Painted Desert

Painted Desert

Monday, June 01, 2009

Everyone knows it's windy

I have plenty of free time again today because we had to come in early from the field. Our field camp will go down in history, it seems: today was the first time, according to the professor, the camp has ever "been blown out of the field." I checked the weather forecast before getting into the van today and mentioned to my roommates, "Hm, it's going to be windy." The forecast was for 20-30 mph winds. That's pretty windy. But when we got out to our area, it soon became evident that the weather had greater ambitions.

I have to say I have never before been in a wind so strong that drops of saliva were actually scoured out of my mouth and blown away every time I opened it to speak. This is a curious sensation. It makes you feel slightly incontinent, and leaves your cheeks damp, as well as the cheeks of whoever you're trying to speak to.

The Beaufort wind scale, developed to allow mariners to estimate wind speeds, allows us to make a guess at just how windy it was in the Bighorn Basin today. It offers:

31 – 38 mph: Whole trees in motion. Effort needed to walk against the wind.
39-46 mph: Some twigs broken from trees. Cars veer on road. Progress on foot is seriously impeded.

Considering the fact that my thighs were bulging as I struggled to walk down a hill this afternoon, I'm going to say wind speeds were consistently around 40 mph today with some gusts at 50. Especially on top of rises, it became nearly impossible to get work done. Just holding the Brunton steady was hard, and the wind kept ripping the topographic maps out from under the clip on my clipboard.

Here is my team for this mapping area. Lying down on the right is Tyson, the other URI student who got a scholarship to this field camp. Tyson is struggling to hold the Brunton steady behind the windblock provided by our other teammates so that he can measure a strike, or the bearing of the intersection of this bed of rock with a horizontal plane. This seemed to take about five minutes. Here's a video of the area we were working in, with us:

We're mapping this area without the Jacob staffs; instead, we're comparing what we see in front of us with topographic maps and aerial photographs to draw in formation boundaries at the appropriate areas. We're also measuring the strikes and dips (inclinations) of the rock beds so we'll be able to do a cross-section later, showing how the rocks have been folded under the earth.
Drawing in different rocks at different places on the topographic map requires getting to a high point and looking around to see where recognizable boundaries (say, between a formation we know is grayish and one we know is black) fall. So at one point we were right up on the highest ridge looking around and discussing what we saw below us. We never did come to a conclusion on the rocks below, mostly because the wind was so strong that despite having our faces within a foot of each other's and screaming at the tops of our lungs, we couldn't hear what anyone was saying. Here's a video of us on the ridge:

Anyway, after about four hours of this, the instructors came to the conclusion that we weren't going to get any quality work done and we piled into the vans to have a look at the other side of the area we were mapping. One of our professors went down into a depression to see if it was less windy and lost his hat (and nearly himself, trying to catch it) and determined it was time to give up. We did take a few moments to get out of the vans and look at the rocks, though:

And pose for photos. Note my teammate on the left, magically transformed into the Michelin Man.

I don't want to reveal too much about the areas we're mapping because the field camp has to use the same exercises year after year, and it wouldn't behoove me to lay everything out on the web for future students to find. But I will say that if you go to Google maps or Google Earth and look in the vicinity of Greybull, WY, you will see some very interesting-looking rocks, and these are the sorts of things we have been mapping.

Below, another shot of today's area:

Most of the rock here is part of the Cloverly Formation, which bears a lot of resemblance to the Chinle Formation that I worked in last summer at Petrified Forest. Despite being 100 million years younger, the Cloverly was formed by basically the same type of environment: meandering rivers and floodplains. Much of it is colorful mudstone that erodes into badlands a lot like those of PEFO, though I think the Cloverly is even more colorful, with additional shades of salmon, yellow and green alongside the red, orange, blue, white and grey that were common in the Painted Desert.

I can't recall if I ever explained what a geologic formation is... it's a convention, a creation, invented by geologists to make rocks easier to work with. A formation is a package of rock with recognizable characteristics that's large enough to be useful to work with at map scale (that is, it wouldn't just be a hair-thin sliver on a topographic map, nor would one formation take up the entire map). Formations have thicknesses... my last team measured the Cloverly to be about 180 feet thick where we were... but how much you actually see at the surface, and how much will thus actually show up on a map, varies depending on whether the rocks are tilted in the area and whether they might be covered with something else.

Formations are also something called "time-transgressive," which is important in geology. It means that the formation is not everywhere the same age, even though it might be the same type of rock. In the east, the Cloverly might be 100 million years old, and in the west 110 million years old (to pick numbers out of a hat). If you were to delineate a package of rock that was all the same age rather than all the same type... say, the package between 100 and 105 million years old... this new rock package would have many types of rock, that would show you which environments were next to each other during that time. A sandstone west of a coal deposit west of some paleosols might show you that there was a beach next to a swamp next to a floodplain during that time. Which would be useful. However, this package of mixed rock types would be a terrible pain to work with and map... never mind trying to figure out exactly where to put these hypothetical age barriers... so most work is done with formations. But as you read me speaking about the Cloverly Formation or the Chinle Formation, remember that it is just a package of rock that it is alike and convenient to map. Like so much in science, it's a human invention for the sake of convenience.

1 comment:

Mom said...

Hi, Jo

The Micheline Man analogy was apt.