Dear Washington State: All is Forgiven...The Airliner Chronicles Returns

The Pacific Northwest has this problem. It has two particular things in great abundance: trees and clouds. It also has volcanoes, but much of the time the first two obscure the latter. At Christmas I drove to the Seattle area and spent three days, and never laid eyes on Mt. Rainier, the gigantic stratovolcano that looms over the Puget Sound region. In the last week I had occasion to fly to the Seattle area, and being the month of May, I figured I had a pretty good chance of seeing some of the Cascade volcanoes. It started out pretty well as we left Sacramento, since I could see Lassen Peak off in the distance and then it disappeared. The clouds obscured the views all the way to Washington with the sole exception of a brief look at Mt. Adams, and the view below of Mt. Rainier.

Yeah, somewhere in there is the summit of Mt. Rainier.

That was okay. I had four days of walking and driving around Kent and Renton, and figured there would be a view once in awhile of the massive volcano. Nothing doing. There were tantalizing glimpses while driving around, but there were always trees in the way. Washington was disappointing me.

The flight home was scheduled to take off at 7:50PM so I figured there were too many things that would happen to either delay the flight until after sunset, or the clouds would be there again. But we boarded the plane on time and while taxiing down the runway I got the best ground-based picture of the mountain on the entire trip. It wasn't much, but it was something. 

And then we took off. It was hazy, and we took off towards the north and did a long turn towards the south, long enough to make me wonder if we were going to pass Rainier on the wrong side. But as the plane banked there was suddenly a very big mountain in the window, and Washington with all her trees and clouds were immediately forgiven. The mountain was stunning in the evening light.

Mt. Rainier from the runway at SeaTac.

At 14,411 feet, Mt. Rainier is the tallest volcano in Cascades Range, and is exceeded in volume only by Mt. Shasta in Northern California. It was once even higher, but glaciers have removed 1,000 feet of rock or more from the summit.  Because it is by far the tallest mountain in the Pacific Northwest it is completely covered by the largest mass of glacial ice in the lower 48 states, about a cubic mile (I read somewhere that it contains half of the all the glacial ice in the lower 48, but I can't find the source and would welcome any corrections from those who know such things). Aside from the "normal" threats that volcanoes might present to a given region (lava flows, ash flows, and that sort of thing), the snow makes the mountain far more dangerous. It's not hard to imagine why: any small eruption would melt a vast amount of ice, forming volcanic mudflows called lahars that are capable of flowing for many tens of miles, and threatening many of the cities along the southern part of the Puget Sound. The entire city of Tacoma is built on a mudflow that thundered down the mountain 5,000 years ago. The last major eruption occurred around a thousand years ago, although minor activity may have occurred several times in the 1800s. 

We flew south as the sun was sinking below the horizon and several other volcanoes appeared out of the gloom. Those pictures will come later. By way of explanation, the term "Airliner Chronicles" refers to the very first blog series I ever put together way back in 2008. One of my earliest posts in the series was also an evening shot of Rainier. By some strange convergence, that post received its first and only comment just two days ago!

The Airliner Chronicles: The San Francisco Peninsula and the San Andreas Fault

Crystal Springs Reservoir is on the upper left, while San Andreas Reservoir is on the lower right

As has been no doubt obvious, I was in Hawai'i last week, and there have already been several posts about some of my adventures. I started through the many pictures in a more chronological manner, and realized there were some neat things I saw before I even left California. I always notice on a flight that some people do such things all the time and are not particularly impressed that they are in a large metal tube traveling at hundreds of miles an hour at 35,000 feet. Others have a sense of history, realizing that for the first few million years of hominid existence, this was an unnatural thing to be doing. I don't get to fly all that often, so I tend to fall into that second category. As soon as we are off the ground, the camera that I surreptitiously placed at my feet swings into place and I start snapping pictures as if I were the first human being ever to see such incredible sights. My photo habit led to my first blog series in 2008, the Airliner Chronicles. Consider this a new entry...

It is the geologist's perspective that provides some insight as to the nature of the landscape below. We left from Oakland Airport and flew over the north end of the San Francisco Peninsula, which provided an outstanding view of the San Andreas fault. Often such faults are indicated by linear valleys owing to the ease with which crushed rock in the fault zone erodes. But on the peninsula the fault is even easier to pick out because of the presence of two reservoirs filling the linear valley, Crystal Springs reservoir, and San Andreas reservoir.

It's quite a coincidence, the fault and the lake both being called "San Andreas", so the question naturally arises, which was named first? The fault may be more famous to most people, but the lake came first. It was constructed in 1868. In 1895, the geologist Andrew Lawson was mapping in the area and discovered the fault, which he named after the lake. He had no idea that the fault was 600 miles long, or that it was particularly active, or that it was the boundary between the Pacific and North American tectonic plates. And he most certainly didn't know that it would shift in 1906 in a most tragic way.

The city has grown in the years since 1906, to say the least. We know a great deal more about fault zones and earthquakes, and thus we have a better understanding about the threats of future quakes in the Bay Area. Both by law and by subsequent experience (Loma Prieta in 1989 and the Napa Valley in 2014), the cities of the peninsula are better prepared for large earthquakes, but no matter how ready they may be, the next large earthquake will cause major damage on the peninsula and many will die or be injured. Seeing the proximity of the fault and the cities from above provides a stark reminder of the need to be prepared.

We flew out over Half Moon Bay, and soon land was left behind. There was more than 2,000 miles of open ocean ahead of us, a five hour flight. I settled in and thought of how the islands were inaccessible to humans of any kind until only a thousand or so years ago, and even a hundred years ago it took weeks or months to cross the ocean. How even more wondrous the number of bird and insect species that survived the journey over the millennia.

Airliner Chronicles: When Disaster Arrived from the Heavens

I thought briefly of making this one of those "What is it?" kind of posts, but it seemed kind of obvious. We were flying home from our weekend in St. Louis, and without a GPS, I was trying to get myself situated correctly into the geography that was drifting by slowly far beneath us. I was not too particularly successful at orienting myself while over the "flyover" states of Oklahoma, Kansas or Texas, but the fracking rigs were obvious, as were the irrigation rings, where farmers are pumping up fossil water from the Great Plains Aquifer and letting it evaporate in the intense sunshine.

Once we reached lands with actual topography, I began to suspect where we were...was that Las Vegas, New Mexico? What about that town? Santa Fe? It turned out I guessed pretty well, and also recognized the holy peak of Mount Taylor in New Mexico, and the Ambrosia Lake Mining District. But it wasn't until I saw the intense magenta of the Painted Desert and the unique road loop near the northern visitor center at Petrified Forest National Park that I knew precisely where I was. And then I realized that Meteor Crater was just ahead. I was sure that the plane would go right over it and it wouldn't be visible, but luckily I was wrong. I had a box seat view (although metal cylinder seat view would be a better description). I was, in a word, thrilled. I'd never seen it before from above.

Meteor Crater is justly famous as one of the best preserved meteorite impact sites in the world. Roughly 50,000 years ago, when camels, horses and mammoths were grazing the grasslands, the sky lit up with fire and a chunk of space rock about fifty feet long impacted the surface at a speed of 30,000 mph. The ensuing cataclysm produced a crater about 1,200 m (3,900 ft) in diameter, and 170 m deep (570 ft).

Meteor Crater is privately owned, but the company has done a good job of protecting this unique site. They are especially good at accommodating school groups on tours. You can check out their website at http://meteorcrater.com/.

The "Airliner Chronicles" was one of my first web series, and whenever I fly somewhere, I add to it. I got a few other shots, so if I am not too distracted with Hawaii preparations, I will post some.

The Airliner Chronicles: the San Andreas Fault in Southern California

The San Andreas fault at Cajon Wash and Lone Pine Canyon at the eastern end of the San Gabriel Mountains

Oh how I love flying. I don't get all that many chances to do it, and flying on days with clear weather happens even less often, but sometimes it works out. One of my first blog series was called the Airliner Chronicles, and in it I featured geology from an aerial perspective. I haven't flown in a number of years, but I had a brief trip to Southern California last month, I scored a window seat, and managed to chose the correct side of the plane, so I got to see some marvelous perspectives of the San Andreas Fault.

Mount San Antonio is the highest peak in the San Gabriel Mountains at 10,069 feet (3,069 meters). The highway in the foreground is Interstate 15 heading towards Cajon Pass.

What made the views so memorable was that they were in the San Gabriel Mountains, which just a few weeks ago were made into a National Monument. These were the mountains of my youth, the peaks and valley where I learned to camp, hike, and climb. I've seen these mountains from down in the canyons, and from the tops of the peaks, but never so well from high above in a plane. The flight was too short!

The San Bernardino Mountains are higher than the San Gabriel Mountains on average, but not generally as rugged. I was on the wrong side of the plane for good pictures, though.

The San Andreas fault slices through 600 miles of California, but the most rugged stretch of its path is along the northern edge of the San Gabriel Mountains. The fault actually crosses the Transverse Ranges, offsetting the San Gabriels from the San Bernardino Mountains at Cajon Pass. The presently active stretch of the fault has shifted at least 130 miles in a right lateral sense (when standing on one side of the fault, the other side shifts to the right; a left lateral moves the opposite direction). The grinding of the rocks along the fault produces a powdery material called gouge that is easily eroded. The fault reveals itself as a series of linear valleys that cut across the mountain ridges. I've provided labeled versions of most of the pictures showing the trace of the fault.

The San Gabriel Mountains are moving northwest along the fault.

I passed the small mountain village of Wrightwood, a town with a lot of geological problems. Not only does it sit directly on the San Andreas fault, it also lies at the base of a steep mountain ridge composed of deeply sheared Pelona schist. When wet, the schist is prone to failure, and there have been a number of serious mudflows over the years including an event in 1941 that buried 190 acres. The scars of the landslides were easily visible from above.

The village of Wrightwood on the San Andreas fault. The Heath Canyon Mudflow started at the scars on the left side of the photo.

The San Andreas has produced a number of very large earthquakes in Southern California, most notably in 1857, an event with an estimated magnitude of 7.9. The quake fractured the ground for a distance of 225 miles (350 kilometers) from Cajon Pass to Parkfield in the Central California Coast Ranges. The ground shifted as much as 30 feet (9 meters), with an average of 15 feet (4.5 meters). Trees that were damaged in the quake can still be seen in Wrightwood. The average recurrence interval over that last few thousand years has been about century, but it varies widely from a few decades to more than 300 years. It is considered one of the more likely faults to produce large earthquakes in coming decades.

Wrightwood on the San Andreas fault in the San Gabriel Mountains

A bit further I could pick out the Mountain High Ski Resort and the deep gorge of the East Fork of the San Gabriel River. The heart of the newly established San Gabriel Mountains National Monument, the East Fork is around 4,000 feet deep, almost as deep as the Grand Canyon.

Mountain High Ski Resort and the East Fork of the San Gabriel Canyon

The canyon is unique. It was the focus of a huge political battle in the 1970s over a wilderness designation that brought much of the canyon under protection from mining and development. There are herds of Nelson Bighorn Sheep and natural trout fisheries in the depths of the canyon tributaries. Development was always a dicey proposition. There is little in the way of flat terrain, and terrible floods have scoured the canyon bottom on numerous occasions. There is a paved "bridge to nowhere" in the lower canyon. The road it was once connected to was washed away long ago.

Further west there is a fine example of a shutter ridge. These are mountain ridges that have been moved laterally by the fault in such a way as to block of the river drainages from the other side of the fault, deflecting the streams sideways.

A shutter ridge along the San Andreas fault in the San Gabriel Mountains

The winding road in the picture is the Angeles Crest Highway, which was opened for traffic in 1956. It is an anachronism, built in a time when development was encouraged in the national forests. It goes for 66 miles from La Canada in the L.A. Basin to Wrightwood. In such steep terrain, keeping the road open is a challenge. Landslides and slope failures are commonplace along the highway.

Shutter ridge on the San Andreas fault

 A special geological treat from the air is Devils Punchbowl, a Los Angeles County Park. The park lies on an ancient strand of the San Andreas fault. The sandstone and conglomerate of the Punchbowl Formation was twisted into a plunging syncline, a downward pointing fold with an axis that slopes to the west (to the right in the picture below).

The Devils Punchbowl, a west plunging syncline in resistant layers of conglomerate and sandstone.

Devils Punchbowl is a marvelous little park with memorable hiking trails that explore the steep fins of sandstone. You can see some pictures from ground level of the region in this post from last year.

Offset stream near Palmdale. The dark line is the California Water Project.

As we neared the town of Palmdale, I could see examples of offset streams. These are stream channels which have been shifted and separated by the lateral motion along the fault.

My flight also included a stretch of the fault system a little farther north. I'll try to include it in the next post.

The Airliner Chronicles: Glory in the Skies (not a religious post, though)

Pilots and frequent fliers are no doubt familiar with the phenomena, but for infrequent fliers like myself (I will qualify for a free flight sometime in the middle or late Anthropocene epoch), this was new. We were headed east in the late afternoon approaching Las Vegas when I saw a strange optical effect in the clouds directly opposite from the sun. I could see a spectrum of colors, but it was most certainly not a rainbow, although some of the same optical physics principles turn out to be involved.

I zoomed on the colorful arc for a better look. I vaguely remembered hearing about the phenomenon but for the life of me I couldn't remember the name. It's called a "glory", or in more modern times, the "glory of the pilot". It happens when the observer has the sun behind, and clouds in front. Light is backscattered in the water droplets of the cloud and diffracted, and as such is similar to the formation of a rainbow, but is different in size and pattern. According to (the always dependable) sources on the Internet, the dynamics of the light pathways are not fully understood. It was first noted by mountain climbers, where it was associated with an apparently magnified shadow of the observer called a Brocken spectre. The climber will see the colorful arc surrounding their head like a halo.

Luckily, we were descending for our landing at Vegas, and we passed right through the clouds, so I was able to catch a few shots of the airplane version of a Brocken spectre: the glory around the shadow of the plane we were in. It was small at first, but then we passed right next to a tall cumulus cloud, and the image was much larger (below). The placement of the glory actually reveals what part of the plane I was sitting in!

The Airliner Chronicles is one of my on-again/off-again serial features, which is usually updated whenever I fly somewhere.

The Airliner Chronicles: A Broken Land of Unspeakable Violence

That's an inflammatory title, and yet in the context of geology it is quite literally true. The land in today's picture is indeed broken, and was the scene of unspeakable violence 760,000 years ago. If such an event were to recur, it's a fair bet that civilization could end up in danger of collapsing into unrecoverable chaos.

Yellowstone National Park gets a lot of attention for being a "supervolcano", and numerous TV documentaries fan the flames of concern about the possibility of a giant eruption in the midst of our country. It's quite true that a full scale explosion like those that have happened three times in the last 2.1 million years could wreak havoc on a wide scale, but Yellowstone hasn't actually had an eruption in 70,000 years.

The proper geological name we geologists use for a "supervolcano" is rhyolite caldera. This works a little better because these calderas are not volcanoes in the normal sense of the word. They are gigantic holes in the ground caused by the collapse of the crust after vast amounts of magma are blasted into the atmosphere. Some calderas were singular mountains at one time (like Mt. Mazama, which collapsed to form Crater Lake in Oregon). Others weren't. They were volcanic centers that included a collection of smaller cones and lava flows. The collapse of giant calderas seem to begin with smaller eruptions that grow in intensity over a time scale measured in decades or centuries. That's why Yellowstone caldera is of somewhat less concern to geologists (that's not to say that lesser eruptions aren't impossible). What is less known to many is that we have more than one recently active rhyolite caldera in the United States; we actually have three. I got a close look at the other two on my plane flight in December.

My flight took a more southerly route than past trips, and as we crossed the crest of the Sierra Nevada, I realized I was flying directly over the north end of the Owens Valley and the Volcanic Tablelands. The Tablelands are the southeastern flank of the Long Valley Caldera, California's version of a "supervolcano". And if anything, it's more dangerous than Yellowstone, if for no other reason than the fact that volcanic activity is ongoing, even though gigantic eruptions like the one that rocked the region 760,000 years ago are unlikely.

The caldera itself was obscured by clouds, but I had a perfect view of the Tablelands, a region adjacent to the caldera that was covered by 400 feet or more of volcanic ash that was so hot when it landed that it welded itself into solid rock. The pink colored rock is called rhyolite tuff. The tuff from this eruption is called the Bishop Tuff.

The scale of the eruption is hard to imagine. For perhaps a week, huge explosions blew ash into the stratosphere. Not a little bit of ash; it amounted to around 150 cubic miles of ash. The ash buried the local landscape under hundreds of feet of hot steaming rock, while some ash deposits have been found as far away as Kansas and Nebraska.

The collapse of the caldera was a stupendous event as well. The hole was around 20 miles long and 10 miles wide, and as much as 1-2 miles deep (much of the caldera was filled with ash during the eruption itself as the ash column collapsed downwards). After 760,000 years, it is still plainly visible in satellite imagery and topographic maps (below).

After the eruptions ceased, water started to fill the caldera, eventually forming a 1,000 foot deep lake. The lake ultimately breached the margin of the caldera and rapidly carved a gorge hundreds of feet deep across the western edge of the Tableland. The walls of the Owens River Gorge expose a fine cross-section of the rhyolite tuff, allowing geologists to work out the sequence of events during the eruption.

Map courtesy of GeoMapApp

The Tablelands provide a window into the tectonic environment of the region. By covering the slope like a thick blanket, the tuff provided a blank slate on which post-eruption faulting can be easily seen and analyzed. There are dozens of faults, mostly trending north or northwest, with scarps that face west (the sunlit terraces) and east (the shadows). Geoblogger Callan Bentley provided a marvelous grounds-eye view of these faults in this post on his old NOVA Geoblog (Callan is now blogging primarily at Mountain Beltway under the auspices of the American Geophysical Union; he's always posting something interesting).

There is a much more extensive example of the broken nature of this landscape. The prominent mountain range on the upper right of the picture below is the White Mountains. In any other setting this mountain range would be a national park, but lying east of the Sierra Nevada, it sort of loses out. It tops out at 14,242 feet, rising as much as two miles above the adjacent Owens Valley. It is a gigantic fault block that formed when the land that is now the Basin and Range province began stretching and collapsing, forming a series of horsts (mountain blocks) and grabens (faulted valleys). The mountains lie in the rain shadow of the Sierra and never formed glaciers of any great extent. The highest arid slopes play host to the most ancient life on planet Earth: the Bristlecone Pines. The oldest Bristlecone is 5,062 years old. The Whites are a fascinating (and lonely) place to visit.

The Airliner Chronicles is one of my on-again/off-again serial features, which is usually updated whenever I fly somewhere.

The Airliner Chronicles: There Were Glaciers Here...

Have you ever wondered about recessional moraines? I guess not too many people have pondered such a deep question, but on my recent flight over the Sierra Nevada, I was excited to see what was without a doubt the best example I've ever seen of this feature.

Recessional moraines are the piles of glacial till (loose debris) that form around the terminal margins of glaciers that are in the process of melting back over decades or centuries. Quickly receding glaciers might not leave such ridges, but if the climate briefly stabilizes, the moraines will form around the end of the glacier. Such moraines can be hard to see at times. There are several prominent moraines in places like Yosemite Valley and Kings Canyon, but they are covered by forests and are thus difficult to see from above. When the reservoir holding back Lake Thomas A. Edison in the upper drainage of the San Joaquin River was constructed, the forest cover was removed. During the winter, the lake is mostly drained, and with the low sun angle on snow, the moraines stood out in sharp relief.

The moraines were mapped by Joseph Birman in the 1950s as Tioga stage glaciers, dating back to around 20,000 to 13,000 years ago. This was the last major glacial episode to affect the Sierra canyons, and was responsible for most of the lakes and glacial polish that can be found in the mountains today.

Moments later we were flying along Mono Creek leading to the Sierra Crest, where I could see a multitude of classical glacial features. In one view I could see all the features I am always trying to sketch on the chalkboard in my classes illustrating the erosional features of alpine glaciation. I've labeled some of the most obvious features below.

As uncomfortable and inconvenient as flying can be, I was having a pretty good time!

The Airliner Chronicles is one of my on-again/off-again serial features, which is usually updated whenever I fly somewhere.

The Airliner Chronicles: Three Faces of California's Great Valley

According to this interesting article from the New York Times, it's larger than 9 American states. It is the largest patch of Class 1 Soil in the world (i.e., the best for agriculture). More than 230 kinds of crops and produce are grown there, and the output represents 8% of the nation's agricultural output (on 1% of the land). Around 6.8 million people live there, and the average per capita income is lower than most of the rest of the country (it has three of the five poorest cities), and unemployment is far higher. It is California's Great Valley, my home.

From http://en.wikipedia.org/wiki/File:Map_california_central_valley.jpg

The valley is 400 miles long, 30-50 miles wide, and is almost entirely flat (except for the Sutter Buttes, the highest elevations are 400 feet or less). It is drained by several major rivers, including the Feather and Sacramento Rivers to the north, and the San Joaquin, Kings and Kern Rivers to the south. Although most of the rivers leave the valley through the Sacramento Delta into San Francisco Bay, those in the south do not. They once ended in huge lakes like Tulare and Buena Vista, but today the lakes are long gone, having been dried up by agricultural diversions upstream.

I've long heard that only 5% of the valley remains in the natural state that existed prior to agricultural development, and from the air, this is obvious. All the times I've flown over it, I have been struck by the continuous patchwork of plowed fields (it clearly resembles the kinds of blankets my grandmother used to make out of the leftover fabric squares). There are a few tracts of undeveloped grasslands off to the south, but for the most part only the rivers retain much of their original vegetation, but only in a few places.

Today's photos come from three distinctly different parts of the valley's river systems. In the colorful top photo, we can see a portion of the Sacramento Delta, where the San Joaquin and Sacramento Rivers come together in a maze of islands that have been mostly converted to farmlands. The islands are protected (somewhat) from seasonal floods by a series of poorly constructed levees that are subject to destruction from even moderate earthquakes. This has set up what potentially could end up as California's worst possible natural disaster (at least in the monetary sense). The islands have been sinking due to groundwater withdrawal, soil loss, and oxidation of organic material in the soils. Most of them are now below sea level, with only the vulnerable levees keeping them from being flooded. Since the intake pumps for the California Water Project lie in the midst of these islands, broken levees will draw salt water into the delta, where the domestic water supply for most of the southern state is tapped. An earthquake has the capability to disrupt the state water system for several years.

The north end of the Great Valley is drained by the Sacramento River which can be seen in the photo above, taken near Colusa. The landscape has been completely co-opted by agricultural fields, right up to river's edge. It looks like the river has been "conquered" and tamed by the works of humankind, but floods like those of 1997 and especially of 1861-62 could leave just about the entire area in the photo above under 10-20 feet of water (see my take on these ARkstorms here).

The San Joaquin River drainage contains some of last remaining natural grasslands and riparian landscapes in the Great Valley. The structure of the valley is that of a series of shallow basins separated by the alluvial fan systems formed by the Merced and San Joaquin Rivers. The basins have essentially caused the river to back up and develop wide floodplains where the streams meandered widely, changing channels in unpredictable ways. The area in the picture above is just north of the town of Los Banos, an area of abandoned meanders, bogs and swamps protected as the San Luis National Wildlife Refuge and Great Valley Grasslands State Park. The land is not entirely unaffected...decreased flows caused by reservoirs and diversions upstream have caused many of the swampy areas to dry up. Efforts (and negotiations) are ongoing to increase river flows in a hope of rebuilding the disrupted ecosystems, especially those of the salmon which used to be common in these waters.

The Airliner Chronicles is one of my on-again/off-again serial features, which is usually updated whenever I fly somewhere.

The Airliner Chronicles: Wrinkles Tell a Lot About a Person (and the Earth, too)

My grandfather had wrinkles. Lots of them. He was a man who spent a large part of his life working outdoors in the days before sunscreen lotions. You could see in his face the rigors of the Great Depression and the tough choices that came with trying to farm in Oklahoma and Texas in the Dust Bowl years.

In the same way, the Earth tells a story through the pattern of wrinkles on the surface of the planet. Some rocks are softer, others are harder, and some are in horizontal layers while others are tilted. Some aren't in layers at all, such as plutonic intrusive rocks, so the type of rock exposed is fairly uniform, unless it has been broken up by jointing. Water and other agents of erosion attack the rocks in a differential manner, and reveal something of the underlying structure in the way that streams cross the landscape (the most commonly recognized drainage patterns are shown in the diagram below).

The top left frame should be labeled "Dendritic", and the top right "Parallel". From NASA (http://daac.gsfc.nasa.gov/geomorphology/GEO_4/GEO_CHAPTER_4.shtml)

In the case of my last airline trip, it was a quick way of determining what part of California's Coast Ranges I was flying over. The Coast Ranges are about as schizophrenic as can be: crossed by the iconic San Andreas fault and dozens of others, numerous tracts of rock are juxtaposed against each other. These rock groupings, called terranes, include rocks related to the Sierra Nevada batholith (the Salinian Block), the Franciscan Complex (rocks formed within a trench-subduction zone during Mesozoic time), the Great Valley Group (rocks that formed in a forearc basin between the trench and the Sierra Nevada volcanic arc), and the Coast Ranges Ophiolite (rocks derived from the oceanic crust of the Pacific/Farallon plates and the underlying mantle).

The first photo above doesn't reveal a lot of rock, as most of the surfaces are covered by grass and brush. If you concentrate on any one drainage, you will notice that many small tributary channels gather into larger and larger channels in the way that a tree has multitudes of branches that end up at a single trunk. This is an example of dendritic ("tree-like") drainage pattern, which indicates that the underlying rock is fairly uniform. There is no evidence of sedimentary layering, and thus the rocks must be part of the Salinian Block, the Coast Range Ophiolite, or the Franciscan Complex (layers are found over short distances in the latter two, but not enough to effect the overall drainage pattern). Of course, this part of the Coast Ranges is right in my backyard, so I knew I was seeing mainly the ophiolite found in the upper part of Del Puerto Canyon above the town of Patterson.

On the other hand, look at the picture above, from the easternmost part of the Coast Ranges (the town of Patterson is the light colored area in the upper right hand side). The shadows on the right half of the picture run parallel to each other, but at right angles to the eastern margin of the mountain range. Streams that would be expected to run from left to right down the slope of the mountains are deflected into northwest trending strips. Clearly some of the rock here is more resistant to erosion, and the pattern suggests sedimentary layers that have been turned on edge. This is the hallmark of the Great Valley Group. These rocks were laid down in a shallow sea that subsided and collected more sediments and subsided under the weight of the overlying sediments again, over and over. Eventually the sediments reached a thickness of 20,000-25,000 feet. Later deformation turned this incredibly thick sequence on end forming a vast homocline, indicated by the trellis drainage pattern.

I saw one other really distinctive drainage pattern on my trip, but far removed from these first two photos. If you look at the photo below, you might pick out that many of the smaller channels are dendritic, but that the larger channels are roughly parallel to each other. This is called a parallel drainage pattern, caused by streams eroding uniform, but slightly sloping rocks. I was lost at the moment because we had been flying over clouds for several hours, but the moment I saw these channels, I knew exactly where we were: on the flanks of the Valles Caldera (sometimes called the Jemez Caldera). There is no other place in New Mexico (and indeed most of the southwest) quite like it.

The caldera is a vast volcanic feature which formed when a gigantic eruption about 1.15 million years ago coated the entire region with around 70 cubic miles of volcanic ash. The volume of volcanic ash blown out of the volcanic vent was so great that the center of the volcano collapsed inwards, forming the caldera. Popular media outlets call these calderas "supervolcanoes" (Yellowstone being the most famous example). The NASA image below gives a wider perspective of the volcano. The circular mounds in the central area are volcanic cones that erupted years later. From this perspective (and distance), the drainage could be considered more of a radial pattern.

Image courtesy of NASA (http://earthobservatory.nasa.gov/IOTD/view.php?id=50666)

The Airliner Chronicles is one of my on-again/off-again serial features, which is usually updated whenever I fly somewhere. These pics were from a flight to and from St. Louis during the Christmas break.

The Return of the Airliner Chronicles! The San Andreas Fault in San Francisco

I love flying. Well, I don't like airports. Or security lines. Or airliner food. Or uncontrollably crying babies (though I have sympathy for the poor parents sometimes). Or the incredibly small seats. Or the lack of foot room. Or looking for lost baggage. Or airport shuttles. I don't like all of that stuff.

But put me in a window seat on a clear day, and a route over a geologically interesting place, and I will be deliriously happy. I will easily snap dozens of pictures when conditions are right. The Airliner Chronicles was my first idea for a blog series, and I abandoned it for a few years only because I haven't flown anywhere since 2009. But I flew this holiday vacation, so I am pleased to return to the Chronicles once again.

I usually fly out of San Francisco, but it has been rare that I have had a clear view of the San Andreas fault in the Bay Area. On this flight, I almost felt the pilot knew I was on the left side, and that I wanted as many sight angles on the fault as possible, so he or she banked us nicely for four perspectives of the San Andreas fault as it runs from the hills above San Jose to the sea at Daly City near San Francisco.

Have you ever wondered how the San Andreas fault got its name? In 1895, U.C. Berkeley professor Andrew C. Lawson mapped a fault in the Bay Area that crossed San Andreas Lake/Reservoir (which is at the bottom of the first three photos; the other lake is Crystal Springs Reservoir). The 1906 San Francisco Earthquake made it clear that the fault was a much larger feature (200 miles fractured in 1906, but the fault extends some 600 miles to the Salton Sea area in Southern California).

The dam that holds back San Andreas Reservoir was damaged in the 1906 event, but the dam held. The west side of the fault (right side in the photo above) lurched about 9 feet northwest during the quake. Faults that move sideways like this are called strike-slip faults, and if the side of the fault opposite the observer moves to the right, it is a right-lateral strike-slip fault. The San Andreas is this type of fault.

Even more importantly, the San Andreas fault is a transform boundary, marking the spot where the Pacific Plate is moving northwest relative to the North American Plate (or the Sierra Nevada Microplate if you want to be really specific). The fault has been moving for nearly 30 million years, and has shifted 200 miles or more (roughly 2 inches per year). It would be more correct to say that the fault would shift 2 inches per year, but friction holds the sides of the fault in place until enough stress has built up (a century or two) that the fault breaks and moves 10-20 feet all at once in a large earthquake like the one in 1906.

We banked one more time and had a wonderful look at the entire San Francisco Peninsula before heading east towards the Sierra Nevada...

The Airliner Chronicles: Epicenter of a Geological Education

I had forgotten how much I enjoyed going through my aerial shots when I first started blogging, so I am reviving my Airliner Chronicles, just for the heck of it. I was on a flight to Williamsburg a few years ago when I realized with a start that I was flying right over my thesis area. Though I was never really thrilled with the final product, I did in fact complete the thesis and they let me graduate, to the heartache of 20 years worth of community college students who have taken my classes.

For my thesis, I was looking for evidence of Holocene faulting in the Sierra Nevada/Great Basin Boundary Zone in the area around the Sweetwater Mountains and Antelope Valley. The West Walker River flows through the area, on its way to evaporate in the sump of Walker Lake, a remnant of Pleistocene Lake Lahontan.

Some of my relatives had a house in Walker, California, that served as my base camp for the summers that I spent exploring the region (Walker is the village in the lower half of the photo; the house is one of those on the river just left of center). As can be seen in the photo above, the West Walker emerges from a deep canyon carved in typical Sierra Nevada granites, and forms a modified alluvial fan at the south end of Antelope Valley, a deep fault graben marking the edge of the Basin and Range Province. The bank of the West Walker River served as a wonderful outdoor lab on hydrological processes. Over a 15 year period I was able to monitor drought conditions, floods, bank erosion, and riparian vegetation changes. I learned a great deal, but there was nothing in my experience on the river to compare with the events of New Years Day, 1997.

For those of you who lived in California or western Nevada at the time, the floods of 1997 will be remembered for a long time. A record snowpack coated the Sierra Nevada, but a Pineapple Express, a warm tropical storm out of the Pacific, took aim at Central California. Precipitation amounts in a two day period reached as much of three feet, mostly falling as warm rain on the snowpack. Record flows were recorded on numerous rivers, but I don't think any of floods smashed the old records the way the West Walker did...until 1997, no flood had ever exceeded 6,800 cubic feet per second. On January 2, 1997, the river hit 12,500 cfs. This is an estimated 500 year flood (a one in 500 chance of occurring in any one year).

The effects on the little village and surrounding region were profound, to say the least. Highway 395, the primary north-south artery between Reno and the Los Angeles region, was simply erased in the ten miles upstream of Walker. The ripped up road fragments, granite boulders, and uprooted trees became battering rams that pounded the unprotected hamlet of 500 or so people. Numerous houses, cabins and businesses were washed away. Much of the floodplain adjacent to the river channel was buried under several feet of gravel and cobbles, and the original river course had been split into two or three separate channels. Flooding in Reno and Carson City tied up emergency personnel, so the people of Walker were left to their own devices, and the hard work of the handful of highway patrol officers and county sheriffs in the area. Eventually a helicopter was brought in to rescue some stranded motorists. There weren't any television cameras recording the drama; they were too busy elsewhere.

I was not there to see the worst of it. I knew from the news reports that terrible things must be happening up there. It was about two days before we found a route into town, and the property was a mess. Against all odds, the house on the river survived the onslaught. Knowing the odds of a flood, my relatives had built an earthen berm around the house, almost like a fortress wall. The river had flowed full force into the berm, and was in the process of undercutting the foundation when a large pine got wedged into the opening, diverting the flow to the south (and eventually burying their truck in the mud). Their doors even held back the mud, and they might have been ok...except for the cat-door. Mud and silt flooded into the house to a depth of a foot or two. There would be a lot of cleaning up to do in coming months. Thankfully the relatives had flood insurance.

The following month had only one cold storm, and that February was one of the driest on record. No one minded. Clean up went on, and eventually the Army Corps of Engineers decided they wanted to put the river back where it used to be. This was an impressive process to watch. They had really big bulldozers to clear the old channel of debris, and I was sitting on the riverbank the day they made the cut that diverted the prodigal river back where it was supposed to be. We cheered as the river came back home...

After that flood, my relatives decided they had other priorities for their lives and sold the house. The new buyer found out that the legal floodplain level was now two feet higher than it had once been, and the house was now out of compliance. He solved the problem by taking the entire house and lifting it up eight feet and inserting a garage and basement underneath. I didn't recognize it the next time I came through town.

Do you have a good flood story?