Monday, November 19, 2018

The Way It Was: The Deep Grassy Valley of the Ahwahnee


No geology exposition in today's post. Our state is choking in a toxic inversion layer filled with ash and particulate soot that is a sad reminder of the lives lost and lives destroyed by a horrific wildfire in the North State. Just for today, a reminder that beauty surrounds us in the depths of tragedy and suffering.
Half Dome reflected in the waters of the Merced River at Sentinel Bridge
Ahwahnee was the Native American name for Yosemite Valley. It's meaning is muddled in time, but it probably means the "Big Mouth", or the "Deep Grassy Valley". It was an island of clear skies and clean air above the smoke and ash. We only had a few hours to visit, so we headed to Sentinel Bridge for a short stroll, and as the sun set in the west we made for the Gateway View at the west end of the valley.
Sentinel Rock from Sentinel Bridge
Sentinel Rock is an astounding vertical cliff that rises nearly 3,000 feet above the valley floor. It receives somewhat less attention than some other rocks and cliffs in Yosemite Valley because it rises behind people who are staring in awe at Yosemite Falls on the north side of the valley.
Yosemite Point and the dry Yosemite Falls
Speaking of Yosemite Falls, there wasn't much to see of them. There was the barest trickle of water that did no more than wet part of the cliff. That should change this week as the first winter storm of year arrives (weeks late). We need it desperately, and many storms thereafter. When the falls aren't there, one's eyes are free to wander over the incredible cliffs that surround the dry watercourse. Yosemite Point and the Lost Arrow stood out boldly in the sun (in the picture above).
We barely had time to reach the Gateway View before the sun settled below the horizon. Only the vertical face of El Capitan was still catching the rays of light, and it soon faded.
The Moon peeked out from the cliffs to our right.
As the valley floor settled into darkness, the sky still glowed. It was a peaceful scene, filled with a serenity that is so sadly lacking right now. We enjoyed the scene until the darkness descended and we headed home.

To help those whose lives have been destroyed in the fire, you can find some ideas here: https://www.sfgate.com/california-wildfires/article/How-to-help-fire-victims-13381066.php

Friday, November 16, 2018

A Journey of Ten Million Years...the Salmon of the Sierra Nevada


Chinook Salmon attempting to enter the fish ladder at Camanche Dam on the Mokelumne River
They've been coming here for at least ten million years. Every year, without fail. The lands changed, but still they came. If one waterway was blocked, they eventually found another. Sometimes they were isolated, and could never return to the sea, but they survived anyway. They are the salmon and trout of the Sierra Nevada.
Stanislaus River at Knight's Ferry

Anadromous fish are those that live much of their lives in the oceans, but which return to freshwater streams to reproduce. One might wonder why they would have such a complicated breeding scheme. In all likelihood, it had to do with the survival of the young fish. Rivers and streams tend to offer more hiding places than open ocean, and the young have a chance to grow large enough to survive. The most familiar of these fish are the various species of salmon and Steelhead Trout. I had several opportunities to view the November migration of the Chinook Salmon this week on three different rivers: the Mokelumne, the Tuolumne, and the Stanislaus.
In historical times, the fish ranged far into the interior of the Sierra Nevada and Cascades Range, being stopped only by cascades and waterfalls too high for them to jump. They numbered in the millions. As European and American colonizers replaced the Native Americans across the state, the fish began a steep decline.

One of the first and worst events was the Gold Rush of 1848. Miners tore up miles and miles of river gravels and disrupted the flow of the rivers with their placer mines (sluices, long-toms, and cradles). Hydraulic mines (water cannons) ripped away billions of cubic yards of gravels from the hillsides and choked riverbeds with egg-smothering silt and clay. Vast amounts of water were diverted from river headwaters to feed the hydraulic mines through a system of flumes and pipelines.

Somehow the fish survived this onslaught, but then something more insidious happened. The dam-makers arrived in the late 1800s and early 1900s to build reservoirs to divert water for irrigation purposes. The dams themselves were barriers to the upstream movement of the fish, but even worse was that water diversions left the rivers to small and warm for their survival. The mega-dams were constructed in the 1960s and 1970s, diverting even more water. One river, the San Joaquin, ceased to flow most years over a stretch of about sixty miles. By the time the last dam was built, more than 95% of the historical breeding grounds for the fish had been made inaccessible to their migration (see the map below).
The blue portions of the rivers have salmon. The historical range is shown in black. Source: https://noaa.maps.arcgis.com/apps/MapJournal/index.html?appid=ceebefd9685143daa5bf30d5a7e0c7fa
Millions of years ago, this landscape was much different. The Sierra Crest was lower than it is today, but the summit region was covered by volcanic complexes not unlike the Lassen Peak complex and other parts of the Cascades. Periodic eruptions sent steaming lahars (volcanic mudflows) down the river canyons and onto the floor of the Great Valley (which may have actually been a shallow sea in this area). The rocks from this time period, 5 to 12 million years ago, are called the Mehrten Formation and they can be found throughout the Mother Lode foothills.

The Mehrten Formation has yielded up a treasure trove of fossil species. At Turlock Lake fossils were found of Giant Tortoises and Oncorhynchus rastrosus, the Spike-toothed Salmon. These remarkable salmon were as long as eight feet. They apparently used their "tusks" to fight for territory. Otherwise their lives were similar to the salmon of today. The riverbanks were populated by horses, camels, bison, antelope, giant ground sloths, mastodons, and carnivores, including the ancestors of the bears and wolves. The woodlands were dominated by sycamore and oak. For an excellent overview of the fossil record, check out the technical article by Sankey, Biewer and others, or read their excellent book The Giant Spike-Toothed Salmon and Other Extinct Wildlife of Central California.
Oncorhynchus rastrosus, the Giant Spike-toothed Salmon. Artist: Jake Biewer

Erosional processes steal nutrients from the land and carry them to the sea. It has been remarked that salmon and other anadromous fish return the gift. After they fight their way up the streams and rivers, and after they lay and fertilize their eggs, the fish die. Their bodies provide food for a host of carnivores and scavengers. Long before I found any fish in the Mokelumne River the other day I sensed the lurking presence of several dozen Turkey Vultures. I wasn't actually thinking about fish at that moment, but wondered why so many vultures were hanging around the river.

Moments later the reason was clear, as many were already feasting on the dead fish. The alert eyes that followed the movement of the fish are of an ancient lineage as well. Turkey Vultures are the most common of the avian scavengers, but their ancestors and Condor relatives patrolled these rivers millions of years ago.
These fish have survived for at least ten million years, and it has taken only a century and a half to threaten their very existence. Even now intense controversy follows the negotiations over how much water to devote to agriculture and how much to preserve the future of the salmon and the entire ecosystem that they inhabit. It's not a fish versus people proposition as some have portrayed it. It is a larger question of whether we want to preserve healthy river habitats for clean water, a diverse ecosystem, and for our own recreation and inspiration. Agricultural interests in the drainage of the San Joaquin showed in the 1940s that they were more than willing to destroy a river to apportion every drop of water. Things began to change in the 2000s as agreements were reached to restore flows to the lower river and bring back viable populations of Chinook Salmon. I hope we can be as wise in the other water conflicts around the San Joaquin Valley.


These videos are from the Mokelumne River below Camanche Reservoir, the end of the road for the Chinook Salmon. I had never visited the area before, so I was exploring the trails at the day use area below the fish hatchery. There were lots of fish in the river, and large numbers of them were struggling to break through the gates of the fish ladder, which was closed. I followed the fish ladder into the hatchery grounds, wondering if it actually provided access to the reservoir, but it didn't. It led to holding ponds that were already full of salmon. When the fish are ready, the eggs are harvested and fertilized, providing the stock for the hatchery. The young fish are later released into the river at the hatchery and other locations downstream.



These hatcheries are one way of dealing with the devastating loss of habitat for the salmon, but it seems it would be better if we could provide access to their ancestral breeding grounds upstream. I don't claim any expertise in these matters, but there have to be better answers than what we see happening today. They've been here for at least ten million years, and deserve a chance to be around for a few more.


Saturday, November 10, 2018

Horrible



And you know the sun's settin' fast 
And just like they say nothing good ever lasts 
Well, go on now and kiss it goodbye but hold on to your lover 
'Cause your heart's bound to die 
Go on now and say goodbye to our town, to our town 
Can't you see the sun's settin' down on our town, on our town 
Goodnight

Our Town, by Iris Dement

I'm heartbroken over the tragedies unfolding around my beautiful state.

I snapped this photo from a Home Depot parking lot near Modesto. Paradise is a long distance from us, but the smoke moved south very quickly, darkening the evening sky to the west. We've been hit hard this year by these fast-moving wildfires and we are long past when the winter rains should have arrived and put an end to the fire season. It's been savage.

Help out if you can. We've only got each other.

Charity Navigator: https://www.charitynavigator.org/index.cfm?bay=content.view&cpid=489

American Red Cross: https://www.redcross.org/about-us/news-and-events/news/2018/california-wildfires-red-cross-helps-as-thousands-evacuate.html

Friday, November 2, 2018

I Went Rock Collecting Today...For Really, Really Big Rocks

I'm thinking how many times I've been on a field trip looking at a massive boulder composed of some kind of interesting rock and making a joke about how we would need a crane to get the thing back to school. I'll be darned if that very thing didn't come true today.

I was up in the Sierra Nevada foothills, choosing out some really big rocks, and we may very well be using a crane to move them back to campus. At least one of them weighs about 3 1/2 tons, and in total there will be about 60 tons of them. So yes, maybe my rock collecting habit has gotten out of hand. I need professional help.
Well, I might need professional help for something, but it's not for a colossal rock-collecting habit. I was selecting rocks representative of the geology of the Sierra Nevada foothills to become part of the landscaping of our new Great Valley Outdoor Nature Lab that is being constructed right now adjacent to the Great Valley Museum at Modesto Junior College.
At this particular quarry near Knight's Ferry on the Stanislaus River I was selecting boulders of Table Mountain latite (a volcanic rock broadly similar to basalt). These are the rocks that make up the dramatic inverted stream that winds its way among the towns of Sonora and Jamestown along Highway 108. I was also picking out some large granite and greenstone boulders to representing the bedrock found in the Sierra Nevada. We'll also be choosing some of the unique metamorphic "tombstone" rocks that stick out of the ground across the Mother Lode.

Meanwhile back on the campus of Modesto Junior College the outdoor nature lab is starting to take shape. We live in a flat valley, but the lab will have some topography, some small hills at the east end to represent the foothills. They will be planted with native trees and shrubs, and the trails and pathways will be lined with the rocks and boulders that we selected today. One of these days, the lab might look something like the scene below (which is actually at the quarry; they're showcasing what can be done with their rocks). It's incredible that the lab is finally happening. The science faculty at MJC have been fighting for an outdoor lab for three decades. It's been hard to be patient!

Sunday, October 28, 2018

The Magic of a Pristine Cave: Wanderings in the Black Chasm

The miners were not kind to the caverns of the Sierra Nevada.

The search for gold in the foothills led fortune-seekers all over the hills and valleys of the Mother Lode in the Sierra Nevada, and practically every slope and hollow was prospected for the elusive metal. They usually came up empty of the riches they sought so eagerly, but many times the miners would encounter an unexpected opening in the outcrops of marble that occurred here and there in the Calaveras Complex. They discovered dozens of caverns.
Helictites at Black Chasm cave
For light they used torches and candles, and they didn't hesitate to break off cave decorations (speleothems) as souvenirs. A few enterprising miners realized they wouldn't get rich with gold so they charged admission to their caverns and made money from tourism instead. But they didn't control the behavior of their guests, and more speleothems disappeared. The once beautiful and intricate caverns were reduced to mere holes in the ground, and what decorations remained were grimy with soot and muddy fingerprints from visitors using them as handholds.
The "dragon" at Black Chasm
To be sure, times haven't changed that much. Spelunkers learned long ago that publicizing a newly discovered cave was often a death knell, so locations are kept a highly-guarded secret, and when possible vulnerable caves are fitted with locking gates. But there are two exceptions. California Caverns and Black Chasm cave have rooms that were inaccessible and undiscovered during the Gold Rush, and these have been developed carefully in such a way that the original appearance of the cave has been preserved. We visited Black Chasm today as part of my field class on the caverns and karst topography of the Mother Lode
Soda straws (straight) and helictites (twisted) at Black Chasm cave
Folks are sometimes surprised to find out the true color of stalactites and other speleothems; they're pure white. And they are so incredibly delicate. So-called soda straws and helictites are so fragile that a single touch will break them off, destroying thousands of years of exceedingly slow growth.
Soda straws (straight) and helictites (twisted) at Black Chasm cave
The helictites of Black Chasm are particularly memorable. There are thousands and thousands of them, possibly the greatest accumulation of any cave in the country. The room where the visitors can view them is just one of several. The others are off-limits, and appropriately so. The origin of the helictites is obscure and is debated by cave researchers (speleologists). They obviously ignore gravity.
Black Chasm cave is privately owned and offers tours (for a fee of course) all year long. They are located adjacent to the village of Volcano a few miles up the hill from Jackson on Highway 88. There are other "attractions" for kids at the site (panning for gems, breaking open geodes and that kind of thing), but they also offer some surprising sophisticated cave research publications for sale. They have always been very cooperative about arranging tours for our college groups. If you are ever in the Mother Lode, don't pass up this opportunity to see some truly pristine caverns.

Wednesday, October 24, 2018

Getting Under the Skin of a Volcano: Travels in Lava Beds National Monument


What in the world is going on here?? What are these spikes coming out of the ceiling? Is it some kind of deadly trap for Indiana Jones or Lara Croft? Well, no, but they'll hurt like the dickens if you try exploring them without a hardhat. In some of the previous posts in this short series we explored the deep heart of the magma chamber beneath a volcano, and we went both on and above Mt. Shasta to see the dramatic exterior of a volcano. Today we burrow under the skin of a volcano.

Medicine Lake Highland is the biggest volcano in California. It may be barely half as high as Mt. Shasta, but it makes up for the height deficit with broad gentle slopes, giving it a volume of around 130 cubic miles, compared to about 85 for Mt. Shasta. It is classed as a shield or "shield-type" volcano, composed largely of basalt, but with varying amounts of andesite and rhyolite. As such, it displays a wide variety of volcanic phenomena, not the least of which is a dizzying array of lava tubes. A flank of the volcano is preserved as Lava Beds National Monument, and the park has within its borders the highest concentration of lava tubes in the country, if not the world. More than 700 individual caves are known at Lava Beds with a total length of more than 70 miles.

How do lava tubes form? The picture above shows an active lava flow at Pu'u'o'o Crater on the Kilauea volcano on the Big Island of Hawai'i in 2009. The scale in this aerial view is difficult to discern but the skylight (where the red lava is visible) is probably 30 feet across. The tubes develop when river-like lava flows crust over. The lava continues to flow just beneath the surface, sometimes for many miles, being insulated by the overlying crust. The flow in the picture above flowed seven miles to the shoreline and was only a few tens of degrees cooler than it was when it emerged at the vent of Pu'u'o'o. When the eruption ends, the lava drains from the tubes.
The tubes can be quite complex, with bifurcating passageways and multiple levels (one particularly complex cave is called the Catacombs). During our recent visit at Lava Beds we explored Valentine Cave, one of the most accessible in the park. The majority of the tubes are in the Mammoth Crater flow which is around 30,000 years old. Valentine is in a younger flow, around 12,000 years old, so it has less collapse debris than many of the older caves (although it is true that many fallen boulders were removed by CCC workers during the Great Depression). In any case, the passages are easy to negotiate.


Being composed of very dark rock that tends to absorb light, tubes are notoriously hard to photograph. Flash photography tends to produce washed-out photos with little depth. I was using a bright flashlight for illumination and was holding it at arms length to get shadows that provide a sense of depth. I tried using my normal 'sophisticated' camera, but I actually got better results from my Samsung phone!
There are many interesting flow structures in the caves, including the pahoehoe flows on the floor of the caves, and "bathtub rings" on the walls showing that some flows only filled the cave a third full.
The basalt fractured as it cooled, forming the numerous cracks in the roof of the cave. Subsequent weathering in the soils above produced sodium bicarbonate and other chemicals that stain the edges of the fractures.
A lava cascade emerges from a side passage in Valentine Cave.
The lava tubes of Lava Beds National Monument are a fascinating environment to explore. Some of the caves have multiple levels, and some are decorated with permanent ice. One, Fern Cave, has numerous Native American pictographs and also ferns, which is interesting because ferns are not otherwise found in the park; they are a species of the western Cascades. The cool damp environment of the cave provided the right conditions for the plants, which may have arrived on birds feet (I'm guessing here).

There is a lot to do in Lava Beds. The ice cave and Fern Cave can only be visited with a ranger guide, but around twenty caves are open and developed for unaccompanied exploration. One, Mushpot Cave, is lit and has interpretive signs, and even a small amphitheater for ranger talks. On the surface there are lots of hiking trails that allow for the exploration of cinder cones, spatter cones, fault scarps, and the human history of the region (which will be covered in a separate post).

All in all, it's a good place to get under the skin of a volcano!

Saturday, October 20, 2018

Earth as Inspiration: The Exploring of Beautiful Places.


There was a very intense meeting that took place in the NASA offices almost half a century ago. The Apollo 15 mission was practically all planned out, but they could not decide where to land on the Moon. The crux of the problem was that three previous missions had been successes, but there would only be three more missions, and some technicians were advocating for another landing on the "safe" lunar plains near a crater and some possible volcanic features. Others were arguing for a more daring landing, near the Moon's Apennine Mountains and the Hadley Rill. It was a potentially hazardous landing, in part because NASA didn't have high quality images of the proposed site. The final decision was strongly influenced by mission commander Dave Scott.
Source: NASA

His decision was based in large part on the geology field training that he had received from geologist Leon Silver of Caltech. The moment was dramatized in Tom Hanks' incredible HBO mini-series From the Earth to the Moon:

"...but from what I've learned out in the field; Hadley Apennine, with it's complex variety of features, both impact and volcanic, is the best choice for putting together a picture of how the moon came to be. Maybe a little riskier...but... also the Apennines have something else... Grandeur. And I believe there's something to be said for... exploring beautiful places... It's good for the spirit."

And what he said (in the screenplay anyway) is true. It's good for the spirit to explore the beautiful places. And so it seemed fitting that I would end Earth Science Week by taking my students to a place of grandeur to learn some basics about the Earth: subduction zones, plutonic rocks, glaciers, flooding, and mass-wasting. We headed out to Yosemite Valley. It's a no-brainer kind of choice. We've got fascinating geology all around us here in California, but sometimes it can be a bit tricky to inspire the desire to learn geology by showing the students an outcrop of part of an ophiolite in a dry dusty canyon in the Coast Ranges somewhere. It can be done, mind you, and I've done such trips with reasonable success, but when you live just 90 minutes from one of the most beautiful national parks in the world, you take advantage of that fact!
We did the trip on Friday because Yosemite is, besides being very beautiful, very popular. Four million people visit the park each year, and most of them come on weekends. Our Saturday field trips in recent years have been nightmares of logistics with heavy traffic, long wait lines at the park entrance and problems trying to find parking spaces. Yesterday the valley was pretty quiet, with trams running half-empty (except when my whole class invaded one of them) and no waiting at the entrance station. I sent the students forth to do some research on their own for a few hours and commenced a journey from one end of the valley (sort of) to the other (Yosemite Lodge to Happy Isles).
Since I moved to Central California 30 years ago, I've visited the park more than a hundred times, and I never fail to be inspired by the dramatic in-your-face geology: 3,000 foot cliffs of granitic, high waterfalls (in season), colorful vegetation (again, in season), and interesting birds and animals. It is a wonderful place to learn some basic geological principles.
I wish it were possible for everyone to see the incredible beauty that surrounds our mean grubby cities. So many people are more concerned about getting food and shelter than they are for learning about their planet, a problem of human existence that is completely understandable. But that is the real value and potential of the internet: anyone can experience these places through the eyes and words of others. Earth Science Week is about our awakening to the incredible planet that we live on, a place of great beauty, but at times a place of great danger. Our lives are enriched by learning about both of these things.