Want to See Some Incredible Volcanoes Up Close? Geology of California's Volcanoes, Sept. 27-Oct. 1, with Modesto Junior College

I write so much about my travels around the American West and elsewhere, and some might wonder where I find the time. Well...I tend to have a group of students with me. Geology, perhaps more than any other science, is best learned in the field, and our school recognizes the importance of field experiences. The community college system in California is of course one of the best alternatives for beginning a college education, a gateway to transferring into universities, but we also recognize lifelong learning as a part of our mission. Education doesn't just end with a degree. Professionals in one career can benefit from courses in related disciplines as a way of improving their job performance, or advancing up the pay scale. And all citizens can benefit from becoming better informed on the political issues of the day, such as climate change, or energy development (pulling some examples from geology).

With this in mind, I wanted to let my Modesto area-based readers know about some great field studies trips coming up this fall. On September 27-October 1, I'll be teaching Geology 185, the Geology of California's Volcanoes. We'll be exploring Mt. Shasta, Lava Beds National Monument, Medicine Lake Highland, and Lassen Volcanic National Park, as well as Castle Crags and McArthur-Burney Falls State Parks. We will be camping at Woodson Bridge State Park the first night, spend two nights at Lava Beds National Monument, and the last night at McArthur-Burney Falls State Park. There will be hiking and caving opportunities, and some simply incredible scenery among some of the youngest volcanic features in the western United States.

If this sounds intriguing, you can find more information at http://hayesg.faculty.mjc.edu/Cascades_field_studies.html. California residents pay the normal tuition rate (2 semester units), but the rate is higher for out of state participants. The $80 fee for the course covers the van transportation and fees at the various parks and campgrounds. The students provide their own food (we'll have stoves and fuel). For my local readers, we'll have an organizational meeting on Thursday, September 13 in the Science Community Center at Modesto Junior College, room 326, at 5:30 PM. Contact me if you have questions.

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.

You've Read About Them: How About Seeing Them in Person? California's Volcanoes Field Studies, Sept. 22-26, 2016

Mt. Shasta, the second tallest and most voluminous volcano in the Cascades

I write so much about my travels around the American West and elsewhere, and some might wonder where I find the time. Well...I tend to have a group of students with me. Geology, perhaps more than any other science, is best learned in the field, and our school recognizes the importance of field experiences.

Lava Beds National Monument

The community college system in California is of course one of the best alternatives for beginning a college education, a gateway to transferring into universities, but we also recognize lifelong learning as a part of our mission. Education doesn't just end with a degree. Professionals in one career can benefit from courses in related disciplines as a way of improving their job performance, or advancing up the pay scale. And all citizens can benefit from becoming better informed on the political issues of the day, such as climate change, or energy development (pulling some examples from geology).

Medicine Lake, glacio-volcanic lake occupying a large caldera.

With this in mind, I wanted to let my Modesto-based readers know about some great field studies trips coming up this fall. On September 22-26, I'll be teaching Geology 185, the Geology of California's Volcanoes. We'll be exploring Mt. Shasta, Lava Beds National Monument, Medicine Lake Highland, and Lassen Volcanic National Park, as well as Castle Crags and McArthur-Burney Falls State Parks. We will be camping at Woodson Bridge State Park the first night, spend two nights at Lava Beds National Monument, and the last night at McArthur-Burney Falls State Park. There will be hiking and caving opportunities, and some simply incredible scenery among some of the youngest volcanic features in the western United States.

Jot Dean Ice Cave. The ice persists in the cave year-round.

If this sounds intriguing, you can find more information at http://hayesg.faculty.mjc.edu/Cascades_field_studies.html. California residents pay the normal tuition rate (2 semester units), but the rate is higher for out of state participants. The $90 fee for the course covers the van transportation and fees at the various parks and campgrounds. The students provide their own food (we'll have stoves and fuel). For my local readers, we'll have an organizational meeting on Thursday, September 8 in the Science Community Center at Modesto Junior College, room 326, at 5:30 PM. Contact me if you have questions.

Lassen Peak and Manzanita Lake. Lassen erupted in 1914-15, while Manzanita Lake formed behind a debris avalanche about 300 years ago.

This isn't our only field studies opportunity! Watch for other announcements soon.

Exploring the Southern Cascade Range or Yosemite National Park for College Credit! Sept. 24-28 and Oct. 9-11

Captain Jack's Stronghold, where the Modoc people held out for months against U.S. troops. The site is protected today as Lava Beds National Monument.

This message is primarily for my readers in the Modesto region, but others are invited to consider this opportunity. Modesto Junior College has an active geology field studies program that offers the chance to explore some of the best geology on the planet, in the mountains and deserts of California and other parts of the American West. The courses provide valuable field experience for geology majors and teachers of earth science, and can provide rich life experiences for people who are casually interested in geology. We have a bit of room if you wish to join us!

The opening of Skull Cave, the largest lava tube entrance in Lava Beds National Monument.

We are offering two extended overnight trips this semester. On September 24-28, we will explore the geology of California's volcanoes (Geology 185; 2 semester units), and on October 9-11, we spend three days in and around Yosemite National Park (Geology 180; 1 semester unit). Both trips involve camping out in sometimes rugged conditions, using vans supplied by the department. The cost includes the per-unit registration fee, and an additional $90 for Geology 185, and $45 for Geology 180.

Valentine Cave in Lava Beds National Monument

The trip for Geology of California's Volcanoes will include stops at Castle Crags State Park in the Klamath Mountains, Mt. Shasta (including a drive to the end of the road at 8,000 feet), Lava Beds National Monument, Medicine Lake Highland (the biggest but not highest volcano in California), and Lassen Volcanic National Park. Some challenging hikes (and cave explorations) will be offered, but not required. One will be able to complete the course without great physical exertion, although one should be in reasonably good health to be out there traveling and camping.

McArthur-Burney Falls in the Cascade Range

The Geology 180 course, Geology of the Central Sierra Nevada, will explore all of the accessible parts of Yosemite National Park, including Yosemite Valley, Tuolumne Meadows, Glacier Point, and possibly Hetch Hetchy. We will be camping at Wawona and Crane Flat during the trip.

Lassen Peak is the most recent volcano to erupt in California, in 1914-15.

If you are in the Modesto area, we are having an organizational meeting for both of the trips on Thursday, Sept. 17 at 5:30 PM in Science Community Center 326 on the West Campus of MJC. If you can't make the meeting, contact me (hayesg(at)yosemite.edu). More information can be found at http://hayesg.faculty.mjc.edu/Cascades_field_studies.html and http://hayesg.faculty.mjc.edu/Yosemite_3_day.html. Several day trips will be offered later on in the semester, to the Mother Lode (if it hasn't burned completely up), and to Pinnacles National Park and the San Andreas fault.

That Volcano is Dead Right? There's No More Hot Magma? Bumpass Hell at Lassen Volcanic National Park

"Now, I don't know,  I don't know where I'm a gonna go, when the volcano blow"
Jimmy Buffett

Mt. Tehama is long gone, and Lassen Peak blew off all her accumulated stresses and frustrations with the eruption in 194-17, right? I mean, it's all a national park now, and that means it's like an amusement park and the park service would never allow the volcano to go erupting on all the tourists, right?

Actually, the Lassen Volcanic Center is on the short list of the most likely sites of volcanic activity in California, according the the California Volcano Observatory. And there is plenty of evidence that hot magma still lurks beneath the surface in the national park: there are five active geothermal areas in the park boundaries.

It was the last day and the last stop of our late September field studies adventure through the Cascades of Northern California. We had explored the Castle Crags, Mt. Shasta, Lava Beds National Monument, Medicine Lake Highland, and McArthur-Burney Falls, as well as Chaos Crags, Lassen Peak, and Mt. Tehama in Lassen Volcanic National Park. Our destination was Bumpass Hell, at the end of a spectacular 1-1/2 mile hike.

Bumpass Hell was named after an early pioneer rancher in the area, Kendall Bumpass who had good reason to call this place his hell: he inadvertently put his leg through a thin crust of silica and plunged it into the boiling acidic water beneath. He eventually lost the leg.

Being the most active geothermal area in the park, one might think that Bumpass Hell sits atop the magma chamber, but it actually lies a mile or two east of the body of molten rock (which sits at a depth of about 3 miles). Water at depth is heated until it turns to steam at temperatures exceeding 400 degrees, and the steam rises along fractures and fault lines where it condenses and reacts with local pockets of groundwater. The water is general highly acidic, and emerges at the boiling temperature (as discovered by Bumpass and numerous careless tourists who choose not to heed caution signs).

In a general way there are four kinds of geothermal features, and three of them can be viewed at Bumpass Hell. If it is the dry season, there might not be very much water and the vents will be filled with the clay and mud formed from the decomposition of the surrounding andesitic volcanic rock. The mucky cauldrons are called boiling mudpots. These acidic pits are definitely not recommended for facial care schemes.

The black sludge in the picture below is made of finely divided particles of iron pyrite (fool's gold). That might be counter-intuitive given the familiar brassy luster of the mineral, but geology lab students will recall that the streak (color of the powder of a mineral) is black.

More familiar features are hot springs. Hot springs can be found in many geologic settings, including along fault lines, but volcanic hot springs are in a class by themselves. They are not the kind of springs that one would want to be soaking in. The temperatures at Bumpass Hell are at the boiling point, and as previously noted, the water is highly acidic.

If there is not very much water available, for instance in the late summer or fall, steam vents will be common. They are called fumaroles. Fumaroles are a good spot to see sulfur crystals growing (see the picture below). At the top of my list of worst possible jobs would be that of sulfur miner. I've seen articles on mine workers in South America who have to climb into volcanic craters and scrape off the sulfur crystals from active fumaroles, risking scalding burns and the scarring their lungs by breathing in the acid-rich air.

The only type of geothermal feature that is not found at Lassen Volcanic National Park is a geyser. Geysers like those found at Yellowstone National Park (where something like 70% of all the world's geysers are found) require very specific conditions underground that are not present at Lassen. The main reason is probably that the rocks and magmas at Lassen are not as silica-rich as those at Yellowstone. The groundwater plumbing maze beneath Yellowstone is coated with silica deposits which produced a closed system in which the pressures can build high enough to produce the spouting fountains. There are too many "holes" in the plumbing at Lassen.

Does the presence of magma underground at Lassen mean that an eruption is coming soon? It's hard to say. It may be that the eruption of Lassen in 1914-17 really did relieve pressure and stress in the magma system and that the magma today is simply cooling off and solidifying. This is suggested by the relative rarity of eruptions at Lassen (the recent event, Chaos Crags a thousand years ago, and the formation of Lassen around 28,000 years ago). But it could also be that the magma chamber still has an eruption or two left in it. In any case, we can be fairly confident that we will know something is afoot, because magmas don't sneak up to the surface without causing other forms of mayhem, such as earthquakes, changes in ground elevations, gas emissions, and increased geothermal activity.

I'll be watching. And when everyone else is running away from the eruption, me and lots of other geologists will be trying to get closer!

I hope you've enjoyed this little vignette on the Cascades of Northern California. Look for an exploration of the central coast of California next!

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!

The Volcano That Doesn't Exactly Look Like a Volcano: California's Lassen Peak

Lassen Peak is an odd one. Most people have a stereotypical view of what a volcano "should" look like, and to most people, Lassen doesn't fit the stereotype. Yes, it is an isolated peak from most angles, but where is the cone shape, and where is the crater on top?

We were on the last day of our late September field studies course through the Cascades of Northern California, and were having a look at the volcanic features of Lassen Volcanic National Park. In the previous post we took in a fascinating set of six plug domes, the Chaos Crags, and the debris avalanches that thundered down their flanks forming the Chaos Jumbles.

Like the Chaos Crags, Lassen Peak is a plug dome, a steep rubble-covered peak composed of dacite or rhyolite. It may be the largest plug dome in the world, rising about 2,000 feet above its base (most domes are half of that). It lacks the characteristic cone shape of stratovolcanoes because its lavas were so viscous upon emerging from the depths that they barely flowed at all, forming a steep pile of lava rather than relatively smooth slopes. As the lava cooled, it contracted and broke up, forming the talus slopes that coat most of the mountain.  A few rugged cliffs of solid dacite stick out here and there. The peak tops out at 10,457 feet, so it is often coated with snow.

Lassen Peak emerged during a series of eruptions about 28,000 years ago. The entire mountain probably developed in just a few years. Its shape was modified by latest episode of Pleistocene glaciations, but it was otherwise dormant for tens of thousands of years. Until 1914, that is...

In May of 1914 a steam explosion rocked the top of the mountain, producing a small crater on the summit. Over the next year at least 180 explosions blasted away at the summit, ultimately producing a 1,000 foot wide crater. The eruption made news across the country. Brave but foolhardy souls climbed to the summit to have a look, including several men who were standing at the summit on June 14th when B.F. Loomis made the famous images reproduced below (these are pictures I took of the displays in the Loomis Museum at Manzanita Lake).

One of the men, Lance Graham, was walloped by a rock in the shoulder and in the panicky moments that followed was left for dead near the top of the mountain. A rather lurid NY Times story described him as actually being dead, his arms cut off, a deep gash exposing his heart, and his body nearly torn in half; a later correction stated : "...he was reported to be dead, but the latest word is that he still is alive, although fatally injured". He apparently survived to live a long life (I recounted this story in one of my classes, and a surprised student piped up saying "Graham? He was my great grandfather!").

On May 19th of 1915, lava emerged from the volcano for the first time. The thick flow melted thick banks of snow and produced a major mudflow, or lahar, that traveled many miles down two valleys on the north flank of the mountain, destroying six ranch houses.

Source: National Park Service. Photograph by R.E. Stinson

The volcano was quiet for two days, and some may have thought the eruption was subsiding. It wasn't. On May 22nd, a huge explosion lifted ash 30,000 feet into the sky. A plume of hot ash swept down the north flank of the mountain, destroying the forest and all living things over an area of three square miles (these hot ash clouds are called pyroclastic flows or surges). This site is called the Devastated Area, and the demarcation between the old forest and the pyroclastic flow is still clear. The mountain has been quiet since 1917 (except for a puff or two of activity in 1921)

The eruption of Lassen Peak was for sixty years the only volcanic activity to take place in the lower 48 states, and as such was often the main topic of discussion in the volcanoes chapter of geology text books. It was a "nice" eruption in that it displayed many diverse phenomena (steam explosions, ash flows, lava flows, and mudflows), and didn't kill anybody (despite Lance Graham's near miss with mortality). Even though Mt. St. Helens stole all the attention, Lassen Volcanic National Park remains one of the best places I know of to learn about volcanism. And it is a beautiful place to visit.

More in the next post!

An excellent description of the 1914-17 eruption can be seen here: http://www.nps.gov/lavo/naturescience/upload/eruptions_of_lassen_peak.pdf

Chaos! The Jumbles and Crags of Lassen Volcanic National Park

Lassen Volcanic National Park is one of the lesser-known and less visited of the national parks in California. Many have heard of Lassen Peak, but the park is located in the northern reaches of the state relatively far from most population centers. It's a fascinating place, and if one is interested in volcanism, there are examples of practically every type of volcanic feature within the borders of the park. How many places in the world have shields, lava plateaus, stratovolcanoes, plug domes, cinder cones, and calderas, as well as active geothermal fields (fumaroles, boiling mudpots, and hot springs; everything except geysers, so Yellowstone can rest easy). The park is also noted for the recency of many of these features, with numerous cones and flows that are less than a few thousand years old (Lassen itself erupted from 1914-1917).

On our recent trip, we approached the park from the north, and the first sight we beheld was beautiful Reflection Lake. In the morning light it was serene and quiet, and it was strange to consider the violence that led to the lake's formation (along with nearby Manzanita Lake). The forest hides the hummocky surface of the landscape that surrounds the lake, but a short distance up the road, the origin of the lake becomes clear.

The Chaos Jumbles is the remains of a large debris avalanche that thundered down the slopes of  nearby Chaos Crags. The lack of soil and vegetation suggests that the avalanche deposits are not old (there are at least three of them), and indeed none of the trees on the slide date to more than three hundred years. The slide traveled on a cushion of compressed air, traveling for more than two miles and climbing some four hundred feet up the slope on the far side of the valley. It blocked several streams, ultimately forming the beautiful lakes.

The rocks that make up the slide are quite interesting as well. They are volcanic, but not the black basaltic rock that people associate with lava flows and volcanoes. It is a pinkish brown volcanic rock called dacite. Dacite is intermediate in composition between rhyolite and andesite, containing the minerals quartz, plagioclase, hornblende and biotite. The volcanic rock also contains enclaves of a darker volcanic rock, an andesitic basalt that shows that two different magma chambers were comingling and mixing. The mixing probably was a factor in the eruptions of the dacite.

An aerial shot of the Lassen vicinity shows the Chaos Crags in sharp outline. They are the barren snow-free peaks to the left of the main cone of Lassen Peak (the Crags lie north of Lassen; the picture is oriented towards the southeast). Given the dense thick forest that surrounds the volcanoes and the barren nature of the Crags, they have to be exceedingly young, and dating indeed places their age at about 1,100 years before the present. Six individual domes were erupted during a period of about 60 years.

The Chaos Crags are excellent examples of plug domes, short steep cones produced by highly viscous lava flows. The lava emerged like toothpaste from the ground, and as it cooled, the surface of the lava contracted, breaking up and forming huge debris piles on the margins of the cone.

The six domes have been creatively named A, B, C, D, E, and F. Domes E and F can be seen in the picture below, while Dome D dominates the bottom picture.

In any other setting, the Chaos Crags would be the central focus of a volcanic park, but the much taller peak of Lassen stands less than two miles away, so they tend to be somewhat ignored. That's too bad because there are few better examples of plug domes to be found anywhere, and the youthfulness of the Jumbles suggests continuing geologic activity. A stop among the chaos of the Crags and Jumbles is a great introduction to the geology of Lassen Volcanic National Park!