Ever wonder whether rock weathers?

When driving along Interstate 80 between Cheyenne and Laramie, you may have marveled at one of Wyoming's most colorful natural landmarks: Vedauwoo, a collection of plump pink granite rock hills.  Janet Dewey, a researcher in the Department of Geology and Geophysics, believes that their curious shape results in part from variable rates of chemical weathering of different rocks, and gradual erosion through rainfall, snowmelt, and temperature changes.  As she explains, "The rate at which different rocks weather governs the landscape, topographic expression, and the porosity in the rock."  Vedauwoo is one striking example of a phenomenon that shapes the intermountain west.

Rock varieties in Wyoming, including pink granite on the far left
(photo credit: Janet Dewey)

Since weathering affects the form and density of rocks, it also plays a major role in how water flows and where it is stored.  Weathering can change the chemical composition of rocks, as when weather leaches out elements like calcium.  When rocks and water come in contact, the chemical composition of both can change; this in turn changes the relationship between the two.  For example, if dissolving a portion of the rock changes the acidity of the water, then the rate of chemical weathering can also change.  Weathering and erosion can also include factors like slope and aspect.  One side of the mountain might be steeper, and one side might spend more time in direct sunlight.

Weathering also influences climate.  Weathering of silicate rock is "a pretty big sink" for carbon dioxide.  "Silicate minerals in the rock react with carbonic acid, consume carbon dioxide and produce weathering products that depend on the minerals present," explained Dewey.

Dewey and others on the weathering research team hope to identify what controls rates of weathering and erosion of rocks in the Laramie Range.  "Like many scientific problems, it's a scaling issue.  What we see at the micro scale is not necessarily what we see at the landscape scale."

Glass column reactors
(photo credit: Janet Dewey)

Their study near the Laramie area includes several different techniques.  First is the micro (or very small) scale which includes column experiments to test the weathering of different kinds of rock.  Dewey and her team have build glass column reactors containing three kinds of crushed rock, including the pink granite that is iconic to Vedauwoo.  Water continuously flows through the columns and is allowed to react with the minerals in the rock.  They test the water runoff for traces of elements like calcium, iron, and phosphorus.  You can see a picture of these columns at left.

Another step involves taking samples of rock at different locations and mapping weathering profiles.  Researchers can also look at thinly-sliced rock under a petrographic microscope to analyze the structure, mineralogy, and grain size of the various rock types and how those features might influence weathering.  The group also uses techniques that will help them determine the landscape-scale erosion rates.  These data will be combined with geophysical data to create a multilayered map of the region.

Graph showing different minerals found in column reactor runoff
(image credit: Cassie Nauer)

After this phase, the team increases the "suite," or set of rocks in the water column study.  The researchers are currently testing three types of rock, but will increase to eight types.  They will also test faster rates of water flow, to determine if there is a predictable relationship between flow and rate of chemical weathering.

Graph showing column reactor runoff rates over time
(image credit: Cassie Nauer)

Dewey's motivation to explore weathering comes from an interest in understanding the future and a curiosity about the past.  She says, "From my perspective, one of the biggest issues confronting us in the future is going to be water quantity and quality.  We need to know as much as we can about the relationship between water and the rock it passes through.  Without that understanding it's easy for us to make mistakes."

In considering the past, she added, "If you've ever gone out on the landscape at Veedauwoo and stood there by those rocks, you think: Why do they tower four stories above me and I'm standing on flat weathered rock that seems to be made of the same material?  Why does that beautiful landscape exist - that we take pictures of, and climb on, and love to visit year round?  If we are sitting on one giant granite batholith, why isn't it the same across the landscape?  That's a cool question."

by Jess White 

ICCE Expedition on Dinwoody Glacier

Dinwoody Glacier (photo credit: Kyle Nicholoff)

The word glacier conjures polar ice and Patagonian steppes, so you might be surprised to learn that the largest glacier in the lower forty-eight states is right here in Wyoming, in the Wind River Basin Mountain Range: Gannet Glacier, on the east and north slopes of Gannet Peak.   

The unique composition of glaciers offers infinite opportunities for research, especially in hydrology and earth science.  This summer, Central Wyoming College (CWC) instructor, Jacki Klancher, took student researchers up to Wind River’s Dinwoody Glacier on the second annual Interdisciplinary Climate Change Expedition (ICCE), an eleven-day investigative adventure.  She was accompanied by Wyoming EPSCoR’s own Dr. Sarah Konrad, as well as archaeologist and CWC professor Todd Guenther. 

Outdoor Education students, led by instructor Darren Wells, provided valuable assistance comprised the ICCE Glacier team. They worked on projects both on and off the ice and worked in concert with the entire team to transport all of the equipment up and down the mountain.  As Klancher said, “It’s really a testament to the team’s skills that we all got up there, completed all of our research, gathered all of our data, and got everyone back down to the parking lot without any incident.  That’s got to be a fundamental consideration – how do you keep students safe.” 

One group of students focused on black carbon, dark particulate matter sometimes found on glacial ice.  Black carbon is related to industrial pollution and can increase snow temperature and accelerate snowmelt.  Students collected snow samples to test for the presence of black carbon and establish a baseline level that can be used to compare data from this coming year.  The team also hopes to use isotopic measurements which can allow scientists to trace the black carbon to its source.

ICCE team members on the move
(photo credit: Kyle Nicholoff)

Dinwoody Glacier is a popular backpacking and hiking site, and students wanted to test to see if human waste material had contaminated Dinwoody’s streams and surface waters.  Testing for E.coli on the mountaintop was a challenge, but two archaeology students found a creative solution: a chicken-egg incubator from Ace Hardware, small enough to carry up the mountain and perfect for housing E.coli cultures.  Next year, the team plans to return with laboratory-grade testing equipment, to expand on their research.  Student researchers also collected water and ice samples to test for temperature and acidity, and surveyed aquatic macroinvertebrate populations.

The ICCE team (photo credit: Kyle Nicholoff)

Guenther's archaeology team made several exciting discoveries on the mountaintop, including a buffalo jump at nearly 11,000 feet - the highest documented jump site in the Central Rockies.  The archaeology team also found what appear to be two Paleoindian camp sites just below the glacial moraine, showing that people were living immediately under the ice some eight to ten thousand years ago.  Researchers found what appear to be several stone cairns and a large store of stone tools.  They hope to return next year to continue their investigation of the site, and are excited to learn more about early human life at high altitude.  

The ICCE expedition also created several maps of the terrain.  Geospatial data collection using global positioning systems (GPS) and maps created using Geographic Information Systems (GIS)- is a significant component of the student research.   Students use GPS to translate data into visuals that they can then use to present their research.  In the future, these visual aids will be an essential part of journal articles and conference presentations will be essential; CWC’s students have a strong head start. 

Guenther pointed out that students are already reaping professional rewards: “We are hired by the BLM and other organizations to complete archaeological projects for them, data collection using professional grade GPS units and professional maps created using ArcGIS software– students who come out of this program are trained not only in archaeology but also GIS and that opens a number of doors for them, so they can take advantage of future opportunities.”

(photo credit: Kyle Nicholoff)

Next year, the team hopes to collaborate with UW’s Dr. Paul Johnson on collecting and analyzing surface water samples to test again for E. coli  Team leaders also hope to collect seismic data on the glacier.

Most of the focus, however, will remain on the students: “We hope to keep expanding, both to enhance the quality of the student experience and the quality of our data.”

By Jess White