Monday, November 30, 2009
It didn't take long to figure out how to find the places "everyone knows": I was on the road, there was a tourist trap with bathrooms, and a bunch of postcards for sale. What better place could there be for the attention-deficit-disorder tourist to find out the important sights to see. I grabbed two postcards showing the whole state (50 cents apiece or 3 for a dollar; I grabbed a third card that shows the famous Tehachapi Loop). The cards are published by Scope Enterprises, Inc (no web presence that I could find).
The first card has a lot of information packed in a small space: LA, San Francisco, San Diego, Disneyland, Napa-Sonoma, and much to my surprise, a whole gamut of Central Valley cities: Sacramento, my own Modesto, Stockton, Fresno, Visalia and Bakersfield. The national parks are there: Yosemite, Sequoia/Kings Canyon, Lassen Volcanic, Redwoods, Death Valley, Joshua Tree, and Channel Islands. Mentions of the coast, Hollywood, Salton Sea. All in all a pretty good effort at nailing down the main tourist destinations, pretty much a checklist for the first-time California traveler. It even includes a few of our state symbols, the Golden Poppy, the California Quail, and the state flag.
I like the second card even more: the Natural Wonders of the State. The same national parks, plus Lake Tahoe, the Colorado River (so big and wide that it looks like California is probably already falling into the sea), the Mojave Desert, Bristlecone Pines, California Condors, Sea Otters, Mt. Shasta, and Morro Rock. Best of all, a red dotted line representing the San Andreas fault winds its crooked way across the state. I don't necessarily expect perfection in postcard maps, but this one takes the cake!
So, in future posts about the "other" California, these are generally the places I won't be talking about (I may make an exception over Morro Rock and perhaps the Bristlecone Pines).
Saturday, November 28, 2009
Tuesday, November 24, 2009
There are several distinct regions of prairies around our valley. Farther south, near Coalinga and Bakersfield, and adjacent to the Coast Ranges, the prairies are drier and more alkaline, more nearly a desert landscape. A portion of this region has been preserved as the Carrizo Plains National Monument, which I may describe in a separate post. It is also a great place to see the San Andreas fault!
The region in which I live is a transition zone between the rich agricultural soils of the Central Valley around Fresno, Merced and Modesto, and the rocky ridges of the Sierra Nevada foothills. The underlying rocks include alluvial fans that developed as muddy rivers flowed off the Sierra Nevada block during the ice ages, and some of the volcanic lahar deposits and ash flows that preceded the glacial times. Rivers have not flowed across these surfaces for tens of thousands of years since the ice last invaded the high country. This long period of chemical weathering has resulted in the development of a clay-filled soil rich in iron oxide and hardpan (caliche deposits). The occasional winter rains that we get cannot sink far into the surface, so the primary vegetation is grass and wildflowers. A few oaks dot the higher hills.
In historic time, before the ranches, these prairies were grazed by tule elk and pronghorn antelope. The pronghorns were hunted to extinction by 1920, and the elk that roam a few isolated refuges are descended from single pair found in Kern County in the 1920's. California grizzly bears also lived here. In much earlier times, prior to about 12,000 years ago, the fauna included horses, camels, bison, mastodons, and mammoths. Giant condors flew overhead. Sabertooth cats, dire wolves and American lions hunted the grazers.
Some surfaces (as in the photo above) are covered by a regular pattern of small hummocks called mima mounds. Their origin is enigmatic, but is probably related to thousands of generations of ground squirrels occupying the same individual hills year after year. Other more exotic explanations involve Native American burials, odd earthquake waves, and periglacial soil activity.
The bottom photo shows the geological relationships in the prairie outside my town. In the foreground, the protruding rocks are part of the metamorphic bedrock of the Sierra Nevada, dating to Mesozoic time. These rocks were highly deformed and deeply eroded during the late Cretaceous and early Cenozoic, between 80 and 40 million years ago (approximate dates, and mildly controversial). The erosional unconformity is covered by ash flow deposits from about 22-28 million years ago that originated near the present-day Sierra Crest around 40 miles to the east (the Valley Springs Formation). The ash is in turn covered by voluminous lahar deposits (volcanic mudflows) of the Mehrten Formation, dating to around 9-11 million years. The lahars are probably responsible for the prominent ledges on the hillsides.
Monday, November 23, 2009
Hill, M.L. and Dibblee, T.W. Jr., 1953, San Andreas, Garlock, and Big Pine faults, California - A Study of the character, history and tectonic significance of their displacements: Geological Society of America Bulletin, volume 64, pp. 443-458.
Matthews, V., 1976, Correlation of Pinnacles and Neenach volcanic formations and their bearing on San Andreas Fault problems AAPG Bulletin 60: 2128-2141
Sunday, November 22, 2009
The DeRose, under one name or another, is one of the oldest wineries in California, dating back to 1854. It was once called the Cienega Winery because of the nearby marsh that turned out to be a sag pond along the active trace of the San Andreas fault. The foundations on the original building failed for (then) unknown reasons, and the winery was rebuilt in the same location. That building came apart as well, and was again rebuilt in 1948. When the present building began cracking up, investigations by geologists showed that the winery had been constructed on top of an actively creeping section of the San Andreas fault! It has been a field trip destination for generations of geology students since the 1960's.
Saturday, November 21, 2009
Geologists get to be heros.
Oh, and Woody Harrelson dies one of the greatest geological movie deaths ever.
A lot of stuff happens, and practically everyone else dies too.
Monday, November 16, 2009
At the farm in the picture above, one has to wonder why a sharp linear hill rises out of the ground in the middle of the valley of the San Benito River. This is a scarp of the San Andreas fault, created as a hillside was split laterally and transported into the valley (because the ridge blocks off stream flow across the valley, it has been called a shutter ridge). The fault literally follows the fence line! I can think of few places where the fault is so clearly delineated.
Sunday, November 15, 2009
Thursday, November 12, 2009
THE WORLD IS NOT GOING TO END ON DECEMBER 21, 2012!
A movie is coming out, and the moviemakers benefit from lots of free publicity generated by everyone who is easily swayed by the newest and most bizarre conspiracy "theory". So it's going to be laid on really thick for the next two years, until the big day comes, and nothing happens.
It may be useless to try and explain the faulty and ridiculous logic to the true believers, because in addition to their lack of critical thinking, they also see us scientists as part of the vast conspiracy. But that doesn't mean we shouldn't try. Who knows, when the world doesn't end, maybe they will remember that we tried to explain to them just why it wouldn't.
A commenter from my previous post on this subject...
...our planet will experience a powerful event. This time we're not talking about Planet X, Nibiru or a "killer" solar flare, this event will originate deep within the core of our planet, forcing a catastrophic change in our protective magnetic field. Not only will we notice a rapid reduction in magnetic field strength, we'll also see the magnetic poles rapidly reverse polarity (i.e. the north magnetic pole will be located over the South Pole and vice versa). So what does this mean to us? If we are to believe the doomsayers, we'll be exposed to the vast quantities of radiation blasting from the Sun; with a reversing magnetic field comes a weakening in the Earth's ability to deflect cosmic rays. Our armada of communication and military satellites will drop from orbit, adding to the chaos on the ground. There will be social unrest, warfare, famine and economic collapse. Without GPS, our airliners will also plough into the ground…
Wednesday, November 11, 2009
Tuesday, November 10, 2009
Saturday, November 7, 2009
A photo from my flight to a GSA meeting in Seattle a few years ago recalls a question that had different answers, depending on when you asked the question, or more like, no answers if you go back far enough in time: Why are these volcanoes here?
The subject popped up in my head as a result of the passing of one on of my professors this last month, Donald B. McIntyre. In reading some of the tributes to his life, I recalled that he had studied under Arthur Holmes, who was one of the pioneers in the acceptance of the hypothesis of Continental Drift, which was later refined into the theory of Plate Tectonics, an idea so radical that it pretty much rewrote an entire science (imagine if the chemists discovered an idea to replace atomic theory). Dr. McIntyre was actually involved in two revolutions of geology: he was also a historian who documented the life of James Hutton in several books.
It just happened that I had picked up and started reading Plate Tectonics: An Insider's History of the Modern Theory of the Earth, edited by Naomi Oreskes. It is composed of 17 essays by the researchers who uncovered the evidence for plate tectonics in which they remember the events in their own lives that led to the new theory. It is fascinating to learn what was in their minds during the 1950's and 1960's as the realization slowly dawned that what they had always accepted about the structure and history of the earth was not necessarily true. What happens when a bunch of young professors and graduate students stumble onto something that was both unknown and unimagined?
Reading these stories made me wonder about something else. What was it like to be a teacher or professor in the 1960's when the revolution of the science was at its height? I came on the scene a bit late to really know, taking my first class in geology in 1975, when plate tectonics was already becoming established in the classroom. If you were in the classroom in the 1960's, how much of the debate filtered into your curriculum? Was it a topic of discussion in classes, or was there even a realization that something big was going on in the science? I'm wondering what it was like for the people who weren't necessarily the pioneers at the forefront of radical research. Anyone want to contribute some thoughts and memories?
The picture is of Mt. St. Helens and Mt. Adams of the Cascade Range. These volcanoes are now known to originate from melting of the crust that occurs as ocean crust (and water) are carried beneath the continent at subduction zones. It was once thought that the extra weight of sediments accumulating on the edge of the continents pushed downwards on the crust to where the heat of the planet melted the deepest rocks.
Thursday, November 5, 2009
Welcome to the Sacramento Delta. The Sacramento and San Joaquin Rivers drain most of the Sierra Nevada and Central Valley, and represent 50% of the available water resources in the state. The Delta is practically unique in the world. Most deltas extend out to the sea, like the Nile or Mississippi, but the Sacramento is far inland. This is a consequence of sea level rise following the end of the last ice age, and the arrangement of structural blocks that compose the Coast Ranges, which forces the vast drainage through a single channel at the Carquinez Straits. The Sacramento and other rivers break up into a series of sloughs and channels that define around 60 "islands". These islands were once rather ephemeral, changing as a result of yearly floods and runoff events. When the agricultural potential of the islands was recognized in the 1800's, they were surrounded and outlined by a series of levees to stop the seasonal flooding. Ultimately an area of 1,150 square miles came under the plow.
The law of unintended consequences was certainly in effect here. The peat-rich soils were originally anaerobic marshes, and buried carbon stayed buried. Once farming began, the groundwater was not constantly being recharged, the drier soils began to oxidize, and the land began to subside at a rate of an inch or two every year. Today the majority of the islands are below sea level, in many cases by as much as 10 to 25 feet. The levees prevent flooding by holding back the rivers and sloughs on a year-round basis. It is quite interesting to drive across the delta, and climb uphill in order to cross the rivers and channels!
The construction of the levees had another effect that is essentially a positive, but is also a problem. The delta is subject to tidal changes, and saltwater intrudes into the delta during high tides and droughts. Prior to levee construction, the saltwater intruded many miles further into the delta, but in recent decades the intrusion has been far less (this is also an effect of water releases from dams far upstream).
Which leads us to California's huge vulnerability: what happens if the 1800's-vintage levees fail? We have a pretty good idea because it happens on a much too regular basis, more than 100 times since 1890. Major flood events like the 1997 disaster caused levee failures in several places. Some failures have been caused by trivial things like muskrat burrowings. Singular events such as these have flooded thousands of acres. But what would happen if dozens of the islands were flooded all at once? Unthinkable? Unfortunately a very real possibility. It's all about earthquakes.
The saturated earthen levees are subject to liquefaction, where a loss of cohesion of the soil results from the breakdown of the surface tension of the water that was holding the grains together. Think of it this way. A sand castle holds its shape in damp sand, but loses it if too much water is added. If you stomp on wet sand at the beach, it will liquefy, and you will sink a few inches. The same thing can happen on a large scale with a levee, and thus earthquakes stand as one of the most greatest threats to the integrity of the levee system. And the system has not been truly tested: many of the levees hadn't yet been finished in 1906, and the 1989 Loma Prieta quake (magnitude 6.9) was too distant from the delta to have much of an effect. But a number of active faults pass through or near to the delta, and it won't require a "BIG ONE" to do the damage. A 6.0-6.5 near by on one of these faults will be more than enough.
If widespread levee failure takes place, dozens of islands will be flooded with saltwater, and the thousands of acres of prime agricultural lands will be lost. To be sure, thousands of people live on these tracts, and they will be homeless, perhaps permanently (is it really worth it to reclaim an island that is 25 feet deep in salt water?). But this isn't the biggest problem. It's that fact that 23 million people, most of the population of the state, are depending on delta water for their domestic and agricultural use.
The California Water Project and other systems pump water out of the delta for use by cities and farms off to the south. In the event of a worst-case scenario earthquake, the pumps will be fouled by salt water for months or even years. The state's single largest source of fresh water will be gone. It's a huge problem that until recently was not receiving attention, but apparently that has changed, and the legislature and governor are catching up to the pleas of the water managers about the huge vulnerability of our water systems.
There are great many other issues with the use of water in California, of which the problems of the delta are only a part: a rather extensive review can be found here. Droughts, climate change, ecosystem deterioration, and water waste are all serious problems that have to be dealt with pretty much immediately. But preventing a Katrina-style levee failure has to be near the top of the list. It could literally happen tomorrow...
I snapped today's picture if the Sacramento Delta on a flight out of San Francisco in 2006.
Wednesday, November 4, 2009
This is how one would imagine mother nature would express her sentiments about our inability to reduce global warming. It seemed an obvious place for her to appear, on the front of a retreating ice shelf, crying.
Volcanic activity may split the African continent in two due to a recent geological crack in northeastern Ethiopia, researchers said on Tuesday.
If you are expecting a story of massive disruptions of the crust, giant tsunamis, magnitude 12 earthquakes, and millions of people dead, well, no the article doesn't do that. It is a half-decent attempt (and I mean "half") by a non-science journalist (or so I assume) to describe research going on in the Afar Rift, a region where the crust is splitting and moving slowly apart.
I'm a little disappointed that the editors let such a headline go by (I wonder HOW such a thing could happen?), and even more disappointed that it took until the last paragraph of the article to point out that the process they are describing would unfold over millions of years. I've often imagined that the whole misconception that California would fall into the Pacific during the "BIG ONE" started this way. Someone read a report describing how strike-slip motion on the San Andreas Fault would eventually move part of California into the Pacific forming an island, and somehow revved up the timetable from millions of years to a single earthquake. It has unfortunately become the one thing that everyone seems to know about the San Andreas fault.
No links were provided in the article, and it didn't help that the article misspelled the researcher's name (somehow 'Ayele' became 'Arefe'). I think the article also mistook 'magnetic' for 'magmatic' (my students do that sometimes). I finally tracked down the article, the citation is below, and the abstract can be found here.
Ayele, A., D. Keir, C. Ebinger, T. J. Wright, G. W. Stuart, W. R. Buck, E. Jacques, G. Ogubazghi, and J. Sholan (2009), September 2005 mega-dike emplacement in the Manda-Harraro nascent oceanic rift (Afar depression), Geophys. Res. Lett., 36, L20306, doi:10.1029/2009GL039605.
In Paleogene time (I still like saying "Tertiary time"), the Sierra Nevada was a vastly different place. The mountains were lower, and large rivers traversed the landscape in shallow valleys. Flowing across the Mother Lode quartz veins, the rivers picked large amounts of gold, and carried it downstream. A particular channel, the Tertiary Calaveras River, flowed across an exposure of marble, part of a metamorphic exotic terrane called the Calaveras Complex.