References

Boudette, E.L., R.F. Marvin, and C.E. Hedge. 1966. Biotite, potassiumfeldspar, and whole-rock ages of adamellite, Clarke Mountains, West Antarc-tica. (U.S. Geological Survey Professional Paper, 550-D.) Washington,D.C.: U.S. Geological Survey.

Delisle, G., and K. Fromm. 1989. Further evidence for a Cretaceousthermal event in north Victoria Land. Geologisches Jahrbuch (Han-nover), E38, 143-151.

Faure, G., M.L. Kallstrom, and TM. Mensing. 1984. Classification andage of terrestrial boulders in the Elephant and Reckling Moraines.Antarctic Journal of the U.S., 19(5), 28-29.

Faure, G., K.T. Wehn, J.M. Montello, E.H. Hagen, M.L. Strobel, andK.S. Johnson. In preparation. Isotope composition of the ice andsubglacial geology near the Allan Hills, Victoria Land, Antarctica. InR. Findlay (Ed.), Proceedings, Gondwana 8. Rotterdam: Balkema.

Halpern, M. 1971. Evidence for Gondwanaland from a review of WestAntarctic radiometric ages. In Research in the Antarctic. Washington,D.C.: American Association for the Advancement of Science.

Halpern, M. 1972. Rb-Sr total rock and mineral ages from the Mar-guerite Bay area, Kohler Range and Fosdick Mountains. In R.J. Adie(Ed.), Antarctic geology and geophysics. Oslo: Universitetsforla get.

Krenzer, H., A. HOhndorf, H. Lenz, U. Vetter, F Tessensohn, P. Miller,H. Jordan, W. Harre, C. Besang. 1981. KIAr and Rb/Sr dating ofigneous rocks from North Victoria Lake, Antarctica. Geologisches Jahr-buch, 41, 467-473.

Kyle, P.R., R.J. Pankhurst, and J.R. Bowman. 1983. Isotopic and chem-ical variations in Kirkpatrick Basalt Group rocks from southern Vic-toria Land. In R.L. Oliver, P.R. James, and J.B. Jago (Eds.), AntarcticEarth Science. Canberra: Austrialian Academy of Sciences.

Mensing, T.M. 1987 Geology and petrogenesis of the Kirkpatrick Bas-alt, Pain Mesa and Solo Nunatak, northern Victoria Land, Antarctica.(Unpublished doctoral dissertation, Ohio State University, Colum-bus, Ohio.)

Mensing, TM., G. Faure, L.M. Jones, and J . Hoefs. 1991. Stratigraphiccorrelation and magma evolution of the Kirkpatrick Basalt in theMesa Range, northern Victoria Land, Antarctica. In H. Ulbrich andA.C. Rocha Campas (Eds.), Proceedings, Gondwana Z Sao Paulo, Bra-zil: Universidade de Sao Paulo.

Mensing, TM., G. Faure, and L.M. Jones. In preparation. Cretaceousalteration of Jurassic volcanic rocks, Mesa Range, northern VictoriaLand. Earth and Planetary Science Letters..

Schmidt, D.L., and P.D. Rowley. 1986. Continental rifting and trans-form faulting along the Jurassic Transantarctic rift, Antarctica. Tecton-ics, 5(2), 279-291.

Short-term variationsin the rate of eolian processes,

southern Victoria Land,Antarctica

MICHAEL C. MALIN*

Department of GeologyArizona State University

Tempe, Arizona 85287-1404

In the absence of contemporary fluvial and other geologicaland biological processes capable of removing weathered mate-rial from rock surfaces, eolian abrasion acts as an importantlimit on the rate and magnitude of erosion in the antarctic colddesert. As noted in previous Antarctic Journal of the U.S. prog-ress reports from this study, the amount of abrasion dependson sediment supply, wind speeds and turbulence, and the het-erogeneity of target materials. Earlier reports were based onsingle-year observations at the 11 test sites scattered through-out the ice-free valleys and transantarctic ranges in southernVictoria Land (figure; Malin 1985, 1988). Only one site had morethan a single year of observation. In addition to providing spe-cific numerical values for short-term abrasion, Malin (1988) con-cluded, first, that abrasion rates determined from single-year

*Current address: Malin Space Science Systems, San Diego, California 92121

observations were probably not representative of long-term av-erages, although they indicated in general the order of magni-tude of abrasion, and, second, that field values were nearly twoorders of magnitude lower than laboratory measurements, re-flecting primarily the differences between duration and cumu-lative exposures for the two types of studies.

Samples deployed during the austral summer of 1983-1984were retrieved during the austral summer of 1988-1989, afterexposure for approximately 5 years. The 5-year sample suiteincludes three different materials (basalt, dolerite, and non-welded volcanic tuff) arrayed at five different heights above thesurface (nominally 7, 14, 21, 35, and 70 centimeters) facing fourorthogonal directions (oriented true north, east, south, andwest) at 10 sites, plus two materials (dolerite and tuff) at fiveheights and facing four directions from site 11, on the "blueice" adjacent to the Allan Hills. Sand collectors deployedthroughout the experiment, facing the same directions and col-lecting at the same heights, were also sampled; the results ofanalysis of these specimens will not be reported here.

Because the 5-year exposure included the effects that oc-curred during the single-year exposure, two computations weremade to assess the magnitude of the longer term average abra-sion. First, the 5-year exposures were divided by 5, weightingthe first year equally with subsequent years. Second, the single-year results were subtracted from the 5-year results, and theresulting value for the 4 years was then divided by 4, to separateeffects of the first year's abrasion from that which occurred inlater years.

On average, a minimum of 67 to 75 percent of abrasion meas-ured after 5 years occurred during the first year of the study.At some sites and in some directions, all the abrasion (to theability to measure mass changes) occurred during that singleyear, while at other locations and in other directions the firstyear's mass loss was less than the average of the remaining

1991 REVIEW 27

Computer simulated view of ice-free valleys of southern Victoria Land, Antarctica, showing locations of 9 of 11 test sites from an altitudeof approximately 15,000 meters over Marble Point, looking west. Wright Valley is in the center of the image, the Victoria Valleys are to theright (north).

years' mass loss. Despite the philosophical problems inherentin averaging such wildly variable data, it appears, averaging allheights, all directions, and all materials, that an order of mag-nitude more abrasion occurred during 1984 than in each of thesubsequent 4 years. This result is not surprising, because otherfactors (for example, the condition of the target racks and sandcollectors, the failures of automated weather stations, and soforth) had indicated that the winter of 1984 had been anoma-lous. In addition, simultaneous collection of sediment is con-sistent with this view; it indicates that significantly more ma-terial was in motion during 1984 than in subsequent years. Themass of sediment collected, the susceptibility of the target ma-terials known from both laboratory and field studies, and themagnitude of abrasion also suggest that sediment transportvelocities were much higher in 1984 than in the subsequent 4years.

Two sedimentological factors appear to play important rolesin determining where abrasion occurs: the availability of loose,wind-transportable debris and the small-scale configuration ofthe surface. As noted in earlier studies (Malin 1984, 1985, 1986,1988), surfaces mostly or partly covered with loose, wind-trans-portable material show the most abrasion: site 1, in the VictoriaValley dunes, and site 7, on the northern flank of central Wright

Valley east of Bull Pass and a few hundred meters above theOnyx River floodplain, experienced abrasion that was factorsof .2 to 5 greater than other areas. Site 6 (lower Wright Valleynear Lake Brownworth) and site 9 (upper Taylor Valley on Bon-ney Riegel above Lake Bonney), however, also show significantabrasion, and yet have much less freely mobile sediment. Sur-face configuration at these two sites probably contributes indi-rectly to enhanced abrasion in two ways. First, sand saltatingacross rock-strewn, armored surfaces attains greater kineticenergy (primarily because of higher rebound heights), and evena small amount is more effective in abrading. Second, coarsesand and gravel are often the only wind-transportable particlesexposed on such surfaces (owing to previous exportation offiner fractions), which require higher winds to move and, oncein motion, have greater kinetic energy owing to both largermass and higher velocities of transport.

The 5-year study confirms the conclusion based upon thesingle-year results that indicated that abrasion of rock targetswas occurring at site 11, despite the fact that the moving sedi-ment there was particulate ice. Although abrasion at the AllanHills site was the lowest of any site during 1984, the averageover 5 years, despite occasional burial by drifted snow, wascomparable to that at site 5 (eastern Asgard Range), site 8

28 ANTARCTIC JOURNAL

(North Fork, Upper Wright Valley), site 10 (Cirque 4, AsgardRange), and site 3 (northern Bull Pass). The average amount ofabrasion at site 11 (dolerite approximately 0.001 grams persquare centimeter per year and nonwelded tuff approximately0.01 grams per square centimeter per year or about 3 microm-eters and 80 micrometers, respectively) is a factor of 5 to 10 lessthan the estimate in Maim (1988) based on the single-year mea-surement and is consistent with codicils attached to that pre-vious estimate. Despite a fivefold increase in exposure, suchsmall values remain near the limit of experimental uncertainty;longer exposures presently underway should continue to re-duce this uncertainty.

In many environments, chemical and biochemical weather-ing of rocks is limited by the ability of the weathered materialsto be removed and transported away from the rock. Althoughslow in comparison to other environments, removal of weath-ered material from antarctic rocks in areas subjected to wind-transport of loose sediment appears to be sufficiently rapid tocontinually replenish fresh surfaces for further weathering. Inother areas, however, this is not the case, and weathering prod-ucts and silica and iron-oxide deposition "choke-off" weather-ing. The rates and amounts of abrasion determined in thisstudy may be combined with numerical and analytical studiesof chemical activity to further constrain rates of geomorphicmodification in Antarctica.

I am indebted to many people for their help with this re-search. Dean B. Eppler prepared the materials for, and partic-ipated in, deployment of the test equipment during the 1983-1984 field season. Michael A. Ravine assisted in recovery of theequipment during the 1988-1989 season. Diana Michna per-formed the pre- and postdeployment measurements. I am es-pecially indebted to numerous VXE-6 helicopter pilots and crewchiefs who enthusiastically supported this effort without sub-stantially adding to the abrasion of the test targets. This workwas supported under National Science Foundation grants DPP82-06391 and DPP 87-16505.

References

Malin, M.C. 1984. Preliminary abrasion rate observations in VictoriaValley, Antarctica. Antarctic Journal of the U.S., 18(5), 25-26.

Malin, M. 1985. Abrasion rate observations in Victoria Valley, Antarc-tica: 340-day experiment. Antarctic Journal of the U.S., 19(5), 14-16.

Maim, M. 1986. Rates of geomorphic modification in ice-free areas,southern Victoria Land, Antarctica. Antarctic Journal of the U.S., 20(5),18-21.

Maim, M.C. 1988. Abrasion in ice-free areas of southern Victoria Land,Antarctica. Antarctic Journal of the U.S., 22(5), 38-39.

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