Long-term Boulder and Rock Fragment Weathering in McMurdo Dry Valleys, Antarctica

Wednesday, 17 December 2014
Jaakko Putkonen, University of North Dakota, Harold Hamm School of Geology and Geological Engineering, Grand Forks, ND, United States, Daniel J Morgan, Vanderbilt University, Earth and Environmental Sciences, Nashville, TN, United States and Greg Balco, Berkeley Geochronology Center, Berkeley, CA, United States
Antarctica has some of the slowest rock weathering and regolith erosion rates on Earth. In the ice free areas the erosion rates have been consistently slow for the past few million years. Therefore we can observe the products of the slow in situ disintegration of the rocks. The resulting regolith and dispersal patterns reflect long period of time and yet the resulting rock chips are still clearly observable.

As the surficial boulders weather and break the chips fall next to the boulder. On a slope the chips are slowly transported downhill along with other eolian driven regolith. In this environment the breakdown of the rocks and the subsequent transportation are so slow that many of the chips can still be observed next to the boulder and in case of a locally rare lithology they form a distinct trail downslope of the source boulder. In McMurdo Dry Valleys we observed tens of in situ weathering boulders that had distinct chips on the downhill side forming a trail.

We found that the length of the dispersal patterns generally increase with the slope angle. We modeled the weathering rates of source boulders and resulting fragments, and the transport rates, constrained by observations of dispersal patterns and fragment characteristics. We determined that the source boulders spall a fragment over 250 times more often than the resulting fragment re-breaks.