Into the Valley of Death (Part 2): Ventifacts and Dunes
Wind gets far more credit for shaping the surface of the Earth than it should. Contrary to popular belief, wind is a relatively poor sculptor of landscapes, especially when compared to water in its many forms.
Remove water from the equation though, and the influence of wind becomes magnified. The planet Mars is a great example. Dry for billions of years, with no streams or ocean waves to shape its landscape, Mars has become a barren land of sand dunes and sandblasted rocks.
If you want to experience a Mars-like landscape without the inconvenience of a long flight, Death Valley just might be your best bet. Here, water is so sparse that the effects of wind are more prominent and striking than anywhere I’ve ever visited.
Martian-like landscape on Ventifact Ridge, Death Valley National Park. A snow-dusted Telescope Peak (11,043′) is visible in the background.
Looking east along Ventifact Ridge toward the Black Mountains
My personal favorite wind-driven geologic phenomenon are what are geologists call “ventifacts.” Ventifacts are rocks (usually boulder-sized) that have essentially been sandblasted by wind-blown sand particles for extended periods of time. Ventifacts are consequently pockmarked with an array of pits, grooves, gouges, striations, and etchings that betray their uncomfortable past. Near Badwater in southern Death Valley, a low, linear ridge covered in boulders of dark black volcanic rock juts out into the valley, intercepting the strong winds that often blow along the valley’s length. Nearly every rock on this ridge shows these telltale signs of sandblasting. Combined with the lack of vegetation, photos from here resemble many of those taken by the Mars rovers more than just about anywhere else on Earth.
Ventifact and sand ripples, Death Valley National Park
A pair of excessively pockmarked ventifacts. Note that the top portion of the foreground ventifact has been completely eaten away near the top.
Larger ventifacts like the one below often take on an exceptionally strange shape. This is because wind (even very strong wind) is incapable of picking up anything bigger than a large grain of sand, and even then it can’t lift it more than a few feet off the ground. The result is that the bottom two or three feet of the bounder gets abraded away, while the top remains relatively intact, leading to the classic “hourglass” shape of large ventifacts.
Yours truly atop a large roadside ventifact in Death Valley
All of the sand blown along the valley has to go somewhere. In several locations around Death Valley National Park, mountain ranges act as obstacles to wind, and where the wind stops or slows, the sand is deposited in large dune fields.
Death Valley has not shortage of dunes but the most accessible are the Mesquite Flat Dunes near Stovepipe Wells. Unfortunately, the proximity of these dunes to paved highways means that they are also one of the most visited locations in the park. Upon arrival at the dunes a bit before sunset, we were immediately greeted by the high-pitched insectile buzz of an amateur drone (currently prohibited in national parks) hovering overhead. Fortunately, such devices have a limited range and we were soon free of the annoyance. Even though the Sun was getting low, our plan was to stay awhile. Before long, the Sun set, the stars came out and we had the dunes almost entirely to ourselves as the nearly full Moon illuminated our path:
A clear winter night in the Mesquite Flat Sand Dunes, Death Valley National Park. The yellowish glow on the horizon at right is light pollution from Las Vegas, nearly three hours away.
Ripples in the sand, Mesquite Flat Sand Dunes, Death Valley
One unique feature of the these dunes is the presence of large patches of dried & cracked mud between the dune crests. Having been to dozens of different sand dunes, seeing anything other than sand (and the occasional hardy bush) in a field of sand dunes in a strange sight. The origin of the mud is connected to the fact that the dunes lie nestled against the base of the Panamint Mountains. Periodically, mudflows and debris flows burst forth from the canyons at the foot of these mountains, migrating their way into the low spots between the dunes. The mud dries quickly in the arid climate, forming the large mudcracks. The sand dunes, constantly in a state of motion, eventually bury most of the mudflow deposits, leaving only portions peeking through.
Mudcracks in the Mesquite Flat Sand Dunes, the dried remains of mudflows from the Panamint Mountains that occasionally penetrate the dunes. The Pleaides star cluster is visible near the top of the photo.
Coming up in part three, we leave the valley behind and explore the myriad of canyons cut into the mountains ringing Death Valley. Then it’s on to Joshua Tree!
Geology Research in Paradise
I have decided that there are few things in this world as gratifying as going for a swim on a tropical beach at sunset after spending all day in the field hiking over boot-shredding, leg-puncturing, sunburn inside your nostrils-inducing, lava flows. Such pleasures occur when one has the opportunity to do geology field work in Hawaii for a week, as I had the fortune of doing this past week as part of my senior thesis project. Oddly enough, I’m not actually studying Hawaii, but rather water and lava flows on Mars (more on that in a bit). However, since present-day Mars experiences very little in the way of surface erosion, many of the lava flows there look as fresh as the day they were erupted hundreds of millions of years ago. Since a field trip to Mars was a bit over the budget for this project (darn government cutbacks…), we instead must resort to trying to find places on Earth with fresh, unaltered lava flows in order to compare, contrast, and understand what we see on Mars. Hmm…I wonder where could I find some of those?
Hawaii in a nutshell: palm trees growing out of lava flows
Ah yes, Hawaii will do quite nicely, now won’t it? As luck would have it, Kilauea (the main active volcano in Hawaii) is currently going through a relatively dormant phase. When I visited Hawaii back in 2008, it obligingly started spewing massive quantities of lava into the ocean a few weeks before our arrival:
Kilauea lava flows, circa 2008
No such luck this time. This and this happened a few months ago and the volcano’s magma reservoir and crater has been slowly refilling ever since. (Seriously, watch the videos. And keep in mind that the 1st one takes place over the course of just 24 hours.) A geologist with the Hawaiian Volcano Observatory told us he though there was a decent, but not great, chance of an eruption during our time there but despite our sacrifice of several geology students to Pele, that never materialized. We did however get to see the main vent of Kilauea glowing bright orange at night due to a molten lake of lava lying about 150m beneath the surface:
Halema'uma'u Crater at night
Even if my childhood dream of roasting marshmallows over hot, molten, lava once again went unfulfilled, that sure as heck isn’t something you see everyday.
Anyways, from our base at the Apapane Lodge in the tiny settlement of Volcano, HI, we (myself, three other students, and two geologists) spent much of our time hiking across young (<200 years in most places) lava flows looking at features such as lava tubes, vents, channels, and collapse pits trying to decipher features that we see on Martian volcanoes. More specifically, the project I am involved in seeks to determine what causes features like this on Mars:
Conventional wisdom says that such features are formed by water, and especially since the Mars Exploration Rovers uncovered chemical evidence that water existed on Mars at some point in the past, this has been the prevailing view for some time. However, lava is capable of doing some very weird things and more recent work has shown that many of the features that have long thought to have been formed by water are more likely the work of lava flows. So why do we care? If this is indeed the case, it has serious consequences for our understanding of Mars as a whole. The presence of channels such as this one has long been one of the key pieces of evidence supporting the idea of flowing water on Mars in the past. If instead these features were formed by lava then we have a lot of questions to ask ourselves, most importantly: Did flowing water ever exist on the surface of Mars in large enough quantities to carve such channels? Water, of course, is the key to life (at least that’s what we think…) so figuring out if water flowed on Mars in the past (and if so, how much) is essential for understanding how planets evolve over the long term and for determining if life ever existed on Mars. The role of water on Mars is also important from a practical standpoint as we try to determine if Mars is potentially a habitable planet for humans in the future.
A typical scene in the field. This is a channel within a large lava flow thought to be analogous to some of the channels we see on Mars. On a side note, I never thought it was possible to completely destroy a perfectly good pair of hikin boots in just four days. Hawaii's infamous "a'a" lave like this proved me very wrong.
Younger lava flows pour into a channel formed by the collapse of an old lava tube
The team after a tour of the Hawaiian Volcano Observatory
When you see signs like this, you know you're having fun!
As sad as it was to leave Hawaii, the trip “home” was even less fun. Given that I arrived in Washington D.C about 10 hrs later than planned and sans any clothing apart from what I was wearing, I hereby nominate American Airlines for the “Worst Airline in the Universe” award. In addition, when I finally did get my luggage returned this afternoon, all my outdoor gear and camera equipment were intact but all but three of the rock samples I collected in Hawaii (NONE of which were from the National Park before anyone starts harping on me…) were missing. Explain that one to me…
Mauna Loa (left) and Mauna Kea (right background) at sunrise from Kilauea Summit
Zach Schierl Photography 