Landscape evolution in the McMurdo Dry Valleys

1
Landscape evolution in the McMurdo Dry Valleys
Melvin Donaldson1 and Jaakko Putkonen2
1 Department of Bioengineering 2 Department of
Earth and Space Sciences, Mentor
The McMurdo Dry Valleys compose the largest
ice-free region in Antarctica. The understanding
of this area is key to the understanding of the
dynamics of the East Antarctic Ice Sheet (EAIS).
One major hypothesis suggests that the EAIS has
remained virtually unchanged since its creation
in the mid-Miocene1. Dated ash deposits in the
area are consistent with this stable ice sheet
hypothesis2. However, this hypothesis requires
abnormally low sediment erosion rates, which, if
confirmed, would be the smallest ever reported on
Earth.
The data was initially organized by numerous
variables to aid discovery of correlations. The
strongest correlations were among the slope of a
hill and the length of boulder trails on it.
Slope acts as a positive bound trail length
(fig. 3).
Fig. 5 Mean topographic diffusivities for all
methods and published values
The boulder trial methods present a minimum
bounding for the topographic diffusivity for the
area because the boulder trail calculations are
unable to account for transport volume and mass
below the half-centimeter size. For a discussion
of the other methods see Regolith Transport in
the Dry Valleys of Antarctica, Putkonen et al.
This project was an initial attempt at
understanding the mechanisms of sediment
transport in the McMurdo Dry Valleys. This data
has not been looked at before and there is not
much published research on quantizing these data.
As such, this project was a successful means of
evaluating the direction of the overall project.
We were able to use the boulder trail data to
support some logical variable correlation. What
we were unable to accurately calculate were
transportation rates. We compared the data of
this project with the data calculated in another
project of a different methodology and the data
differed significantly. As a result, we decided
to return to the field, this time to the glacial
moraines of Leavenworth and Mt. Adams to gather
comparative data and to further refine the
quantitative techniques. Upon returning to the
field sites in the spring the team should be able
to use the methods weve practiced in the new
field areas to bring to the original field areas.
This may lead to a return trip to the Dry Valleys
to collect additional data.
Fig. 3 Bounding action of hillslope on boulder
trail length separated by lithology
We also found a negative bound of the position
along a boulder trail and the concentration of
rock chips. Analysis required the development of
two independent equations relating the trail data
and the soil flux of the terrain where ? is
the topographic diffusivity, Vn is the volume of
the n-th transported pebble and d is the
transport distance. Two formulas were used to
serve as an error checking mechanism within the
calculations. Both equations were intended to
calculate the same value, but the pebble flux
arrives at the figure through the individual
transported material whereas the boulder flux
utilizes the total volume crossing the plane of
the source boulder. Though the range of these
values was large, the two formulas returned
similar values (fig. 4).
The research was guided by three questions
developed by the team. First, can we use
discovered boulder trails as a quantitative tool
for analysis and how? Second, how do the measured
transport rates for the Dry Valleys compare to
values measured elsewhere? And finally, what
impact do the measured values ultimately have on
current hypotheses of the formation of the EAIS?
In the 2004-2005 and '05-'06 Antarctic field
seasons, Jaakko Putkonen and his team visited the
McMurdo Dry Valleys on a data collection trip.
Data regarding sediment transportation relevant
to this project was collected using boulder
trails, a geological phenomenon so named by the
team. The boulder trails provided a visible
representation of erosion otherwise too slow to
be seen. The boulder trails were measured and
data regarding the features of the immediate
terrain were collected for the sake of
comparison. In addition, sample boxes that were
placed to trap sediment proved useful when paired
with before and after area images, to provide a
topographic means to quantify sediment transport.
Other data, unrelated to sediment transport but
pertinent to the project as a whole, was also
collected. This included topographic data used to
create images of the area, colluvium data used to
expand the understanding of glacial feature
formation, and sediment samples for 40Ar/39Ar
dating and comparison to current numbers.
Special thanks to the Washington NASA Space Grant
and Tracy Morrissey for support this summer, to
the Mary Gates Endowment for funding, and to
Jaakko Putkonen for his daily assistance and for
having me on the project. Also special thanks to
the Undergraduate Research Program for helping
coordinate my participation in the National
Conference on Undergraduate Research at the
Dominican University of California.
1Sugden, D.E., Summerfield, M.A., Denton, G.H.,
Wilch, T.I., McIntosh, W.C., Marchant, D.R., and
Rutford, R.H. 1999. Landscape development in the
Royal Society Range, southern Victoria Land,
Antarctica stability since the mid-Miocene.
Geomorphology 28, 181-200. 2Marchant, D.R.,
Denton, G.H., Swisher III, C.C., and Potter, N.,
Jr. 1996. Late Cenozoic Antarctic paleoclimate
reconstructed from volcanic ashes in the Dry
Valleys region, south Victoria Land. Geological
Society of America Bulletin 108, (2)
181-194. 3Putkonen, J., Rosales, M., Turpen, N.,
Morgan, D., Balco, G., and Donaldson, M. 2007.
Regolith transport in the Dry Valleys of
Antarctica.
Fig. 4 Tight grouping of corresponding flux
values around the line y x
When tabulated with the results from other
simultaneous methodologies, the calculated flux
values span three orders of magnitude
corresponding to smallest values recorded on
Earth (fig. 5).
Fig. 2 Boulder trail and the measurement process