Saturday, August 31, 2013

Into the Great Unknown: Exploring the Heart of a Long-Gone Mountain Range (and words from home!)

 We were really out of touch. In the eight days we had been gone on the Colorado River (the Great Unknown), I sent one text from camp the first night (surprise, cellular coverage at mile 6!), and on the second or third night I had a two-minute conversation on the emergency satellite phone (we couldn't download a waiting message on the phone so we each checked on our loved ones; it turned out to be a "Welcome to Verizon" message or whatever satellite company it was). I had seen not a single sign of any sort since we left Lee's Ferry aside from some number markers on the Unkar Ruins trail. So the beginning of our day was a real culture shock. Less than a quarter mile from our camp at Cremation, a bridge came into view!
And what a bridge! For something like 400 miles, from Lee's Ferry to Pat Tilman Bridge and Hoover Dam not a single bridge crosses the Colorado River. How many rivers in the world in this day and age have that kind of a record? In any case, it was not a bridge for cars, but for hikers and mule trains. We had reached Grand Central Station of the Grand Canyon: Phantom Ranch.
Just how urbanized is Phantom Ranch? It has signs for one, like this one that greets boaters fresh off the river. And there are water spigots with treated water just 100 yards from the boat beach (our fresh water stores were becoming slim). And there were two dozen or more things called permanent "buildings", which apparently are used by other human beings for cooking, sleeping, showering, and even eliminating human waste! With flushing water! One of the most amazing contraptions I saw was a "pay telephone", an instrument I was able to use to contact the outside world for news. I was relieved to find that there had been no zombie apocalypse, and that life was more or less normal beyond the rim of the canyon.

And...there is green stuff all over the place, in spite of the 100+ degree temperatures that last all through the summer season. Cottonwood trees and grass and stuff. It turns out that Phantom Ranch was located along Bright Angel Creek, one of the larger tributary streams flowing into the Grand Canyon. Bright Angel Creek begins in earnest at Roaring Springs around 10 miles upstream. The water bursts out of the rock at the base of the Muav Limestone as an instant river. There is so much water that pumping stations were built so that the springs supply the water needs of the developments at both the North Rim and South Rim of Grand Canyon National Park: all the hotels, the campgrounds, the visitor centers, and the restrooms. And there is enough left over that the creek flows all year at the Ranch and supports a robust population of fish (eight native species originally and two introduced trout species that are being removed).
After talking on the phone, mailing postcards, and consuming both the most expensive and most refreshing iced lemonade I've ever had, we got back on the rafts and began the second half of our journey. A short distance downstream, just below the second footbridge, we met the new members of our party, and had lunch (salmon salad pitas).
We were deep within the Granite Gorge and not a whole lot of granite was to be seen. The cliffs were mostly composed of dark schist or gneiss. There were thin dikes and stringers of red and pink granite  and pegmatite here and there. But still, looking at the sheer walls coming straight down to the water, I could understand the apprehension of John Wesley Powell and his men as they ventured through this canyon in 1869. They were getting used to rapids by this point, but they had almost always been able to portage the boats around the worst rapids, or let them down the raging river by rope. Both of these methods were difficult at best, but with the sheer walls they were forced to run some rapids that they would have rather avoided.
 We were approaching our first class 9 rapid at Horn Creek. As we went in, I experienced one of the really big holes with a huge standing wave. We kind of shot right through it, meaning I was thoroughly and completely drenched.
It took awhile to dry off enough that I felt I could retrieve my camera from the dry bag, so my picture looking back at Horn Creek Rapid makes it look a great deal smaller than it actually is (below).
 Perhaps the comic I drew that night can provide some perspective...

We moved on downstream. It was a short day on the river, only five miles total, so we drifted with the current for awhile, passing gigantic towers of schist and granite. The peak in the picture below reminded me of Sentinel Rock in Yosemite Valley.
We passed an intriguing little island just before camp, with a tamarisk tree surviving somehow on a solid mass of schist and granite. This rock and the tree must surely be inundated during high water, and soil must be washed away on a continual basis. Then again, as of 1963 the flows of the river have been tightly controlled, with only a few floods (planned and unplanned) since then.
With the leisurely day, I had a chance to take some close up shots of the metamorphic rocks.
The forms are fascinating. As we noted in yesterday's post, these rocks are the deep crust remnants of a 1.7 billion year old mountain range that once extended from at least California (Death Valley area) to Mexico and perhaps Oklahoma and Arkansas. The mountains were pushed up as a result of the collisions between a series of island terranes and the core of the North American continent.

These rocks used to be mud and silt on the ocean floor, or volcanic rock like one sees in Japan or the Aleutian Islands. The rocks were crushed, buried, and heated nearly to the melting point, but not quite (different minerals melt at different temperatures, so part of the rock could have been molten, but not all of it). The rocks were twisted and folded like saltwater taffy, and later on they were intruded by hot masses of granitic magma, forming the pink rock in these pictures.
The granite has huge crystals of potassium feldspar (the pink/orange mineral), clear quartz, and plates or sheets of shiny muscovite mica. Such rocks are called pegmatites. Other beautiful minerals can sometimes be seen, including black biotite mica, and reddish brown garnet.

I was walking in a small unnamed canyon just upstream of Salt Creek (our camp was very creatively called "Above Salt Creek"). There was a small trickle of water.

The little bit of erosion has attacked the boundary between the schist and the granite, highlighting a fold in the schist.

My ankles were bothering me again, so there was no way I was going try to climb the jumble of boulders at the head of the canyon, but before I got there my attention was drawn to one of the strangest rocks I had seen in awhile. It was bright red.

Most of the time, geologists are pretty loose with their definition of the color red, using it to describe a lot of brown and reddish brown rocks and sediments. But this stuff was really red. It was essentially fine-grained, but may have had small phenocrysts (small crystals) of a white mineral, maybe feldspar. I couldn't tell, and to my shame I was caught in the wild without my handlens! It was fairly easy to weather, as you can see from the mineral veins that stand out in relief (this is material, probably calcium carbonate, that filled cracks and fissures in the rock much later).

I'm guessing it might have been some kind of metavolcanic rock, but really as a non-petrologist, I am not at all sure. Any ideas out there, gang?

The shadows grew longer in the dark canyon as the boatmen checked their rigs. Tomorrow was promising to be the most challenging day of the trip, with at least ten major rapids, including Granite (8), Hermit (8), and Crystal (9-10).
We were treated to a wonderful sunset. Once again I hit the sack early, just moments after sunset.

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.

Wednesday, August 28, 2013

Into the Great Unknown: In the Depths of Grand Canyon, There are Three More Grand Canyons...Checking out the Supergroup

It was now day six of my journey down the Colorado River through the Grand Canyon, a trip I've been calling Into the Great Unknown, in honor of John Wesley Powell and his crew, who first navigated the river in 1869. We had floated down 65 miles from Lee's Ferry, and had now worked our way through 4,000 feet of Paleozoic sedimentary rocks that told a story of transgressing seas, tropical reefs, the growth of mountain ranges in strange places, vast sand seas, and once again a transgressing sea. It is an incredible story encompassing 300 million years, but it turns out these layers are only a small part of the whole story of Grand Canyon.

On this day we reached the hidden depths of the canyon that reveal a sequence of rocks three times as thick as the Paleozoic section. These rocks record another 550 million years of history in the time prior to the Paleozoic Era.  The rocks are known collectively as the Grand Canyon Supergroup and they range in age from 1.25 billion years to 700 million years, part of the time period we call the Proterozoic Eon.
We set out from our camp at Carbon Creek and floated past exposures of the Dox Formation, which formed in river floodplains and coastal complexes. It is more than 1,000 feet thick.
Dark cliffs appeared on both sides of the river. We had reached the lava flows and intrusions of the Cardenas Lavas which were erupted just over a billion years ago on top of the Dox Formation.

How does one fit 12,000 feet of sediments and lava flows into the bottom 1,000 feet of the Grand Canyon? The rocks are tilted! In the picture below, the Tapeats Sandstone can be seen as a horizontal layer at the top of the cliff. Beneath the Tapeats are tilted layers of black Cardenas Lavas and reddish Dox Formation. The eroded surface that forms the boundary between the two sequences is called an angular unconformity. The next question might be "how did they get tilted?".

Moments later we had an answer: the rocks of the Grand Canyon Supergroup were tilted by major faults that formed when the North American continent was breaking away from Australia and Antarctica in latest Proterozoic time. We passed one of these major fault lines, the Butte Fault, near mile 66. The sedimentary layers have been dragged to a nearly vertical orientation (below).

The character of the canyon was changing once again (as I've mentioned previously, there is no single Grand Canyon; it was different every day and practically every hour). For nearly a week we had been in a deep gorge with vertical walls hundreds or thousands of feet high. Now the canyon was much wider and more open.

We saw one of the truly rare evidences of human activity from our vantage point on the river. In the picture below one can barely make out the Desert View Watchtower (just left of center on the rim). The tower is three or four stories high, and yet was barely visible among the high cliffs. The tower is one of the main tourist centers on the South Rim of Grand Canyon National Park. I thought of how many times I had stood at Desert View looking down and wondering what it would be like to float down the river. This week it was finally happening, after a wait of forty years!

We reached Tanner Rapid and pulled over to hike up to some petroglyphs on boulders that had tumbled down the slopes of the Dox Sandstone. The openness of the canyon was refreshingly different.

To many people, the canyon was not the "Great Unknown". It was their home.
I always wonder what was being said by the individuals who chipped these messages in the rock.

It was a hot day. I had the outdoor lead for the thermometer in the river and the indoor lead on the boat. 113 degrees! Yikes. We decided against a hike at lunch near Tanner for lack of shade. We went a bit farther down the river where we needed to scout Unkar Rapid.
The Unkar Delta was one of the largest settled areas along the Colorado River in Grand Canyon. The sites were occupied between 850 and 1200 AD, some 350 years! They were partly excavated in the late 1960s, and the park service has constructed a trail that visits many of the sites.

Despite the heat, I hiked the whole loop. It was hard to think of this barren area as a possible "home", but it was probable that the inhabitants moved higher up in the canyon in the hottest times of year (and conversely this would be far more comfortable a home in winter).
Meanwhile, the oarsmen were scouting Unkar Rapids (6 on a scale of 10). It looked rather ferocious, but these rafters know their craft, and the run was splashy and fun.

Ron in the other raft was pointing towards the North Rim. I looked up and saw for just a moment the arch of Angel's Window, a popular viewpoint on the Walhalla Plateau.
I've stood near Angel's Window many times, looking at the Colorado River framed in the arch (the picture below is from a trip in 2012). Look at the size of the people on the arch and consider how small they are from a river point of view! When Coronado's troops saw the Grand Canyon for the first time in 1540, they thought the river was only six feet across. They were only off by 200-300 feet! The Grand Canyon can have a huge effect on one's sense of scale.
We pulled into our camp at Upper Nevills. The river was wide and calm at the campsite, and there were nice rock ledges that made cleaning and laundry convenient. I also for the first time decided to actually test my personal flotation device and did a dunk in the river. At 52-53 degrees, the river was COLD! I commented in my journal that I was glad I hadn't been involuntarily dunked in the river yet (literary note: this sentence is an example of foreshadowing...).
Tomorrow was a big day. We were facing some of the monster rapids, including Hance (8), Sockdolager (7), and Grapevine (7). I hit the sack.