Badwater Basin in Death Valley, the lowest (and hottest) point in North America at 282 feet below sea level, has long been on my list of places to visit in person. In part because of the superlative involved but also because Death Valley on the whole is a geological Mecca of sorts. A few weeks ago, I finally got to make my pilgrimage, but not without a few surprises. First of all, I never expected to be wearing four layers (including thermal underwear) and a winter hat when taking my picture next to the famous Badwater sign. I also didn’t expect visiting Badwater to be one of the least interesting things that I saw in Death Valley. This is not a knock against Badwater, but rather a testament to the fact that even after visiting 32 of the 59 national parks in the US, I can honestly say that Death Valley was one of the most spectacular and diverse I have been fortunate enough to spend time in.
With a week off before Christmas, we were looking for someplace “warm” to camp. We had originally planned to head to southern New Mexico and Texas to check out the Big Bend and Guadalupe Mountains area. However, in the days leading up to our departure, the forecast lows plunged into the low 20s. It wouldn’t kill us, but we figured we could do better. Heading to Death Valley turned out to be a good audible as the lows were only in the low to mid 40s, quite pleasant by December standards. Oddly enough it was a bad experience during the depths of winter in 1849-50 that gave Death Valley its foreboding name. One member of a lost and ragged group of prospectors is said to have quipped “goodbye Death Valley” as they finally departed the basin that had given them such torment. Today though, armed with an automobile and several large water jugs, winter is an ideal time to take in the spectacular sights of Death Valley. After several days in the park, saying “goodbye” was the last thing I wanted to do.
The first thing to know about Death Valley: it’s big. Nearly 3,000 square miles big. The national park that protects it and the surrounding mountains covers upwards of 3.3 million acres—about the size of Yellowstone and Grand Canyon National Parks combined—making it the largest national park in the U.S. outside of Alaska. It takes awhile to get around and the character of the valley varies wildly along its 100+ mile length. All parts of the valley share some common characteristics though: heat (average July high: 116.5 F), aridity (2.3 inches in a good year), and low elevation (over 500 square miles of the valley lie below sea level).
Death Valley has been low for a long time but the dryness is a comparatively recent development. During the last glacial maximum (geologist-speak for “ice age”) 12,000-30,000 years ago, the surrounding mountains received so much precipitation that Death Valley turned into an 100 mile-long lake known as Lake Manly. Since Death Valley is bordered on all sides by mountains, streams draining out of the mountains had no easy way out. Over time, as the climate dried and the lake evaporated, thick layers of salt were deposited on the valley bottom. This is why most of the valley floor appears white. With the encouragement of the rangers, I tasted it and can confirm that it is indeed salt!
In many locations (in particular a spot known as “Devil’s Golf Course”), the salt grows into some fantastical yet potentially dangerous formations. The valley here is a wonderland of 1-2 foot high irregular mounds of salt & mud, all encrusted with razor sharp blades and daggers made of salt crystals (see photos below). While the salt is relatively brittle, falls are still to be avoided at all cost. Walking around Devil’s Golf Course reminded me of the time I completed shredded a brand new pair of leather hiking boots in one week of doing geology field work on fresh, sharp a’a lava flows in Hawaii. The only difference was the a fall here would quite literally rub salt in your wound, not a pleasant thought at all.
Near Badwater Basin are some spectacular and very colorful badlands sculpted out of young, soft, clay-rich sedimentary rocks. We arrived in Death Valley our first day just in time to catch sunset over the badlands (photo at top of page) and then hiked through them the next day after we started to desiccate from walking around on the salt flats too much.
If salt daggers, ancient lakes, and badlands aren’t enough excitement for one day, you’ll be happy to know that the northern end of Death Valley has experienced some volcanic activity within the past few thousand years. In a stark contrast to the bleak white salt flats of the southern valley, the valley landscape here is shrouded in dark black cinders and volcanic cones. The centerpiece is a large hole known as Ubehebe Crater, a type of volcanic feature known as a “maar.” Maars are the result of “phreatomagmatic eruptions” (your new scrabble word for the day; it will just take you a few turns and some incredibly good luck to be able to play it…), which occur when magma beneath the Earth’s surface comes into contact with groundwater. The heat from the magma causes the groundwater to flash into steam, creating a violent explosion, and, as so often happens with violent explosions, a large hole in the ground. The red and white sedimentary rocks that existed prior to the eruption still appear beneath the volcanic cinders in places creating a beautiful palette of colors.
More photos of sand dunes, mountain canyons, and the spectacular geology of Death Valley to come!
Continuing on with our recent geological theme here at Pyroclastic Pixels (you’d almost think I was a geology grad student or something…), today we are going to take a look at one of the most picturesque geological curiosities you’ll ever find: honeycomb weathering, also frequently referred to as “tafoni”. Those two terms aren’t really exactly quite completely equivalent but we’re not going to journey down the nit-picky fork in the road today. Honeycomb weathering is pretty cool. About the only thing that would make it better is if the holes were actually filled with honey. That joke sounded way better in my head than it looks on the screen.
Specific geographic and geologic conditions are needed for honeycomb weathering to develop, yet these conditions can be satisfied in a variety of places, from the arid deserts of the American Southwest, to the storm-battered shores of the Pacific Ocean. Here in northwestern Washington State, honeycomb weathering occurs along the coast, along and just above the high tide mark, in areas where a rock unit known as the Chuckanut Formation is present. The pictures on this page were taken at Teddy Bear Cove, just south of Bellingham, WA, which has some of the most spectacular examples I’ve ever seen. The Chuckanut Formation, or “the Nut” as I like to call it when I’m feeling lazy, is a thick series of sandstones, conglomerates, and occasional coal seams that were deposited about 60 million years ago when NW Washington occupied a large basin at the foot of an ancient mountain range that occupied more or less the same space that the Modern Cascades now occupy.
There is a good reason that sandstone is one of the rock types most susceptible to this type of weathering. Sandstone is essentially composed of countless tiny, sand-sized particles of various minerals (mostly quartz and feldspar in the case of “the Nut”) which are held together by some sort of substance, known as cement, that “glues” them all together into a solid mass. In most sandstones, this substance is either calcium carbonate (CaCO3) or silica dioxide (SiO2), also known as quartz. Honeycomb weathering forms when salt-laden sea spray lands on the sandstone. As the salty sea water evaporates, tiny salt crystals form on the surface of the rock. The growth of these salt crystals on the surface of the rock physically separates the sand particles from the cement. Over time (a long time…), this creates a small depression in the rock. Once a small indentation forms, a positive feedback effect is created; the hole has a greater surface area than a flat surface and thus more rock is exposed to incoming sea spray. Sand grains are thus separated from the cement at a faster rate, thereby enlarging the hole. In some locations, you can actually see little piles of sand grains in the cavities, grains that were once part of the rock but have now been forcibly removed by the salt. I’ve found that this is most prevalent in areas just above the high tide line where wave action can’t wash the sand grains back out to sea.
But Zach, you say…how then does honeycomb weathering form in places like the desert Southwest where the closest thing to sea spray you’re going to find is mule deer pee? Ah…well I’m glad you asked. We often observe honeycomb weathering in sandstone in places such as Southern Utah that are far away from the sea. I had some difficulty finding a halfway decent picture of desert honeycomb weathering from my archives, but I was able to find one that I took in 2008 in Capitol Reef National Park (see below). If you want to see a lot better examples, just do a Google image search for “Utah tafoni”. While the exact cause may vary, and the individual pits tend to be larger, the process involved is essentially the same. We still need to find some way to separate our sand grains from the cement. Many washes in the southwest are dry for most of the year but are very rich in dissolved salts when they do flood. In desert environments, it’s no surprise then that we tend to find honeycomb weathering predominantly along dry stream beds and canyons. When a flood comes through, even though the water may not be as saline as the ocean, it is still salty enough to form small salt crystals when it evaporates, which it invariably does. In other locations, slightly acidic groundwater percolating through rocks can actually chemically dissolve calcium carbonate cement, leaving the sand grains with nothing to cling to.
Hard as it might be for you to believe, this has been only a cursory explanation of the honeycomb weathering formation process. If your brain hasn’t begun to resemble honeycomb weathering by now and you are interested in the gritty details (perhaps you arrived here in the process of researching a paper or maybe you’re a geology nerd like me and just like knowing about such things), an excellent academic paper on the formation of honeycomb weathering can be found here. Regardless, your next step should be to pull out a geologic map, find the closest beach with some sandstone, pull your boots on and go find yourself some honeycomb weathering! Or you could always just look at the rest of these pictures I suppose…