Saturday, February 12, 2011

Accretionary Wedge Carnival #31: Geological Surprises and the Abyss of Time


Jazinator is hosting the 31st Accretionary Wedge, asking:

What geological concept or idea did you hear about that you had no notion of before (and likely surprised you in some way)?

Part of my wedge entry comes from an earlier blog post (self-plagiarism?), but I was actually talking about something else at the time, the discovery of my first fossil.

From Geotripper in May of 2009:

"It took only a split second to take me back forty years to the North Rim of the Grand Canyon, where a 10 year old boy was on his first trip to the beautiful national park. But I had found out something strange at the small visitor center there. The ground I was walking on at more than 8,000 feet had once been on the bottom of the sea! Say what? How could that be? I was already at an age where I had figured out that Noah's Flood couldn't account for this. Where was all the water that it could even cover Mt. Everest and all the other mountains of the world? It was clear that something had happened, but I wasn't quite in a place where I could understand the idea of vast uplift across an entire region. I spent days musing about this, enough that the memory is clear after all these years."

It was years before I revisited the problem of marine rocks at the tops of mountains and high plateaus (I had all those teen years to get through), but it made a huge impression on me that the Earth's crust was so mobile that it could lift mountains and plateaus out of the sea. It was one of the life-long mysteries (hey, 10 years to a 20-year-old is half a lifetime!) that plunged me into a career as a geologist and teacher. It might seem almost a mundane observation once a geologist has explored the depths of the crust and mantle and the full breadth of geological history, but a first realization is a powerful thing.

A human life is a series of discoveries that replay the discoveries of mankind in compressed time. Those who came before us paved the road for our understanding, allowing us to comprehend in a few days or months what took others decades or centuries to discover (I teach the basics of plate tectonics in 40 minutes or so, when it took the greatest geological minds 50 years to discover and accept the concept). When I read of James Hutton and John Playfair discussing the geology at Siccar Point (below) in Scotland in the late 1700's, I realized that a similar revelation was the foundation of an entire new science:

"What clearer evidence could we have had of the different formation of these rocks, and of the long interval which separated their formation, had we actually seen them emerging from the bosom the deep? We felt ourselves necessarily carried back to the time when the schistus on which we stood was yet at the bottom of the sea, and when the sandstone before us was only beginning to be deposited in the shape of sand or mud, from the waters of a superincumbent ocean. An epocha still more remote presented itself, when even the most ancient of these rocks instead of standing upright in vertical beds, lay in horizontal planes at the bottom of the sea, and was not yet disturbed by that immeasurable force which has burst asunder the solid pavement of the globe. Revolutions still more remote appeared in the distance of this extraordinary perspective. The mind seemed to grow giddy by looking so far into the abyss of time...."
To those students, geologists, teachers and bloggers who haven't contributed to the Accretionary Wedge before, think about it! I know I have a few students who blog on geological topics. If you don't blog, but would like to contribute, I would be more than pleased to host your entry as a guest-blogger on Geotripper. Jump in!

7 comments:

Anonymous said...

Another great post.

It also brings to mind something I've been wondering regarding the Dardanelles off highway 108. One of my favorite places to go backpacking is Carson-Iceberg Wilderness for the solitude, beauty, and volcanic formations(see some of my pics of the area here: http://www.panoramio.com/user/3189284?comment_page=1&photo_page=1 ). As a layman interested in geology, I am wondering why this formation stands out so starkly? It has always been a bit of a mystery to me, and I just assume it's because the Dardanelles just happen to be made of stronger volcanic stuff than what surrounds them.

Garry Hayes said...

The Dardanelles are volcanic necks and other eroded volcanic features from a volcanic center near the Sierra crest around 10-12 million years ago. The flows covered much of the summit region, and some flowed down river canyons up to 60 miles, the Stanislaus Table Mountain at Sonora and Jamestown being an outstanding example.

KC said...

Thanks for the answer!

I'm often in the foothills for work and the Stanislaus Table Mountain is truly a site to behold. I find it to be most striking as one travels northeast along highway 120 and east along Obyrnes Ferry Road as one rises above Tulloch Reservoir. Just spectacular.

About my Dardanelles summit attempt, when I was trying to get to the top, I was blocked by the mountaineers plague, Whitethorn. About 300 feet from the top I had to turn around. My legs just couldn't take anymore scratches. I got some wonderful pictures of the Dardanelles Cone and Butte though. Plus, I did an excellent day hike to a saddle beneath the Dardanelles Cone, which offered an outstanding view to some of the peaks near Pacific Valley off highway 4.

Again, love the site, and thanks for the unexpected answer.

Garry Hayes said...

Glad to help! Thanks for the comments! I have a little article with aerial photos of Table Mtn on my images site: http://geotripperimages.com/Stanislaus_Table_Mtn.htm

KC said...

Those photos are great. They give an excellent perspective of the flow, far better than what one can see from the ground.

Just curious, but do geologists have any idea of the size of the vents the lava flowed from? Are there still remnants of these vents? I also find the difference between say volcanism evinced by Carson-Iceberg Wilderness--its much older feel--versus the activity of Lassen.

Jazinator said...

Thanks for the great entry. This gets me excited about my upcoming trip to the Grand Canyon. I hope to have these all compiled shortly.

Garry Hayes said...

KC, you've just about reached the margins of my expertise about the geology of the volcanics at Sonora Pass! I posted a bit (http://geotripper.blogspot.com/2010/05/other-california-other-side-of-sierra.html) that included a resource for some current research out there.