Wednesday, April 30, 2008
Looking through my files, I found only three pictures of the falls, and all were wintertime shots when the falls were frozen. I am also guilty of ignoring them!
Tuesday, April 29, 2008
Todays relatively unknown waterfall is another that shows up for just a few months in the spring: Royal Arch Cascades. They are most noticiable through the trees behind the Ahwahnee Lodge on the north side of the valley floor. They form a long, sloping millrace down the cliff, dropping about 1,200 feet, before disappearing into the forest on the valley floor.
I actually find them to be sort of unremarkable from most angles, but it turns out that the base of the falls is very easy to access, and they reveal a beautiful mosiac pattern on the cliffs when viewed from that location. You merely need to follow the trail at the east end of the Ahwahnee Lodge parking lot for a few hundred yards, and then scramble up the talus slope for just a few yards.
The falls spill over a cliff of the Half Dome granodiorite which was intruded around 86 to 88 million years ago. In addition to the requisite feldspar, quartz and biotite, a careful search of the rock will reveal little yellowish crystals of sphene. The rock is relatively free of joints, and this leads to the formation of some interesting reverse exfoliation features at the Royal Arches themselves just to the east of the falls (probably a future post).
Nearly four million people visit Yosemite Valley every year. I doubt that more than a few dozen ever see Royal Arch Cascades from the base. Give it a look!
Monday, April 28, 2008
Today's post, continuing the theme of the less recognized sights in Yosemite Valley and other parts of the Yosemite National Park, is a sight that is sometimes noticed by visitors in April and May, but never seen by the vast majority of summer tourists. It is dry most years by June. And yet it is the tallest unbroken waterfall in Yosemite Valley: Ribbon Fall. The more familiar Yosemite Falls include three segments, the tallest of which is the Upper Falls at 1,430 feet. Ribbon Fall leaps nearly 200 feet more: 1,612 feet. The fall lies just west of El Capitan, and the cliff it leaps from is composed of the same mostly unjointed El Capitan granite. It is most easily seen from the parking area on the main park road just east of Bridalveil Fall Parking Lot. No trails approach the fall, not from the bottom, and not from the top.
I photographed Ribbon Fall many times, and thought that it leaped from a sheer planar wall of rock, but in 2005, a low cloud layer brought a different perspective: it lies within a narrow alcove that is outlined by a series of vertical joints. The waterfall is barely visible in the left alcove in the picture below. The cliff on the far right is the west wall of El Capitan.
The fall was beautiful last week. Be sure to check it out if you are in Yosemite in the next few weeks!
Friday, April 25, 2008
I offer today a picture of my most sacred spot on the planet (so far): the edge of Cedar Mesa at Muley Point. The cliff below the rocks drops 800 feet straight down to a flat plain which is then carved by the San Juan River into intricate canyons some 1,200 feet deeper still. Monument Valley and the Raplee Anticline lie in the distance, as well as the towns of Cortez CO and Farmington NM. It is a precious place to me, full of mystery, beauty and solitude. Ghosts of the Ancestral Pueblo people lurk here, and the fossils of Permian reptiles as well.
But...hidden in the bottom of the deep canyon is the greatest upstream extent of the artifical evaporation pond of Lake Powell. On a 1964 topographic map of the National Recreational Area, there is a notation at Muley Point: "slated for development". In the distance, at Mexican Hat, oil wells pump the black liquid from the ground, and around Farmington, a GoogleEarth view reveals hundreds or thousands of gas wells. Coal is mined from Black Mesa, off to the south, and evaporite minerals are torn from the ground to the north of Canyonlands National Park. Power lines criss-cross the region. My favorite place is under siege.
Of course, we need all these things to live, but the point of my entry today is this: there is a price to be paid. The price takes many forms, from high prices on commodities, in foul air, polluted rivers, extinct plants and animals, and in the almost never recognized loss of the wild places of our planet, the gauntlet in which our ancestors survived and thrived. We have lost touch with the earth that gave us our birth, and which continues to nurture us, despite our abuse. And our abusive ways are about to come to an end, one way or another: we will finally destroy the last of the wild places, drill the last drops of oil and shovel the last lumps of coal, we will melt the last glaciers, and deplete the last soils. Or, we will choose not to do these things, and exist on our planet in a new way: a sustainable existence that finds a way to give something back to our planet.
The environmental movement on our planet has been demonized, trivialized, and marginalized, because, I suppose, it has always threatened the perceived profits of somebody. What have environmental groups tried to do since the hey-day of the 1970's and the first Earth Day? A short list might include:
- Increase mileage standards and encourage the use of mass-transit
- Encourage the development of alternative energy resources
- Decrease emissions from our vehicles, including greenhouse gases and ozone destroying compounds
- Encouraged laws to protect our water, air and soil
- Protect the wild places that still remain on our planet
The oil is running out, and thus the price spikes. We will never see cheap oil again. The mass conversion of agricultural fields to the growth of biofuels is causing grain prices to spike, and we are becoming less and less able to feed the hungriest people on the planet (Malthus is in the air; "Running Out of Planet to Exploit," ). The prices of metals are climbing.
Change is possible, and I sometimes see hopeful signs, and part of my optimism comes from Earth Day, and the works of good people to bring awareness to those who are waking up to the spectre of high prices and resource limits. We have a choice though...we can let the decisions about the future to be made by energy companies and their political lackeys, or we can demand a future based on sustainability. It will take education, and an end to the corporate media's obsession with Britney and Paris, and kidnapped white women, and American Flag Lapels. People, when given the right information, can make the right choices.
Those are my thoughts this week. You are welcome to comment!
Monday, April 21, 2008
I've not had the pleasure (I'm getting a bit too old and fat to even contemplate this kind of exercise), but if you are wondering what the view is like looking down, check out http://www.100megsfree.com/dew4theq/rock/yosemite/yosemite02.htm.
Saturday, April 19, 2008
Huber passed away recently, after a long career with the USGS, and later as a populizer of geology for the Yosemite Association. His final book, Geological Ramblings in Yosemite (http://www.yosemitestore.com/Templates/frmTemplateP1.asp?SubFolderID=114&SearchYN=N&t=9&p=3) is a delightful collection of essays culled and adapted from articles he did for the Yosemite Association Magazine. In one of them, he explains the mystery. Yosemite Creek did follow the cleft! And probably for a very long time. But, during one of the last glaciations, a lateral moraine blocked the old waterway, and forced Yosemite Creek over the brink of the sheer cliff where it now flows. The old waterway seems more obvious in a picture where the falls are dry, such as the photo below, taken in October.
I appreciate the insight of geologists like Huber, and of the way they make the information accessible to the lay population.
The "quirk" in the history of Yosemite Falls lies in the next post, because I don't understand the quirk in Blogger that only allows the first of my posted pictures to be thumbnailed. Does anyone have advice about that? Next post in a few moments.....
Friday, April 18, 2008
Thursday, April 17, 2008
Can you imagine the singular fame of the rock if it were any place in the world besides Yosemite Valley? Tomorrow: one of the lesser known waterfalls....
Wednesday, April 16, 2008
Today, our view is of the lowermost Cathedral Rocks next to Bridalveil Fall (which at 620 feet provides the scale for the picture). The triangular shape of the cliff results from intersecting vertical joint sets. The cliffs are composed primarily of El Capitan granite (about 102 Ma), which is a coarse-grained, white to light-gray biotite granite and biotite granodiorite containing quartz (gray glassy looking grains), orthoclase feldspar (white grains), and biotite mica (black grains)..
Exfoliated Sentinel Dome can be seen at the top of the photograph. The Glacier Point Road pulls to within a quarter mile or so of the summit, and it is an easy climb for an incredible payoff of a view (see some future post!).
Update on the Earthquake Watch: didn't feel any of them today, but the Historical Geology Class got to see an incoming quake on the seismometer this evening. It was probably the 6.5 magnitude quake in the Andreanof Islands in the Aleutian chain. 29 years and 364 days to go....
Monday, April 14, 2008
Memories fade so easily. I was a new teacher at Modesto Junior College in 1989 at the time of the Loma Prieta quake, the 7.1 magnitude event that occurred at the worst possible moment of a most miraculous day (5:06 PM on a commuting day; but on the day of the one and only Bay Area World Series between the A's and the Giants...everyone was already home, and deaths were very much reduced by the coincidence). That quake, and effects that it had on our lives here in northern California, was profound; but now, I am one of the old teachers at MJC, and I am getting students who were babies, or not even born yet in 1989. It is no longer a part of our collective consciousness.
The problem of a social recognition of earthquake dangers is somewhat less in southern California, given the tragedy of the 1994 Northridge quake, but I still find that many of my students are unprepared for the eventuality of large quakes. They were apparently convinced that the Y2K computer meltdown would affect their lives more. Few have water, food, and first aid supplies set aside, and few really know what to do if a quake takes place. Many still intend to try and stand in a doorway if one happens.
The picture of the day above is part of the scarp formed by the Landers quake of 1991 (actually 1992, I was sloppy and writing too quickly, thanks, andrew ), a 7.5 magnitude event that produced a 50-mile long tear in the Mojave Desert, and killed two people. The new fault line offset pipelines, streets, fences, and houses, and only the remote location kept the death toll down. The picture was snapped in 2003; the dry environment has allowed the scarp to persist.
We got lots of little reminders that we live in earthquake country. The Alum Rock quake last November took place minutes after my night class took their earthquake quiz. They were standing outside, and most of them rushed into the building to check out the department seismometer (everyone else was running outside). We are currently experiencing some mysterious activity offshore of Oregon (Earthquake Swarm off Oregon Coast). And always, the little tremors continue all over the state (586 in the last week at magnitude 1 and above at http://quake.usgs.gov/recenteqs/latest.htm; that's about twice as many as normal for the last few years).
Oh, and I wasn't sure I should even bring it up, but last night's episode of Eli Stone involved a crank prediction of a 6.8 quake that is going to bring down the Golden Gate Bridge...and then...a quake happens, and the Bridge collapses! Given the "story arc" style of the show, it will be interesting to see if the earthquake continues to be a factor in future plots. And the special effects of the bridge collapse were pretty good for television, at least on my little set.
Diagrams and maps of the California faults in this study can be found at http://www.scec.org/ucerf/ including probabilities of particular faults (http://www.scec.org/core/public/sceccontext.php/3935/13664) and the overall probability map (http://www.scec.org/core/public/sceccontext.php/3935/13661).
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!
Friday, April 11, 2008
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
Wednesday, April 9, 2008
Sunday, April 6, 2008
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!
Saturday, April 5, 2008
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!
Friday, April 4, 2008
Somewhere, Miss Frizzle and her magic school bus must be jealous....
Tuesday, April 1, 2008
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.