Grand Canyon in the News Again: It's Grand!

I follow with great interest the latest research on the origins of the Grand Canyon. In some ways, the Grand Canyon is deceptively simple: on one level, the canyon is simply a pile of stacked layers (which makes for the simplest of creation-science narratives). It was recognized very early on that the Inner Gorge hides great secrets: something like 3,000 meters of tilted Proterozoic layers, some three times thicker than the obvious overlying Paleozoic layers. And John Wesley Powell recognized right away the deepest parts of the canyon reveal the very ancient metamorphic rocks that contain evidence of hundreds of millions of years of history that greatly predates any of the overlying sediments.

But as I am always telling my students, the rocks tell only part of the story. Here we stand at the edge of a huge abyss, one of the greatest geological showplaces on the planet, and we can't exactly tell how old the gorge itself actually is. Erosion of canyons removes evidence, and in the case of the Grand Canyon, there are multiple ways of defining the age of the canyon formation anyway.

A flurry of stories a few weeks ago discussed how the canyon was older than previous thought [see Grand Canyon Old, Says the News (But Not the Data) for a discussion]. Another article that I noticed today discusses a Grand Canyon that is 55-65 million years old (Grand Canyon May Be As Old As Dinosaurs, 40-50 Million Years Older Than Previously Thought). The article linked here reports on a paper by Flowers, Wernicke, and Farley (May issue of the GSA Bulletin) in which cooling rates of apatite indicate the presence of a deep canyon throughout Cenozoic time. The article makes it clear that the canyon they are discussing was being carved through the thousands of meters thick Mesozoic cover, and they also correctly point out that different parts of the canyon formed at different times and were only recently integrated into the river system we see today.

A moment of linking produced a story from several years back concerning portions of the canyon, as much as 700 meters worth, that may have been carved within the last 700,000 years when the Colorado Rivers was swollen to many times its present size due to glacial runoff from the Rocky Mountains (New Evidence Of Lava Dam Failure And Fault Activity Supports Theory That Grand Canyon Is Geologic Infant). The lava dams discussed in the article yet another example of the fascinating stories concerning the origin of the canyon.

Great pictures for the imagination. Powell wrote eloquently of the violence of lava meeting water in the canyon bottom. I have talked with my students of previous hypotheses of stream piracy on a monumental scale in the region. What a sight it would have been, to have seen the moment that a river changes its entire course for good! And imagine seeing a 1,000,000 cubic feet per second flood on the Colorado River! The biggest flood on record was only a third of that, in 1884. But such flows may have been common during the Pleistocene. And during all of these events, eyes other than our own species were witnesses: mammoths, mastodons, sabertooth cats, American lions, sloths, giant cave bears, maybe dire wolves, and condors with 11-12 foot wingspans (one of my recent delights was seeing some of Grand Canyon's recently released condors).

The Grand Canyon...grand in so many ways!

Touring the Underside of the Volcanoes, Part 2

Yosemite Valley and Yosemite National Park contain incredible exposures of the magma chambers that once fed eruptions of volcanoes that topped the Ancestral Sierra Nevada, the mountain edifice that graced the Cretaceous landscape of California and western Nevada (now, when is the last time you heard Yosemite introduced that way?).

As a glacially carved valley (ignoring for the moment the work of rivers and mass wasting), Yosemite doesn't really fit the stereotype of a U-shaped valley. It has a very flat valley floor, and instead of a relatively linear valley, it has many reentrants and coves. This in large part is responsible for the unique scenery of this beautiful place. The flat floor exists because lake sediments filled the trough in the area upstream of some of the valley moraines. The walls vary, because more than one kind of granitic rock is present, and in fact at least eleven intrusions are defined in the area (see the map at http://virtual.yosemite.cc.ca.us/ghayes/geology.htm).

Ironically, the rocks are not all that easily observed up close. The cliff base is often covered with loose and unstable talus, and many of the accessible exposures are covered with lichens. Hetch Hetchy Valley is often a better bet, having been more recently scoured by glacial ice (see my very first picture post: Photo of the Day).

A slide in 1982 brought down huge boulders of the El Capitan granite, one of which is pictured above. The photo shows a large number of darker colored enclaves*, blobs of dark rock that probably originated as two different intruding magmas mixed. The enclaves can perhaps be thought of as globules of oil floating in the vinegar of Italian salad dressing.

*Enclave: Body of external origin in an igneous rock. The main varieties are xenoliths (fragments of solid rocks) and microgranitoid enclaves (former magma globules derived by mingling of magmas).
Vernon, R.H., 2004, A Practical Guide to Rock Microstructure, Cambridge University Press

Standing Underneath Volcanoes

Into the last two weeks of the semester, and things are getting hectic, so blogging has been intermittent. But field trips have been part of the fun for the last week, and last week's exploration of the innards of a subduction zone in the Coast Ranges now lead to the rest of the story....where are the volcanoes of the magmatic arc that must of have been part of a convergent boundary? When oceanic crust and sediment is subducted into the mantle, water released into hot mantle lowers the melting point of the rocks in the base of the crust, resulting in the formation of magma, and ultimately of volcanoes.

When tourists visit Yosemite National Park, if they think of geology at all, they will probably think about glaciers, and how they sculpted the valley. The story is more complex than that, of course, as Yosemite has been carved as much by river erosion and mass-wasting. But when I stand near the famous view of the valley at the Wawona Tunnel exit, I think of how I am standing three or four miles beneath the volcanoes that once existed there. The granitic rocks that make up much of the Sierra Nevada were the product of the subduction zone that lay to the west near the present site of the Coast Ranges, which I explored in last week's posts.

Although the volcanoes have long since eroded away at the latitude of Yosemite Valley, the cobbles and boulders of these vents can be found in Upper Cretaceous sediments in places like San Luis Reservoir (but that is a trip for a future post). Today's picture of a view of Yosemite Valley, taken from the same spot that tens of millions of other photos have been snapped, is really a plea to stop and think about how even a familiar scene can be newly appreciated. Can you imagine what it must of been like for those who discovered the valley for the first time (whether speaking of native Americans or of their European conquerors)? I hope in some future posts to get a few people to see Yosemite for the first time, despite having seen pictures a hundred times over.

For those who are not as familiar with this view of the valley, here is a short tour: the vast cliff on the left is El Capitan, with a 3,000 foot sheer cliff that is a magnet to rock climbers. The snowy peak in the upper end of the valley is Clouds Rest, which at 9,926 feet is the highest point visible from the valley floor (at 4,000 feet). Half Dome lies just to the right. In the center of the photo lies Sentinel Rock, which I have always thought was one of the less appreciated cliffs of Yosemite Valley; in any other setting, it would be renowned. The three triangular peaks on the right are the Cathedral Rocks, with Bridalveil Falls (620 ft) in their foreground. The last prominent spire on the right is the Leaning Tower, but a different angle is required to appreciate the origin of the name.

Continuing Journey in the Earth - Taking the Time Machine

How much can you see in an afternoon in the Coast Ranges of California? In two previous posts, I described how my students had the opportunity to explore the earth's interior, right down to the mantle. Del Puerto Canyon is a geological treasure, even if it lacks some of the dramatic scenery of other more famous locales.

Our trip also encompassed some interesting time travel...the Upper Cretaceous Moreno Formation also includes the K/T boundary in the uppermost section (http://gsa.confex.com/gsa/2004RM/finalprogram/abstract_72988.htm). I have not heard of any studies about the presence of iridium, or clay layers, or shocked quartz in this particular region, or if the section is even conformable, but it is still a neat moment to stand near the mouth of the canyon and point out that the saddle on the skyline separates the "dinosaur layers" from the "non-dinosaur layers".

Even better, not more than a kilometer up the canyon is the locality of the first-ever discovery of a dinosaur in California. In 1998, I had the opportunity to tour the canyon in the company of Al Bennison, who discovered the hadrosaur remains in the 1930's when he was a teen. If I understood correctly, the bones came from the scarp at the head of the large slump, near the triangular brush field in the upper left-hand side of the photo below.


All in all, a great place to teach and learn geology. Check it out some time if you ever make it out to California. Coming up next...seeing a volcano from underneath!

Journey to the Center of the Earth (well, the mantle at least)

Continuing our trip up Del Puerto Canyon (and into the earth's mantle; see Photo of the Day - Feeling Crushed?), we reached a huge pod of mantle peridotite and dunite in the upper canyon that had escaped the most extensive alteration during the long journey to the earth's surface (in most places the rock is serpentinized). A few unusual minerals are found in the area, including mercury (cinnabar) and chromite (shown above). The chromite crystals are dark and metallic-looking.

The United States imports almost all the chromium that it uses, but in wartime, imports are disrupted, so the mines in the upper canyon were utilized off and on during the two world wars. The mercury was considered far more valuable, given its role in the production of gold during California's Gold Rush of the 1850's. I've heard that the mercury miners could earn a much higher wage mining mercury than they could mining gold, but they also tended to go mad, and die a lot sooner. It's not as if the gold miners had such a great life expectancy, though. We make jokes and complain sometimes about workplace safety regulations, but it is a great deal safer in the mines today than it was 140 years ago. And sometimes, workers even get to enjoy some kind of retirement plan!

Photo of the Day - Feeling Crushed?

I took my physical geology students geotripping this week instead of their lab sections...Del Puerto Canyon cuts a deep swath through the eastern Diablo Range of Coast Ranges of California. In this single gorge, one can pass through a 6 kilometer thick section of the Great Valley Group (deposited within a forearc basin), a thick and nearly complete ophiolite sequence and underlying mantle peridotite (the Coast Range ophiolite), and a section of the Franciscan Complex (part of an accretionary wedge complex). How many places are there in the world where one can drive right through the crust into a subduction zone, and into the underlying mantle? The picture above is a section of highly deformed cherts of the Franciscan Complex.

Somewhere, Miss Frizzle and her magic school bus must be jealous....

That's reasonable...hey, wait a minute! How to write a Creation Science narrative

Was this done in a few weeks?

Thanks to everyone for the kind (more or less) responses to my previous post regarding, ahem, research in California. I have been the victim of several such articles in past April issues of Discover Magazine, including one on the discovery of arctic moles who tunnel through ice by having an extra warm nose or something like that. Ron Schott expressed a bit of concern about how much pseudoscience exists on the Internet, and that is the purpose of this latest missive.

Writing a devious April Fool's joke involves taking a germ of truth, depending on a certain amount of trust on the part of the reader, and then letting loose with an outrageous distortion that, uh, can't be true, uh, but everything else was so reasonable...and such is the way that so much misinformation becomes part of the pop culture narrative.

In this instance, I started with an appeal to authority (link to a 'journal' and important sounding names of people who probably have PhD's), and then I took some known facts about the Sierra Nevada (rapid Cenozoic uplift; mantle drip) and mixed it up with some geological terminology that quickly zoomed off into ridiculous territory (magnitude 10.5, a salute to a very bad TV movie). What's the problem with a little fun amongst geological friends?

But this is the way it is done on the battleground of public perception in geology and evolution, and the stakes are a great deal higher than an April Fool's prank. Consider...would a person without a geological background be able to recognize the prank? And what if I changed the word "millions" to "thousands" of years? This suddenly becomes a reasonable-sounding creationist explanation of the origin of the Sierra, Central Valley and Coast Ranges from a young-earth perspective. If it were presented as such, could you refute it succinctly, quickly and clearly, without going into a long winded explanation? It isn't necessarily easy, especially if your client doesn't trust you in the first place.

This is what we face in Creation-Science world. This is a place where all of the sedimentary layers of the Grand Canyon were deposited in weeks or months, and were eroded just as quickly when Noah's flood drained from the continents. It is a world where fossils were formed in a matter of days as the flood swept all life away, and where dinosaurs like T-Rex munched on fruits and vegetables until Eve bit the apple. It is a place where evolution doesn't occur. At all. Except in small bits within "kinds". Oh, and the relatively few "kinds" on the ark (e.g. dog, cat, mouse, deer, cow, and antelope) changed into the thousands of species in the world today during the last 4,000 years since the flood subsided. The dog 'kind' for instance, became all the wolves, coyotes, foxes and domestic dogs (but this wasn't evolution because it happened too 'fast'). And so on, and so on, and so on. These kinds of statements are transparent and ridiculous to those educated in geology, but they are perfectly reasonable to someone whose religion seems to demand belief in a worldwide flood around 4,000 years ago. It supports their faith. And the people providing these stories have their trust because they say they are Christians too. And Christians don't lie or deceive about these things.

I realize that many of you are aware of the kinds of thing that organizations like the Institute of Creation Research are up to, and the kinds of deceptive articles they publish. But if you haven't seen what they do, you should check it out, starting right here http://www.icr.org/aaf/. And keep in mind: the people they write for are predisposed to believe every word they read.

This is the challenge that geologists and teachers must face in the public arena. It is important to know where people are coming from when they ask strange questions about our science.

What's the strangest thing you've come across in Creation-Science World?