Grain-Size Sampling and Characterization of Eolian lag Surfaces within Alpine Tundra, Niwot Ridge, Front Range, Colorado, U.S.A.

Abstract

A method was developed to sample vegetation-free eolian lag surfaces on the alpine tundra of Niwot Ridge, Front Range, Colorado, U.S.A. Using commercial duct tape, surficial soil materials from lag surfaces on terracettes were removed by pressing the tape onto the unvegetated surface. The procedure was repeated with a second strip of tape. Adhering materials were removed from the tape with boiling distilled water and then subjected to grain-size analysis. The first layer removed was quite coarse; the average percent of material coarser than −2 φ (larger than 4.00 mm) was 84% for the 15 samples analyzed. The second layer was less coarse; the average percent of material coarser than −2 φ (larger than 4.00 mm) was 44% for the 15 samples. The grain-size distributions of both layers complement the distribution of contemporary eolian deposits in the Front Range, i.e., there is very little overlap. These grain-size distributions of the lag surfaces are in marked contrast to those of the underlying material which was sampled at 0- to 1- and 4.5- to 5.5-cm depths. These two sample depths were less coarse than the lag samples and similar to vegetated surfaces on the ridge. The average of the percent of material coarser than −2 φ (larger than 4.00 mm) was 7.4% for the fifteen 0- to 1-cm samples and 10.2% for the fifteen 4.5- to 5.5-cm samples.

Comparisons of the clay/silt ratios from the two sets of underlying samples with those from other tundra environments suggest that the lag surfaces are areas of normal soil development that are suffering recent shallow surface stripping by the wind.