Wednesday, August 15, 2018

The Sliding Stones of (Not) Racetrack Playa, and One of the Less Important Consequences of Climate Change


UNR field studies stop on the Carson Sink and Highway 50, circa 1983
There are lots of mystery spots in the world. My garage is one of them. Over the decades it has collected the flotsam and jetsam of our lives, and it hasn't happened in any kind of organized manner. The last few weeks of this summer has seen one of our most ambitious attempts yet to clear out the debris and preserve the important records of our lives. I even had a yard sale! There have been lots of precious little discoveries, and one of them was the snapshot above, of another mystery spot in the world. It was taken in 1983 or 1984 when I was attending grad school at the University of Nevada, Reno.

I know that for some of you, seeing the tracks across the playa surface can only mean one place on the planet: Racetrack Playa in Death Valley National Park. For years and years geologists and others noted the strange trackways made by pebbles and boulders and pondered how in the world they happened. There have been the "boring" scientific hypotheses involving wind, water and ice, and the more exotic fringe ideas like weird magnetic currents and aliens. I took the picture, but I've never been to Racetrack Playa and therefore am not guilty of tampering with the stones (the National Park Service and geologists take a very dim view of such things). It turns out the strange sliding stones have been found in other places. I know of at least three of them.
Paul is going to solve the mystery of Bonnie Claire Playa, no matter the cost.
There seem to be at least three important factors to get sliding stones: a flat playa surface, a nearby source of rocks, and the possibility of freezing windy conditions. The Racetrack has the Grandstand, an island of rock in the midst of the playa and a high enough altitude to get freezing conditions once in awhile. Bonnie Claire Playa in the vicinity of Death Valley has an active alluvial fan and similar elevation. And Highway 50 in the Carson Sink of Nevada has Highway 50. The highway has to cross the playa and to prevent flooding it has been built on a roadway of stones brought in from elsewhere. That's where I was when I snapped the opening picture of this post. Some of the stones escaped from the highway and set off across the playa surface. My fellow students were trying to suggest an origin of the trackways as being the result of high winds and too many drunk geologists being blown across the dry lake surface.
Moving stones on Bonnie Claire Playa
Some hypotheses involved only extreme winds blowing over a very slick muddy playa surface. Some experiments suggested that pebbles could be set in motion by hurricane force winds, but wind by itself cannot explain the fact that some of the moving stones weigh hundreds of pounds. The fact that some rock trails run parallel to each other suggest that they were locked together. A sheet of ice covering the playa provides a possible explanation. It the ice were to break up into smaller sheets, the ice could presumably act as a sail. Most observers figured that high winds were still a necessity.
Stone tracks on Bonnie Claire Playa
In 2013 cameras caught the movement of the stones (see it here). Ice was indeed involved, but hurricane force winds weren't required. The sheets of ice were pushing the rocks around in winds as little as 10 miles per hour. It's not clear if this process can explain the movement of the larger boulders.

The greatest irony of the mystery of the sliding stones is that they might soon no longer move at all. As the climate changes and warms over the coming decades, the required conditions, particularly that of ice formation, will no longer exist.
Here is one more mystery for you. When we last visited Bonnie Claire Playa, we found this circular structure. I welcome any explanation you can provide for this one! UFOs need not apply, even though Area 51 is only a few hundred miles away. You can see some more pictures of the strange feature in my post here: https://geotripper.blogspot.com/2015/02/a-little-mystery-to-accompany-moving.html

Learn more about the research on the sliding stones of Racetrack Playa here:
https://scripps.ucsd.edu/news/mystery-solved-sailing-stones-death-valley-seen-action-first-time

Tuesday, August 14, 2018

A Collared Lizard for World Lizard Day

I was thinking and planning my next post on our recent trip to the Pacific Northwest, but was getting writer's block. I caught a post from the Ash Meadows National Wildlife Refuge that today was World Lizard Day. I don't know how such things are determined (there is also a Collect Rocks Day), but it was enough to make me look for the best picture I could remember taking of a lizard. It was a Collared Lizard (Crotaphytus collaris) that I saw during a field trip stop at Canyon of the Ancients National Monument in southwest Colorado.

Lizards evolved in late Permian or Triassic Time (~250 million years ago). They were part of the dinosaurian ecosystem, but they are not closely related to dinosaurs having split off from more primitive reptiles before the dinosaurs evolved. In a sense birds are closer relatives to the dinosaurs than lizards are, given that birds directly evolved from a group (the theropods) within the dinosaur clade. There are about 6,000 species of lizard in the world today, and they occupy habitats from tropical rainforests to the tundra.

Saturday, August 11, 2018

The Disappointing Cape: Land's End and Rock Pillows



Just over 200 years ago, the first expedition of Americans reached the Pacific Ocean after following the Missouri River over the Rocky Mountains and down the Columbia River. Lewis and Clark and their crew arrived in November of 1805, and they knew they could not make the return trip until the winter snows abated.

They explored the area around the mouth of the Columbia for an decent campsite to stay in several months. They ultimately settled on the south side of the river at Fort Clatsop, but for a time they spent a week at "that dismal little nitch" on the north side of the river. They explored around the rocky peninsula that had already been given the name Cape Disappointment by fur trader John Meares who, because of a storm, turned his ship around in 1788, just missing the mouth of the Columbia. The credited discovery was four years later, although we know that history has a serious bias; the river was discovered more than 10,000 years ago by humans.

The peninsula is today a state park, and it has a well-developed campground complex that fronts a wide sandy beach, with a more modest sandy cove on the east side called Waikiki Beach (it memorializes a Hawaiian seaman who perished during a shipwreck).

The winter encampment of the Lewis and Clark expedition at Fort Clatsop was largely a miserable affair with constant hunger and lack of supplies. They had hoped to flag down a sailing ship coming down the coast to trade for supplies, but their fort was a couple of miles from the beach and they missed ships for lack of a good lookout point. One might wonder why they didn't set up camp on the wide sandy beaches of Cape Disappointment. The answer is pretty straightforward: the beach didn't exist when they were there. It was a rocky peninsula as can be seen on their sketched map (below)

The mouth of the Columbia River is a nightmare for shipping. The discharge is more than enough to support even large freighters as far upstream as Portland, but the river carries vast amounts of sand and silt, and the shifting bars have caused vast numbers of shipwrecks. In an effort to stabilize the shifting sand bars, jetties were constructed in 1886. One extends for several miles from Cape Disappointment. Although the rock wall helps to keep the river channel clear, it also serves as a barrier to the southward movement of sand along the coast north of the Cape. The sand started backing up immediately forming the wide flat beaches that can be explored today (see the map below...sand is the yellow unit marked "Qb").
Source: US Geological Survey and https://nwgeology.wordpress.com/the-fieldtrips/pillow-lava-sites-in-washington/pillows-in-the-crescent-formation-cape-disappointment-state-park/

One of the coolest things about exploring Cape Disappointment is the privilege to actually see the rocks. The wave-carved cliffs are not totally covered by vegetation as is so often the case in western Washington. And the rocks are weird. They are not layered, and instead are marked by strange globular masses of what turns out to be weathered and oxidized orange basalt (we would normally expect basalt to be black like the lava flows in Hawaii). How did they get this way?
Note the cormorant for scale (upper left)
When basalt erupts underwater, it forms these globs that are about the size of thick down pillows. It looks like toothpaste being squeezed out and then getting pinched off. Although these rocks are on land today, they were once on the bottom of the Pacific Ocean. They formed in eruptions at the mid-ocean ridge on the seafloor. They traveled like a conveyor belt for hundreds of miles (at the stunning rate of several inches a year) and were scraped off and added to the edge of the continent in the subduction zone that forms the western boundary of the North American Plate in Washington and Oregon. These rocks, the Crescent Formation, are Eocene in age (around 40 million years ago).

Cape Disappointment is a fascinating place to explore (it's neither dismal or disappointing). Watch the weather, though. Not only for the incessant rain, but for fog. It's said to be the foggiest place in the country which helps explain why the peninsula has not one, but two lighthouses.


Monday, August 6, 2018

Damned if You Do Dam, Damned if You...Well, Don't Dam: The Days of Dennett Dam are Done



One does not usually equate the city of Modesto with dams and reservoirs. It's true there is a Modesto Reservoir, but it is fifteen miles east of the city. But there is a dam in the city limits, and it has been a problem and an eyesore for decades. Back in 1933 someone had the bright idea of building a small dam on the Tuolumne River by the 9th Street bridge and constructing a nice park built around boating and swimming. Dennett Dam was built, and it lasted an entire seven years before being mostly destroyed by flooding. The park never materialized, and the remains of the dam lay abandoned. At some point, someone thought it would be a good idea to cut an opening in the dam to allow fish to surmount the structure and swim upstream (the Tuolumne is a salmon river).
The unintended consequences mounted. The opening set up unpredictable whirlpools in the river current, and at least three people have been trapped and drowned nearby. The structure impeded flows of the river and during low water, vast amounts of the invasive weed River Hyacinth would accumulate, blocking the migration of fish, and crowding out native vegetation. And the fish, which the opening was meant to help, were devastated by predators, especially introduced bass. The newly born fish were forced to utilize the narrow opening, and were easy marks for the predator fish waiting in the deep pools beyond.
Dennett Dam during a bad River Hyacinth year. Picture courtesy of Patrick Koepele of the Tuolumne River Trust

What was to be done? No one wanted to own the dam or be responsible for the problems it was causing. The city of Modesto set aside some funds around 2006, but unexpectedly high costs torpedoed the project. In 2010, the Tuolumne River Trust got involved and began to organizing fundraising efforts, both from individual contributions and grants from the State Lands Commission, California Department of Fish and Wildlife, California Department of Water Resources, USA Fish and Wildlife Service, and local agencies. Ultimately, $1.6 million was raised and work has begun. It's sort of a complicated process.
For one, they need to move the river out of the way, so the construction firm (Innovative Construction Solutions) has cut a temporary channel around the dam. It will be filled in when the dam is removed. The deep pools below the dam will need to be filled in.
When the project is completed, a major impediment to the migration of salmon will have been removed, and some 37 river miles will become more available for spawning. The land around the dam is slated for park improvement, although much or most of the "development" will consist of rebuilding the riparian habitat that had been disrupted by agricultural and industrial development. The river can become the treasure it has always had the potential to be.

If you want to see the progress over the next few weeks (or months?), it's easy to find. The dam is almost under the 9th Street Bridge in south Modesto. There is a pedestrian sidewalk on the bridge, so just park nearby and walk out.

Note: I stole the pun that I used in the title. Years ago my dad was working on a paper that he ended up titling "Damned if you do Dam, Damned if you don't Dam". I've always appreciated it.

Saturday, August 4, 2018

The Flip Side of Dune Stabilization: Dunes Unleashed in Central Oregon



In our last post, we had a look at the "carpeted" dunes of Florence, the ridges of wind-blown sand along the coast that have been "stabilized" by invasive European Beach Grass. The grass was planted in the 1920s and has spread from California to British Columbia. It's a real problem, and huge changes have taken place in the geography of the dune environments along the west coast, especially  at Oregon Dunes National Recreation Area.

The beach grass has displaced native plants and animals, and caused massive foredunes to rise above the beaches. The inland areas behind the foredunes became starved of sand, forming deflation basins where pools and lakes formed and forests thrived. These are all problems for the original ecosystem of the dunes, but there is the flip side: the stabilization of the dunes was done for a reason.

Not all of the dunes in the Florence region are covered by dune grasses. Sand that blew away from the deflation basin formed dunes on the eastern edge of the dune field and many of those dunes have not been covered by beach grasses. The dunes are still active, migrating eastward with the prevailing wind. And that's a problem, at least in some areas.

I was at a shopping center in town on a recent trip, and I wasn't having much fun (it was Christmas shopping or some such thing), but I had noticed the dune sands behind the complex and headed out to have a look. The sand ridge was huge and so steep I had to really search to find a spot to climb to the crest. I huffed and puffed my way up and was presented with the awesome view of clean dunes and a distant lake in the deflation basin (the picture at the top of the post).

But the crux of the sand problem was the steepness of the dune behind the store complex. It was  steeper than the angle of repose (the natural angle of the sand slope). It was immediately obvious that the huge pile of sand was encroaching onto the business complex, and there was a lot of sand. The dune tops were twice as high as the building. There is an ongoing battle to stop or slow the movement of the sand.

It looks like they've been bulldozing sand, undercutting and increasing the slope of the dune. It's no doubt an expensive fix, but falling back to the "solution" of the 1920s would be unthinkable today. The movement of sand is unrelenting, and there will always be problems at the back of this business complex.

Our sojourn in Florence was about to end. We didn't quite know what lay ahead, since we had only a single camp reservation for one night for the next four days. We were going vagabonding, a tradition (and sometimes a source of stress!). More to come...



Sunday, July 29, 2018

The Carpeted Dunes of Oregon's Central Coast: The Principle of Unintended Consequences

So how about this plush carpeting on a sand dune? What? It doesn't look like a sand dune? Some people are such skeptics....let's find a trail...
There's the sand, with three or four feet of grassroots on either side.

We are at the north end of Oregon Dunes National Recreation Area near the estuary of the Siuslaw River in Florence. The grass growing on and covering these dunes is European Beachgrass (Ammophila arenaria), an invasive plant that was introduced in the 1920s. It was an excellent example of the principle of unintended consequences. The apparent solution of one problem resulted in a number of others.
There are some very specific problems associated with living along the Oregon coast between Florence and Coos Bay. The forty-mile stretch of sandy beaches and dunes ranges up to three miles inland and any roads or towns built there must contend with the instability of windblown sand and dune migration. The introduction of the European Beachgrass was seen as a way of stabilizing the dunes. In a sense, the grass did the job too well.
The grass has deep roots and spreads rapidly, overwhelming and replacing the native plant species. By anchoring the sand just above the shoreline, new sand blowing in from the beach is trapped in the grasses, causing the foredunes to grow higher and higher. Little of the new sand on the beach gets past the foredune system, and a form of stability is achieved.
Deflation basin in the south jetty area of the Siuslaw River

Without the infusion of new sand, the area inland of the foredune system becomes starved of sediment. The wind blows just as much and carries what sand there is farther inland, sometimes burying the forests growing there. What had been a dune complex with occasional islands of trees and vegetation becomes a deflation basin, a place where sand is removed to the local groundwater level. The wet ground and ponds found there become a stable surface where a thick forest can start growing. The dunes are stabilized to an extent, but much of the dune environment with all the native plants and animals is lost (see the comparison below).

Another problem with many invasive species is that they don't tend to stay where they are supposed to. The desired level of control was achieved in some places, but the grass continued to spread far beyond, invading areas like the Oregon Dunes where open dune environments were still desired. The beach grass is now found on coasts from Southern California to British Columbia. And it is extremely difficult to control or remove.

The grass can be pulled manually (by volunteers most of the time) but roots are always left deep in the sand and the grass soon sprouts again. The shoots have to be pulled seven or eight times before the grass is truly gone. It's hard work. Bulldozers and other mechanical means can be used, but the expenses are high. Some herbicides can be used as well, but the disruptions to the native species can be profound. All in all it is a sticky problem.
The coastal sand dune environment is a fascinating place to visit, and there are many recreational opportunities, but there are also opportunities to volunteer and help achieve a return to the natural conditions that existed before humans tried to mold the landscape to their liking. One place to start is the Oregon Dunes Restoration Collaborative which works to preserve and rehabilitate the dune system.

Thursday, July 26, 2018

That's a Huge River! Well, Not Exactly...Sediments in the Siuslaw River Estuary


In the photo above we're on a hill overlooking the Siuslaw River near Florence, Oregon. From this point of view the river looks huge and indeed the channel is navigable and leads to a working marina a mile or two upstream. But looks can be deceiving, and a careful observer will note that the "river" spends half of the time flowing the wrong direction. Like two of the last posts here on Geotripper, the Moon is part of the story...this is a tidal estuary. The Moon has the greatest influence on the intensity of the tides.

There is a Siuslaw River, of course, but it is just not quite this big. It is 120 miles long, starting at an elevation of 636 feet in the Oregon Coast Ranges, draining an area of about 773 square miles. The discharge of the river varies greatly depending on the season. The long-term average is around 3,000 cubic feet per second, but last week when I was there it was a mere 145 cubic feet per second. During the worst of flooding the river can exceed 50,000 cfs. But it is the lower part of the river that is affected most by the tides. During extreme high tides, changes in river level can be noted 26 miles upstream.
An estuary is the portion of a river influenced by tides where there is a constant mixing of salt and fresh water. Estuaries are rich in nutrients and one of the richest biomass producers on the planet. The estuary of the Siuslaw River developed at the end of the last Ice Age. With so much water locked up in glacial ice, sea level was hundreds of feet lower than it is today, and the Siuslaw River occupied a deep channel that continued for miles west of the current coastline. As the ice melted, sea level rose and flooded the river valley, but the Siuslaw River carried vast amounts of sediment to fill the flooded channel, forming the flat level valley we can see today. Additional sediment is added by wind blowing sand from the coastal dunes that line the lower channel (the Siuslaw is at the northern end of Oregon Dunes National Recreational Area).
When I was there a week or two ago, we experienced an intense low tide that exposed some rarely seen sedimentary structures in the channel. When the tides rise, water rushes upstream, and when the tides fall, the water goes out to sea. Flowing over the loose silt and sand, the flow causes the development of gigantic ripples like those in the pictures above and below.

It didn't occur to me at the time, but this is not a natural channel. Because of the ship traffic, the channel is dredged to maintain sufficient depth for the boats to pass through. There are other changes in the last century. The drainage of the Siuslaw is one of the most heavily logged regions in Oregon, and the clearcutting of timber has changed the nature of slope failure and flooding on the river. Trees and logjams used to trap sediment upstream, providing a rich breeding ground for salmon. The logjams were removed and the river scoured the channel to bedrock in many places. One of the most destructive activities was the process of "splash-dam" logging. Temporary dams were built across the river and trees were cut and floated in the reservoir. The reservoir was then dynamited and the resulting flood carried the logs downstream to the mills. The practice, needless to say, was hugely destructive of the salmon fisheries. Over the years the salmon runs declined from hundreds of thousands of fish each year to mere thousands.
Some of the sources I checked pointed out that the Siuslaw once was the second richest salmon fishery in Oregon after the Columbia River. Efforts are being made to improve the environment to build the salmon runs. They'll never be what they were a century ago given the vast changes upstream, but there is a lot of potential for growth of fish populations. In the meantime, it is an interesting place to visit if you are ever lucky enough to find yourself on the central Oregon coast (especially during the present heat wave!).