Sunday, October 22, 2017

How Does a Pristine Cavern Look? Black Chasm Provides a Clue

Some things can only be experienced once. The discovery of a new plant or animal that no one has ever seen, a new mineral, a new planet in space, to see a vista that no one has witnessed before. Exploration of new things is one of the great joys of being human. One of the saddest lines I've ever seen in a move was from The Truman Show (1998):

Young Truman: I'd like to be an explorer, like the great Magellan.
Teacher: [rolling down a map of the world] Oh, you're too late. There's really nothing left to explore.
Entrance room of Black Chasm cave. The dirt on the decorations is from soil seeping in from above, but many of them are broken from early explorers and visitors.

And there are things that can be destroyed only once. The extinction of a species, a beautiful canyon marred by a poorly-planned development, the destruction of a culture or a people.
If there is anything I have learned as a scientist and a teacher, it is that there is never an end to exploration. I was reminded of this as I took a group of students on a field studies journey on Saturday. Ostensibly the trip was about caverns and karst topography in the Sierra Nevada Mother Lode, although it included a great deal of information about the 1848 Gold Rush as well. We toured Highway 49 between Jackson and Columbia, but included an excursion through Black Chasm Cave near the village of Volcano.
Helictites in Black Chasm Cave
So many caves that are known today were discovered in previous centuries, and have been explored and vandalized to a shocking degree. My opening point about a single moment of discovery and a single final moment of destruction applies in many ways to caverns. A cavern can only be discovered and explored once. From that time on, in human terms, it is moving inexorably towards destruction. Caverns cannot recover from the damage inflicted by human visitors in any kind of time frame that people would recognize.
Helictites in Black Chasm Cave
Non-cavers are often confused or bemused by the nearly maniacal lengths that cavers take to prevent causing damage to pristine caves. But the cavers themselves understand. Many experienced cavers have watched some of their favorite places turn from a mystical underground fairyland to a dark dirty troll's den in the space of a few years. Research literature documents the destruction of caves as their location becomes known to the public at large. For this reason, the location of the vast majority of caverns is a closely held secret. A pristine cave is a rare and precious resource that is too easily lost to vandals. As a consequence, most casual cave visitors will never know the experience of a newly discovered cave. But there is a way that they can come close.
Helictites and stalactites in Black Chasm Cave
There are around a thousand known caves in the Sierra Nevada, and six are open for tours: Crystal (in Sequoia National Park), Boyden (just outside Kings Canyon National Park), Moaning (near Columbia), California (outside San Andreas), Mercer (near Murphys), and Black Chasm. Each of them have their charms and educational value, but Black Chasm stands out. It is one of the few that has the feel of an undefiled cave, at least once you've crossed the "chasm".
The "Dragon", mascot of Black Chasm. That's not the normal color...the guide was using a laser pointer on it.
The miners who discovered most of the Sierra caves explored them with smoky torches or candles, and they as well as those who followed over the years had no compunctions about touching and breaking off the speleothems (cave decorations) found in the caves. Owners even encouraged visitors to take a souvenir, thinking that the stalactites would grow back within a few years. These caves ended up with dirty walls and ceilings, and the only stalactites left were those that were out of reach of visitors. This also happened at Black Chasm.
But a short distance into the steep cave entrance the rocks drop off into the inky darkness of the chasm itself. It's around 90 feet deep with sheer walls and a series of small lakes or ponds at the bottom. Getting to the rooms beyond required technical climbing skills that weren't practical until the 1960s and 1970s. Those who were then able to explore deeper into the cave were careful spelunkers, not vandals, and the rooms they found were spectacular.
When the owners decided to develop the cave, they constructed a series of stairs and bridges that provided access to the back rooms of the cave, but the stairwells also prevent tourists from getting too close to the pristine decorations. And what wonderful decorations they are! The first thing I always notice is the pearly white color of the dripstone and flowstone features. They don't have any soot or dirt on them at all. The next thing that comes to my attention is the total lack of broken features. They quite literally look the way they did when they were first discovered except for the lighting. Because the flowstone and other features are translucent, the owners were able to place the lighting behind the features so the light could glow through. The photographic results sans flash are wonderful. Flash pictures always seem to make the speleothems look flat and featureless.
The crowning feature of Black Chasm Cave is the number and variety of helictites. They can be thought of as stalactites on drugs. They don't believe in gravity and have instead grown in all kinds of directions, almost as if someone took handfuls of spaghetti noodles and tossed them onto the wall. They are rare in caves, especially those open to tourists, in part because of their incredibly fragile nature. A single touch would be more than enough to snap them off. But it hasn't happened at Black Chasm. The sheer number on some walls (thousands of them) have resulted in the cave being declared a National Natural Landmark, a federal program that encourages owners of outstanding natural features to protect their resource (of course it doesn't hurt their public relations).
The owners of Black Chasm Cave have done a great job of protecting their resource, and their tours are done well. In addition, they encourage educational groups by offering steep discounts, so I have no problem recommending them to my fellow educators. Information about visitation and tours can be found on their website at They also have an excellent nature trail on the property (that will be in the next post), plus a curio shop with some surprisingly sophisticated speleology texts for sale, along with the usual geodes and t-shirts.

Don't ever stop exploring!

Friday, October 20, 2017

Can't See the Forest for the Creek; Or is it the Other Way Around? California's Mega-droughts

The eastern Sierra Nevada is home to one of the strangest forests I know of. It's not the species of tree that is odd; they are mostly Ponderosa, a pretty but unremarkable tree which can also be found on the adjacent slopes. What's strange is that these trees are dead. Not the "recent forest fire" kind of dead. It's that they have been dead for the nearly a thousand years. Oh, and they are still standing, and are located in the middle of a good sized river.

The West Walker River drains a rather large region in the vicinity of Leavitt Meadows and Sonora Pass. Several forks come together near the junction of Highways 108 and 395, and the river plunges into a narrow gorge before spreading out into the Antelope Valley near Topaz Lake on the Nevada border. The trees, and there are several dozen, are found at the head of the gorge near the campground at Chris Flat. Studies have found that these trees sprouted, grew to maturity, and died within a relatively limited period of time between about 800 and 1350 C.E. (common era, equivalent to A.D.).

The weird part is that the trees pretty much filled the entire canyon bottom. They don't do well immersed in water, which seems to suggest that there was almost no room for a river channel when these trees were growing. This implies that the river was much smaller and therefore there were two crippling droughts that lasted on the order of 200 years  and 140 years respectively. Once the droughts ended, the river filled the channel with sediment again, perhaps supplemented by outwash gravels from the Matthes glaciation (the Little Ice Age).

These ghostly forests exist in other parts of the Sierra Nevada. Tenaya Lake, Lake Tahoe, and Fallen Leaf Lake all have submerged forests that grew to maturity during these periods when the lakes didn't have enough water to flow through their outlets. Oral histories of California's Native Americans also hint at terrible droughts.

In human time frames, droughts are a fact of life here in California. We had extended droughts from 1928-1934, 1960-61, 1976-77, 1988-92, and most notably, from 2011-2016.  Our population has grown so large that each drought becomes more problematic, and we muddle through on the strength of a few extraordinary precipitation years like 2017 that fill reservoirs for a time. What would we do if another century-long drought were to come? And what role will anthropogenic global warming play? I might not be here to find out, but my grandchildren might have a real struggle.

Tuesday, October 17, 2017

28th Anniversary of the Loma Prieta Earthquake - It Was a Warning That is Still Operative

What a different world... on Oct. 17, 1989, there were no smart phones, the internet barely existed, and we still depended on things like newspapers, television and radio to keep up with the world. Most of my current students had not yet been born, and that means that most of my students have never felt or experienced a major earthquake. Today we joke that when the BIG ONE hits, the tweets and Instagram posts will outrace the P-waves across the surface of the planet (there is a small bit of truth in the joke).

Earthquakes are not a joking matter though, and it is sobering to think that damage of a magnitude 7.8 quake in Los Angeles or San Francisco will have effects that will put California into a world of hurt not all that different than what is happening now in Puerto Rico or the Virgin Islands. Although we have had 28 years since our vivid warning in the hills above Santa Cruz, we are still not as ready as we should be, and many of our fellow citizens are complacent about earthquake safety. The ongoing experiences of hurricanes and wildfires across our country remind us of the importance of being ready with water, food, first aid, communications plans, and escape routes. As has been sadly demonstrated, we cannot depend on the federal government to act on our behalf in an effective manner, given the depletion of their resources following other major disasters, and stupid politics currently infecting Washington D.C.

I have yet to be in the middle of a major tremor; I've been on the outskirts of several, including 1989, and the 1971 Sylmar earthquake in Southern California. I was on the scene of the 1992 Landers quake (magnitude 7.3) within a week to see the ripped up ground. My experiences were mostly of the learning kind, not that of personal loss. Still, there is something to be learned in every experience. What follows is an abridged version of my story from a post on the 20th anniversary.
In 1989 I was a brand-new instructor at Modesto Junior College, in my third semester. I taught classes in the old 1950's-era Science Building on our east campus, up on the second floor. I had all the modern teaching technology; there was a chalkboard, and two television monitors hung from the ceiling for showing those newfangled "videotape cassettes". The monitors also served as my decidedly low-tech seismometers. They shook noticeably during the smallest of earthquakes (most memorably during a class test on earthquakes; no one but me even noticed).

On October 17th at 5:04 PM, my physical geology laboratory had just finished and almost everyone had gone home to watch the World Series. A couple of students were helping me (it was Maureen and Sonny; funny how I remember the names of the first students I had better than the ones I had last semester). We were 100 kilometers from the epicenter, so when the seismic waves started to shake our building, the movement was a strong rolling motion instead of sharp vibrations. We looked at swaying TV monitors, and commented that it was an earthquake. It was a most scholarly discussion, actually. We realized the shaking was not stopping, and we thought we could sense the direction of the quake as well. We started to guess where it might be happening, but when the shaking reached the 40 second mark (the energy was spreading out, it lasted only 10 seconds or so near the epicenter), we realized it was a major event, and that fatalities were probably occurring (and unfortunately we were right). The deodar trees out the window were whipping back and forth as if they were in a high wind. The strangest part for me was the unconscious decision I was making as the shaking progressed. Despite having a quiet scholarly discussion, my body was moving from the front of the podium to the back, where there was a nice solid space to hide under. I would have dived under if the quake had lasted any longer.
The Cypress Structure in Oakland where 44 people died

In hindsight, I should have been a bit more aggressive about taking shelter under the desk. An analysis of our building a year or two later revealed an architectural weakness that suggested the building could collapse if the seismic waves hit it from a particular direction. A seismic retrofit a decade later included some massive shear walls in the lab I taught in.

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

The Loma Prieta earthquake, a magnitude 6.9 event at a depth of 11 miles, was a tragedy: 63 people died, and 3,700 were injured. The Bay Area was in chaos for days and months passed before life got back to normal. We were on the fringes, so instead of pain and suffering, we had a profound learning experience that was remembered by my students for the next decade and a half. But it has been 28 years now, and as I said, many of my students weren't born when the quake happened. Few of them have felt a quake at all. The large quakes like Loma Prieta and Northridge are ancient history, and there is less of that innate knowledge of what they should do when one hits. Few admit to having any kind of emergency kits at home, and they have no plan for what to do when the next big one hits.

Fault studies across California make it clear that more big tremors are coming, almost surely within the next decade or two. We educators must keep these past events alive in the minds of our students so they will be ready for these events when they come.
I'm sorry I can't provide a source for these photos. They are scans from a slide set that I purchased many years ago, soon after the quake occurred.

Saturday, October 14, 2017

Feeling a Bit Sheepish: A Bit of Glacial Mutton in the Sierra Nevada

Pothole Dome in Tuolumne Meadows at Yosemite National Park
Sometimes glacial terms represent some kind of logical relationship to reality. "Horns" that are sharp pointed glacial peaks, "cirques" that are circular-shaped glacial bowls, "glacial polish" referring to rock worn smooth by glaciers, or "moraine lakes" that are lakes dammed by glacial moraines. Then there are the others: tarns, eskers, kettles, aretes, and cols, the kinds of terms that cause misery among my first-year geology students. But one term seems to depart from all reality...roche moutonnée
Unnamed roche moutonnée just north of Lembert Dome in Tuolumne Meadows
The term roche moutonnée describes an asymmetrical glacially scoured rock outcrop that has a smooth slope on the side facing the flowing ice, and a steep cliff on the side where the glacier pulled away from the outcrop ("stoss and lee structure" is a related term). The scale can range from a few meters to many hundreds. They are common features in regions of bedrock that have been scoured by massive continental ice sheets, but are a bit less common in mountainous areas eroded by alpine glaciers. These glaciers are the kind that filled valleys, but didn't overwhelm the surrounding peaks, such as those that flowed through most canyons of the Sierra Nevada. Yosemite Valley is the most famous, but glaciers filled dozens of other major river canyons from south of Sequoia National Park all the way north to the Lassen Volcanic National Park region. At their height, these glaciers covered about 30% of the mountain range.
Hiking the gentle slope of Lembert Dome in Tuolumne Meadows
The Tuolumne Meadows region of Yosemite National Park was an odd exception to the usual Sierra Nevada glaciers. The area surrounding the meadows was covered by a 2,000 foot thick mass of ice that was far more like a continental ice sheet than an alpine glacier. The ice spilled over ridges into several other drainages, including that of the Merced River, which carved Yosemite Valley. The addition of ice from the Tuolumne drainage gave the Yosemite glaciers an extra bit of "oomph", allowing them to erode deeper and farther than they would have otherwise.
Looking down the western edge of Lembert Dome. Note the glacial polish on the summit ridge.
There are numerous roche moutonnées in the Tuolumne Meadows area, including the easily seen Pothole Dome (first picture of this post), and Lembert Dome near the Tuolumne Meadows campground (below). The summits of each are easily climbed (from the right direction, anyway), and both provide stunning views of the region.
The problem with roche moutonnée as a geological term is that we geologists can only barely agree on its meaning. It's derived from French, and the "roche" part isn't a problem. It means "rock". But "moutonnée" is the tricky one. It can be translated loosely as "sheep" (think "mutton""), but not exactly (French: "mouton"). Moutonnée (with the extra e's) translates to "frizzy", and is taken as a reference to sheep's wool. The term originated in the 1700s with a naturalist named Horace-Bénédict de Saussure (it would be decades before the term "geologist" was coined) who noted that the rocks looked like a type of wig apparently well-known at the time whose locks were held in place with mutton grease. Except that there seem to be few or no references to wigs that were actually called that (the closest version was a tête de mouton).

So we teachers are left with trying to define the term as meaning "rock sheep" based on the nebulous idea that the rocks look like sheep grazing in meadows. Which they really don't. But it's still easier than trying to describe obscure French wigs from the 1700s and mutton grease.
A few weeks back we were on our field studies trip to the eastern Sierra Nevada, and we descended from Sonora Pass into the drainage of the West Walker River at Leavitt Meadows. I was describing various glacier features and even mentioned the presence of a few ill-defined roche moutonnées upstream of the meadow. You can see them in the picture below. But then I noticed something else in the midst of the meadow. I saw them, and now you are hoping that Geotripper won't go there, but he will...
Yes. It was actual....
...rock sheep! In a meadow.

But I still don't think they look like eroded glacial domes.

For an excellent description of the derivation of the geologic term, check out this great story from the Atlantic.

Thursday, October 12, 2017

You Just Can't Take Sonora Pass for Granite: Travels Around the Sierra Nevada High Country

Sonora Pass in the Sierra Nevada is a sort of forgotten step-sister of the more famous Tioga Pass in Yosemite National Park. A paved road, State Highway 108, crosses the crest of the Sierra about forty miles north of Tioga, cresting out at 9,624 feet, but it sees far less traffic. There are, for instance, no national parks, no major ski areas (Dodge Ridge is thirty miles to the west), and no major resorts, and snowdrifts keep the pass closed for much of the year. But Sonora Pass is an incredible place to visit if you ever get a chance, and it makes for a nice loop trip out of the Central Valley, including Tioga on the way back.
The road is steep and winding towards the top, but the views are extraordinary. We are in the headwaters of the Stanislaus River, and the region was heavily glaciated during the ice ages, making for spectacular alpine scenery. But one thing seems to stand out as one approaches the summit. You can't take this pass for granite. At least not all of it. This bad pun can be understood in two ways: there is volcanic rock at the top of the pass, not granite, and what "granite" there is along the lower reaches isn't actually granite.
First off, there are lots of fine exposures of granitic rock below the pass, and along the highway for a considerable distance downstream to the west. But it is not technically granite. If one has had a basic earth science course, a person may have learned that there is granite, diorite and gabbro as the plutonic igneous rocks (light, medium, and dark). But if one takes physical geology or an upper division petrology course, one finds there are other rocks intermediate between granite and diorite. The differences come from the proportions of potassium feldspar, plagioclase feldspar, and quartz. As such, true "granite" is actually somewhat rare in the Sierra Nevada, perhaps accounting for 10% of the total. The most common rock is granodiorite, a granite-looking rock rich in plagioclase, but lacking in potassium feldspar.
I'm the first to admit that the difference to a layperson may seem trivial, but recognizing these differences allows researchers to draw many conclusions about the circumstances and timing of the intrusions that formed the backbone of the Sierra Nevada. And some of the other
"granitics" are truly beautiful rocks. At Sonora Pass, the common granitic rock is called the granodiorite of Topaz Lake, and it is one of the younger intrusions in the Sierra Nevada, having cooled about 89-93 million years ago. It has massively large crystals of potassium feldspar, 2-3 inches long, embedded in a groundmass (matrix) of smaller crystals of quartz and plagioclase. Such rocks with two distinct grain sizes are described as porphyritic. Glaciers have smoothed off the rock in many places ('glacial polish'), almost providing the effect of a polished countertop.
The other way that Sonora Pass cannot be taken for granite is the fact that the rocks at the pass are actually volcanic in nature. Between 11 and 9 million years ago, this area was an extensive volcanic center broadly similar to the one that exists today at Lassen Volcanic National Park, with andesitic stratovolcanoes, lava domes, and a modest caldera complex.
The volcanoes are long extinct, and glacial erosion has greatly modified their original outline. The mountains are striking if for no other reason than that they are different from many of the light-colored peaks of granitic rocks seen elsewhere. In a sense, they almost seem somber and dark. John Muir would no doubt have seen their beauty, but probably wouldn't have been inspired to call them the "Range of Light".
If you ever want to brag about your hiking exploits, but just don't have the energy, you can go to Sonora Pass, and wander a few yards up the trail that crosses the pass going north and south, perpendicular to the highway. That way, when people ask what you did last summer, you can truthfully say something like "I spent a bit of time on the Pacific Crest Trail"!

If you long to spend time in the Sierra Nevada, and just can't fathom the thought of fighting the crowds at Yosemite Valley and other parts of the national park, give Sonora Pass a look. I'm pretty sure you won't be disappointed. If you need a guide, my colleague Noah Hughes and I edited a field trip guide for the region for a meeting of the National Association of Geoscience Teachers in 2012, and the book we published is for sale (details are here; all proceeds support the scholarship program of the NAGT-Far Western Section).

Thursday, October 5, 2017

Fall Colors in the Eastern Sierra Nevada!

We've returned from a field studies expedition to the eastern Sierra Nevada, and I can report that fall has arrived! We've had a very warm summer, and the heat waves continued into September, but then we had a sudden cold snap, and even some snow. Tioga and Sonora Passes briefly closed, but opened again in time for our trip. The aspens and cottonwoods have responded to the sudden cold conditions.

Our route took us over Sonora Pass, where fresh snow still lingered on the high slopes. It's a sight I'm not used to. We spent a lot of time in the Bodie area and in the White Mountains where there aren't many deciduous trees, but late in the weekend we moved into the canyons below the Sierra Crest.
One of the special places is Convict Lake, which is dammed by a moraine of the Tioga glaciation that ended about 13,000 years ago. Aspens and cottonwoods crowd the shoreline, providing vivid color.
On our last day, we took the June Lake Loop, and stopped to explore Silver Lake. The canyon of Reversed Creek and Rush Creek is a spectacular glacial valley with high peaks above, and a string of beautiful lakes.
As we wandered among the trees, we heard a rockfall on the slopes high above. It wasn't all that big, leaving little dust in the air, but it was exciting to listen to geology in action.
It's been a long summer, but the drought finally broke, and the forest was looking healthy. Our mountains might not have the color range of the eastern hardwood forests, but then again, those forests don't have the mountain backdrop of our beloved Sierra Nevada.