Saturday, April 14, 2018

After the Deluge: Dam! We Almost Lost a Dam!

But for the vagaries of the weather, we would never have seen it. Running field studies courses in the winter and spring always involves an element of chance, but in the dry year that we've had, it seemed safe enough to schedule a trip to Yosemite National Park in early April. But as the previous two posts have shown, an epic atmospheric river storm, a Pineapple Express, pummeled the area last Saturday. We postponed our trip to Sunday, and had a fine day, but we reversed the direction of our trip, because we still weren't sure if Yosemite Valley would open up in time for us to visit. If the valley remained closed, we wanted the choice of going to Hetch Hetchy Valley instead, and to allow that we needed to go by way of Highway 120 through Big Oak Flat and Groveland, instead of Highway 140 through Mariposa.

I had heard that Moccasin Reservoir almost failed a few weeks earlier, but didn't give it much thought while I was bustling about trying to think of alternate field trip stops. We had left the Red Hills Area of Critical Environmental Concern and were approaching the Priest Grade when I remembered the dam episode. During an intense storm on March 22, floodwaters overwhelmed the spillway of the small earthen dam on Moccasin Creek. Moccasin Dam is about 700 feet across and about 60 feet high, holding back about 554 acre-feet of water when full.

There is one very strange fact about the dam. Even though it blocks Moccasin Creek, it doesn't hold water from Moccasin Creek! In instead contains Tuolumne River water that has been diverted into the Hetch Hetchy system and pumped through a hydroelectric plant on lower Moccasin Creek. The dam is a small forebay that feeds into the much larger Don Pedro Reservoir and Lake just a mile downstream. Moccasin Creek was heavily mined during the Gold Rush, and the sediments may be contaminated by mercury and other toxic metals related to the gold extraction process. The water of Moccasin Creek is diverted around the reservoir.
As we drove by, I commented on the radios that the flood had happened, but I saw that a lot of the damage was visible from the highway and we screeched to a stop to have a look. It had clearly been a serious storm. The flood had ripped out trees, roads, and telephone poles. The dam itself looked undamaged, but the spillway downstream had been severely eroded. Few people were threatened by the flooding, but roads were closed. If the dam had failed, the effects would have been limited because Don Pedro Lake, only a mile downstream, would have easily absorbed the extra water.

Maybe the saddest aspect of the flood was the near destruction of the fish hatchery. As can be seen in the picture below by Mark Brooks and aired on several news outlets, the entire hatchery was flooded, and all of the fish either killed by turbulent mud, or carried downstream to Don Pedro (when does fishing season start?).
Geology and weather are capricious beasts. One of the lessons of the earth sciences is that no place anywhere on this planet is free of the possibility of natural disasters. Some places are more dangerous than others, but there is always a big advantage to understanding the possible hazards where one lives and works. One may think they may never happen in one's lifetime, and they might not, but that's a dangerous gamble to make.
Photo by Mark Brooks

Thursday, April 12, 2018

After the Deluge: Yosemite Valley a Day Later (and a sight I've never seen in more than 100 visits)

Yosemite National Park is a treasure. And the gem of the park is Yosemite Valley. There are spectacular spots to visit throughout the park and region, but ultimately, the sheer granite walls and booming waterfalls are the heart of this part of the Sierra Nevada. Most people know this of course, and the valley struggles with the desires of millions of people who wish to see the park for themselves. There are horror stories of absolute gridlock throughout the valley, with upset families who wait for hours just to get into the park, and then never find a place to park and get to know it better. I can barely imagine the frustration of devoting a hard-earned vacation to see the place and then have it spoiled by the chaos of too many people.
Bridalveil Fall (620 feet) and the Leaning Tower at the west end of the valley
I've been privileged to live relatively close to the park, and in 30 years, I've been there over a hundred times. I've quite literally never had a bad time, but part of the reason is that I've been able to pick and choose the times I visited. It turns out that the time most people set aside for vacation, in July or August, is possibly the least interesting time to do so. It's still spectacular, but the crowds are the worst, the waterfalls mostly dry, and it's hot. In fall, the valley is quieter, and the oaks and dogwoods add a splash of color. Winter brings snow and silence. Spring is noisy because of the waterfalls booming from the canyon rim. If your schedule allows, go there in the off season!
Ribbon Falls only flows in the spring; it's the highest free-falling waterfall in the park at 1,612 feet.
Of course, if you come at another time of year, you would be taking a chance with the weather. That's what happened to me last week. I was scheduled to take my students there on Saturday, but fate intervened with an epic warm tropical storm that dumped inches of rain on the snowpack. The Merced River swelled to nearly 14 feet (10 is official flood level) and major roads in the valley were under a few feet of water. For one of very few times in its history, the park was closed as a precaution and people were evacuated. I was luckily able to reschedule for Sunday, because the sun came up in a cloudless sky and the difference between the two days was astounding.
Upper Yosemite Falls, 1,430 feet high, the second highest in the park after Ribbon Falls (above).
I included some direct comparisons between Saturday and Sunday in my previous post (with thanks to the Park Service for posting pictures of the storm). Today I am offering views of some of the classic views in the park, revealing the vast amounts of water still flowing into and through the valley. The Merced River had subsided somewhat but was still flowing at flood level, but only barely. The main effect was the low-lying valley meadows that were still underwater (the next two pictures).
A flooded Cook's Meadow forms the foreground for Upper Yosemite Falls.
The occasional flooding of the meadows is part of what maintains the meadows as open areas. Tree saplings are smothered underwater, and only grasses and sedges that can survive the high water table. Not all of the meadows have survived however. Since the park was established, some of the original meadows have progressed into thick forest...there are only about 65 acres of meadows left out of the original 745 acres that existed at the time of European discovery. The growth of the forest is largely the result of fire suppression. The park service will occasional burn some of the meadow margins on purpose to help maintain the integrity of the open spaces.
No visit to Yosemite Valley would seem complete without a view of Half Dome, but I have been there a fair number of times when my students never had a chance to see it. When rain is falling, it can be completely hidden in the clouds. But on Sunday it was there in all its glory. The unique shape is due to a combination of exfoliation (the fracturing of rocks parallel to the surface, and jointing, which is the result of expansion as the rock is exposed at the surface. Exfoliation, which tends to remove corners and edges, leads to the rounding of the rock into the dome shape. But a prominent joint crossed the dome, and glacial quarrying at the base caused the rock on one side of the joint to be eroded away, forming the prominent cliff, or face, of Half Dome. When seen from other angles, it is clear that Half Dome should have been called Four-fifths Dome...
Directly across from Half Dome are North Dome and the Washington Column (below). The Royal Arches, in the center-left of the picture, are the result of a sort of reverse exfoliation, where the rock snapped out and fell from the middle of the arch, instead of the overlying cliff.
At the end of our day, we made a final stop at Valley View, one of the unheralded pullouts (only eight parking spaces) with one of the finest views to be had in all the valley (which is maybe why they call it "Valley View"). El Capitan, the sheer 3,000 feet cliff, looms on the left, while the Cathedral Rocks and Bridalveil Falls dominate the right side of the valley. A swollen flooded Merced River fills the foreground, with Bridalveil Meadow just across the raging waters. Only one of the ice age glaciers made it past this point, the so-called Pre-Tahoe (or Sherwin) Glaciation that took place around 800,000 years ago. The subsequent Tahoe and Tioga glaciers only reached the base of El Capitan and Cathedral Rocks. The Pre-Tahoe Glaciation probably did the most work in shaping the valley we see today.
I promised in the title of the post that we would include a sight I have never seen in more than 100 visits to the valley. We arrived that day when the gates to the valley reopened, at noon. A great many other people arrived at the same time, and for the first two hours the valley felt crowded. But by 4 PM, most of the visitors were already on their way back home, and the parking lots were practically empty. That is a sight in itself. But it was the drive out that astounded me.  Every time I visit the valley, Northside Drive from Curry Village to the Visitor Center area is always full of cars. Always.
But these two pictures show the astounding sight...not a single car ahead of us or behind us. For a few precious moments, we had the valley to ourselves. It's something I've never seen before, ever.

There's a secret though...even on the most crowded days in Yosemite Valley, you can find peace, serenity, and quiet. It requires that you park the car and get out. Not every trail is crowded, and in some places you can make your own path through the forest. The number of fellow hikers decreases exponentially with the distance from any paved road. If you are ever given a precious few moments in this grandest of valleys, give it a try. You won't regret it.
And that's the way it was, after the deluge...

Monday, April 9, 2018

The Difference a Day Makes: Yosemite 24 hours after the Deluge

Photographed by Garry Hayes


First off, thank you to the National Park Service for making the flood photographs available on their Facebook page. And second of all, kudos to the National Park Service for weathering the flood and opening the park again so soon afterwards.

I was in Yosemite Valley today, leading my students on a postponed field studies class in the park. Why did we postpone the trip? Well, mainly it supposed to take place on Saturday, but it turned out that the valley was in the midst of dealing with one of the larger floods it has experienced, about the fourth or fifth largest in 30 years or so. Plus, they closed and evacuated the park in advance of the storm. They only opened up again at noon today, and we were at the park boundary at precisely 12:11 PM.

The storm was epic. It was an atmospheric river storm, a "Pineapple Express" that brought many inches of very warm rain to a snowpack that had fallen only in the last few weeks. Rain was falling at elevations as high as 10,000 feet. The runoff gathered quickly into the streams and rivers, and the Merced went from around 1,000 cubic feet per second to more than 12,000 cfs. Water level at the Pohono Bridge gaging station rose from 5 feet to almost 14 feet. For reference, official flood stage begins at 10 feet, and at 12 feet the main valley roads are covered with water. It could have been a disaster if the valley had been full of tourists.
Source: https://www.cnrfc.noaa.gov/graphicalRVF.php?id=POHC1

But instead, the weather cleared, and the park service maintenance people worked quickly to clear debris from the roads and bridges. It couldn't have been easy, and there were lots of anxious tourists hoping their vacations wouldn't be totally ruined. They came through, and now you can compare the difference 24 hours can make.
Source: National Park Service

24 hours ago, clouds obscured the cliffs, and one could barely making out the raging torrents of Upper Yosemite Falls. This afternoon, there was not a cloud in the sky, and while slightly diminished in volume, the falls were as powerful as they will probably be for the rest of the year.
Photograph by Garry Hayes

The river rose to cover Cook's Meadow, but as the sign shows, nowhere near the level of 1997's even more epic flood. The discharge was twice as high then as it was yesterday, at 24,600 cubic feet per second.
Source: National Park Service
Today the sun shone brightly on a still-flooded meadow, but the water had receded enough that we could follow the boardwalk across the open space.
Photograph by Garry Hayes

I may be posting more pictures soon, but I had to lead off with these since by chance I was standing close to where the photographer was standing yesterday.

Saturday, April 7, 2018

Red Fox Family on the Tuolumne River

Be warned: cuteness alert. I was out on the Tuolumne Parkway Trail this afternoon, checking things out after more than two inches of rain in two days. It was sunny and lots of birds were out and about, but just before I got to the end of the trail, I saw something I've never seen before: a fox family.
I've seen foxes a number of times over the last three years. One fox that I photographed early on was actually used on the interpretive signs for the trail. I could never figure out from year to year if I was looking at a family or not because I never saw more than one at a time.
I haven't seen the foxes for many months now, and I was worried that they might have moved on (silly me). Finally in the last few weeks I've noticed an acrid odor that I suspect was related to the foxes, so I've been watching the grass and shrubs much more carefully. Today, though, I came face to face with the one in the first picture above. I couldn't distinguish the size very well, but I noticed the shorter face and realized it was a pup. A moment later a second head popped up! I didn't get a good shot of both of them at once before they disappeared into their den. It occurred to me that momma must be around somewhere, and then I realized she was in plain sight up on the log above. As you can see in the photos, she was very nervous about me (she could barely stay awake, actually). I've seen momma in previous years; she was wounded in one eye, giving her a distinctive appearance
Red Foxes are one of the most widespread carnivores on the planet, being found across the northern hemisphere. The populations in California are a mixture of native and non-native individuals. The rarest is the Sierra Nevada Red Fox, which is only found in the northern Sierra and southern Cascades at high elevations. It was recently sighted in the vicinity of Sonora Pass, north of Yosemite. The populations in the Central Valley were thought to be escapees from fur farms, but recent work has determined that the valley north of Sacramento has an endemic population. There seems to be little if any information about native Red Foxes in the south valley. There is a native species, the Gray Fox, which I have seen once or twice along the river. There is also the rare and endangered San Joaquin Kit Fox, which I have never seen.

I hope I'll have a chance to watch them grow up!

Liveblogging the Deluge: Merced River in Yosemite Reaches Flood Stage

This picture is a cheat. I'm not in Yosemite, this picture is from two years ago
I was supposed to be in Yosemite right now. We had scheduled a field studies class today that would have sent us up the Merced River to Yosemite Valley and back, but nature has intruded with an unusual April atmospheric river storm that is setting some daily rainfall records across Central California. San Francisco, for instance, received rain equivalent to an average April in a single day. My backyard rain gauge in the Central Valley has recorded 2.2 inches since yesterday. In 26 years of measuring, there have only been three Aprils where we've received that much in the entire month.

I had already decided to postpone the trip by last Monday when the forecasts called for flooding on the Merced River in Yosemite Valley. In short, the river jumps its banks at the 10 foot level (about 6,000 cubic feet per second). At 12 feet (9,500 cfs), the flooding river covers some of the main roads in the valley. Today's storm is expected to result in a river that crests at 14 feet, or 14,000 cubic feet per second. Even if I had decided to go ahead with the field trip, we would not have reached our goal, because the park service closed Yosemite Valley yesterday. We're going to try and make the trip tomorrow to check out any flood damage, but if the valley floor is still closed, we'll try to see Hetch Hetchy instead.
Yosemite Valley is especially prone to flooding because it is high up in the mountains close to the headwaters of the Merced River, and when rain falls, it falls on mostly barren granite. The water flows into channels very quickly, and the channels gather into the Merced River and Tenaya Creek just as quickly. There are no reservoirs upstream for flood control (nor should there ever be).

If it drives home the point, Yosemite Valley has only been closed a few times in its history, most notably in 1997 during the unprecedented floods of that year, and during a few government shutdowns. It takes a major event to convince the park administration to shut down the iconic valley.

I hope to be back tomorrow with pictures of Yosemite Valley. We'll see what happens! I will update the flood hydrograph in the space below when the river flow peaks.

UPDATE: At 1:00 PM, the river has reached 10,800 cubic feet per second (12.85 feet). If I'm reading the data right (below), this is only the fourth time the flow has reached this level since 1996.

Here is the 1:00 PM report:

Also, here is a link to video of the main road in Yosemite Valley at the moment, courtesy of the Fresno Bee.

UPDATE 2: We've reached 12,100 cubic feet per second as of 5:00PM, and 13.68 feet (10 feet is flood  level), and the flood may be peaking. The discharge only increased by 100 cfs in the last hour.

FINAL UPDATE: It looks like the flood has peaked at 12,100 cfs, as it has been there for two hours. I expect it will now start dropping. I'm hoping the valley will reopen in time for our visit tomorrow. If not, I guess we'll check out Hetch Hetchy!

WELL, OKAY, ONE MORE UPDATE: Yosemite National Park has posted pictures of the flooding today: https://www.facebook.com/pg/YosemiteNPS/photos/?tab=album&album_id=1650167855031490

Friday, April 6, 2018

An Incredible Spot in the Mojave Desert, the Hole in the Wall. You could see it for yourself this summer

Summer is coming soon. If you are casting about wondering what to do, how about the adventure of a lifetime? Our department is offering a dyad class, Geology 191/Anthropology 191, the Geology and Anthropology of the Colorado Plateau, and it is an incredible chance to check out some marvelous geology along our southwestern tier of states: California, Arizona, Colorado, Utah, and Nevada. I want to give you a bit of a preview of the kinds of places we will be visiting...
The Mojave National Preserve is one of our nation's newest parks (established in 1994). It was carved out from Bureau of Land Management lands in the eastern Mojave Desert, preserving one of the most awesome sand dune complexes in the country, the Kelso Dunes, a barren landscape of geologically recent volcanic cinder cones, one of the largest Joshua Tree forests in existence, and some of the highest mountain ranges in the Mojave Desert, with rocks as old as 1.7 billion years old, as ancient as those in the bottom of the Grand Canyon. The preserve also encompasses a California State Recreation Area, the Providence Mountains, and Mitchell Caverns, a unique limestone cave system. The caverns were closed during the recession, and then severely vandalized, but they have finally been reopened for visitation (see this Facebook page for updates).
One of the most interesting corners of the park is called Hole in the Wall, along with Banshee Canyon. We will be staying at the nearby campground our first night on the road on June 2. It is a wonderfully isolated spot, 25 miles off the main highway, and even farther from developments of any kind. It has some of the darkest night skies I've ever seen, and it is serenely quiet (except for crickets and coyote yowls).
The region is quite unlike other parts of the Mojave. Instead of deeply eroded mountain ranges and wide flat valleys, the area around Hole in the Wall is composed of mesas and plateaus that seem to share more in common with the Colorado Plateau province just to the east. But these mesas aren't like Arizona's either. They are composed not of sedimentary layers, but of volcanic tuff, rock derived from unimaginably huge volcanic explosions the likes of which modern humans have never experienced.
Twenty million years ago, the region was one of low relief, the result of tens of millions of years of erosion and relative stability. But conditions were changing as the crust was stretched and broken up into a series of tilted fault blocks. The release of pressure on the underlying mantle allowed partial melting to take place, and volcanic activity exploded across the region.
The first eruptions took place about 18.5 million years ago when the Peach Springs tuff coated the entire region from an eruption center near Oatman, Arizona. The eruption involved as much as 150 cubic miles (640 km3) of powdery white ash that was so hot that in many places it welded into solid rock as it landed.
Shortly afterward (in geologic terms anyway, as it was 700,000 years later), a second caldera developed. It was located even closer, in the adjacent Woods Mountains. The eruptive "crater", actually a collapse pit, was about 5-6 miles across, roughly similar in size to Crater Lake. Once again, all life was obliterated for hundreds of square miles as hot ash blanketed the landscape. The Wild Horse Mesa Tuff makes up most of the rock found at Hole in the Wall.
The strange holes that gave Hole in the Wall its name are called tafoni. Small differences in the degree of solidification or cementation cause depressions to form which end up staying wet longer, and the minerals decay into small fragments that can easily wash or blow away.
A short trail (1.5 miles) loops around Banshee Mountain and explores the best of the eroded tuff. Starting at the small visitor center, the trail drops through a rugged narrow canyon. There are some drop-offs, but rings have been attached to the canyon wall, making it a lot easier to climb up or down. Once past the narrows, the trail has a gentle gradient, and provides interesting views in all directions. There is a nice collection of petroglyphs on some of the boulders around the south end of the mountain.
If you want to visit this fascinating corner of the desert with us this June, please check out the previous post for details. We will be on the road for two weeks, and this will be only the first of many wonders that we will explore.

Wednesday, April 4, 2018

The Most Extraordinary Landscape on Planet Earth: Geotripping on the Colorado Plateau, June 2-17, 2018

North Rim of Grand Canyon National Park

There is no place on this planet like the Colorado Plateau. It's hard to find anyplace else on Earth where the crust remained relatively stable for upwards of a billion years, accumulating several miles of horizontal sediments, only to be lifted up rapidly in the last few million. The Colorado River and her tributaries then stripped away much of the sedimentary cover, and cut deep into the underlying metamorphic rocks. Those metamorphic rocks record a violent geologic history of colliding landmasses and mountain-building. The resulting landscape is one of the most beautiful places imaginable.
Angels Landing Trail in Zion National Park, Utah
The plateau country is a training ground for geologists and earth scientists, and has been since the days of John Wesley Powell and Joseph Ives, who were the first to lead research parties into the region (they didn't "discover" the plateau, of course; Native Americans have known the region for thousands of years). If you are curious about learning geology in this incredible region, you might consider joining us as a student (of any age) on our geology field studies course Geology 191, offered under the auspices of Modesto Junior College in Modesto, California. The course is designed to fulfil the curiosity of lay geologists and archaeologists, but also to build the skills of geology and archaeologists as well.
Goosenecks of the San Juan River, Utah
Our field course will be a grand loop through the plateau country, with investigations of the Mojave National Scenic Preserve, Grand Canyon, Zion, Bryce Canyon, Arches, Canyonlands, Capitol Reef, Black Canyon of the Gunnison, Mesa Verde and Great Basin National Parks, as well as many monuments, including Bear's Ears, Grand Staircase-Escalante, Natural Bridges, Navajo, Hovenweep, and Colorado National Monuments. It will be an unforgettable two week trip from June 2-17, 2018, beginning and ending in Modesto, California. Information can be found soon at my school website at http://hayesg.faculty.mjc.edu/Geology_191_Colorado_Plateau.html .
Black Canyon of the Gunnison National Park in Colorado
It's not a comfortable trip...we travel in school vans (which of course are known for their luxuriousness!), we camp every night, and the days can be hot, windy, cold, or stormy, and we are out in the middle of anything that happens. But we are staying in beautiful places each night, and there are even showers and laundry available every third day or so! Extensive hiking is not required, but there will be many chances to explore the trails in each park and monument.
Double Arch in Arches National Park in Utah
Geology 191 is a 3 semester unit course which will be taught as a dyad with Anthropology 191 (also 3 units). By end of the course, you will be able to see the landscape the way geologists do: by identifying rocks, minerals and fossils, and interpreting the geological history of an area by working out the sequence of events as exposed in outcrops. If you are a science teacher, you will come home with a collection of photographs that illustrate most of the important principles of geology, and a selection of rocks, minerals and fossils that will make a great classroom teaching tool (legally collected, of course; there are many localities outside of protected parks from which to collect samples). The dual nature of the course means that you will also have a mastery of the archaeology of the plateau region, the home of the Ancestral Puebloans, the Fremont people, the Navajo, the Utes, and others.
Canyonlands National Park, Utah
The cost of the trip will be $850.00 plus the cost of tuition (Currently $46 per unit for California residents, and $222 per unit for out-of-state residents). The cost includes transportation, food, camp fees, and entrance fees. Participants would want to bring a few dollars along for showers, laundry, and souvenirs.  The food is tasty and plentiful (everyone helps cook and clean!), and the school vans...are vans.

For those of you who live in the Modesto region, we are having an organizational meeting on Monday, April 16 in Room 326 of the Science Community Center on the west campus of Modesto Junior College from 6:30-7:30 PM. If you are unable to make it to the meeting, you can contact me for details and handouts.

If you are not in the area, we will be glad to arrange for transportation from nearby airports and train stations (we actually have an Amtrak station in town). Enrollment can be completed online once you are registered with the college (http://www.mjc.edu). Please contact me through the class website if you have any questions.
Bryce Canyon National Park
Hope to see you out there, back of beyond!