Ventifacts and wind-abraded rock features in the Taylor Valley, Antarctica

An area north of Lake Fryxell in the Taylor Valley, Antarctica, was surveyed to determine the frequency of occurrence of rocks that show strong evidence of wind abrasion and ventifaction, which is defined here as rocks having well-developed faceting, to define their relative abundance in this area of the ice-free McMurdo Dry Valley system and to provide an indication of the role of wind as a geomorphic agent in this area. The orientation of abrasion-caused features (facets, keels, and grooves) with respect to the present day wind regime is also described. Rocks were examined on five linear transects ranging from 300 to 510 m in length. A total of 1324 rocks were examined. On average, 60% of all rocks exhibited distinct wind abrasion features with polish being the most common feature and polished rocks were distributed equally between survey lines, suggesting abrasion was ubiquitous in the study area. Approximately 4% of the rocks had distinct facets and/or keels, and fine-grained ultramafic peridotite-type rocks produced the most finely-featured forms (i.e., sharp facet edges and keels). A larger percentage, ≈ 12.5%, had grooves. Grooves were typically associated with a tabular form of mafic diabase-type igneous rock. The distribution of faceted ventifacts and grooved rocks was not uniform for the five transects, suggesting that the distribution mechanism for the surface rocks and the source areas determined, to a large extent, what form of ventifact could be produced at a location. The orientation of the grooves and dip directions of the facets indicates the direction of the abrasive winds had a strong westerly component, which coincides with the modern wind regime of winter katabatic flows that move down valley toward the Ross Sea. The orientation of the facets and grooves suggests that the rate of formation of the ventifacts proceeds at a pace greater than other surficial processes (e.g., down-slope soil movement, cryoturbation), which should tend to remove trends in the facet and groove orientations, or that the down-slope movement of the surface is approximately perpendicular to the wind allowing preservation of the alignment.