The Other California Goes Underground: Hella Hot Helictites at Black Chasm Cave

The guesses regarding the odd features in Wednesday's "Whatsit?" were all over the place, including a great story of the albino cave tarantulas, but a number of people remembered their obscure cave decorations and called them by their correct name: helictites. We were in Black Chasm Cavern near the towns of Volcano and Pine Grove in the Sierra Nevada Mother Lode. The state of California has a number of caverns offering tours, in the Sierra, the Klamath Mountains, and the Mojave Desert, but I find that Black Chasm, though small, is also one of the most spectacular. A big reason is the preponderance and variety of helictites that can be seen in the inner chamber.
Helictites are one of the stranger cave decorations because they seem to (and indeed do) defy gravity. Stalactites and Stalagmites form as water drips from the ceiling of a cave and splashes on the floor. Stalactites grow downwards from the top while stalagmites grow upwards from the floor. They occasionally grow big enough to link up, forming a column. In a nutshell, helictites are stalactites on drugs. Their origin is not clearly understood, but is thought to be related to water pressure and capillary action which can operate in opposition to gravity. Imagine a stalactite with water dripping form the the tip, but with water being squeezed outwards to the side rather than dripping straight down. The calcium carbonate precipitates out in an uneven manner, and the helictite grows in odd directions. Cave winds have also been suggested as an origin, but many caves that have helictites do not have strong wind currents.
Black Chasm has been granted National Landmark status because of the beautiful helictites that cover several walls. Why are they here in such abundance? One reason is that helictites are so delicate that they rarely survive the early discovery of a cave. Cave visitors in the 1800's and early 1900's tended to take cave decorations as souvenirs, and helictites were the easiest to break off (whether on purpose, or by accident). Black Chasm was discovered in the middle 1800's, and the outer rooms suffered a lot of damage, but there was a true chasm in the cave interior that kept out casual visitors. It is nearly 100 feet deep, and required ropes and climbing skills to cross. When the cave was developed in the 1990's, a stairway was constructed that allowed easy access to the inner chamber, but the operators of the cave have done a good job of keeping vandals from the delicate decorations.
Another reason I like the cave so much is that it is strategically lit to emphasize the best of the other speleothems (cave decorations), especially some beautiful drapery formations (above). Early cave explorers used smoky torches for light and were inclined to touch and muddy most of the accessible cave features. Through heavy visitation and abuse, most tourist caves have dirt covering the speleothems. This is not the case in Black Chasm, and the operators have made the most of it, by showing the beautiful translucence of the thin filmy draperies.

Caves are fragile, irreplaceable, and worthy of our protection. I wrote about Black Chasm last year, and ended with the following:

If you are interested in exploring wild caves, preservation and protection is the highest priority. As such, you should get in touch with the local grotto of the National Speleological Society if you want to be involved in protecting this special resource. If you have followed my blog for any period of time, you will know that I think that cave vandals are one of the lowest and most moronic forms of humanity in existence.

I Don't Believe in Evolution Either...

I'm off to Death Valley for what promises to be a wet and wild weekend in drought-stricken California. The storm door is open across the state, and I am sincerely hoping that the rain and snow can ease the dry conditions. That remains to be seen, of course. I just don't know why the storms seem to be always coming on the Presidential Birthday weekend when I take the students on our long field trip.

In addition to a presidential birthday, it also happens to the be the 200th birthday of Charles Darwin. When I am making my way across the desert in the next few days, I will have a few opportunities to meditate on the intellectual advances that he and Alfred Wallace introduced to the world of science.

Like the Ethical Paleontologist, I would like to state here in no uncertain terms that I DO NOT BELIEVE IN EVOLUTION. Of course, I also don't believe in gravity, and I most certainly do not believe in atoms. What I DO believe, especially in the subject area of higher beings, is actually not your business, and is not germane to a discussion about evolution. If you would like a serious discussion about such issues, you are free to contact me in other ways.

Of course, despite my professed non-beliefs listed above, the world continues to behave EXACTLY AS IF evolution, or gravity, or atoms exist. My continued existence is in fact possible only because each of these phenomena do exist, and science has provided a framework for understanding each of them. In the case of evolution, my continued existence is actually threatened as I continue to fight off an infection that has proved resistant to antibiotics (don't worry, it's not that serious yet).

Death Valley National Park is a place to witness a few incredible examples of evolutionary change in action, both in the past and in the present day. The park contains something like seven vertical miles of sedimentary deposits that preserve one of the most complete fossil records of the development of life from over a billion years ago to the end of Paleozoic time to be found anywhere. The first picture above is a trilobite that same or crawled in the Cambrian coastline around 520 million years ago. Thousands of species evolved over millions of years before they went extinct around 250 million years ago.

The innocuous-looking fish in the second photo are cyprinodon pupfish, one of the most unlikely living creatures to be found in the driest place in North America. Sorry for the photo quality; they aren't easy to photograph. The pupfish are the ancestors of a species that lived in the Colorado River system and in fresh-water lakes that filled these desert valleys during the Pleistocene Ice Ages. As the ice ages ended, the lakes dried up, and doubtless many species and individual fish perished, but in a few watercourses and springs a few of the pupfish survived. In the last few tens of thousands of years, some of the fish populations thrived in freshwater springs, but others were trapped in increasingly salty ponds and creeks (like Salt Creek on the floor of Death Valley). The fish adapted to the conditions, eventually forming at least four or five species, and perhaps a dozen subspecies. No other fish is known to survive in water as salty as one of the species, and one of the species is known to survive in 100 degree conditions. No other fish is that hardy. Others survive in freezing conditions.

The most familiar species is the Devils Hole Pupfish. The entire species lives in a single water-filled cavern opening in the Ash Meadows area east of the main park. In that one hole, they have survived for thousands of years. Their population crashed a few years ago, down to a few dozen, but they may be recovering (several have been taken to other refugia to preserve the species in case of disaster).

They are luckier than the Tecopa Pupfish. The entire species was wiped out in an afternoon when bulldozers destroyed the springs they lived in to build a hot springs spa in the 1940's. What a shame to lose out due to human interence after so many thousands of years.

Happy birthday, Mr. Darwin! You enriched our understanding our world in many ways!

A Short Primer on Mass Wasting, Courtesy of California's Atmospheric River Storms

I live in California's Great Valley, known to some as the plain old "Central Valley", and most know it as a very flat place. A VERY flat place. Over the four-hundred-mile length of the valley elevations barely rise above 300 feet above sea level, and much of the valley is floodplain. As we emerge from the unrelenting series of atmospheric river storms that dropped near-record (and some record) amounts of precipitation all over the state, one might assume the greatest problem here is flooding. Some areas have indeed been hit very hard, and lives were lost.

One might be surprised to hear that even though the rivers rose, some areas were less affected by the flooding. In the case of my home county, Stanislaus, there were (and continue to be) problems along the lower reaches of the Tuolumne and San Joaquin Rivers, but on the east side of the valley there were few ill effects. Along my usual walkway, the Tuolumne River Parkway Trail in Waterford, the damage was of a type not often associated with a flat valley floor: mass wasting, or mass movement.

The reason has to do with a quirk of the geological history of our region. During the Pleistocene ice ages over the last two million years, glaciers covered perhaps 30% of the Sierra Nevada on repeated occasions. The ice never reached the Great Valley, but the streams of ice ground up vast amounts of rock to sand and mud, and the rivers were swollen with muddy meltwater. Rivers like the Tuolumne and Merced built up vast alluvial fans that resulted in higher elevations near the mountain's edge, on the order of a few tens of feet. That doesn't sound like much, but when the glaciers ebbed, the muddy rivers turned clear, and the rivers began to erode into those old alluvial fans, forming terraces and bluffs.

On the one hand, these bluffs and terraces have protected towns like Modesto and Turlock from river flooding because even the worst of floods cannot overtop the bluffs where most of the region's cities are located. On the other hand, the bluffs are steep and are composed of loosely consolidated sediments. That's the ideal recipe for mass wasting, the downhill movement of loose debris and rock under the influence of gravity. I got an excellent introduction to a variety of mass wasting events after the final storm last week. It was a mess along the trail.

Mass wasting happens because of gravity, but an overaccumulation of water can substantially add to the intensity and degree of movement. The movement takes three forms: falls, flows, and slides. I saw examples of all three this week.

In the picture above, there was so much water built up in the soil that the slope failed rapidly and the fluid mix of silt and water flowed and covered part of the trail below. This is called a mudflow. In different circumstances, especially involving glaciers and erupting volcanoes or desert cloudbursts, mudflows are one of the most dangerous forms of mass wasting. A single volcanic mudflow in Colombia in 1985 killed some 25,000 people. 

A short distance away, the slope was more coherent, but water had added a great deal of weight to an already steepened slope (from the carving of the trail itself), and the slope failed as a single mass that slid downhill as a slump (above). Slumps are usually much slower-moving than a mudflow and thus rarely kill anyone. But they can do considerable damage to homes, roads and other developments. The slump shown above is inconsequential, but I saw a much more serious problem a short ways down the trail... 

The town's water treatment plant has been built on a lower terrace next to the Tuolumne River at the base of the steep bluff. A paved access road was necessary, and they carved it into the slope, oversteepening the upper slopes, and putting additional weight on the slope below the road. A slump has begun forming right next to the road, and is ominously slipping an inch or two a day so far. I don't know if it will stabilize now that we've had some dry weather, but they are going to have to do some mitigation work in coming weeks.

The over-steepened slope above the access road has always been a problem, as rockfalls have been a constant, if minor, problem even in dry weather. The rains made the problem far, far worse, and after the final storm, the road was a real mess. There had been some wild tobacco shrubs whose roots helped hold back the rock, but they could do little to stabilize things in the face of intense rain.

Mass wasting consists of flows, falls, and slides, but one of the most pervasive and efficient forms of mass-wasting is almost mundane in the face of all the drama seen above. Over time all exposed surface weather and develop into a loose ground cover called regolith. If the regolith can support plant life, it is referred to as soil. If any slope exists at all, the soil and regolith will move move downhill imperceptibly over many months or years. Soil creep is not dramatic, but in the big picture it probably moves more material than any other form of mass wasting. It never kills anyone, but it will deform and bulldoze structures built into the slope over time. It's why old barbwire fences on hilly country roads always seem to be tilting over. It can even tilt telephone poles.

Soil creep was not much in evidence as a result of the storms, but it is clear that the trail builders knew it would be a problem over time. That's why many sections of the trail have walls built on the uphill side of the trail, to hold back the process for awhile (see below).

In one week, my modest hiking trail showed off nearly all the major forms of mass wasting, with the only exception (thankfully) of a debris avalanche that is capable of wreaking serious havoc, and solifluction, a form of creep known from artic environments. How did things play out where you live? I've heard a lot of stories of serious damage coming from around the state. I hope you've avoided the worst of it.

A Tale of Two Slides: Mass Wasting in the Yosemite Region

First-time visitors to Yosemite Valley who enter the park via Highway 140 from Mariposa are treated with views of a spectacular river canyon along with sights of some interesting ongoing geological processes. One of the odd places along the drive is a stoplight in the middle of the highway near Savage's Trading Post, and a narrow bridge that only allows one-way traffic. After a wait of several minutes, the light changes and traffic crosses the river, only to cross over another narrow bridge a short distance later. What's going on?

The reason becomes clear when one looks across the river. A vast pile of rock covers the old stretch of highway, and the slope above the debris looks not so stable, with big chunks of rock that seem to be taking aim at the river. This is the Ferguson Slide, one of the real headaches for engineers who designed the highway. The present mess dates to 2006, but the slope had been a problem for years. One of my former students who worked for CalTrans kept me posted about the "next thing" they were trying to keep the slope from collapsing onto the highway. It appears that the rock moved as a semi-coherent mass, termed a slump. I think of such slides as mimicking what I do when I hit a recliner at the end of a long day; I slide down into the chair until friction keeps me from moving further. Also, I am usually semi-coherent at that point.

Welcome to the process of mass wasting, the downhill movement of rocks and debris under the influence of gravity. Rivers get a lot of credit for eroding the landscape, but they only cover a very small percentage of the land. Mass wasting processes move material down slopes to where rivers can carry it away. Downcutting rivers steepen slopes, but gravity moves the rocks into the rivers.

The Ferguson Slide is just one example of a problem area along the river. Almost every time I drive the highway, boulders and cobbles from the overlying slopes are littered across the highway. The rocks are ancient volcanic and sedimentary rocks that have been metamorphosed and deformed by compressional forces in the crust related to the subduction zone that once existed in Central California. The rocks are cracked and fissured and are naturally unstable on the steep slopes of the deep canyon. There are few flat places on the valley floor near the river, so roadcuts contribute to the instability of the slopes.

The Ferguson Slide has been active for years, as the scarp at the top of the slide is thousands of years old. There were (and still are) fears that the slope could completely fail, and that a large mass could block the river forming a dam and lake that could inundate developments upstream, and block traffic for years.

A mass wasting event of a different sort is revealed along the highway shortly after entering the national park. In this area the metamorphic rock has been replaced by the more familiar granitic rock the typifies most bedrock exposures in the park. Huge boulders choke the riverbed, boulders far larger than the river could ever move. Glaciers can move such rocks, but glaciers haven't been in this particular area for more than 700,000 years. These rocks have no lichens or stains at all; they broke from the local cliffs much more recently. In 1982, to be exact.

The Cookie Slide covered Highway 140 for months, and broke the main sewer line that served Yosemite Valley (the river wasn't such a nice place to swim for awhile). Granite is a very solid rock, and can form cliffs thousands of feet high (the vast cliffs of Yosemite being an example). But on their way to being exposed at the earth's surface by erosion, the rocks expand from the pressure release, and form cracks and fractures called joints. The joints provide an avenue for water to move through the rock, and also provide a surface for slope failures. The rocks detached from the cliff, broke up into a chaotic mass and tumbled and slid down into the canyon.

Rock falls and slides are a common occurrence in Yosemite National Park and the surrounding region. These are just two examples, but many more can be found with a bit of research and observation. In my travels, I have heard numerous rocks falling, and witnessed two larger rockfalls (which were described in an earlier post here and here).

What's Wrong With This Picture? A Short Rant

(slight paraphrase)

"We have to do this the scientific way

Observe....

Theorize...

Try and prove it....."

I was grading papers tonight. Given that I fall asleep easily while doing this means that I need distractions, so I was watching an old episode of Star Trek: The Next Generation. In the first season episode "Home Soil" the good doctor Beverly Crusher delivered this stunner of a statement about "science". As much as Star Trek was a half-decent attempt at good science fiction (don't ask a physicist, maybe), the statement above represents the kind of television/movie silliness that science teachers have fought against for decades: a fundamental misunderstanding of how we gain knowledge in an objective manner.

The term "theory" has been misused for a long time, I suppose because it is harder to get actors to say "hypothesis" in a convincing manner. And to get the science right means cluttering up a crisp script where everything has to happen in the 47 minutes or so that isn't commercials in an hour-long broadcast (and yes, I know all about 47 and Star Trek). How many times have you heard someone say that an explanation is "just a theory"? Or, "here's my theory about why something happened the way it did". These statements only work when the word "theory" is replaced by "hypothesis".

Theories, on the other hand, are models that are accepted and understood by scientists as to the way the universe works: atoms are theoretical; so is gravity. And evolution. We don't "believe" in atoms or evolution, we accept them on the basis of years of research and exploration. And the world and universe behave exactly as if these phenomena are in operation. One can choose not to believe in gravity, but trip over a rock and you will land on your face anyway.

In any case, the Creation-Science/Intelligent Design movements use a method much like that at the start of the post: Decide upon the truth, and garner all the evidence that supports this truth. You can try to call this approach "science", but it is not science.

So, to assist the Star Trek writers, here is Beverly Crusher's statement, updated to reflect the way things work in scientific research. Sorry I'm 20 years too late for this episode...

"We have to do this the scientific way...."

"Observe the phenomena, collect evidence and organize all the data, formulate as many possible explanations (hypotheses) as we can, and design tests that can disprove our hypotheses. If one explanation is finally supported by the evidence and cannot be disproven, we will accept the explanation and act accordingly, knowing even then that our explanation could be disproven if new evidence emerges".

Sorry script-writers, science is sometimes hard to jam into a sentence (and this, among many reasons, is why I am not writing scripts for a living). I welcome any of my readers to try to make this more succinct. But I wish Hollywood would try a bit harder; it would be better for us all.

Thus endeth a short mini-rant...

A Geologist (also named Hayes) Sits Through "San Andreas", the Movie

What the heck is this? These are fault slickensides (scraping marks from fault motions) at Hoover Dam. Where the movie says there are no faults.

I love sitting through geology-based movies, so I can sit and smirk at the screen and criticize the horrible geology presented therein. And thus, I expected to do the same this afternoon, when I finally found time to catch "San Andreas". Mind you, there were plenty of geological issues with the movie, but I have to admit I actually enjoyed myself. It was entertaining. So here are some of the thoughts from another geologist named Hayes (the main geologist character in the movie was Lawrence Hayes. I'd feel complimented, but I noticed the movie's screenwriters, at least at some point, were also named Hayes. Plus, CalTech would never hire me).

WARNING: SPOILERS AHEAD!
Let's get the biggest spoiler out of the way first. Hoover Dam, Los Angeles, and San Francisco get destroyed in this movie. Strangely enough, Bakersfield gets nailed pretty badly too. The Hollywood sign and the Golden Gate Bridge get destroyed. If I was the maintenance guy for the Hollywood Sign, I'd be pretty tired of constantly replacing it by now.

Hoover Dam. It has its faults...

So, the opening scene as I recall involved a distracted young lady driving a mountain highway in the San Gabriel Mountains. A rock hits her windshield, and over the side she goes, at a rate of speed that defied the laws of gravity, and into a canyon so utterly steep that it defied gravity too. I grew up next to the San Gabriel Mountains, and yes, the mountains are steep, but yeesh. This was to establish our star as a superhero (Dwayne Johnson, aka "The Rock", doing better as a sensitive kind of guy than I would have expected).

Here's a steep canyon in the San Gabriel Mountains, but I don't think "The Rock" could fly a helicopter through it.

After the death-defying rescue, there was a lot of talking for awhile to establish the characters and bits of foreshadowing here and there. Estranged spouses, busy geologists, that kind of thing. I especially liked the poor professor very dramatically presenting the story of the worst earthquakes in history (this part was factually spot on, by the way), and then all his students waking up as the lights come back on in the classroom. One student asks ominously, "could it happen here?". What have they been studying all semester????

I get that a lot, too.

The geologists, who've worked as a team to try and predict earthquakes, predict earthquakes at Hoover Dam, and go there to investigate. Their little harmless quakes escalate quickly into a big quake, and the dam is destroyed. A couple of things: the geologists say there are no faults at Hoover Dam. The picture above is a fault at Hoover Dam. Actually, there are lots of faults at Hoover Dam. It might be more correct to say that faults there are not known to be active. Dams are known to reactivate dormant faults on occasion, due to water pressure along the fractures. Also, there was a variant of the movie trope of the black brother getting killed first. Paul Giamatti was the white guy geologist, and his associate was Asian. We immediately know he's doomed. By the way, Giamatti was pretty much my favorite character in the film. He always said very logical things, like "stop, drop and cover", and kept a cool demeanor all through the film. Oh, and laptop computers report the magnitude of earthquakes while they're still happening. It was then or later in the film that a grad student said something like "it just jumped from a 6.5 to an 8.5", again, right in the middle of the quake. It doesn't exactly happen that way. But I guess I'm being picky. Oh, and no one can predict earthquakes.

Well, almost nobody. These people predict earthquakes all the time (credit: Amanda).

The destruction of Hoover Dam showed the advances of thirty-five years of special effects technology. I liked the destruction of Hoover (or Glen Canyon) Dam in the original "Superman" movie with Christopher Reeves, but in "San Andreas" it was really something to see. I know they couldn't spend time on this kind of thing, but I sure would have liked to hear about the effects downstream on the Colorado River of having an entire year's flow happen in one day. It would have destroyed a string of dams all the way to Mexico, and flooded out of existence a number of towns. But that would have taken up an entire movie, and we had to get back to the destruction about to take place in California. Hoover was almost immediately forgotten.

An approximation of the remainder of the movie "San Andreas", courtesy of Amanda

So, for the rest of the movie, we see Los Angeles get devastated by the worst earthquake in west coast history, a 9.1 or so (no, it can't happen). Geologist realizes that it is only a precursor to a much larger quake in San Francisco, and warns people to get out of town. And go where? Modesto? We have some room in our campus gym, but that's about it. The giant quake hits, the city is largely destroyed, and our characters go about surviving one way or another. Oh yeah, there are characters in the movie. I almost forgot.

So here's the thing. The San Andreas is a transform fault, meaning it shifts sideways during earthquakes. It behaves in a segmented manner, with a history of large, but not gigantic, earthquakes  (in the real world, the quakes top out at about 7.8-8.0 magnitude, about 1/30th the size of a magnitude 9 quake. The northern segment broke in 1906, the famous San Francisco quake at magnitude 7.8 (the movie "San Francisco", 1936, still stands as one of the best earthquake movies ever). The central segment, from Cajon Pass to Parkfield, broke less famously in 1857. The southernmost segment, down in the Palm Springs/Coachella Valley region, has not gone off in about 350 years. It is pretty much the most dangerous stretch of the fault in California. No, there aren't going to be any magnitude 9+ quakes in California. You'll have to look north to the Cascadia Subduction Zone in Washington and Oregon (and far north California) for that kind of thing.

Now I know it was there because the plot progression demanded it, but this will not happen. The San Andreas will slip sideways 10 or 20 feet, but the ground isn't going to open up like this. The plot was slowing down after Ray's helicopter crash-landed in Bakersfield, and the drive to San Francisco was going to take a boring four hours. Something was needed to make them steal an airplane and get there faster. Oh, and the San Andreas fault is a right lateral fault, meaning during the quake, the side of the fault opposite the observer would shift to the right. The photo is showing a left lateral fault. Oh, and they said this was the Central Valley. The San Andreas doesn't go through the Central Valley. Oh, and because the fault motion is primarily lateral, it doesn't disturb the seafloor enough to do this:

In fact, even the world's worst earthquakes don't make tsunamis this big. Nor do they curl in like a surfer wave on the North Shore of Oahu. But heck, by now our heroes are on a boat, so there are some cool dramatic scenes of ships being destroyed. The cargo ship was great (you'll just have to see the movie). Because the plot demanded it, the movie's only "bad" guy was on the bridge when the wave hit, and he looked just like the lawyer in "Jurassic Park" before the lawyer got munched by a T-rex. Only he wasn't on a toilet.

So there are screams, and explosions, and falling buildings. Really, someone needs to sue the architects, because their skyscrapers kept falling down everywhere. This is another point that needs to be addressed. Most modern buildings will not collapse during the "big one". You will just be asking for a world of hurt if you are trying to get out of such buildings during the quake. As the geologists in the movie said, over and over, "stop, drop, and cover". You'll be much better off.

This is the absolute best lesson in the entire movie. Get under cover, preferably with an attractive person. If the building really does collapse, who do you want to spend time with while waiting to be rescued?

Those are my thoughts in the immediate aftermath of the movie, except for one thing. A really big thing, and it isn't geological. Our movie hero is a search and rescue hotshot for Los Angeles. A big earthquake hits, and his first action? He takes a helicopter that is badly needed for rescue operations, and flies off to find his estranged wife. They then take off to San Francisco in what is now clearly a stolen helicopter, in a clear case of dereliction of his sworn duty as a public servant. He crashes the helicopter in Bakersfield and steals a truck, with the justification that he stole it from someone else who had stolen it (that makes it right, right?). He gives the truck to a kindly old couple, making them guilty of receiving stolen property, and steals an airplane. He purposely crashes the plane (well, the airports were destroyed), and then steals a boat. All this to find and "rescue" a daughter who actually has spent the entire movie making incredible good and smart decisions, as well as saving a number of people (more than dad, certainly). So Ray, Dwayne, Rock, or whatever, you should have stayed in LA and saved people. Your daughter was doing fine. That's what made Giamatti, the geologist Hayes, the greatest hero: he had information that could save countless lives, found a way to pass that information on to the people of California, and thus there were still some people left at the end of the movie to rebuild the state (so it can fall over again in a century or two).

But like I said, I rather enjoyed the whole movie, and the special effects were quite good, even if these were things that wouldn't happen in real life. Don't use this movie as your education in the nature of earthquakes. I highly recommend this sort of thing: http://www.earthquakecountry.org/roots/. Or this: http://earthquake.usgs.gov/earthquakes/.

Cave Bacon and Stalactites on Drugs: The Mother Lode Underground

During our field trip outdoors last weekend, we spent a lot of time underground. One of our stops included a tour of Black Chasm Cavern near the town of Volcano in the Mother Lode of the Sierra Nevada. It is a strikingly beautiful cave in a region that is not really known for its cave systems, but they are there and they are a truly unique place to learn about geological processes in the Sierra Nevada.

Most people, if they ever think of it all, will associate the Sierra Nevada with granite, an igneous rock that forms from the slow cooling of magma miles beneath the surface. As a point of fact, only about three-quarters of the Sierra is composed of granitic rocks, and only a small percentage of that is technically granite (mostly it is granodiorite). The remainder of the range is covered by volcanic rocks, or is composed of older metamorphic rocks, including a significant amount of marble. Marble is derived from the heating and deformation of limestone, which formed on the floors of Mesozoic and Paleozoic tropical seas, possibly as coral reefs or carbonate shelf deposits. The rocks were lifted from the ocean floor and added to the edge of the North American continent when the terranes collided with the Cordilleran subduction zone in Mesozoic time.

Marble, like the limestone from which it was derived, is composed of the mineral calcite. Weak acids in the soil and groundwater react with the calcite, carrying it away in solution, forming the openings that eventually become the caverns. As the Sierra Nevada rose and deep canyons were eroded across the range, the groundwater table dropped, exposing the caverns to the atmosphere. Water dripping or seeping into the cavern evaporates, leaving behind the mineral deposits that hang from the ceiling of the cave or rise from the floor (dripstone deposits), or which cover the walls of the cave (flowstone deposits). Collectively these cave decorations are called speleothems.

More than 1,000 caverns grace the Sierra Nevada foothills. Some of the caves are world-class in their intricacy and decoration. One cave in Kings Canyon National Park has more than 2o miles of passageways. Many of the caves are also extremely dangerous: most are developed in vertical passageways with deep unexpected dropoffs, and these serve as sinks for "bad" air (carbon dioxide is a heavier gas). On the other hand, some of the very nice caves are open for guided tours: Crystal Cave in Sequoia National Park, Boyden Cave near Kings Canyon, Moaning Cave north of Columbia, Mercer Cavern at Murphys, California Cavern up the hill from San Andreas, and Black Chasm, site of our exploration last week. A trail near New Melones Reservoir leads to the Natural Bridges, where Coyote Creek flows through a cavern.

Black Chasm is named for the deep cleft not far from the cavern entrance that drops 90 feet or so into a small lake. The lake extends at least another 60 feet downwards into the mountain. The chasm prevented the miners and other early explorers from exploring (and vandalizing) the more remote passages of the cave. As a consequence, the owners were able to develop the cave with a mind towards preserving the most pristine parts of the cave. They constructed stairwells and pathways across the chasm, with handrails preventing visitors from accessing and breaking the most fragile speleothems. The cave was opened for tours about 2001, and it quickly became my favorite choice for our geology field trips.

Besides the well-placed lighting system that highlights some beautiful draperies (cave bacon) and stalactites (see the second picture), the cavern offers some of the best developed helictites to be found anywhere (top picture). Helictites are essentially stalactites that have forgotten to follow the law of gravity. The precise details of the their origin are enigmatic, but water pressure clearly plays a greater role than gravity does. They are exceedingly fragile and are usually the first things to be vandalized in unprotected caves. Black Chasm has a spectacular wall covered with them (my photo is of a small corner of the entire panel).

The operators of Black Chasm offer a group discount, and the guides enjoy speaking to geology groups when they get the opportunity. It is well worth a visit!

If you are interested in exploring wild caves, preservation and protection is the highest priority. As such, you should get in touch with the local grotto of the National Speleological Society if you want to be involved in protecting this special resource. If you have followed my blog for any period of time, you will know that I think that cave vandals are one of the lowest and most moronic forms of humanity in existence.

Star Trek at Fifty Years, and the First Week of a New Semester

Source: Copyright Paramount Pictures https://en.wikipedia.org/wiki/File:STIn_Beauty.jpg

I spent part of my evening watching some Smithsonian Channel shows regarding the 50th anniversary of the initial voyage of the Starship Enterprise on Star Trek (TOS; that's "The Original Series" for those of you who aren't Trekkies). The show was a part of my youth; I am one of those lucky people who saw at least some of the episodes during their original airings on network television. It was in black and white (in my home, anyway), but I found it fascinating. This minor television hit from the 1960s had such an optimistic view of the future of humankind, as well as being filled with really neat devices and technology.

I talk about Star Trek during the first week of every class I teach. I ask my students about their attitude towards "science", and two words invariable come up: boring and hard. As we continue a discussion about how science works we talk about how science is a body of knowledge, a codified organization of facts and principles that we agree are "real" despite the cultural background of anyone studying science. In other words, we can believe whatever we wish. We can even decide, for instance, to deny the existence of gravity. But no matter how hard one believes that gravity isn't real, one will still drop like a rock if one steps off a cliff. So we start to collectively begin to understand how science works. But still, there are challenges in learning and mastering science. It can indeed be hard (and maybe boring, but I can't imagine how...). On the other hand, what a privilege to be living in the times that we do, with the knowledge that we have access to!

This was the Solar System of my youth

That's where Star Trek comes in. Episode after episode imagined "strange new worlds", and most of them included bizarre planets far removed from our own. To me, back in those primitive years before the Hubble Space Telescope and the Voyager satellites, the science of astronomy was an exercise in frustration. I would head to the library week after week, checking out every astronomy book in the stacks, hungering to understand our own Solar System. And we knew so little! Venus was shrouded in clouds. Mars had visible features, but they were unidentifiable from earthbound telescopes. Jupiter and Saturn had spectacular clouds, but their moons were simple points of light. Nothing could be discerned on their surfaces. Neptune and Uranus were small disks, and diminutive Pluto was a dot of light. I wanted to know more!

Mars, up close. The various orbiters we've sent have mapped the surface of Mars with more detail than much of the Earth, since oceans obscure much of our own planet.

The advances came so slowly (at least to this young growing child). The first satellite missions to Mars in the 1960s revealed surface features (and a lack of alien civilizations). And in the late 1970s, the two Voyager spacecraft began the grand tour of the outer gaseous planets. It was an excruciating wait as the small satellites passed first Jupiter, then Saturn, followed by Uranus and Neptune (years passed between each visit). Then, knowing the satellites had arrived, there was the excruciating wait for the pictures to be downloaded and processed. It was worth the wait. The pictures and data were astounding, revealing worlds never imagined by humans, even on Star Trek! Volcanic moons, ice moons, cratered moons, moons with atmospheres, rivers, lakes and seas. It was a menagerie of strange new worlds, and they were in our own back yard.

Jupiter from the Galileo mission

The Voyager missions were one of humankind's greatest adventures, and they continue as the satellites actually leave the Solar System and enter interstellar space. They continue to send data, even after 39 years. And other incredible missions followed, the Galileo to Jupiter, Cassini to Saturn, the New Horizons to Pluto. And most recently, the arrival of Juno at Jupiter. We are only now seeing the first pictures.The quality of the photographs and scientific data are astounding.

From the Juno mission THIS WEEK! Our first ever view of the north pole of Jupiter.

And what about all that cool Star Trek technology? Who could have believed that some of the craziest bits of technology from the original show would be commonplace less than fifty years later. Communicators and tricorders became the flip-phones and smart phones and tablets of today. Essentially the entire library of human knowledge can be carried in anyone's pocket (and what do we do with it? Send each other pictures of kitties...priorities!).

Saturn

And this is what keeps me going every day as I approach my thirty-fifth year in the front of a classroom. The adventure in space continues, as it does in all areas of science, including my own in geology. Just in the last year we saw Pluto up close for the first time, as well as the largest of the asteroids, Ceres. More planets and planetoids remain to be discovered. The launch of the Webb Space Telescope in a few years promises to extend our vision to the edge of the known Universe. It is an incredible time to be alive! I feel privileged to have seen a vision of adventure in outer space through the many permutations of Star Trek, as well as seeing a vision of humankind at its potential best. But I'm glad I'm still around to see the real human adventure of science exploration continuing.. And that's what I hope my students will come to understand as well.

From Paramount Pictures

Thanks Gene Roddenberry, and all the cast members, living and gone, who've been part of the Star Trek universe. Happy 50th anniversary!

The Sierra Nevada Underground: Into the Black Chasm

California is full of delightful geological surprises. Mention "caverns" and most Americans will think of places like Mammoth Cave, Kentucky, or Carlsbad Caverns in New Mexico. Not too many people will think of California, but California does have an unexpected number of world-class cavern systems.

The state has such a complex geologic history involving granite intrusions, volcanic eruptions and earthquakes that it is easy to forget that for vast stretches of geologic time, California was stunningly boring passive continental margin. In Paleozoic time, the region was a shallow sea, slowly collecting mud and lime deposits in a tropical environment. In some cases, the tropical islands and shorelines were elsewhere, but the rocks were transported to California on the giant conveyor belt of the Pacific and Farallon tectonic plates. As the Farallon plate was subducted beneath the continental margin, the limestone sequences were scraped off and added to the metamorphic sequences of the western Cordillera.

The limestone was baked and transformed into marble, and a great deal of marble was preserved in a tract of crust (or terrane) in the western Sierra Nevada Metamorphic Belt called the Calaveras Complex. The Calaveras hosts many of the caverns found in the state; there are hundreds of them. Unless I lost count somewhere along the line, six caverns in the Sierra Nevada have been developed for public tours: Crystal Cave in Sequoia National Park, Boyden Cave in Kings Canyon, and four caves in the Mother Lode: Moaning Cave, Mercer Cavern, California Caverns, and today's destination, Black Chasm Cavern.

I was at Black Chasm yesterday with twenty of my students, on a field studies trip through a portion of the Mother Lode. The cave is privately owned, but it has been granted National Landmark Status, a designation that recognizes the geologic or historic importance of the cave, and encourages the preservation of the feature. The owners have done an good job at Black Chasm. It is one of the best places I know of that gives the casual visitor the experience of seeing a cave that is close to pristine condition, much as when it was first discovered.

The problem is that many Sierra caves were discovered by miners in the 1850s, and they became well-known and well-visited. It was not at all unusual for the cave owners to encourage their visitors to take a stalactite as a memento of their visit, and the caves were stripped of their decorations (speleothems would be the proper term for the stalactites and other features of caves). The early explorers often used torches for light, and the soot left its mark on the remaining speleothems.

Black Chasm was discovered early on, but it was the cave's namesake that protected it from the worst damage. The entrance into the cave is very steep, and after clambering down the steep slope, probably hanging onto a rope, the early visitors passed through one interesting room, but then found themselves perched on the brink of an eighty foot cliff that ended in the darkness below. Without technical equipment there was no going forward or going down. The interior passages of the cave were protected from vandals by inaccessibility.

When the owners of Black Chasm decided to open the cave for tourism, they constructed a walkway that clings to the wall of the Black Chasm and passes into the rooms beyond. The contrast between the first room of the cave and the last room is striking. Many of the stalactites and other speleothems are broken off, and the remaining ones have a patina of orange-red mud that comes from seepage of iron oxides from soils above, but also from soot and dirt from the early visitors. The room is still pretty, but not exceptional to anyone who has visited other caverns.

Then you pass through the namesake chasm. The walls on both sides are vertical, and in the inky darkness below there is a deep lake. The cave is host to a unique species of amphipod, which I hope is immune to the effects of fallen eyeglasses, cameras and other paraphernalia dropped by visitors. The owners clean up what they can, but cave diving is a seriously dangerous business, and I don't think they do it casually for cleaning things up.They warn you to hold onto your valuables...

And then you start to see what an undamaged and pristine cave is really like...the parallel fins are referred to as cave bacon.

The natural color of most speleothems is a pearly shade of white. It's truly hard to resist touching these decorations, especially since they are so close to the walkway. I trust you won't do it if you visit. It is far too easy to cause damage or mar the appearance. It is such a privilege to be able to see things like this without a plastic screen blocking the way...

The cavern has some nice examples of soda straws (above), which are very thin stalactites that are among the first speleothems to disappear in unprotected caverns. One touch would be enough to break them off. I've seen some in Kartchner Cavern in Arizona that broke off without being even touched. The just broke off, maybe from something as weak as wind currents or the shaking of a distant earthquake (the effects of quakes are muted in caves, as they are much less affected by surface wave shaking).

The draperies in the far room of the tour are nothing short of fantastic. The lighting is nicely placed to allow for back-lighting. Flash photography from handheld cameras almost never works in caverns. The flash washes out any contrasts in color, and without shadows, the features lack depth. I get a lot of non-flash pictures that I have to delete because I shake too much, but the few I get with the back-lighting are far more satisfying.

The final room of the tour is exceptional because of one particular kind of speleothem: helictites. Helictites can be characterized as stalactites that refuse to recognize the law of gravity, or by some descriptions, stalactites on acid. They have grown in random directions, perhaps because the water that formed them was driven as much by capillary action as it was by gravity.

From a distance, the wall looks fuzzy with white "stuff"...

Up closer, the fuzz resolves into thousands of individual helictites.

I can almost imagine them wiggling about and forming into a tourist-eating cave monster...

The complexity of the helictites is just stunning. I never get tired of trying to get another shot. Shawndee, the manager at the cave, probably thinks I'm ignoring her while she is talking to my students, but I do listen. I'm just multitasking, trying to get the perfect shot!

I always see something new whenever I go into Black Chasm. This time it was the dogtooth spar crystals in an obscure cavity along the walkway. Dogtooth spar is a crystal form of calcite, which along with aragonite is the mineral that makes up most of the speleothems in the cave.

Black Chasm Cave, as noted before, is a privately owned business. They are there to make a profit, but they have done a good job of protecting their cave, and I recommend a visit. They offer discounts for educational groups (they can accommodate up to 22 people at a time, so large classes would need to split into two tours). More information about the cave can be found here. Tell them Geotripper sent you!