Sculpting A Plateau

Joel Pederson received his bachelor’s degree in Geology from Gustavus Adolphus College near where he grew up in rural Minnesota. After gaining work experience in environmental remediation, he came to the Southwest for graduate school, earning a master’s degree in Geology from Northern Arizona University and a doctorate in Earth and Planetary Sciences from the University of New Mexico in 1999. Joel has been a faculty member at Utah State University ever since, teaching geomorphology and other courses, mentoring a score of graduate students and many undergraduate researchers, and serving as the Department Head of Geosciences. His geomorphology and geoscience-education research are focused on the landscapes of the Colorado Plateau – how they have evolved by erosion over geologic time, how they respond to climate changes, and the context they provide for prehistoric cultures. Joel is a Fellow of the Geological Society of America and a recipient of GSA’s Biggs Earth Science Teaching Award. 

Utah State University

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Research

Today we are talking with Joel Pederson, Professor and Department Head of geomorphology at Utah State University. Joel’s passion is landscapes and understanding how they came to be.  In studying the incision rates of the Colorado, from the Grand Canyon area, up through Glen and Cataract canyons, and upstream of Moab to the Dewey Bridge area. Joel and his team hypothesize that the fastest rates of incision is now occurring right around the Moab area and upstream to the the mouth of the Dolores River.

Pederson:  I think we can show that the reason why erosion is so fast in southeastern Utah, is because that’s sort of where the wave of incision is now hitting as erosion progresses upstream from the edges of the Colorado Plateau. There’s also an effect of the rocks in southeastern Utah and the Canyonlands district being less resistant and weaker sedimentary rocks, then the rocks tend to be at the edges of the Colorado Plateau. For example, the Grand Canyon also has these layers of sedimentary rock, but a lot of them are really resistant limestones, making the cliffs. Then there’s the basement rocks down at the very bottom of Grand Canyon. So I think you’re getting a wave of incision, that’s also hitting rocks that are really easy to erode and therefore you sort of get this amplified bullseye of incision in the Moab area.

Science Moab:  With your latest research, which includes a lot of outcrop work just north of Moab around Dewey bridge. What sort of new data and or rocks have you come across to kind of further this research?

Pederson:  One of the many evolutions and our capabilities as geoscientists over the last couple of decades, is in ways of geochronology of doing the dating of geologic materials. Most of the research that my students and I do is really based on looking at old river deposits that record where the river used to be in the landscape in the past.  We’ve been employing this dating technique called luminescence dating to date the sand grains within the ancient river gravels deposits.  One thing that’s happened in the last five or 10 years is that with technological advances we can date with luminescence older and older deposits. Ten years ago, we were really limited to about the last 150,000 years of geologic history where we could use that technique and figure out the history of the river. In the last five years, we’ve started using feldspar instead of quartz. So it turns out feldspar as a mineral, ends up accumulating damage and holding it in a useful way over longer time periods. Now we’re able to start doing work where we can look back up to 700,000 years. That has really changed things. 

Science Moab:  What are some of the processes you and your team goes through when you’re trying to study all these river deposits over such a large area?

Pederson:  As we have gone from studying Grand Canyon area, and working upstream into Meander Canyon, and then upstream of Moab, in each one of these places, one of the first things that my students do is, is they just plain old map and document all of the river deposits that are found in that canyon landscape, to some degree geologists have, you know, made maps, of course of this region, and they’ve noticed, yep, there’s some river gravels, here and there, but then, you know, we get to come back in and really document it at a way better level. Then we survey with GPS the locations of all these things, and their exact heights, and positions in the landscape. It is sort of a cool mission of discovery, because we get to go in and just sort of document and explore at a different level, these river deposits that are our focus. For me, that’s part of the fun just to kind of get to see and document where these all are exactly. If we’re lucky enough, we find places where we can sample the sand and come up with the story of incision.

Science Moab

So what are some next steps, you know, in your planning? What else are you trying to figure out here?

Pederson

One thing that I must make clear and admit is that it’s a working hypothesis. there’s still going to be a multi year process of really testing that hypothesis with the data. As you go from Moab upstream, if there is this wave of incision, one pattern we should see is that over recent geologic time, the incision rate should get faster and faster and faster, the closer you get to the front of that wave, and then if you go upstream even farther, that rates would suddenly get really slow, because the wave hasn’t gotten there yet. This is a really good hypothesis;  it is just not tested yet. We have one main key steady reach, which is up between Dewey Bridge up towards Westwater Canyon. We’ve mapped out the deposits. Most of them, we have gotten samples for luminescence dating. maybe in five years we’ll have that all figured out and be able to really say yes, this is what’s happened and what time and the wave is moving this fast.