A Landscape as Bizarre as They Come: The Volcanic Tableland of the Eastern Sierra Nevada

The Volcanic Tableland, with the White Mountains beyond.

There is a bizarre landscape on the far side of the Sierra Nevada between Bishop and Mammoth Lakes. It's not one of stark beauty exactly, it's barren and covered by little more than sagebrush. It's got few roads or trails, primarily because very little of this landscape is of much use to anybody. From above, the surface is riddled with scarps and grabens from numerous faults. This is a broken-up land. It's not...normal.

Source: US Geological Survey

The surface of this landscape isn't "right" either. There are no dark rich soils here. The underlying rock is pink or white, and so is the weathered soil and debris that covers it. Although the surface has an area of several hundred square miles or more, the underlying rock is remarkably uniform. It is a volcanic rock called rhyolite tuff. And with that name, the explanation for this landscape is revealed: it is the remnant of an ancient disaster beyond imagining.

767,000 years ago, an explosion took about 125 cubic miles of pasty magma from the crust and blew it into the atmosphere. The huge void collapsed inwards, forming an oval-shaped depression 20 miles long, 10 miles wide, and a mile or more in depth. The resulting ash spread far and wide, blanketing the western United States. Measureable deposits can be found in Kansas and Nebraska. But most of the ash came straight down. Some of it refilled the caldera, but much of the remainder buried the regional landscape hundreds of feet deep in hot ash. All life would have been extinguished for miles in every direction.

It is difficult to understand the magnitude of such events. From a human perspective, we have nothing to compare it to. An eruption at Tambora in Indonesia in 1815 produced less than a tenth of the ash as Long Valley, and that was enough to cause global cooling with related summer snowfall, crop failures, and famine across the northern hemisphere. The effects of an eruption the size of Long Valley on modern civilization would be appalling. I've heard it said that modern agricultural production has a month-long lead on consumption demand (No, I can't cite a source. It's a factoid I'm sure I heard or read somewhere). Try to imagine a disruption of agricultural production lasting several years. Governmental and societal structures would collapse, and the death toll would be unimaginable. Humans would no doubt survive, but it would be a dystopian landscape as bad as any sci-fi action movie, and maybe worse.

The only good thing that I can think of to say on this possibility is that studies of calderas like Long Valley or Yellowstone suggest that the eruptions will be predictable on a scale of decades or centuries. There would be time to prepare the eruption, or, however unlikely, geo-engineer the caldera to lessen the intensity and effect of the cataclysm.

What happens when a singular event completely reshapes a landscape? The eruption of Long Valley completely disrupted the drainage patterns of the eastern Sierra Nevada and Owens Valley. The land had to start over. Where there had once been river valleys and canyons, there was now a gaping pit miles wide and long. The evidence suggests that for 600,000 years the caldera depression contained a huge lake similar in plan if not in scale to Crater Lake. Crater Lake has no outlet, with the lake level determined by evaporation and seepage. The Long Valley Lake would have been similar, as no evidence exists for an outlet, at least until around 150,000 years ago.

Source: U.S. Geological Survey

For 600,000 years sediment washed into the basin, slowly filling it. Finally, along the south rim of the caldera near the present day site of Crowley Lake, the basin spilled over. In just 150,000-160,000 years, the Owens River carved a 400-500 foot deep gorge down the surface of the Volcanic Tableland, laying bare the full extent and history of the climactic eruption of the caldera. The rate averages out to about a foot every 400 years, but the rate was probably higher at the beginning. The small creek that flows through the gorge today is a mere shadow of its former self. The Los Angeles Department of Water and Power has co-opted most of the water, but a court order several years ago mandated that a minimum flow must be maintained.

Because the LADWP has utilized the water from the Mono Lake Basin to the north, they have constructed penstocks and pipelines that allow them to produce energy as they transport water down the long slope of the Tablelands. That means access roads, and it is thus easy to visit the gorge, and it is fascinating.

The mounds seen occasionally along the rim are the eroded remnants of fumaroles, where steam would have emanated from the interior of the ashflow, leaving mineral deposits that toughened the rock. The tuff at the rim is relatively soft, but as one walks deeper into the gorge, the rock becomes harder (it tuffons up?). When the hot ash landed, it was hot enough to remelt, forming welded tuff, or ignimbrite. Pieces of pumice caught up in the eruption became flattened and smeared in places.

As the rock cooled, it contracted to form columnar joints. Unlike Devils Postpile, a few miles away on the other side of the crest of the Sierra Nevada, these columns are not vertical. Most columnar jointing is not. The intense fracturing of the rock into these columns aided the Owens River in the carving of the gorge, as the crumbling rock could be quarried by the rushing water much more readily than solid rock.

The columns average six sides, but columns with 4, 5, or 7 sides are occasionally seen.

The Volcanic Tableland and the Owens Gorge are otherworldly, but they provide a hint of how quickly landscapes can adjust to new geological conditions. It took 600,000 years to fill a basin 10 by 20 miles with at least 2,000 feet of sediment, and 150,000 years to carve a 400 foot deep gorge. This is fast by geologic standards, but humans, had they been around this region at the time, would not have noticed much change in course of their lifetimes. Just like we aren't noticing the changes now...

What Could be Worse than the Crater Lake Eruption? A look at Smith Rock State Park in Oregon

Standing on the rim of the Crater Lake caldera, as we did in our last post, it is hard to imagine the scale of the catastrophe. In that event just 7,700 years ago, 15 cubic miles of ash was blown into the atmosphere, covering much of western North America with volcanic dust. A similar-sized event at Tambora in 1815 caused the deaths directly of tens of thousands, and worldwide, possibly hundreds of thousands (from climate-induced famine). How could it be any worse? The answer is found not all that far away. On our Pacific Northwest journey last June, we stopped at Smith Rock State Park between the towns of Bend and Madras in Oregon. The two sites are about 120 miles apart.

Smith Rock State Park is small as such things go, only about a square mile, but the setting, as can be seen in these pictures, is rather spectacular. The 600 foot high tan-colored cliffs are popular with climbers, while a flat plateau (on the right side in the picture above) provides flatlands for parking and camping. The Crooked River flows through the park. How did these odd rocks come about?

The flat plateau is perhaps the easiest to explain. Newberry Crater is a massive basaltic shield volcano located about forty miles to the south. About 400,000 years ago, a basalt flow emanating from Newberry flowed north until it was stopped by the cliffs of Smith Rock. The Crooked River then eroded a channel between the contrasting rock types.

It is the tan cliffs that really tell the story of catastrophe. It was a disaster so huge that its dimensions were not recognized until fairly recent times. The cliffs of Smith Rock are part of the northwest corner of the Crooked River caldera, a sunken crater that is 25 miles long and 15 miles wide. Crater Lake's eruption produced around 15 cubic miles of ash. The Crooked River eruption produced around 200 cubic miles. Imagine a dozen Crater Lake eruptions happening at once and you start to get an idea. The eruption rivals some of the worst of the disasters at Yellowstone or Long Valley in eastern California. The only saving grace here is that the eruption took place around 29.5 million years ago. The magma chambers that fed the event have long since cooled.

As the hot ash landed, some parts remelted and cooled to form solid welded tuff. Other parts hardened as hot gases and steam coursed through gaps and openings called fumaroles. The cooling mass contracted and fractured into numerous joints. Differential erosion produced the various pinnacles and spires seen at the park.

Modern human beings have never experienced an eruption of this magnitude. The last one of this size worldwide, at Toba in Indonesia about 75,000 years ago, may have almost done in the human race (a controversial idea, but plausible). It involved around 470 cubic miles of ash.

I notice that Smith Rock sits at the south edge of totality during the coming Solar eclipse. If you are lucky enough to get to the park as a setting for this once in a lifetime event, I hope you'll spend a bit of time pondering the incredible history of these rocks as well.

For some detailed information about the history of the Crooked River Caldera, check this link.

Here We Go Again: Yellowstone is Going to KILL US ALL! Wait a minute...

I'm going to start with the conclusion (I've highlighted some parts using the bold font):

Geological activity at Yellowstone provides no signs that a supereruption will occur in the near future. Indeed, current seismicity, crustal deformation and thermal activity are consistent with the range and magnitude of signals observed historically over the past century [Lowenstern et al., 2006]. Over the past two million years, trends in the volume of eruptions and the magnitude of crustal melting may signal a decline of major volcanism from the Yellowstone region [Christiansen et al., 2007; Watts et al., 2012]. These factors, plus the 3-in-2.1-million annual frequency of past events, suggest a confidence of at least 99.9% that 21st-century society will not experience a Yellowstone supereruption. But over the span of geologic time, supereruptions have recurred somewhere on Earth every 100,000 years on average [Mason et al., 2004; Sparks et al., 2005]. As such, it is important to characterize the potential effects of such events. We hope this work stimulates further examination of ash transport during very large eruptions.

The reason I am doing so is because the media is reporting on the body of the report that came out recently concerning the possible effects of a major caldera eruption at Yellowstone National Park. That means we are getting the usual headlines like:

If Yellowstone Supervolcano Erupts, Ash May Reach NYC

Yellowstone Supervolcano Eruption Would Doom the United States

Eruption of the Yellowstone Supervolcano will turn the US into a Third World Country

Eruption of Yellowstone supervolcano could spell the end of the US

For the most part, the reports themselves aren't too bad (there ARE exceptions). The thing is, we've always known that a Yellowstone caldera plinian supereruption would be devastating. That's old news. The purpose of the research was to model the potential effects of such an event. I get that disaster and omens of disaster are what sell newspapers or put eyes on advertising, so headlines go over the top, just like they always have. But this approach leaves the readers with the wrong impression, and they are going to worry about whether eruptions of Yellowstone need to be added to their fears of terrorist attacks, Megalodon shark attacks on their Caribbean cruise, or whether vaccines cause autism. In other word, useless levels of stress based on incorrect or blatantly wrong information.
 
I want to send kudos to a couple of media outlets with less sensationalistic headlines, such as those from the Billings Gazette: Researchers predict ash fall if Yellowstone supervolcano erupted or the Daily Digest: New computer models show likely fallout of a volcanic eruption in Yellowstone.
These kinds of headlines actually communicate accurate information without the terror-inducing yellow journalism.

This report from the U.S. Geological Survey serves a useful purpose. It is part of the kinds of research that can help cities, states, and nations plan for and cope with natural disasters when they occur. The authors were careful to state in their conclusions the extreme unlikelihood of a rhyolite caldera eruption, but their computer model might be useful in predicting the effects of lesser eruptions elsewhere in the world, eruptions that are far more likely.

You can see the report here:
Mastin, L. G., A. R. Van Eaton, and J. B. Lowenstern (2014), Modeling ash fall distribution from a Yellowstone supereruption, Geochem. Geophys. Geosyst., 15, doi:10.1002/2014GC005469. 

But don't fret. There are still the Yellowstone WOLVES to worry about!

Desert Skies, Hoodoos, and Really Big Rhyolite Explosions: An Innocent Abroad in Phoenix

Some places I don't know very well in the geological sense, and this makes no sense, because I've been in Phoenix a lot over the years. Oh, I glance at the guidebooks, but invariably my brother will get up and say "let's go explore (fill in a feature in any direction from Phoenix)", and it will be some corner of the landscape I've never seen or read about. And so it was that we headed southeast last week towards the towns of Superior and Miami. The legendary Superstition Mountains rose to the north, and we ended up driving through the heart of the Pinal Mountains.

The Superstitions are the home of the Lost Dutchman Mine, which was not exactly lost, and no Dutchman was associated with it, but people look for it anyway. I have a strong feeling that it was found a long time ago, and was mined under a different name with no one the wiser. There wasn't a lot of mineralization up high in the mountains, but a fair amount around the margins, and those areas were exploited a long time ago.

Copper was another story. Vast deposits have been found throughout the area, and Superior, Miami and Globe grew with the mines. I liked the street sign in downtown Superior (below). Magma was the name of one of the mines in the area. Still, it would be nice to see more geologically themed street names in my local town...

We drove east of Superior into the Pinal Mountains and soon encountered some very rugged territory. Although I was ignorant of the fine details, I quickly recognized that we were in the vicinity of some heavy-duty Neogene rhyolite calderas (that's "supervolcanoes" for the Discovery Channel writers). There were at least five calderas in the region. Each one was capable of producing massive explosive eruptions of hot ash in volumes exceeding 100 cubic miles. The pink rocks forming the cliffs around us are called rhyolite tuff which formed when the hot ash hit the ground and re-melted, but quickly cooled and solidified into rock.

I never get tired of photographing the saguaro cacti that are endemic to this region of Arizona. They seem to have unique personalities, if plants can have personalities.

The pinnacles of rock formed as the ash cooled and contracted. The ash flow had to shrink and so formed myriads of fractures, often at angles of about 120 degrees. The fractures provided avenues for water to get in and weather out the rock, often by freezing and expanding.

The towering pinnacles are sometimes called hoodoos. The slopes are exceedingly rugged, and the highway required a tunnel to get through the narrowest part of the gorge.

We took a deserted back road to try and get a view down into the Pinto Valley Mine, one of the region's gigantic open-pit copper mines. We only got a partial view of the upper terraces. Operations have restarted in the last year or two, with copper and molybdenum as the main products.

And then there were the skies over our heads. The clouds were diverse, with a beautiful band of mare's tails off to the west. It looked like sunset would be interesting...

It's winter, so ice crystals make up the clouds. When the sun hits the crystals just right, a prism effect produces brightly colored sun dogs. I've seen lots of sun dogs over the years, but I've never noticed the ray that runs beyond the sun dog away from sun itself (to the right in the photo below).

The sun was getting low in the west, so we headed back down the highway to the vast valley containing Phoenix and its many suburbs. The canyon nicely framed the setting sun.

As we rolled down the slope towards Florence Junction, the haze in the valley gave the low hills in the distance a mystical appearance.

What a beautiful day it was.

The Airliner Chronicles: A Broken Land of Unspeakable Violence

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

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

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

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

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

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

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

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

Map courtesy of GeoMapApp

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

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

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

Vagabonding across the 39th Parallel: We Reach the Wasatch Front, Finding Geologic and Archaeological Violence

Vagabonding across the 39th Parallel is an informal exploration of the geology of an interesting slice of the American West that I traveled in July this year. In the previous set of posts, we were crossing the Basin and Range Province, an exceedingly lonely region. We reached western Utah, and things started to change. Snowcapped mountains appeared on the far horizon, and the landscape became greener. Agricultural fields appeared, and then, a superhighway. Traffic was moving at 80 mph on Interstate 15, and there was a lot of it. We had reached the Wasatch Front.

The Wasatch Range is the transition zone between the Basin and Range, the Colorado Plateau, and the Rocky Mountains. Faults slice through the mountains, but the intervening valleys are not as deep as they are farther west. There is a feeling (not necessarily justified) here of a certain degree of geological stability. The sedimentary layers that are exposed in the area are generally less deformed, and form plateaus and mesas a short distance to the east. That's not to say that there is no activity. The Wasatch Front is a major seismic zone, and there is an uncomfortable possibility of large earthquakes along the frontal fault system.

We turned off Interstate 15, and headed more or less east on Interstate 70. Our rules of the road for this trip dictated that we did not plan too far ahead, so even though it was late in the afternoon, we still didn't know where we would be stopping for the night. We were discussing where the next KOA might be when we saw a turnoff that said "Fremont Indian State Park". What the heck, let's check it out, we thought.

Did I say that the Wasatch seemed like a stable place? A close look quickly reveals a past history of great violence. Those innocuous-looking cliffs at that park (in the picture at the top, and below), which could be mistaken at a distance for sandstone, turn out on close inspection to be rhyolite tuff.

Rhyolite is the most viscous of volcanic lavas, meaning that it flows almost not at all. It comes out of ground with a consistency something like toothpaste. But if the rhyolite is charged with dissolved gases, it doesn't flow at all; it explodes with great violence. The lava is pulverized into dust particles as it bursts into the atmosphere. The scale of rhyolitic eruptions can be huge, sometimes involving dozens, even hundreds of cubic miles of material. As the eruption wanes, the crust of the earth collapses into the void created by the explosion of ash, forming a huge pit called a caldera. The holes can be many miles across. Hot ash falling to the ground near the caldera often remelts, forming a solid rock layer called a welded tuff, or ignimbrite.

At Fremont Indian State Park in Utah, just such an eruption took place around 19 million years ago, forming the Mount Belknap caldera several miles away to the southeast. The welded rhyolite ash is called the Joe Lott tuff. The volume of the eruption was nearly 100 cubic miles, which puts this eruption in the same league as those that formed the Yellowstone caldera in Wyoming, or the Long Valley caldera at Mammoth Lakes in California.

The rhyolite cliffs in the vicinity of Fremont Indian State Park were valuable to the original inhabitants of the region for at least two obvious reasons. Rhyolite often forms obsidian (volcanic glass), which could be formed into sharp tools like arrowheads, spear points, or axes. Cultures with access to obsidian deposits had a valuable and marketable commodity.

The welded tuff cliffs were also relatively soft and easily chipped. The cliffs were an irresistible canvas for chipped rock art, that is, petroglyphs. There are hundreds of them in the vicinity of the park, and a short trail from the museum provides easy access to some excellent examples.

The Fremont people were an enigmatic culture that lived in this area from about 400 to 1300 AD. They didn't construct massive cliff dwellings like those of the late Ancestral Pueblo people farther south at places like Mesa Verde. They lived in less easily preserved pithouses, and farmed maize and beans in a swath of land across central Utah and easternmost Nevada. Their artwork is distinctive and very mystical and symbolic. The meaning of many of the figures is not clear to anthropologists, but I imagine that they are quite obvious to a number of the existing Pueblo cultures who are probably their descendants.

The wavy lines are often interpreted as snakes, although I have seen some speculation that these lines may actually record a memory of violent earthquakes (recall the proximity of the Wasatch fault zones). The petroglyphs on the left side of the picture below are thought to be bird tracks or sprouting corn.

Do you recall a Vietnam War era quote about destroying a village in order to save it? Here at Fremont Indian State Park, they had to save a village in order to destroy it. When the roadbuilders were putting in the Interstate, they had to cut through hill in the picture below. As they started, they discovered a huge Fremont village, the largest ever found. The freeway was going to destroy it. It was excavated, and the artifacts that were recovered became the basis for the collection at the museum in Fremont Indian State Park. I somehow found this conflicting juxtaposition of cultures disturbing.

We had seen a sign that there was camping across the highway. We drove over to check it out; we were in for a big surprise! That will be covered in the next blogpost...

For more information about Fremont Indian State Park:
Park website: http://stateparks.utah.gov/parks/fremont
Park brochure: http://static.stateparks.utah.gov/docs/FremontIndianBrochure.pdf
Chapter 13 of Geology Underfoot in Southern Utah by Orndorff, Wieder, and Futey

Dispatches from the Road: The Last Moment Before Apocalypse...

Hollywood disaster movie-makers don't have much in the way of imagination...a movie like 2012, with pieces of California sundering into the sea, explosive chunks of lava chasing recreational vehicles, continents moving thousands of miles, and arks taking a remnant of the human race to a brighter and more hopeful future...nothing of this can compare to real life adventure that took place here 760,000 years ago. I'm gonna go screenwriter on you and compose a movie idea...

Imagine the group of unlikely compatriots thrown together east of the Sierra Nevada, a giant wall of rock rising thousands of feet above the valley floor, which despite the relative aridity of the region is well-watered by streams coming off the mountains. We can ignore the fact that nobody actually lived in North America 760,000 years ago; this is Hollywood after all, and we can make things up. There's the plucky child, the quiet guy who seems to be hiding something, the excitable guy who complains a lot, the hero type leader, the beautiful woman, the other woman with suspicious moral character, the slightly addled drunk, the old couple who love each other, even after 50 years...you can add some other stereotypes as you wish. Thrown together, they argue, but then up the hill the first eruption begins, throwing a shower of fine ash particles across the landscape. The unlikely band pulls together and starts their quest to redemption.

Every so often, as they make their way across the ash covered landscape, someone dies, either being picked off by hungry predators, or falling off a cliff, or falling into a muddy river while making a desperate crossing. The survivors hold together, finding new truths about themselves and each other, and in general growing in admiration for the pluckiness of the human race.

The ash eruptions continue over the next few days or weeks, leaving behind a layer after layer of cinders and ash particles amounting to several feet in thickness. Our band of people carry on, seeking that redemption that lies just over the next hill.

Then, the paroxysmal eruption begins. The ground shakes violently as a vast plume of ash rises on the horizon. The wall of ash is 18 miles across, and 10 miles wide, and rises into the stratosphere, far higher than any airliner can fly. The amount of ash exceeds 120 cubic miles. It is incandescent, so hot it glows in the night. The hot ash spreads rapidly across the landscape, instantly incinerating anyone and anything in its path. The layer is hundreds of feet deep, and covers thousands of square miles. Areas as distant as Kansas and Nebraska are covered in several inches of ash. World climate changes to the cool side for decades, at least. In the aftermath of the explosion, the land collapses into a giant hole 10 by 18 miles wide, and two miles deep.

Needless to say, our plucky band was incinerated in the first moments of the giant pyroclastic surge, and everyone was dead. But they were plucky and all, and we recall their memory while the screen credits roll...

OK, there's a reason I never went to work in Hollywood as a script writer. But, isn't it cool that you can lay your hand across a moment of catastrophe? That's what is happening in the picture below. There are many such thrilling moments of imagination in geology (and not always catastrophe, either). When you know something about the rocks, you can visualize a practically infinite number of worlds that have passed away, worlds with strange life forms and moving continents and giant earthquakes, and mountains rising and being eroded away.

This was the first stop of our geotour through the Long Valley Caldera this last weekend, courtesy of the National Association of Geoscience Teachers, and the National Earth Science Teachers Association. The site is a pumice quarry in the Chalfant Valley northeast of Bishop.

I took lots of pictures, so more soon...

For a more detailed look at aspects of this incredible eruption, check out this post from Callan Bentley at NOVA Geoblog (now Mountain Beltway)