Article,
Insights on rock abrasion and ventifact formation from laboratory and field analog studies with applications to Mars
Planetary and Space Science, 52 (1-3): 199--213 (2004)
Abstract
Wind tunnel studies are integrated with field observations to better
understand the processes and rates of rock abrasion on Earth and
Mars and how these factors affect ventifact morphology. The wind
tunnel work consists of controlled experiments at terrestrial and
Martian pressures in which known fluxes of sand are blown onto abradable
targets of various geometric shapes. Mass loss and dimensional changes
are measured and shape evolution observed as a function of total
sand flux, wind speed, target shape, and target composition. To provide
ground truth to these experiments, the same types of targets were
placed in a field plot at a Mojave Desert ventifact locality for
6 months and measurements and observations like those in the wind
tunnel were made. Weather data recorded by a co-located station provided
wind speed and direction during this time. These data and results
from the abraded field targets were compared to flute directions
of local ventifacts. Initial results from this work are: (1) initial
rock shape controls the rate of abrasion, with steeper faces abrading
faster than shallower ones, (2) targets also abrade via slope retreat,
with intermediate angled faces becoming shallower (flatter) at a
greater rate than initially flat or steep faces, (3) the direction
of maximum velocity winds exerts a greater control on ventifact flute
orientations than the direction of average velocity winds, (4) irregular
targets with pits or grooves abrade at greater rates than targets
with smooth surfaces, with indentations generally enlarging and faces
becoming rougher with time, and (5) there are many similarities between
the experimental and terrestrial ventifacts, as well as rocks interpreted
as ventifacts on Mars. The pitted and faceted appearance of many
Martian rocks is easily attributable to aeolian abrasion. Many Martian
rocks appear pitted or vesicular, characteristics which our laboratory
experiments show enhance abrasion. Although measured Martian wind
speeds are generally below those necessary to induce saltation, occasional
gusts above threshold may be sufficient for some rock abrasion. Ventifact
formation is potentially a common geomorphic process on Mars provided
there are sufficient supplies of sand and high velocity winds needed
for saltation. (C) 2003 Elsevier Ltd. All rights reserved.
