Monday, April 7, 2014

Out of the Valley of Death: Geology at Fifty-five

One of the first things I tell my students (and occasionally even with some success) is "don't sleep while traveling in the vans". Death Valley National Park is the largest national park in the lower 48 states, and no matter how much time one has, it's hard to take it all in. When you only have four days, it's pretty well impossible, but there is still much to see in transit between stops. On our third day out we were set to explore the northern end of Death Valley, which in a park that is mostly desert wilderness, feels even more isolated and lonely (despite the presence of Scotty's Castle up one of the side canyons).
The day started with a stunning sunrise as seen from one of the most isolated RV parks in the American west, Stovepipe Wells. The campground is literally a parking lot, but it's a parking lot with one of the most incredible views possible. The resort is situated on the distal end of the huge alluvial fan that emerges from Mosaic Canyon on Tucki Mountain, which we'll check out in a future post. The elevation is sea level, but it somehow feels higher, given the spectacular and far-ranging view.
Two great desert mountain ranges form the boundaries of the northern reaches of Death Valley, the Cottonwoods on the left and the Grapevine Mountains on the right in the picture above. The mountains tower over the valley floor, reaching nearly 9,000 feet above a valley floor that is barely above sea level. The view extends thirty miles or more.
A drive north towards the end of the valley reveals a series of classic desert features, starting with the Mesquite Flat sand dunes, sometimes known as Death Valley dunes. Sand dunes are picturesque enough by themselves, but in Death Valley they have a dramatic backdrop of high barren mountains.
We raced by at 55 miles per hour ("Honest, officer!"), but cameras these days are versatile, capturing the image as if we were standing still. And this is the sort of incredible sight one could miss if one is snoring away.
The dunes have formed here because prevailing winds sweep down the northern reaches of Death Valley (and a number of destroyed tents over the years can attest to the power of these winds). The vast bulk of Tucki Mountain at the north end of the Panamint Mountains stands in the path of these winds, causing them to break up and form eddies. The sand accumulated in the region as the powerful winds lose energy and drop their load of sand and dust. They are sometimes referred to as star dunes, or modified sub-barchan dunes. Even if you've never been to Death Valley, you've probably seen these dunes anyway; they formed the backdrop for the droids lost on the planet Tatooine in the original Star Wars movie.

In the picture above, one can see the valley floor beyond the dunes is interrupted by a terrace of some sort. This is the scarp for the Furnace Creek fault zone which is one of the important structural features of the Death Valley graben.
A closer look provides a view of light-colored sedimentary rocks exposed in the face of the scarp. The fine-grained mud and silt layers are part of the Furnace Creek formation, which was deposited into a fault trough similar to present-day Death Valley, but oriented in a more northwest-southeast direction. Crustal stretching has effected the crust in the region more than once. The erosion of the Furnace Creek formation in this dry environment produces badlands topography, which we will explore in greater detail in another post.
The fault system interrupts the surface of the alluvial fan, shifting it in an right lateral direction (the rocks across the fault are displaced to the observer's right). These faults roughly parallel the San Andreas fault, which lies far to the west. The fault is presumably still active, but has not produced a major earthquake in modern times.
Another incredible sight visible from the road is the series of alluvial fans that extend from the edge of the mountains down to the valley floor. They build up as the rare but violent flash floods and mudflows carry boulders and debris across the valley floor. They have a somewhat convex slope, becoming steeper near mountain front. Death Valley is famous for the variety and number of fans it has.
The fans reveal variations in color. The darker surfaces on the fans result from desert varnish, a mixture of manganese oxides and clay that coat the exposed surfaces of the rock. It accumulates over time, and the origin is debated. Bacteria are likely involved in the process.

As we drove further north, the valley floor narrowed, and we soon reached an area where the alluvial fans from the two mountain ranges merged in the center of the valley. We were approaching the end of the Death Valley graben. In the distance we could see dark-colored rocks coating the surface of the alluvial fans. We had reached the volcanoes of Death Valley.

In the next post: the Ubehebes!


biobabbler said...

This was really enjoyable. What an amazing place. One of my favorite things about the desert is getting up to a good vantage point & looking at alluvial fans/bajadas (as I've done in the Anza-Borrego desert) because it feels like you can see the soil flowing down from the mountain. Almost watching geology "happen."

And I'm a sucker for any sand dunes--I love how they can record the passage of such tiny things as beetles. Everything walking on them is betrayed by a clear trail of footprints. Very fun for a biologist w/a wildlife bent.

dbozarth said...

As always, so interesting with awesome photos!

Unknown said...

Professor Hayes: You didn't tell those sleeping that pictures will be posted if you fall asleep during class time. You need to tell them that class starts once in the van and until we stop to camp. You getting soft??? ;)

Gaelyn said...

Oh how your photos take me back. Certainly not a place to sleep with all the diversity. Loved camping at Stovepipe.

Sorry I haven't been around. Missed your geo tours immensely.

Garry Hayes said...

It's nice to have you back, Gaelyn. It feels as if you've been on the other side of the world or something! ;)