Under the Volcano and Into the Abyss: Yosemite National Park

Yosemite National Park is the oldest "national" park in the United States, having been established by Congress and Abraham Lincoln in the midst of the Civil War as a protected reserve deeded to California. It became an official national park in 1890, third after Yellowstone and Sequoia. I did a short blog series (boog? bleeries?) on some of the less familiar sights that one-time visitors might miss if they spend all their time looking at Yosemite Falls or Half Dome. I recalled the series while discussing America's relationship to the national park system in the aftermath of the wonderful Ken Burns documentary "The National Parks: America's Greatest Idea". I have them (semi) organized below in the order that they appeared. I've also included a flurry of posts on some of the rock falls in the last year. If you are ever headed out to Yosemite, check out the NAGT geologic road guide to Yosemite Valley and the western Sierra foothills (the extended wood-pulp version can be ordered here).

Photo of the Day - Feeling Crushed? : this series started far from Yosemite, but rocks in the Coast Ranges are very much part of the story. Sierra granites originate from subduction of crust and subsequent melting of these rocks to form magma. We take a drive into the crust that would make Ms. Frizzle jealous

Journey to the Center of the Earth (well, the mantle at least) A brief look at chrome and mercury mining in the Coast Ranges, in the subduction zone rocks

Continuing Journey in the Earth - Taking the Time Machine When granites were forming under the future Sierra Nevada, dinosaurs and sea-going reptiles prowled the ancient land surfaces

Standing Underneath Volcanoes We arrive at Yosemite Valley and I describe the familiar scene from the Tunnel View, and explain the odd title

Touring the Underside of the Volcanoes, Part 2 How easy is it to visit the underside of a volcano? We find out, and what enclaves are in this post

Under the Volcano: Changing the Emphasis Taking a closer look at the Cathedral Rocks and the El Capitan granite that forms the impressive cliffs

Under the Volcano: Changing the Emphasis -Part 2 Another less familiar cliff is Sentinel Rock (see the second picture above), and the Sentinel granodiorite of which it is composed

Under the Volcano: Changing the Emphasis -Part 3 One of the unknown waterfalls in Yosemite is the rarely seen Sentinel Falls, on the south side of the valley across from Yosemite Falls

Exploring Yosemite, continued and the Rock of the Day A brief foray west of the park on a beautiful spring day, and a look at some of the older metamorphic rocks

Under the Volcano: Changing the Emphasis -Part 4 Who's heard of Lehamite Falls? Many park visitors ignore them, for they are overshadowed by nearby Yosemite Falls

Yosemite Falls: The Spectacle that Almost Wasn't Yosemite Falls are actually an aberration! They were once far more like Lehamite Falls in the previous post...I explain why

Under the Volcano: Changing the Emphasis -Part 5 A look at the Lost Arrow

Under the Volcano: Changing the Emphasis -Part 6 The highest unbroken waterfall in Yosemite is not named Yosemite! I describe it in this post

Under the Volcano: Changing the Emphasis -Part 7 Another little-known fall, the Royal Arch Cascades, behind the Ahwahnee Lodge

Under the Volcano: Changing the Emphasis -Part 8 Silver Strand Falls, another unknown waterfall

Under the Volcano: Changing the Emphasis -Part 9 Sometimes the familiar sights become transformed by different timing. Yosemite Falls at night, one of the few times we ever had the valley to ourselves

Staring into the Abyss - Yosemite as you (maybe) have never seen it We leave the valley floor and take in the view from the edge of the abyss at Taft Point

Staring into the Abyss #2 - Yosemite as you (maybe) have never seen it The Three Brothers from the rim, and Yosemite's largest historically recorded rockfall

Staring into the Abyss #3 - Yosemite as you (maybe) have never seen it Looking west from Taft Point towards the Cathedral Rocks, and what happened to Yosemite's meadows?

Staring into the Abyss #4 - Yosemite as you (maybe) have never seen it (and my 100th Post!) There are many domes in the vicinity of Yosemite Valley, and most did not form because of glaciation. A discussion of North Dome and Basket Dome, from Glacier Point

Staring up out of the Abyss: Check out this fire in Yosemite I link to one of the most extraordinary pictures I've ever seen of Yosemite. A fire was burning on the north rim, dropping embers into the valley. Spectacular!

Staring into the Abyss #5 - Yosemite as you (maybe) have never seen it Nevada and Vernal Falls from the Glacier Point area

Taking the High Ground: Yosemite as you (maybe) haven't seen it Climbing Sentinel Dome. A bit shorter than Half Dome, and a lot easier to climb!

Revisiting Yosemite Several weeks passed, and I made a few last posts before embarking on my journey through the Colorado Plateau. Yosemite Falls on a very windy day

An Alternate View of Upper Yosemite Falls My photo of Upper Yosemite Falls from an odd angle.

Is This the Most Beautiful Tree in the World? Several months passed, and several posts continued the tour of the valley floor; my favorite oak tree started a mini-meme

More Beautiful Trees... The tree meme grows...

Even More Beautiful Trees, and a Sequoia Story ...and grows some more!

How It Was: Yosemite Valley Yesterday... I visit the valley on a rainy November day, and watch Yosemite Falls go from dry to booming in a few short hours

Rocks fall in Yosemite? I had no idea that could happen! A discussion of rock falls in the valley; there was a lot going on in the valley in 2008-09!

Rocks fall in Yosemite: Park Service closes 1/3 of Curry Village More rock falls

During a Drought, What Do You Think About? In the midst of one of the worst drought years in decades, I ruminate on the incredible 1997 floods in Yosemite Valley and downstream

An Extraordinary Picture (at least for us Central Valley denizens) We find that Half Dome is visible from the Central Valley (on those rare clear days, anyway)

How it was: Yosemite Valley on a Saturday in April A springtime trip to the valley in the aftermath of a major rockfall. Several posts followed...

First Look: Ahwiyah Rock Fall in Yosemite A first look at the Ahwiyah Rock Fall from near Half Dome. The view of Yosemite changes forever!

Another Look: The Ahwiyah Slide in Yosemite Got as close as I could to the new rock fall (don't people usually run the other way?)

A Final Look (for now): The Ahwiyah Point Slide in Yosemite The dust settles...

The Ahwiyah Point Rockfall: the View I Wish I Had The National Park Service checks in with some great photos of the rockfall

Ahwiyah Point Rock Fall Update: Before and After Photos Doug Nelson provides a great view of the rockfall from Glacier Point

Geologic Change in Yosemite: Remembering the Happy Isles Slide of 1996 A look at the big slide behind Happy Isles...

Another Rock Fall in Yosemite ...and the next day, another fall takes place!

Ollie Hopnoodle's Haven of Bliss and America's Greatest Idea And we arrive at the most recent post on my favorite park.

I intend to continue some photo-essays on Yosemite National Park. I'll update this post as they appear. If you take the time to check them out, I thank you and hope you enjoy the series!

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!

I've Been Under, Over, and On a Volcano. Now Let's Go Into a Volcano

Being on a volcano isn't too bad,at least if it isn't erupting. In Hawaii, I've even enjoyed being on an erupting volcano. "On" isn't too hard as a rule. You just drive or walk on it. Being over a volcano takes a little aerial technology, but flying to Seattle on a clear day does the trick. I've occasionally posted aerial shots of the Cascades volcanoes.

Getting under a volcano is a bit trickier. One needs to find a place where the magma chambers feeding a volcano have cooled and solidified, and then wait a few tens of millions of years while the crust rises and is stripped away by erosion. The exposed rocks would include granite, granodiorite, tonalite, and diorite. There are some very nice places to see such rocks, especially in my backyard, at Yosemite, Sequoia, and Kings Canyon National Parks in the Sierra Nevada. Needless to say, I've written just a little bit about these places...

Getting into a volcano is pretty much like getting underneath one. It takes less time, since only thousands of feet of erosion are needed, instead of miles. The trick is finding an accessible deeply eroded volcano. One of the most scenic of all eroded volcanoes has to be the half volcano of Pinnacles National Park in California's Coast Ranges. I don't mean "half" in the sense of half eroded away. Half of the volcano is missing for other reasons (read on...).

We took our last official field trip of the semester a few weeks back, and our destination was Pinnacles, being our nation's national park, and one of the most scenic and geologically interesting parts of the Coast Ranges (although there are many things that are geologically interesting about the Coast Ranges). Of course, as is my wont, I lectured and talked about the geology, but no lecture can ever compete with field experience. I sent the students up the trails to see the geology up close.

I headed up the Condor Gulch Trail. It connects after 1.7 miles with the High Peaks Trail, which is one of the finest short hikes in North America. My heart was there, but not the time. I made for the Condor Gulch Overlook, and continued another half mile to gain some wonderful views of the surrounding territory.

The volcano at Pinnacles National Park was a composite cone with at least five vents or domes composed of rhyolite lava and breccias. I imagine the closest analog to the volcano in California today wold be Mammoth Mountain in the eastern Sierra Nevada, although Pinnacles was situated much closer to the ocean, and may have been partly under water. Most of the rocks exposed along the trail began as mudflows on the flanks of the volcano, the summit of which was located a couple of miles south of the trail I was following.

From the Condor Gulch Overlook, one can look into a series of potholes where the intermittent stream flows over the volcanic bedrock. Boulders in the swirling currents have eroded the holes, which may hold water for weeks or months after major storms. The water is can be critical for wildlife in the area.

The Pinnacles volcano erupted near the newly forming San Andreas fault system, and the volcano was actually split in half by the fault motions. One part of it remained in southern California where the exposures are called the Neenach Volcanics. They can be seen in the Lancaster area quite close to the Antelope Valley Poppy Preserve. The rocks on the other side of the fault were carried north some 195 miles (314 kilometers) over 23 million years. It wasn't wasn't fast...maybe 2 inches per year, but the manner in which it happened was pretty violent. Every century or so there would be an earthquake in the range of magnitude 7.5-8.0 that moved the fault 10-20 feet all at once. The process continues today, with the San Francisco earthquake of 1906, the Fort Tejon earthquake of 1857, and the Loma Prieta earthquake of 1989. Enough stress is built up on various segments of the faults to produce large and damaging earthquakes, events that California needs to be prepared for.

From the ridgetop, the landscape appears gentle and serene. The thick brush and Gray Pines hide evidence of a violent past: volcanic eruptions, earthquakes, mudflows, and landslides. Today, the park is a delightful place to explore, with 30 miles of trails. I certainly enjoyed the three miles I traveled the other day.

If you are having trouble visualizing what 195 miles looks like, check out the fault map below that shows the location of the San Andreas, the Pinnacles volcano, and the Neenach volcanics.

California's (not) Biggest, (not) Most Recently Active, and (not) Most Dangerous Volcano

Photo by Mrs. Geotripper

Mt. Shasta is no doubt the most dominating volcano in all of California. It's huge, topping out at well above 14,000 feet, and is visible from over a hundred miles in a number of directions. It was the first main stop on our recent journey exploring the Pacific Northwest and Northern Rocky Mountains, and it really stood out as we essentially circled it on our way to Lava Beds National Monument.

It's big, it's active, and it's potentially destructive. So how bad could it be? Is Shasta the biggest, most recently active and most dangerous volcano in the state? Actually...no. California has a great many volcanic features, and even though some are not as familiar to many of us, they do actually present a hazard for a great many more people than you might suspect. That's not to say that Shasta is not dangerous, however.

Castle Crags in the Klamath Mountains of northern California (photo by Mrs. Geotripper)

As Interstate 5 winds northward into the Klamath Mountains north of Redding, Shasta occasionally peeks out between the trees (the top picture), but for a brief moment near Dunsmuir a totally different set of mountain spires appear off to the west. They are the Castle Crags, a granite stock (an intrusive body of granite exposed over an area of less than 40 square miles; batholiths are larger).

Castle Crags (seen below in a picture from a plane flight a few years back) were relevant to our explorations because they represent a volcano from inside out. About 160 million years ago, the land surface was five or six miles above, and molten magma was moving up through the crust. Some of the magma reached the surface to flow in volcanic eruptions, building up volcanoes maybe similar to Shasta and others of the Cascades. The rest of the molten rock cooled slowly for tens of thousands of years, forming the crystalline granitic rock exposed today at the Crags.

Moments later, we made the imaginary journey up through the crust and onto the flanks of the modern volcanic edifice of Mt. Shasta. We followed the Everitt Highway up the mountain to the about the 7,500 foot level to have a look around. Even though we were on the first day of a crippling heat wave in California, the air was cool, and the snowbanks made it clear that winter was not yet entirely over.

Bunny Flats was the end of the road for us on this particular day. The last two or three miles of pavement above were covered by snow. The road used to end at a ski area, but the resort was closed years ago, due to avalanche danger (as I understand it; there is a newer resort on the lower slopes of the volcano). Working and playing on the slopes of a volcano does have its hazards...

There are a lot of hazards around Shasta. Lava flows might seem to be one of them, but andesite lava tends to be sluggish and slow. Lava doesn't worry me so much. Ash eruptions are certainly a danger, due to their speed and mobility. Shasta has had such eruptions, but they haven't been the usual modus operandi over the years. But...lava or ash flowing onto thick snow: that's a problem. The melting snow and debris quickly turns into a mudflow that can travel for tens of miles at high rates of speed. The Indonesians called them lahars, and the name has stuck. Most of the lower flanks of Shasta are mantled with lahar deposits, and the towns of Weed and Shasta City are built on them. Mudflows have even happened when there have been no eruptions. Meltwater can build up under the glaciers that cover much of the mountain and burst out with no warning (Icelanders call these glacial bursts jökulhlaups). All in all, it's a pretty dangerous volcano.

And it's active. There have been a number of eruptions in the last 10,000 years, including those that built up Shastina and Black Butte. The entire upper part of Shasta, the Hotlum Cone, is less than 9,000 years old. The volcano may have erupted in 1786. So is it the most recently active volcano in California? Nope.

From our vantage point at Bunny Flat, we had an unobstructed view southeast towards Lassen Peak and Brokeoff Mountain. Lassen is the winner of the "most recently active" designation. The plug dome began making noise in 1914, and let loose in 1915 with a lava flow, a destructive lahar, and an ash eruption that interrupted train service out in Winnemucca, Nevada. The eruption produced a mushroom cloud five or six miles high. Geothermal activity continues today in what is now Lassen Volcanic National Park.

Lassen Peak (left) and Brokeoff Mountain (right) from Bunny Flat

So what about the biggest? Surely a mountain 14,000 feet tall is the biggest volcano in the state of California? Well, it's certainly the tallest, and it is the most voluminous stratovolcano in the Cascades, but it actually isn't the biggest volcano in the state. When we camped that evening, we were ensconced on the flank of a massive shield volcano called Medicine Lake Highland. With the gentle slopes composed of basalt lava flows, it hardly looks like a volcano at all, but when you compare the width of the volcano in the picture below (it takes up three quarters of the skyline), you realize it is really big. It consists of around 130 cubic miles of lava, compared to about 108 for Mt. Shasta (which is the snow-capped peak on the right).

So it's the most dangerous, right?

Well...that's a hard concept to quantify. There are lots of volcanoes in California, and some are closer to population centers than others, and some are more capable of chaos and violence than others. The Clear Lake Volcanic Field, north of the Bay Area, has been active as recently as 10,000 years ago, and the Geysers Geothermal Area nearby shows that magma is still present at a relatively shallow depth. Several thousand people live in the general vicinity.

The Lassen Volcanic Center is an obvious threat, given the activity in 1914-17. There are only a few small villages in the immediate vicinity of the volcano, but it is a major tourist destination in the summer season. Lahars could presumably reach the Sacramento Valley.

The aforementioned Medicine Lake Highland is certainly still active, with eruptions as recently as 950 years ago. Although basaltic shields aren't known for violent eruptions, the presence of rhyolite plug domes around the summit area show that such eruptions are not out of the question. Like the others, the region is lightly populated.

Volcanism is also a possibility in Southern California, perhaps to the surprise of some. Young cinder cones dot parts of the Mojave Desert (the Lavic Lake Volcanic Center), and the Coachella Valley (the Salton Buttes). Some of the small volcanic cones are younger than 2,000 years old.

The "elephant in the room" in terms of volcanic hazards of California has to be the Long Valley Caldera, and the nearby Inyo-Mono Craters. Every time there is a jiggle on a seismometer in Yellowstone National Park the internet lights up with predictions of death and destruction, but the conspiracy nuts pretty much totally ignore California's version of a death volcano. An eruption that took place 760,000 years ago produced 125 cubic miles of ash that covered most of the American West (the three Yellowstone eruptions ranged from 67 to 600 cubic miles). Yellowstone has not had a volcanic eruption in 70,000 years. The volcanoes in the Long Valley area of California have erupted as recently as 300 years ago. No one is talking about a repeat of the catastrophe of the 760,000 years ago, but smaller eruptions could certain cause havoc in this very popular tourist area. There was a huge brouhaha in the 1980s that had a lot of implications for how public officials respond to potential geological disasters. I wrote an extensive blog post about the event a couple of years ago; you can read it here (it's one of my favorites).

So Mt. Shasta isn't the biggest volcano in the state, isn't the most recently active, and may or may not be the most dangerous. But does that mean we can disregard the volcano? Hardly. It could cause all kinds of mayhem in the wrong circumstances. And there is one more hazard here that is unique.

The area north of Mt. Shasta is a landscape characterized by a strange hummocky surface composed of volcanic rock, but the hummocks don't look like cinder cones or other volcanic features. Geologists didn't know what to make of this weird topography. Until Mt. St. Helens exploded on May 18th, 1980, that is. One of the most astounding events of that eruption was the collapse of the entire flank of the mountain into a debris avalanche that traveled for twelve miles down the Toutle River. It turned out that an ancient iteration of Mt. Shasta had a similar fate around 300,000 years ago, with a debris avalanche that traveled 28 miles, almost to the present location of the town of Yreka.

The debris avalanche on the north flank of Mt. Shasta. Shasta Lake, a reservoir, is on the left within the debris field (photo by Geotripper)..

It is hard to imagine events on this scale, but the geological world is full of events that challenge our perception. That was one of our themes as we set out on our two week journey, and it was only our first day on the road.

The Other California: California's Biggest Volcano

In reference to yesterday's question of the day, well, there was a bit of trickery involved. Mt. Shasta was correctly identified in the photo by several readers, and Mt. Shasta is a huge volcano. It is certainly the tallest volcano in California, it is the largest stratovolcano (composite cone) in the Cascades Range (second in height behind Mt. Rainier, but bulkier), and by some accounts could be the biggest stratovolcano on the planet (I can't confirm that one). But...it wasn't the biggest volcano in the picture. On the boundary between the Cascades and the Modoc Plateau provinces are several shield volcano complexes, including Newberry Volcano in Oregon, and the broad dome of Medicine Lake Highland in California. Even though the highest summit on MLH does not exceed 8,000 feet, the volume of the complex is more than 130 cubic miles, as compared to Shasta's 108 cubic miles. It is California's biggest volcano.

Shields are largely composed of basaltic lavas, which tend to be less viscous, and thus less likely to develop steep slopes as they congeal. So the slopes of the mountains are usually quite gentle, and rarely produce strikingly high mountains (here is a photo of Mauna Loa, one of the biggest shields on the planet). In yesterday's photo, MLH takes up most of the photo, with Shasta on the far right-hand side. In the photo above, I was standing on a cinder cone on the flank of MLH, and couldn't fit the whole mountain in the frame.

As far as my biased self is concerned, MLH is one of the best places to visit a volcano in California. It will take a number of blog entries to cover all the fascinating features scattered around the mountain. Most of the volcano is under the jurisdiction of U.S. Forest Service, but a significant portion of the northeast flank is preserved as Lava Beds National Monument.

A picture from one of the summits of the complex, Little Mt. Hoffman, shows one of the oddities of the giant shield of MLH. The gray edifice in the foreground is Little Glass Mountain, a dome of pumice and obsidian of rhyolitic composition. On a volcano largely composed of black basalt, viscous flows of rhyolite (a completely different lava) should be deemed a bit strange. That's Mt. Shasta in the distance.

The Medicine Lake Highland sits astride an ill-defined boundary between the Cascades and the Modoc Plateau. For purpose of these blogs, I'm going to lump it with the Modoc Plateau, as some of the story I will be telling about the mountain will spill into Modoc territory. The Modoc Plateau is a lonely flat region in northeastern California floored by thousands of feet of basaltic lavas and intervening layers of lake and river sediments. The region is sliced by a lot of normal faults, and punctuated by numerous small cinder cones. The area is not considered all that volcanically active in the present day, except for the Medicine Lake Highland, which has cones and flows that are no older than 900 years. If you watch late-night television, you have seen the Modoc Plateau; it's that real estate that Erik Estrada tries to sell in the infomercials...hey, it's pretty country, but it's really isolated and lonely.

Stay tuned!

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?

What Story Can a Single Rock Tell? A Day in the Coast Ranges

Meet my new deskcrop! I was out on the last field trip of the year, a journey through the Diablo Range to the San Andreas fault and Pinnacles National Monument. We had a wonderful day, which we didn't exactly deserve or expect. It poured all night, and somehow the rain stopped at daybreak. We had a few showers during the day, but a big storm was brewing in northern California (four feet of snow expected in Lake Tahoe, for instance). Happily, the deluge didn't start until we arrived back in town, and it has been pouring ever since.

In between we were treated to a beautiful display of clouds and rainbows, and we had a full day learning about California's most famous fault, and a few others as well. I picked up one rock, though, which captured my imagination, and reminded me of why I fell in love with the science of geology so long ago. It's a porphyritic andesite that I picked up on the shoreline of San Luis Reservoir near Pacheco Pass in the Diablo Range. The mountains form the western boundary of the Great Valley of California for a distance of about 125 miles.

It's not a remarkable rock in and of itself. Andesite is one of the most common of volcanic rocks, found pretty much all over the Pacific Rim in places like the Cascades, the Japanese islands, Indonesia, and by incredible coincidence, the Andes! The story of this rock could be very straightforward; it could be as simple as: it erupted...the rock weathered a bit...and I picked it up.

But that isn't the whole story. Context is so important; I picked the rock up from a layer, seen below, that was exposed on the eastern flank of the Coast Ranges. It is a sedimentary conglomerate. Again the story could be fairly simple; conglomerate is a fairly common rock too. We could hypothesize that the rock journeyed a bit further from the volcano, down a river and the river flowed from the mountains onto an alluvial fan. Along the way, it was rounded off by bouncing against other rocks...then I picked it up.

It turns out that story doesn't quite work as a hypothesis either. This conglomerate has some odd features that tell us that it didn't form in a river. It is topped by a gray sandstone that is in turn covered by siltstone and shale. Above it is another layer of conglomerate that is covered by sandstone, siltstone and shale. This pattern is repeated over and over, until we have a sedimentary formation more than 20,000 feet thick (four miles)! The layers contain marine fossils; some are shells of snails and clams, but sometimes the rocks include shark teeth and the remains of giant marine reptiles like ichthyosaurs, plesiosaurs, and mosasaurs.

OK, but what in the world could be moving boulders and cobbles around on the sea floor? Isn't that one of those places where the water is calm all the time? Sometimes that is the case, but not here. These rocks accumulated in large river deltas extending into a shallow sea that lay off the coast of California in late Cretaceous time, the final period of the dinosaurs. Because of constant large earthquakes, the edges of the river deltas were unstable and were often shaken loose. The mass of rocks turned into turbulent chaotic masses flowing along the sea floor at 30 or 40 miles per hour. These violent events are called turbidity currents. The turbidity currents can carry rocks for many miles. As the flow slows down, the larger particles settle first, followed by the finer particles, and so on. The sedimentary beds become graded by grain size (graded beds).

But why earthquakes? And where did the lavas and magma come from? It turns out these things are related too. This story seems to grow more complicated by the moment! In Cretaceous time, there was no San Andreas fault, and there was a lot less of California, at least a California that could be seen from above sea level. A vast subduction zone lay offshore, a place where the Pacific Ocean crust was being pushed under the North American Continent. As the ocean crust was pushed deeper and deeper into the underlying mantle, it heated up, and assisted by the presence of water, melted into magmas that rose upwards through the crust. Some of the magma exploded and flowed out the surface forming andesitic volcanoes, but other magma chambers cooled slowly three or four miles down in the crust, forming crystalline igneous rocks like diorite, granodiorite, and granite. Those are the characteristic rocks of the Sierra Nevada batholith, exposed in places like Yosemite Valley, Tuolumne Meadows, and Sequoia/Kings Canyon National Park.

I've often stood on the edge of Yosemite Valley and looked at the vast exposures of granitic rock, and imagined the volcanoes that once stood above, miles higher. I even wrote an extensive web series about being under the volcano. In my mind I could stand on the flanks of the Mesozoic volcanoes, watching out for predatory dinosaurs and gazing at pterodactyls flying overhead. It took a lot of imagination, but today the feeling was a little more tangible. I was holding a piece of the volcano in my hand.

I love where my geologic journeys lead; there are lots of pretty spectacular places to see in our present world, but so many more incredible landscapes of the past. It was a good day in the Coast Ranges!

A Look Back at Ten Years of Geotripping: The Story Told by a Single Rock

I'm commemorating a decade of blogging by dredging the archives for some of my favorite posts. 2010 was a turbulent year. We were still in the depths of the Great Recession (at least in our area), my summer trip was cancelled for the only time in the last 29 years, we broke ground on our new Community Science Center (affordable only because of the recession and the drop in construction bids), and I posted 298 blog entries, my most productive year on Geotripper. A great many posts continued the Other California series, and a really strange political controversy over the California state rock serpentine accounted for many more(more on this in the next post). It was hard to choose, but my favorite post of the year was the story of a single rock...
From November 20, 2010:

Meet my new deskcrop! I was out on the last field trip of the year, a journey through the Diablo Range to the San Andreas fault and Pinnacles National Monument. We had a wonderful day, which we didn't exactly deserve or expect. It poured all night, and somehow the rain stopped at daybreak. We had a few showers during the day, but a big storm was brewing in northern California (four feet of snow expected in Lake Tahoe, for instance). Happily, the deluge didn't start until we arrived back in town, and it has been pouring ever since.

In between we were treated to a beautiful display of clouds and rainbows, and we had a full day learning about California's most famous fault, and a few others as well. I picked up one rock, though, which captured my imagination, and reminded me of why I fell in love with the science of geology so long ago. It's a porphyritic andesite that I picked up on the shoreline of San Luis Reservoir near Pacheco Pass in the Diablo Range. The mountains form the western boundary of the Great Valley of California for a distance of about 125 miles.

It's not a remarkable rock in and of itself. Andesite is one of the most common of volcanic rocks, found pretty much all over the Pacific Rim in places like the Cascades, the Japanese islands, Indonesia, and by incredible coincidence, the Andes! The story of this rock could be very straightforward; it could be as simple as: it erupted...the rock weathered a bit...and I picked it up.

But that isn't the whole story. Context is so important; I picked the rock up from a layer, seen below, that was exposed on the eastern flank of the Coast Ranges. It is a sedimentary conglomerate. Again the story could be fairly simple; conglomerate is a fairly common rock too. We could hypothesize that the rock journeyed a bit further from the volcano, down a river and the river flowed from the mountains onto an alluvial fan. Along the way, it was rounded off by bouncing against other rocks...then I picked it up.

It turns out that story doesn't quite work as a hypothesis either. This conglomerate has some odd features that tell us that it didn't form in a river. It is topped by a gray sandstone that is in turn covered by siltstone and shale. Above it is another layer of conglomerate that is covered by sandstone, siltstone and shale. This pattern is repeated over and over, until we have a sedimentary formation more than 20,000 feet thick (four miles)! The layers contain marine fossils; some are shells of snails and clams, but sometimes the rocks include shark teeth and the remains of giant marine reptiles like ichthyosaurs, plesiosaurs, and mosasaurs.

OK, but what in the world could be moving boulders and cobbles around on the sea floor? Isn't that one of those places where the water is calm all the time? Sometimes that is the case, but not here. These rocks accumulated in large river deltas extending into a shallow sea that lay off the coast of California in late Cretaceous time, the final period of the dinosaurs. Because of constant large earthquakes, the edges of the river deltas were unstable and were often shaken loose. The mass of rocks turned into turbulent chaotic masses flowing along the sea floor at 30 or 40 miles per hour. These violent events are called turbidity currents. The turbidity currents can carry rocks for many miles. As the flow slows down, the larger particles settle first, followed by the finer particles, and so on. The sedimentary beds become graded by grain size (graded beds).

But why earthquakes? And where did the lavas and magma come from? It turns out these things are related too. This story seems to grow more complicated by the moment! In Cretaceous time, there was no San Andreas fault, and there was a lot less of California, at least a California that could be seen from above sea level. A vast subduction zone lay offshore, a place where the Pacific Ocean crust was being pushed under the North American Continent. As the ocean crust was pushed deeper and deeper into the underlying mantle, it heated up, and assisted by the presence of water, melted into magmas that rose upwards through the crust. Some of the magma exploded and flowed out the surface forming andesitic volcanoes, but other magma chambers cooled slowly three or four miles down in the crust, forming crystalline igneous rocks like diorite, granodiorite, and granite. Those are the characteristic rocks of the Sierra Nevada batholith, exposed in places like Yosemite Valley, Tuolumne Meadows, and Sequoia/Kings Canyon National Park.

I've often stood on the edge of Yosemite Valley and looked at the vast exposures of granitic rock, and imagined the volcanoes that once stood above, miles higher. I even wrote an extensive web series about being under the volcano. In my mind I could stand on the flanks of the Mesozoic volcanoes, watching out for predatory dinosaurs and gazing at pterodactyls flying overhead. It took a lot of imagination, but today the feeling was a little more tangible. I was holding a piece of the volcano in my hand.

I love where my geologic journeys lead; there are lots of pretty spectacular places to see in our present world, but so many more incredible landscapes of the past. It was a good day in the Coast Ranges!

The Mountain That No Climber Can Ever Summit: Mt. Tehama (the Brokeoff Volcano)

The gigantic boulder is a glacial erratic, left behind by sheets of ice that once covered the Lassen region.

After being slightly distracted by ducks and the beautiful fall day in Yosemite, Geotripper is back on track to finish up his exploration of the Cascades volcanoes of Northern California. It was already approaching noon of our last day on the road back at the end of September, and we had six hours of driving ahead, so our list of features we were investigating was becoming short. In fact, one of the features we were interested in just simply wasn't there.

Mt. Tehama, or the Brokeoff Volcano, began erupting around 600,000 years ago just south of the present-day site of Lassen Peak. It was a stratovolcano similar to Mt. Shasta or Mt. Hood, composed mainly of gray andesite with interbedded ash and lava flows. The mountain alternated between explosive eruptions and effusive eruptions and eventually grew to a height in excess of 11,000 feet, hundreds of feet higher than modern Lassen Peak (10,457 feet).

There is a pretty good reason that mountain climbers can never summit Mt. Tehama, though. It's not there anymore. Around 400,000 years ago the magma chamber under the mountain ended volcanic activity. There has been debate about whether the mountain ended with a tantrum or a whimper, but the consensus seems to lie with the latter. The volcano stopped erupting and chemical weathering, river and glacial activity tore it apart. All that remains are a series of lower peaks surrounding the original throat of the volcano including Brokeoff Mountain, Mt. Diller, Eagle Peak and Diamond Peak.

 In the aftermath of the eruptive cycle that ended activity at Tehama, several plug domes erupted and grew on the flanks of the older mountain, including Lassen Peak itself about 28,000 years ago. Hot rock continues to simmer beneath the complex, evidenced by the recent (1914-1917) eruption of Lassen Peak, and the presence of geothermal systems like Bumpass Hell and the Sulphur Works.

From the Bumpass Hell trail, the peaks of Brokeoff Mountain and Mt. Diller seem to provide a near-perfect profile of the long-gone volcano, but the original edifice was much larger, something like 15 miles around. The center of the volcano was in the foreground and the two peaks were just part of the western flank. An aerial photograph of the mountain (from a Canada flight in 2005) offers a different perspective...

I annotated a version of the picture for a previous post on the volcano, and it is reproduced below. I'm mostly satisfied with it, although the height of the peak may be a bit exaggerated. In any case, good luck climbing to the summit!

Up next, the final stop of our trip!