Showing posts with label Pleistocene Ice Age. Show all posts
Showing posts with label Pleistocene Ice Age. Show all posts

Saturday, February 23, 2019

What's the Most Alien Landscape You've Ever Explored? Here's a Candidate

What is the strangest landscape you've ever explored? That is, the kind of place that makes you think that this just isn't part of planet Earth. I got to experience one of those places last week during our field studies trip to Death Valley National Park.
Only this bizarre landscape is not in Death Valley National Park. It's part of the California desert southwest of Death Valley in the Searles Lake valley. It's not part of any national or state park. It's administered by the Bureau of Land Management as an Area of Critical Environmental Concern and more recently as part of the California Desert Conservation Area.
The Bureau of Land Management has always had an uncomfortable fit with land use priorities in the American West. The Bureau began as a land disposal operation under the direction of the Homestead Act back in the latter part of the 1800s. The land that was not selected by settlers from the east was seen as sort of a wasteland of little interest to most people. But land ethics change and by the 1970s many people began to recognize that many BLM lands were every bit as precious as the adjacent national parks and monuments. This is one of those landscapes. They're called the Trona Pinnacles, and I saw them up close for the first time in my life last week.
When one realizes the richness of Death Valley National Park and all of the strange and wonderful features within, one can almost understand why I haven't been to the Trona Pinnacles before. By the time we arrive in their vicinity, we've already seen four days full of strange landscapes and on the last day we have two important geological localities and then a six-hour drive home. There just hasn't been enough time.

This year was different. We arrived at the park in midst of one of the most intense storm events of the year. Record snow and rain was falling in the coastal regions and the Sierra Nevada, but we had mostly benign conditions during our journey. But the storms caused the closure of the road that we needed to access Aguereberry Point, and construction had closed the access to Mosaic Canyon. We needed a last geological stop and I remembered how we often could see the pinnacles in the distance as we headed home. Why not see if we could get there? We headed south on the five-mile gravel road outside of Trona and had little problem reaching the pinnacles. We started exploring. I was awe-struck.
There are 500 of these pinnacles in three groups. They range in size from a few feet to more than 140 feet high, with an average of around 40 to 50 feet. They occur in three groups (the north, central, and south groups). We were exploring the north group, consisting of some 200 pinnacles. But how did they form? Are they volcanic? Are they alien landing beacons? According to the Star Trek canon, that might be the answer...in what is widely regarded as the worst Star Trek movie, The Final Frontier, the pinnacles formed the setting of the final confrontation of Captain Kirk and the "God" who needed a starship to escape his planetary prison ("What does God need with a starship").

So what really happened?
Today the bottom of the Searles Valley is a sun-blasted dry lake full of salts and other soluble chemicals that are mined on a large-scale basis. But between 12,000 and 25,000 years ago the landscape was much different. The last of the major ice ages, the Tioga, produced extensive glaciers throughout the Sierra Nevada. The Sierra rain shadow prevented many glaciers from forming in the mountains to the east, but glacial meltwater filled the basins. One by one they spilled over into the adjacent valley forming a series of large lakes: Mono, Owens, China, Searles, Panamint, and ultimately Manly in the bottom of Death Valley. These are called pluvial lakes. The surrounding valley floors sported grassy prairies and the hills had forests of trees like pinyon, juniper and at higher elevations, firs. The prairies were grazed by bison, horses, camels, and mammoths. They were hunted by Dire Wolves and Saber-tooth Cats and other fearsome carnivores.
The towers are composed of calcium carbonate, which is the mineral calcite. The porous form of calcite is called tufa. The tufa formed when calcite-rich freshwater springs on the lakebed interacted with the alkaline water of the lake. The location of the springs seems to have been guided by faults running through the area. The towers could only have formed when covered with water, so the pinnacles have been exposed to the elements for more than 10,000 years.

More recently formed towers are visible at Mono Lake near Lee Vining and Tioga Pass in the Sierra Nevada. They were still forming when Los Angeles diverted the water from streams flowing into Mono Lake in 1940. The lake began to dry, exposing the tufa towers.
The snowcapped peak in the picture above and below is Telescope Peak, the highest point in Death Valley National Park at 11,043 feet, more than 9,000 feet above the floor of Searles Lake. Such are the extremes of this fascinating landscape.

There was a lot to see in Death Valley and the surrounding region during our journey last week. More blogs will follow! And while you are waiting for the next entry, tell me about the most alien landscape you've ever seen...

Friday, February 24, 2017

A Place Where Water Once Was But Was No Longer, But Once Again Was - Travels in Death Valley

I'm finally not "liveblogging the deluge" anymore. I thought back at the beginning of January that I was monitoring a historic flood event that was going to be over with in just a few days. Somehow, new storms kept blowing through, and I was watching and monitoring flood activity around the state. Those "few days" turned into a six-week series of observations. But now that the storm activity has subsided a bit, the observations are going to be in the past tense. I didn't have much in the way of internet access over the holiday weekend, and we went and stared into the abyss of the storm with little to defend us but waterproof jackets and the nylon walls of our tents. We explored Death Valley National Park during one of its most intense storms of the year.
On the whole, we were pretty lucky. We got drenched by rainstorms on the first two nights of the trip, and rain played havoc with our travel plans during the first two days, but most of the principle roads in and around Death Valley remained open, and we were able to get to most of our objectives. The first day was certainly typical of this; we missed a planned fossil hunt because of the driving rain, but we managed stops at the other three localities, and even added two extra stops that weren't in the original plans. Our first stop was at Red Rock Canyon State Park near Mojave for a look at the colorful terrestrial deposits of the Ricardo (or Dove Springs) formation. If the exposures look familiar, you've probably seen them in a number of Hollywood movies. I've written extensively about the geology of Red Rock in the past; check out this post for some details of this fascinating place.

The real thrill of the day was to see water where water once was but was no longer, but once again was. Shall I explain?

During the Pleistocene Ice Ages between 2 million and 12,000 years ago, the climate of the northern hemisphere swung wildly from warm to cold and back to warm again, perhaps as many as twenty times. Ice accumulated across broad swaths of Canada and northern Europe, and several times crept across the border of the United States, ultimately covering around 30% of the lower 48 states. The thick ice cap never reached Oregon or California, but the Cascades and the Sierra Nevada developed an extensive network of alpine glaciers. Some streams of ice, for instance in the Tuolumne River basin, reached a length of 40 miles.
The glaciers of the Sierra Nevada never reached far into the desert basins to the east, but the influence of the cooler and wetter conditions was unmistakable. Meltwater filled the enclosed basins which then spilled over into adjacent basins, forming a series of what are now called pluvial lakes. Mono Lake is a small remnant of the glacial Lake Russell, and Owens Lake still contained water as recently as the 1920s (before Los Angeles diverted the incoming streams). Other lakes included China Lake, Searles Lake, Panamint, and ultimately Lake Manly in Death Valley. Vigorous fast-flowing rivers connected the widely separated lakes. Our second stop concerned one of those rivers, the one that flowed from Owens Lake to China Lake through the Indian Wells Valley.

From several hundred thousand years to as recently as 10,000 years ago, basaltic lava flowed from cinder cones and fissures of the Coso Volcanic Field. Some of these flows blocked the river, and formed a forty-foot high waterfall. The river scoured a channel, and the waterfall eroded in an upstream direction. Boulders trapped in river eddies swirled around, forming amazingly deep potholes. And then the ice receded. The level of Owens Lake dropped below the rim, and the river through what we call Fossil Falls ended.

The river ended thousands of years ago, but on rare occasions there is an echo of the days when a wild river flowed through the gorge. I've seen it only twice, but when the rains have been plentiful in the Owens Valley, a small stream of water flows through Fossil Falls. That's what we got to witness last week, thanks to the Bombogenesis storm (or Lucifer, or whatever they called it). A river the color of a creamy latte made its way through dark basalts.
It was a fine introduction to our exploration of the geology of the Death Valley region, and it wasn't the first time we were going to see water in places where water was not normally found. Death Valley is a place where the water once was, but was no longer, but once again was...
This last picture is kind of cheat. I didn't climb down into the gorge for a close up, so this is from 2005, the only other time I've seen water at Fossil Falls.