Wednesday, July 21, 2010

Games Geologists Play

While teaching classes on western rivers, I often give descriptions of the upcoming rock units. After describing mappable units, grain size, shape, color and other macro-characterizations, I ask them to determine where the next rock unit appears as we float the river. The winner often receives an extra Oreo cookie at lunch. (A game needs a prize) Other games have included: find the river, and the ever popular where are we.

Can you find the break between the Ladore formation and the Madison limestone?
Last week we were traveling in Northern Colorado and found ourselves looking at some fantastic glacially polished rock. I was explaining to my ever-patient wife about the life and death of glaciers when we created a new game: Find the Equilibrium Line.

The equilibrium line divided the ice sheet into two parts. The upper section is where material was being added to the glacier as more snow was accumulating than melting. We can observe paleo-accumulation zones from the presence of erosional features- such as glacially polished rock.
The area below the equilibrium line is where more material was melting than being accumulated. Because there was an excess of material, ice moved from above the equilibrium line to below the equilibrium line. Paleo-ablation, or melting zones can be determined by observing depositional features such as a moraine. (The image below was shamelessly right-clicked from a google image search as it showed a moraine way better than any of my pictures.)The trick is to find the point where erosion ends and deposition begins.
Here, the elevation of the paleo-equilibrium line is is roughly 11,300 feet above sea level.

For extra cookies, or credit. a very rough estimate of the paleo-climate can be determined with some simple calculations. The difference between the "modern" equilibrium line ( approximately 14,000 feet (a number created a long time ago while in grad school) and the "paleo" equilibrium line is 2700 feet. The dry adiabatic rate is roughly 3.5o F/ 1000 feet, giving us a rough temperature difference between the ice age maximum and now would be 9o F.

I know that there are a multitude of factors not being taken in consideration, but this seems an easy exercise where students can observe geology, do some simple calculations and go home with an answer that makes sense.

And, of course the winner gets an extra Oreo cookie.

Monday, July 19, 2010

Part of the "Why I blog" series

Last month between trips in Utah, one to Grand Staircase and the other to Dinosaur NM, I quickly penned a guest blog for the plainspoken scientist. It took them awhile to fix all of my grammatical mistakes, but it is up and running now.

I hope to get a new blog post up soon...but it is summer.

Tuesday, July 6, 2010

Geological interpretation in a biological world

We spent much of June exploring both front and back county areas of the Grand Staircase NM. Our journeys took us from Bryce Canyon to the Circle Cliffs. This is an amazing country and we are so fortunate that much of it is protected as a national monument.

However, it appears, to me anyway, that much of the interpretation of the natural world is done by biologists. We visited Bryce Canyon with its hoodoos of the Claron Fm eroding out of the plateau. As we walked about I was expecting that most interpretive signs would be about geology...but no. We did learn about the harsh conditions the trees are subjected to as well as how the animals survive in such a dry climate. While biology is quite important, I was hoping for more "rock" signs for obvious reasons. Nothing registered in my mind yet, that is until we visited Escalante Petrified Forest State Park. Once again, with "petrified forest" as the title feature I expected a geology inspired hike. Hiking up the marquee trail we found some cool basaltic boulders left over from eruptive excitement on the nearby Boulder Mountain. Later in the hike we observed handfuls of nodules eroding out of a Navajo Sandstone outcrop. And, of course, all along the hike we were treated to fossilized trees scattered over the hillside. Our little trail guide mentioned only one of these observations, that of the petrified trees. Interestingly, a team from Utah State University has created a fantastic geologic trail guide for the same trail, but copies were not available at the visitors center and I have only seen them online.

A new outreach goal of mine is to help our federal land naturalists with more geologic interpretation.

Bryce canyon at sunrise. The Eocene aged Clarion Fm is a colorful freshwater limestone.
A fantastic cross section of the area from my favorite Utah State Park.
Petrified tree eroding out of the Morrison Fm
nodules from the Navajo Fm
Basaltic boulders transported from nearby Boulder Mt and the Aquarius Plateau