Water can be a formidable force in the desert. From carving canyons to cutting arroyos, water has formed and continues to mold the landscapes around us. Science Moab spoke with Dr. Taylor Joyal, a fluvial-geo-morphologist at the School of Earth and Sustainability at Northern Arizona University, to learn how water sculpts the desert environment.
Science Moab: What is geomorphology?
Joyal: Geomorphology is how water shapes the surface of the earth. In simplest terms, water is the number-one process for shaping terrestrial landscapes. I see morphology as having two large realms: one is watching how water shapes the planet, and the other is examining the information left behind by these processes and understanding those processes enough to look at deposits and say “this is how the system reacted to this event in the past,” so we can make a claim that it might react that way in the future.
Science Moab: Some of your work deals with the driving forces of water and the resisting forces within a landscape. Can you explain how the geology and structure of the landscape can actually resist changes brought about by gravity and water?
Joyal: In both the driving and the resisting forces of landscape evolution, the scale is important to consider. Not just the time scale; spatial and temporal scales also really need to be acknowledged.
If we’re just looking at small bedforms—ripple marks in the bottom of the stream—and we can see it happening, then we can try to quantify the turbulence it’s creating. On the other hand, a smooth, sandy bed is not going to create that resistance and is going to allow that water to zing along a little bit faster. So there’s resistance on that really fine scale.
When we look at something like Canyonlands, where these enormous joint fields [In geology, a joint refers to cracks or fractures present in the rocks. -ed.] have created a pattern of resistance that’s been exaggerated by forces of wind and water and blown apart, like Needles. Or, if you travel down the San Juan River and you go through Lime Ridge, you see these huge upward folds that the river is cutting right through, seemingly disregarding any kind of resistance. The theory behind all these meandering canyon systems is that they represent these slow lowland rivers that used to flow into what was once a basin. Once the area began uplifting, those remnant channels were locked in stone as they were carving down into this uplifting structure from below. The timescale plays a definite role in how that structural resistance was overcome. If the uplift had happened more quickly, the river probably wouldn’t have had the ability to cut through the rock.
Science Moab: How can understanding the way that water moves through a landscape help inform our land-use decisions?
Joyal: If you understand soil hydrology—how water is moving across the surface and through vegetation, then into the subsurface through the soil—you can use simple physics equations and put an entire watershed into a computer spatial model. Then, in that model, you can simulate water moving through a channel and then leaving the watershed. Knowing that, you can simulate something that is really happening now.
In other words, can we manage our landscapes to reduce the impact of climate change? The modeling shows that if we re-forest areas previously converted to pasture, or limit the areas that we convert to pasture, we can see a greatly reduced effect on the watershed hydrology, just by managing the land cover. On the other hand, we can see exaggerated effects of climate change when we clear the forests or otherwise impact soil hydrology through land use. So there’s a real lesson there in terms of understanding processes enough to model a whole range of climates on this landscape. These are the tools we can use to try to mitigate those potential effects.
This interview has been edited for length and clarity. To learn more and listen to the rest of Dr. Taylor Joyal’s interview, visit www.soundcloud.com/user-495802209/how-water-shapes-the-earth.
