California Coast Range! This view is looking SW. Taken summer 2011.

I hope you enjoyed reading about my adventures in the Tahoe National Forest! It's defiantly worth a visit for anyone craving mountains and solidarity.

*I've always really enjoyed the word "chert" because I like to imagine how a British person would say it. Go ahead, try it! Okay, well, I guess I've always been amused by it...

2 comments:

  1. I LOVE chert! Mostly 'cause it's awesome looking and I love chertified corals, but now I like it even more because I'm imagining it being said in a British accent. haha.

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  2. Nice post, Emily! Sounds like you had a great trip. Regarding your moss question, because mosses are not vascular plants, they need moist conditions. In temperate climes of the northern hemisphere, the north side of trees have more shade (sun in the south), which helps them stay moist. I'm not sure about the height of the moss, your idea sounds plausible. Another reason might be animals rubbing on the tree trunks or feasting on the moss (not sure what eats moss!).
    Cheers!
    http://twitter.com/beautyiswhatudo

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