Saturday, November 10, 2018

Horrible



And you know the sun's settin' fast 
And just like they say nothing good ever lasts 
Well, go on now and kiss it goodbye but hold on to your lover 
'Cause your heart's bound to die 
Go on now and say goodbye to our town, to our town 
Can't you see the sun's settin' down on our town, on our town 
Goodnight

Our Town, by Iris Dement

I'm heartbroken over the tragedies unfolding around my beautiful state.

I snapped this photo from a Home Depot parking lot near Modesto. Paradise is a long distance from us, but the smoke moved south very quickly, darkening the evening sky to the west. We've been hit hard this year by these fast-moving wildfires and we are long past when the winter rains should have arrived and put an end to the fire season. It's been savage.

Help out if you can. We've only got each other.

Charity Navigator: https://www.charitynavigator.org/index.cfm?bay=content.view&cpid=489

American Red Cross: https://www.redcross.org/about-us/news-and-events/news/2018/california-wildfires-red-cross-helps-as-thousands-evacuate.html

Friday, November 2, 2018

I Went Rock Collecting Today...For Really, Really Big Rocks

I'm thinking how many times I've been on a field trip looking at a massive boulder composed of some kind of interesting rock and making a joke about how we would need a crane to get the thing back to school. I'll be darned if that very thing didn't come true today.

I was up in the Sierra Nevada foothills, choosing out some really big rocks, and we may very well be using a crane to move them back to campus. At least one of them weighs about 3 1/2 tons, and in total there will be about 60 tons of them. So yes, maybe my rock collecting habit has gotten out of hand. I need professional help.
Well, I might need professional help for something, but it's not for a colossal rock-collecting habit. I was selecting rocks representative of the geology of the Sierra Nevada foothills to become part of the landscaping of our new Great Valley Outdoor Nature Lab that is being constructed right now adjacent to the Great Valley Museum at Modesto Junior College.
At this particular quarry near Knight's Ferry on the Stanislaus River I was selecting boulders of Table Mountain latite (a volcanic rock broadly similar to basalt). These are the rocks that make up the dramatic inverted stream that winds its way among the towns of Sonora and Jamestown along Highway 108. I was also picking out some large granite and greenstone boulders to representing the bedrock found in the Sierra Nevada. We'll also be choosing some of the unique metamorphic "tombstone" rocks that stick out of the ground across the Mother Lode.

Meanwhile back on the campus of Modesto Junior College the outdoor nature lab is starting to take shape. We live in a flat valley, but the lab will have some topography, some small hills at the east end to represent the foothills. They will be planted with native trees and shrubs, and the trails and pathways will be lined with the rocks and boulders that we selected today. One of these days, the lab might look something like the scene below (which is actually at the quarry; they're showcasing what can be done with their rocks). It's incredible that the lab is finally happening. The science faculty at MJC have been fighting for an outdoor lab for three decades. It's been hard to be patient!

Sunday, October 28, 2018

The Magic of a Pristine Cave: Wanderings in the Black Chasm

The miners were not kind to the caverns of the Sierra Nevada.

The search for gold in the foothills led fortune-seekers all over the hills and valleys of the Mother Lode in the Sierra Nevada, and practically every slope and hollow was prospected for the elusive metal. They usually came up empty of the riches they sought so eagerly, but many times the miners would encounter an unexpected opening in the outcrops of marble that occurred here and there in the Calaveras Complex. They discovered dozens of caverns.
Helictites at Black Chasm cave
For light they used torches and candles, and they didn't hesitate to break off cave decorations (speleothems) as souvenirs. A few enterprising miners realized they wouldn't get rich with gold so they charged admission to their caverns and made money from tourism instead. But they didn't control the behavior of their guests, and more speleothems disappeared. The once beautiful and intricate caverns were reduced to mere holes in the ground, and what decorations remained were grimy with soot and muddy fingerprints from visitors using them as handholds.
The "dragon" at Black Chasm
To be sure, times haven't changed that much. Spelunkers learned long ago that publicizing a newly discovered cave was often a death knell, so locations are kept a highly-guarded secret, and when possible vulnerable caves are fitted with locking gates. But there are two exceptions. California Caverns and Black Chasm cave have rooms that were inaccessible and undiscovered during the Gold Rush, and these have been developed carefully in such a way that the original appearance of the cave has been preserved. We visited Black Chasm today as part of my field class on the caverns and karst topography of the Mother Lode
Soda straws (straight) and helictites (twisted) at Black Chasm cave
Folks are sometimes surprised to find out the true color of stalactites and other speleothems; they're pure white. And they are so incredibly delicate. So-called soda straws and helictites are so fragile that a single touch will break them off, destroying thousands of years of exceedingly slow growth.
Soda straws (straight) and helictites (twisted) at Black Chasm cave
The helictites of Black Chasm are particularly memorable. There are thousands and thousands of them, possibly the greatest accumulation of any cave in the country. The room where the visitors can view them is just one of several. The others are off-limits, and appropriately so. The origin of the helictites is obscure and is debated by cave researchers (speleologists). They obviously ignore gravity.
Black Chasm cave is privately owned and offers tours (for a fee of course) all year long. They are located adjacent to the village of Volcano a few miles up the hill from Jackson on Highway 88. There are other "attractions" for kids at the site (panning for gems, breaking open geodes and that kind of thing), but they also offer some surprising sophisticated cave research publications for sale. They have always been very cooperative about arranging tours for our college groups. If you are ever in the Mother Lode, don't pass up this opportunity to see some truly pristine caverns.

Wednesday, October 24, 2018

Getting Under the Skin of a Volcano: Travels in Lava Beds National Monument


What in the world is going on here?? What are these spikes coming out of the ceiling? Is it some kind of deadly trap for Indiana Jones or Lara Croft? Well, no, but they'll hurt like the dickens if you try exploring them without a hardhat. In some of the previous posts in this short series we explored the deep heart of the magma chamber beneath a volcano, and we went both on and above Mt. Shasta to see the dramatic exterior of a volcano. Today we burrow under the skin of a volcano.

Medicine Lake Highland is the biggest volcano in California. It may be barely half as high as Mt. Shasta, but it makes up for the height deficit with broad gentle slopes, giving it a volume of around 130 cubic miles, compared to about 85 for Mt. Shasta. It is classed as a shield or "shield-type" volcano, composed largely of basalt, but with varying amounts of andesite and rhyolite. As such, it displays a wide variety of volcanic phenomena, not the least of which is a dizzying array of lava tubes. A flank of the volcano is preserved as Lava Beds National Monument, and the park has within its borders the highest concentration of lava tubes in the country, if not the world. More than 700 individual caves are known at Lava Beds with a total length of more than 70 miles.

How do lava tubes form? The picture above shows an active lava flow at Pu'u'o'o Crater on the Kilauea volcano on the Big Island of Hawai'i in 2009. The scale in this aerial view is difficult to discern but the skylight (where the red lava is visible) is probably 30 feet across. The tubes develop when river-like lava flows crust over. The lava continues to flow just beneath the surface, sometimes for many miles, being insulated by the overlying crust. The flow in the picture above flowed seven miles to the shoreline and was only a few tens of degrees cooler than it was when it emerged at the vent of Pu'u'o'o. When the eruption ends, the lava drains from the tubes.
The tubes can be quite complex, with bifurcating passageways and multiple levels (one particularly complex cave is called the Catacombs). During our recent visit at Lava Beds we explored Valentine Cave, one of the most accessible in the park. The majority of the tubes are in the Mammoth Crater flow which is around 30,000 years old. Valentine is in a younger flow, around 12,000 years old, so it has less collapse debris than many of the older caves (although it is true that many fallen boulders were removed by CCC workers during the Great Depression). In any case, the passages are easy to negotiate.


Being composed of very dark rock that tends to absorb light, tubes are notoriously hard to photograph. Flash photography tends to produce washed-out photos with little depth. I was using a bright flashlight for illumination and was holding it at arms length to get shadows that provide a sense of depth. I tried using my normal 'sophisticated' camera, but I actually got better results from my Samsung phone!
There are many interesting flow structures in the caves, including the pahoehoe flows on the floor of the caves, and "bathtub rings" on the walls showing that some flows only filled the cave a third full.
The basalt fractured as it cooled, forming the numerous cracks in the roof of the cave. Subsequent weathering in the soils above produced sodium bicarbonate and other chemicals that stain the edges of the fractures.
A lava cascade emerges from a side passage in Valentine Cave.
The lava tubes of Lava Beds National Monument are a fascinating environment to explore. Some of the caves have multiple levels, and some are decorated with permanent ice. One, Fern Cave, has numerous Native American pictographs and also ferns, which is interesting because ferns are not otherwise found in the park; they are a species of the western Cascades. The cool damp environment of the cave provided the right conditions for the plants, which may have arrived on birds feet (I'm guessing here).

There is a lot to do in Lava Beds. The ice cave and Fern Cave can only be visited with a ranger guide, but around twenty caves are open and developed for unaccompanied exploration. One, Mushpot Cave, is lit and has interpretive signs, and even a small amphitheater for ranger talks. On the surface there are lots of hiking trails that allow for the exploration of cinder cones, spatter cones, fault scarps, and the human history of the region (which will be covered in a separate post).

All in all, it's a good place to get under the skin of a volcano!

Saturday, October 20, 2018

Earth as Inspiration: The Exploring of Beautiful Places.


There was a very intense meeting that took place in the NASA offices almost half a century ago. The Apollo 15 mission was practically all planned out, but they could not decide where to land on the Moon. The crux of the problem was that three previous missions had been successes, but there would only be three more missions, and some technicians were advocating for another landing on the "safe" lunar plains near a crater and some possible volcanic features. Others were arguing for a more daring landing, near the Moon's Apennine Mountains and the Hadley Rill. It was a potentially hazardous landing, in part because NASA didn't have high quality images of the proposed site. The final decision was strongly influenced by mission commander Dave Scott.
Source: NASA

His decision was based in large part on the geology field training that he had received from geologist Leon Silver of Caltech. The moment was dramatized in Tom Hanks' incredible HBO mini-series From the Earth to the Moon:

"...but from what I've learned out in the field; Hadley Apennine, with it's complex variety of features, both impact and volcanic, is the best choice for putting together a picture of how the moon came to be. Maybe a little riskier...but... also the Apennines have something else... Grandeur. And I believe there's something to be said for... exploring beautiful places... It's good for the spirit."

And what he said (in the screenplay anyway) is true. It's good for the spirit to explore the beautiful places. And so it seemed fitting that I would end Earth Science Week by taking my students to a place of grandeur to learn some basics about the Earth: subduction zones, plutonic rocks, glaciers, flooding, and mass-wasting. We headed out to Yosemite Valley. It's a no-brainer kind of choice. We've got fascinating geology all around us here in California, but sometimes it can be a bit tricky to inspire the desire to learn geology by showing the students an outcrop of part of an ophiolite in a dry dusty canyon in the Coast Ranges somewhere. It can be done, mind you, and I've done such trips with reasonable success, but when you live just 90 minutes from one of the most beautiful national parks in the world, you take advantage of that fact!
We did the trip on Friday because Yosemite is, besides being very beautiful, very popular. Four million people visit the park each year, and most of them come on weekends. Our Saturday field trips in recent years have been nightmares of logistics with heavy traffic, long wait lines at the park entrance and problems trying to find parking spaces. Yesterday the valley was pretty quiet, with trams running half-empty (except when my whole class invaded one of them) and no waiting at the entrance station. I sent the students forth to do some research on their own for a few hours and commenced a journey from one end of the valley (sort of) to the other (Yosemite Lodge to Happy Isles).
Since I moved to Central California 30 years ago, I've visited the park more than a hundred times, and I never fail to be inspired by the dramatic in-your-face geology: 3,000 foot cliffs of granitic, high waterfalls (in season), colorful vegetation (again, in season), and interesting birds and animals. It is a wonderful place to learn some basic geological principles.
I wish it were possible for everyone to see the incredible beauty that surrounds our mean grubby cities. So many people are more concerned about getting food and shelter than they are for learning about their planet, a problem of human existence that is completely understandable. But that is the real value and potential of the internet: anyone can experience these places through the eyes and words of others. Earth Science Week is about our awakening to the incredible planet that we live on, a place of great beauty, but at times a place of great danger. Our lives are enriched by learning about both of these things.

Thursday, October 18, 2018

Earth as Inspiration: It's Coyote and Roadrunner! (Except that it's not a Coyote, and the bird wasn't a Roadrunner)


It's Earth Science Week, and the theme this year is Earth as Inspiration. It may seem strange that I would open this blog with a picture of cute furry creature when we should be discussing the Earth, but bear with me. I find the inspiration wherever I can!

I live in the midst of California's Great Valley, but to many people it isn't all that "great". Modesto regularly ends up as 48th or 49th on the lists of the "best places to live" in the U.S. We are in a perpetual depression, with unemployment levels that are around twice the national average, and the median household income lags badly behind the national average. Pretty dismal, many things considered, but not all. There are some real treasures to be found among the dusty fields. And those treasures are related to the earth sciences.

The Great Valley originated as a forearc basin between the vast subduction zone that once existed offshore of California during the age of the dinosaurs (the Mesozoic Era), and the chain of volcanoes that erupted miles above the magma chambers that would one day cool to become the granitic rocks of the Sierra Nevada. For most of its history the valley was a shallow sea, home to huge swimming reptiles during the age of dinosaurs, and gigantic sharks and a variety of whales, dolphins and seals during the Cenozoic Era that followed. It was only a few million years ago that the valley floor rose above sea level to become the grassy savanna that it was prior to the arrival of European settlers and farmers. The valley was populated by a bewildering array of strange mammals like mammoths, mastodons, giant ground sloths, gigantic Short-faced Bears, Saber-tooth Cats, Dire Wolves, horses, and camels. Many of these animals went extinct around 12,000 years ago, but even 300 years ago there were herds of Tule Elk, deer, Pronghorn, Grizzly Bears, Wolves, and Mountain Lions. And there were birds. Millions and millions of migratory birds who made the valley wetlands their winter home.

Eventually 95% of the valley was co-opted by agricultural development, and most of the natural primeval landscape was lost. But fragments remain here and there. There are still prairies around the margins of the valley that were simply grazed and not plowed. There were river floodplains that flooded too often to be developed as farmlands. And some animals adapted to the new state of affairs and have thrived in human landscapes.

That is where my inspiration came from this evening. I was out taking my normal walk for exercise and bird-searching when I came across a wild chicken. Well, not really a wild chicken, but apparently an escapee from the campus chicken coop (we have a big agriculture unit at our school). And it looked nervous. A moment later I saw why: it was being stalked by a Gray Fox (Urocyon cinereoargenteus). I've seen Red Foxes on the campus before; they're an introduced species. But this was the first time I got a clear view of the native Gray Fox (I saw one in the dark a few weeks ago).
The fox was very intent on its quarry and didn't notice me at first. I was able to get a few shots of it before it retreated into the bushes behind the farm machinery. The chicken also headed into the bushes, relieved that the chase was at least temporarily put on hold. But the whole episode reminded me of a great thing happening on our campus.

We are building a small version of our valley's native ecosystem on the vacant space north of our Great Valley Museum. It will be called the Great Valley Outdoor Nature Lab, and it will include several acres of native vegetation, a vernal pool, and some of the rocks characteristic of the margins of our valley. It might not be large enough to serve as a home base for the fox, but it will attract the native birds, and maybe some of the native amphibians and reptiles. The work is well underway, and by January we should have a mostly operational outdoor lab. Local school children, many of whom almost never have a chance to leave the city limits, will have an opportunity to see the natural history museum exhibits, and then step outside to see the native trees and vegetation, and perhaps even some native birds, ground squirrels or lizards, and if they are really lucky, a Gray Fox.

Wednesday, October 17, 2018

Earth as Inspiration: Memories on the 29th Anniversary of the Loma Prieta Earthquake

It's Earth Science Week, and "Earth as Inspiration" is the theme for this year. Inspiration can take many forms. Sometimes it is awe-inspiring beauty, something our planet has in great bounty. But the earth can kill, and inspiration can be related to preparation for disasters.
No, this isn't what happens (credit: A. June)
On October 17th at 5:04 PM, my physical geology laboratory had just finished and almost everyone had gone home to watch the World Series. A couple of students were helping me (it was Maureen and Sonny; funny how I remember the names of the first students I had better than the ones I had last semester). We were 100 kilometers from the epicenter, so when the seismic waves started to shake our building, the movement was a strong rolling motion instead of sharp vibrations. We looked at swaying TV monitors, and commented that it was an earthquake. It was a most scholarly discussion, actually. We realized the shaking was not stopping, and we thought we could sense the direction of the quake as well. We started to guess where it might be happening, but when the shaking reached the 40 second mark (the energy was spreading out, it lasted only 10 seconds or so near the epicenter), we realized it was a major event, and that fatalities were probably occurring (and unfortunately we were right). The deodar trees out the window were whipping back and forth as if they were in a high wind. The strangest part for me was the unconscious decision I was making as the shaking progressed. Despite having a quiet scholarly discussion, my body was moving from the front of the podium to the back, where there was a nice solid space to hide under. I would have dived under if the quake had lasted any longer.
Well, this can happen, but most people survive, even in the worst of quakes (credit: A. June)
In hindsight, I should have been a bit more aggressive about taking shelter under the desk. An analysis of our building a year or two later revealed an architectural weakness that suggested the building could collapse if the seismic waves hit it from a particular direction. A seismic retrofit a decade later included some massive shear walls in the lab I taught in.

Meanwhile, at the city library, my children were making me proud. At the time of the quake, there were huge sailing ship models on display, in some cases right on top of the book stacks. The stacks were not reinforced or braced, so there was a real potential for injuries if the quake was strong enough to knock those stacks over. I was told that most people were just standing there watching the bookstacks swaying, but my kids, my well-trained and intelligent kids were the only people in the room to take shelter under the sturdy study tables. Luckily, as I said before, we were on the fringes of the effects of the earthquake and no one was hurt.
The double-decker freeway in Oakland. It was not designed for the amount of shaking that occurred.

The Loma Prieta earthquake, a magnitude 6.9 event at a depth of 11 miles, was a tragedy: 63 people died, and 3,700 were injured. If the World Series game between the A's and the Giants hadn't been about to start, the death toll would have been much higher. Traffic was stunningly light that afternoon. Despite this, the Bay Area was in chaos for days and months passed before life got back to normal. We were on the fringes, so instead of pain and suffering, we had a profound learning experience that was remembered by my students for the next decade and a half. But it has been 29 years now, and many of my students weren't born when the quake happened. Few of them have felt a quake at all. The large quakes like Loma Prieta and Northridge are ancient history, and there is less of that innate knowledge of what they should do when one hits. Few admit to having any kind of emergency kits at home, and they have no plan for what to do when the next big one hits.

Fault studies across California make it clear that more big tremors are coming, almost surely within the next decade or two. We educators must keep these past events alive in the minds of our students so they will be ready for these events when they come.

This is an abridged version of a blogpost from 2009.

Tuesday, October 16, 2018

Earth as Inspiration: Mt. Shasta for Earth Science Week, October 14-20


Mt. Shasta and Shastina from the north

I usually don't need an inspiration to write about Mt. Shasta, but I realized (two days in) that October 14-20 is national Earth Science week, and the theme of the celebration this year is "Earth as Inspiration". In case you have not yet realized this yet, but I am in fact inspired by the Earth. It started early on in my life with family vacations to some stunning places in California and the American Southwest, continued with scouting experiences nearly every weekend in my teens that included extensive work with topographic maps, and right into my college major and subsequent career as a geology professor. And then I found the form of story-telling called blogging in 2008.
Panther Meadows at the 8,000 foot level on Mt. Shasta

Mt. Shasta is an earthly inspiration. We visited two weeks ago as part of our field course on California's volcanoes. The stops included a drive to the end of the highway at Panther Meadows at 8,000 feet on the side of the 14,179 foot high volcano, and another stop on the north flank where we could see the glaciers and one other astounding feature of the volcano (mentioned below). Shasta is the second tallest volcano (behind Mt. Rainier) but is the most voluminous composite cone (stratovolcano) in the range (I'm parsing words here; there is a larger volcano, but it is of a different kind and will be discussed in a future blog). As a classic composite cone, it is composed of the remains of at least four previous incarnations, capped by the current active vent, Hotlum Cone. The oldest lava and ash dates back to around 600,000 years ago, but the youngest is a mere couple of hundred years. It likely erupted in 1786.

As the highest mountain in Northern California, it supports seven glaciers. Whitney Glacier, with a length of two miles, is the longest in the state (below). The glaciers are responsible for one of Shasta's unique hazards: jokulhlaups! These are floods caused when meltwater is sealed underneath the glacial ice which then breaks out in a catastrophic manner. Although caused by eruptions under the glacial ice in places like Iceland, those that occur on Shasta can happen almost any time. They are generally more of a nuisance, messing up roads and bridges, rather than a killer.

The biggest dangers of a volcano like Shasta are volcanic mudflows (lahars), and hot ash flow eruptions. Lava flows, unless they interact with the ice, are of a lesser concern. Andesite lava has a pasty consistency and is not likely to flow overly far from vents on the mountain. Lahars are of the greater concern, as they are capable of producing massive casualties and structural damage. The towns of Mt. Shasta, Weed, and McCloud are constructed on old lahar deposits. Major events could cause the closure of Interstate 5. Hot Pompeii-style ash eruptions are somewhat less likely, based on the previous history of the volcano.
Whitney Glacier, the largest in California
One of the most outrageous landscapes to be found anywhere on the planet lies to the north of Mt. Shasta. When compiling geologic maps of the region in the 1970s, geologists weren't sure how to interpret the vast region extending north from the mountain reaching 28 miles to the edge of the village of Yreka. It was a hummocky landscape, made of hundreds of small hills and cones of lava fragments with intervening hollows, some containing lakes and ponds. Was it some kind of odd field of cinder cones? It didn't make a lot of sense until the eruption of Mt. St. Helens in 1980.
The St. Helens eruption was initiated when an earthquake caused the entire north flank of the volcano to collapse in a gigantic debris avalanche that traveled for twelve miles down the Toutle River valley. Humans had never witnessed a landslide so large. It uncapped the volcano, leading to the very explosive ash eruption that followed.

To the geologists studying the region around Shasta, it was a revelation. The avalanche at St. Helens formed hundreds of hummocks similar to those found at Shasta. It quickly became clear that the deposit on the north flank of Shasta was the remains of a gigantic debris avalanche. The St. Helens avalanche involved less than a cubic mile of material (0.67 cubic miles), but the now-apparent debris avalanche at Shasta was ten times larger (about 6.5 cubic miles), and it traveled twice as far. It seems to have happened between 360,000 and 300,000 years ago. It's stunning just to image seeing something like this happen.

What aspects of the Earth do you find inspiring?

Friday, October 5, 2018

Seeing Volcanoes from the Inside Out: A Visit to Castle Crags State Park in California

We recently completed a rather awesome trip to study the volcanoes of California, most particularly those that are found in the northern part of the state. Nearly all of our sites were the result of recent volcanic activity like Mt. Shasta, Lassen Peak, and Medicine Lake Highland, but our first visit was unique: we were exploring a volcano from the inside out!

It's not easy to visit the underside of a volcano when you think about it. The magma chamber that feeds the volcano may be four or five miles underground, and the temperatures and pressures are far, far beyond the abilities of human technology to conceivably hope to visit any time soon (there is that Unobtainium that was used in Avatar and The Core, but folks might be surprised to find it doesn't exist). About the only thing we can do is be patient. Really, really patient. First, we need to let the hot magma cool down slowly, a process that may take tens of thousands of years. Then we need to wait for a mountain-building event to cause the crust to be uplifted several miles, and then wait for the forces of erosion to remove all of the overlying rock. That's a bit longer, at least several tens of millions of years. But once it's done, the magma chamber will be sitting there, exposed for all to see. Luckily for us, this exact sequence of events took place in the Klamath Mountains of Northern California, just a few miles away from Mt. Shasta. It's a state park called Castle Crags.

The first view of Castle Crags is dramatic. Driving north on Interstate 5, one is treated to miles of forested hills, but at Castella the hills give way to sheer cliffs and spires of granitic rock. The granitic rock exposed in the Crags is the visible evidence of a magma chamber that once fed volcanoes in the along the western margin of North America in the age of dinosaurs 165 million years ago.

The sharp spires and rounded domes of the Crags are the result of having a great weight removed. Having formed at depths of four miles or more, the rocks expanded as erosion removed the heavy overlying rocks. But rocks can't expand like marshmallows; they fracture, much like the crust of baking loaves of bread. Vertical cracks are joints. Closely spaced joints promote the formation of the spires and towers of granitic rock. Fractures parallel to the surface are called exfoliation sheets. Exfoliation tends to remove to remove corners and edges, resulting in the formation of domes (Half Dome in Yosemite is a half-good example).

The Castle Crags were also glaciated, but with top elevations of less than 7,000 feet, the glaciers were small, and had less to do with the overall shape of the mountains than jointing and exfoliation. A few small lakes and moraines are found on the north side of the peaks.

We didn't have the time to hike among the trails that reach the base of the crags, but we stopped along Castle Creek to see what's been carried down the mountain by the glaciers and rivers that tear away at the granite. We could also see the more ancient metamorphic rocks that had been intruded by the granitic rock.


Seen from above (the picture below was taken on a lucky day flying home from Canada a few years back), the Castle Crags can be seen as isolated mass of granitic rock. In our geology textbooks, we find that a batholith is a single intrusion exposed over an area of 100 square kilometers (about 40 square miles). The term can also refer to a vast agglomeration of many dozens of adjacent plutons, as is the case in the Sierra Nevada. There are several of these composite batholiths in the western United States, including the Sierra Nevada, the Idaho, and the Southern California batholiths. The Castle Crags and other small isolated plutons are referred to as stocks. The surrounding rocks are the more easily eroded metamorphic rocks of the Eastern Klamath Terrane (the Trinity Complex).


We finished our subterranean exploration of the ancient volcano and headed back to the Earth's surface to find a more modern version of a volcano: Mt. Shasta. More on that incredible mountain in the next post.

Saturday, September 29, 2018

The Many Sides of California's Incredible Composite Cone Mt. Shasta

Hotlum Cone and Shastina, the two youngest cones of Shasta are seen here from the north on Highway 97

California has a lot of incredible volcanoes, but looming above them all is Mt. Shasta, the huge composite cone that rises above the mountains of Northern California. At 14,179 feet, it towers over all but a few of the highest peaks of the Sierra Nevada, but none of them are close by. It is more than a mile higher than any other nearby peaks. I and my students have been traveling around it the last two days, and we've seen it from every side.

From the south it was largely hidden by the smoke from the recent wildfires, but we drove up the Everritt Memorial Highway to the 8,000 foot level at Panther Meadows. The barren valley once hosted a ski resort until folks realized the lack of trees in the area was because of the constant avalanches. The ski area was moved, but the road remains, and serves as a high trailhead for summit attempts.
The Sargent's Ridge and Misery Hill cones of Mt. Shasta. These cones are older and more deeply eroded.

A careful study of the ridges and valleys reveals that there have been more than one "Shasta". At least five volcanoes have developed over the Shasta magma chamber, but most of them have been removed by erosion, explosion and avalanche. Only the highest cone, Hotlum, and the satellite summit of Shastina seem untouched by serious erosion. They are both less than 10,000 years old, and Hotlum has continued to erupt at intervals of several hundred years.
From the northeast, Shasta is highly symmetrical. That large snowfields remain in the fall season is evidence of the presence of glaciers. Shasta has at least five of the them, and Whitney Glacier is the longest glacier in all of California, at two miles.

The peak shined bright and clear in the morning light, but by this evening, it was shrouded in clouds and lightning was flashing in the skies above. The mountain, a so-called composite cone is a mountain of many moods.

I'm pretty sure I don't want to see the mountain angry...