Saturday, March 30, 2013

At the Gates of Zion and the Parting of the Water

So yesterday we went to Zion National Park.

Now that you've seen 1/10000000 of how awesome and beautiful Zion is (seriously, you should go for yourself) I can tell you about how cool it is geologically.

Zion is the middle step in something called the Grand Staircase, which is basically a staircase running through the Grand Canyon, Zion, and Bryce National Parks where the earth has been shifted up and the layers that make the top of the Grand Canyon are the same as the layers on the bottom of Zion, and the layers that make the top of Zion are the same as the layers on the top of Bryce. The Grand part comes from how beautiful the layers look, alternating limestone, sandstone, siltstone and mudstone in shades of red, orange, brown and gray.

These layers are the remnants of oceans, and then shallow seas in the area, as well as sand dunes in Zion's case. The crisscrossing patterns you see in the last photo above show some of this sand dune formation, as it was blown across a desert similar to the Sahara that crossed through several different states. There are several types of sand dunes, and using the cross-sections in the rock, geologists can estimate the size of the dune and speed of the wind moving the sand around. Based on things like the distance sand was blown over the tops of dunes, and the angles of its slope, these sand dunes were estimated to be 30 meters high and would need average daily winds of 52 mph! Seeing what was left was impressive enough. Also, if you look at the last picture again, you can see that the lines are cut off in places, indicating that the wind changed direction and thus changed the shape of the sand dune (and its cross-section). The sand probably all crystallized at once, due to silica and iron liquids cementing it together.

Zion is also beautiful because of the very distinct layering. We went on a hike up through the mountains, crossing through several of the layers (the Moenave and Navajo in particular). Each layer has distinguishing marks (although some could probably be easier lumped together by color than by time period) and some even contain dinosaur footprints and petrified wood!

We also got a look at Checkerboard Mesa where fractures in the rock created regular cracks that look like a checkerboard (sorry for the crappy shot, it was taken through the window of a moving vehicle).

We didn't have time to see much else, although we did get to buy souvenirs! I got two awesome books on petroglyphs, which are kind of like pictograms that Native Americans would draw on the walls. Two squiggly lines represent a canyon, and a black circle with a white cross symbolized the God of Life. Those are the few I remember, but I plan on learning them all. They reminded me in some ways of the hobo symbols used during the Great Depression to communicate food, lodging and danger.


Anyway, Zion was exciting, and we all were exhausted by the time we finally went to bed. I personally fell asleep at 8.30 pm, which was weird and strange considering my MIT bedtime of 5 am.

Today instead of nature engineering we checked out some human engineering.
First we stopped at a town called St. George's, which was flooded by Lake Mead but now stands uncovered since the waters have dropped 30+ feet. It was a cute town, apparently fertile and awesome until Hoover Dam was installed and it was submerged. I didn't bring a camera on the hike so I have no pictures, but imagine cement foundations peaking out of sand, clam shells (from when the Colorado river flowed) and desert grasses.

The next stop was the Hoover Dam itself, where civil engineers delighted and danced around.

Dancing doesn't show up well in pictures.

We got a private tour through the underbelly of the dam, where we got to see the pipes used to divert water from the work area during construction. The pipes were so big (30 ft in diameter) that a plant had to be build to make them, since they couldn't be shipped.
Here's a layout of the dam during and after construction. The bottom, once water was diverted, was dredged up to 135 to get to the bedrock before building could begin. Then construction crews worked for 5 years, 363 days a year, filling in concrete blocks one at a time and cooling the concrete with cold water inside of pipes running through the blocks. This was the only way to get the concrete to set in time - otherwise it would have taken the concrete 150 years to cool. The dam was built with both time and money to spare; in the midst of the Great Depression. No wonder civil engineers love this place so much. 96 official deaths were reported during construction, but many more weren't recorded. Although the dam provides both water in the form of Lake Mead and hydroelectric power from generators powered by the Colorado River, the land flooded also covered towns and farms such as those at St. George's. More water is left standing, but over a wider surface area. Part of the trouble of large surface areas in the desert is the evaporation rate lowers the water by a lot. Overuse also has a lot to do with it. Hoover Dam and Lake Mead are partly so interesting because of their part in the challenge of water conservation in the Southwest, which may soon drive out people from cities like Phoenix and Las Vegas.

For my part, I'm just glad we can see these things without 30 meter sand dunes covering it all. Its been an amazing trip. Thank you Terrascope, and everyone in it, for making it so good.

Till then, cheers!

No comments:

Post a Comment