Friday, August 30, 2013

Into the Great Unknown: Journeying to my Roots, and to the Roots of Mountains

The photo above is my favorite self portrait from my journey down the Colorado River, into the Great Unknown. It's true that I appear in only a half dozen of my two thousand pictures from the trip, but this one captures best the sense of wonderment that I felt during the entire 227 mile long boating adventure. It was taken on one of the really special days of the trip, when we reached the ancients roots of a massive mountain range that today is long gone. It was also a day when I explored the roots of my own life adventure as a geologist and teacher.

And a day when I started to pay really close attention to the rapids on the river.

As a passenger on a raft (really, only a fool would allow me access to the oars in any rapid bigger than a riffle), we trust the boatmen. They are the ones who can quickly read and assess a rapid, either by standing up and observing just before entering, or by pulling ashore and scouting from above. They are the ones who make the snap decisions in the midst of chaos, deciding in an instant whether to pull left or right to get by the unexpected hole or pourover or eddy wall. They are the ones who keep their cool when the giant waves threaten to completely envelop the raft and sometimes tip it over (flipping is a highly undesirable outcome in a rapid; there's nothing fun about it at all). We trust them, and when they do their job really well, a passenger can actually become a bit complacent. If we've managed 40 or 50 rapids without problems, well, it can't really be that hard can it? And that's when things can get dicey.

Passengers play an important role in the run of a rapid, so we have to be paying attention as well. It's hard to imagine that pulling the oars makes any difference in the chaos of a rapid, but it does make a big one. Inches sometimes count. And when the raft threatens to flip over, the passengers have to be thinking fast enough to "highside", to fling themselves towards the rising side of the boat during a tip-over, using their weight to hopefully push the boat back towards the horizontal.

Why was I suddenly watching rapids with a renewed interest? We had reached the point on the river where John Wesley Powell was inspired to write one of his most famous passages, the one which also inspired the name of this blog series:

We are now ready to start on our way down the Great Unknown...We are three quarters of a mile in the depths of the earth...We have an unknown distance yet to run, an unknown river yet to explore. What falls there are, we know not; what rocks beset the channel, we know not; what walls rise over the river, we know not.

The next morning he adds:

At daybreak we walk down the bank of the river, on a little sandy beach, to take a view of a new feature in the canyon. Heretofore, hard rocks have given us bad river; soft rocks, smooth water; and a series of rocks harder than any we have experienced sets in. The river enters the granite!

We can see but a little way into the granite gorge, but it looks threatening.

He and the mountain men who served as his crew had already been on the the river system for two months, and with their inadequate clumsy boats had run or portaged many dozens of rapids that were terrifying. They were running very low on food (the diet: unleavened flour, dried apples and rancid bacon). And now the nature of the rocks exposed along the river promised rapids far worse than any they had encountered upstream.
Why were the rapids worse?

Indirectly, it was indeed the harder rocks. They were entering a part of the canyon composed of harder rocks than anywhere else along the river. It isn't the rocks themselves that make bad rapids, though. The river does not fall over ledges and waterfalls. Rapids on the Colorado River happen because of debris flows that enter the channel from the small tributary canyons. The debris in essence dams the river and forces the river channel to the side, making the cross-sectional area of the channel much smaller. Since the same amount of water in a river passes a given point in a given amount of time (cubic feet per second is one measure), the river must speed up to pass the barrier. You can see this effect in the picture above in Nevill's Rapid.

The severity of a rapid is determined by the volume and size of the boulders in the debris flows, and canyons cut into harder rocks produce larger boulders. Sprinkling a few giant boulders throughout a rapid turns a riffle into a terrifying roller coaster ride.
So that was the day we were facing. We would be entering the Granite Gorge of the Grand Canyon for the first time, and we would now need to run a gauntlet of the biggest rapids to be found on the entire river. It started with Hance (8 on a scale of 10), Sockdolager (7), and Grapevine (7). The next day would include Horn Creek (9). The day after that, Granite (8), Hermit (8), and the ultimate rapid, Crystal (10). These would be followed the same day by the seven rapids of the gemstones (Agate, Sapphire, Turquoise, Emerald, Ruby and Serpentine, ranging from 5 to 7). And 70 miles downstream (with plenty more rapids in-between) Lava Falls (10) awaited our arrival.
We came around a bend in the river, and I encountered a familiar sight in the midst of the Great Unknown. I had been here before! Not on a river rafting expedition, but on a backpacking trip in 1976. It had been one of the most important events in my young life, because it was the trip that set me on the road to becoming a geologist and teacher.

Geology of the Grand Canyon was actually one of the more difficult courses I had ever taken because not only did we need to master a lot of geology in a short time, but we also had to prepare for a challenging backpack down and then back up a series of officially unmaintained trails in the canyon (the New Hance and Grandview trails). The co-requisite for the class was a 2 unit physical education course in backcountry camping that including an entirely separate shakedown trip in the mountains of Southern California. When I came out of the Grand Canyon six days later I knew what I wanted to do with my life.

Of course, a few things have changed since 1976. Geotripper weighs, um, a lot more than that gawky teenager on the right in the picture below. Picture quality has improved, not so much because of better photographers, but it used to be expensive to take and develop pictures, so we never took very many. Plus we were using the old Kodak Instamatic cameras or something similar.

Still, seeing these pictures a few years ago on Facebook (thanks to J. Elson) brought a shock of memories, and now for the first time in forty years I was once again standing at the rapid that made a geologist out of me.
Only this time my mind was on other things. Back then when we finished, we turned around and started hiking back out of the canyon.
We were about to run a major Grand Canyon rapid in boats that suddenly seemed really small. Just like these river rafters in 1976. I noticed that the two biggest boulders haven't moved, and that the rapid was as chaotic looking as ever.

We had reached the base of the Grand Canyon Supergroup, and could now see the three formations that make up the oldest units: the Shinumo Quartzite, the bright red Hakatai Shale, and the basal Bass Limestone (intruded by basaltic dikes). The rocks are tilted about 15 degrees, giving the illusion that the river gradient is even steeper than it already seems. It can't have been a comforting sight to Powell and his men in 1869.

The Grand Canyon Supergroup sits on a mountain range of Andean proportions. Or more properly stated, the layers were deposited on the low erosional plain left behind when a mountain range of Andean proportions was completely washed away. The black schists and reddish granite intrusions once lay some five miles deep in the crust, and now they have been laid bare by the cutting of the Grand Canyon.

The rocks today are called the Granite Gorge Metamorphic Suite, and they formed in a series of collisions between a group of volcanic islands (called terranes), and the ancient North American continent around 1.7 billion years ago. The metamorphic schist and gness units were intruded by granitic magmas at intervals between 1.7 and 1.4 billion years ago. And now those rocks are exposed in the very deepest part of the Grand Canyon.
We successfully negotiated Hance Rapid (not without getting positively soaked), and looking back upstream, I could see the basalt dike that I had found so utterly fascinating on my first trip into the canyon.
The canyon was dark, but I did not feel as sense of brooding. I was exhilarated, my imagination seeing the peaks and canyons that must have existed here in the distant past, mountain slopes which would have been utterly lifeless and barren. Deep gorges must have been cut by rushing rivers that were never seen by any living thing. Entire Grand Canyons could have been carved here and we will never know of their existence. We now entered a fascinating world of exceedingly rugged vertical canyon walls. The silt and sand polished the hard granite and metamorphic rock.

Sockdolager Rapid (the word is an archaic term for knockout blow in boxing) was a fun ride, nothing like the terror-filled lining and portage in Powell's writings.

It was hard to find a spot to scout, so the boatmen checked out the rapid by standing up as they approached.
Between rapids the river was calm, and the canyon walls rose straight from the water.
The metamorphic suite was composed of the most diverse and beautiful rocks that I had seen anywhere on the trip. The polishing simply added to the beautiful sculpted appearance of the rock.
We arrived at camp in Cremation Canyon by 2:30. We had pulled in early because we would be saying goodbye to three of our fellow travelers who would be hiking out of the canyon from Phantom Ranch, and meeting three others who would take their place for the remainder of our journey.

I turned in early once again...tomorrow we faced the biggest rapids so far on the trip.


Gaelyn said...

The schist in the bottom is like natures art with all the colors, swirls and sculptures.

Your story now continues into territory I traveled. Yet I want to see it again.

intaminag said...

The exposure of an entity so old and yet today accessible to touch, billions of years later, is quite the awe-inspring thought.

Amazing as usual, sir.