Article,
AEOLIAN PROCESSES ON VENUS
EARTH MOON AND PLANETS, (1990)
Abstract
In this pre-Magellan review of aeolian processes on Venus we show
that the average rate of resurfacing is less than 2 to 4 km/Ga, based
on the impact crater size frequency distribution derived from Venera
observations, reasonable values of the impact flux, and the assumption
of steady state conditions between crater production and obliteration.
Viscous relaxation of crater topography, burial by volcanic deposits,
tectonic disruption, chemical and mechanical weathering and erosion,
and accumulation of windblown sediments probably all contribute to
resurfacing. Based on the rate of disappearance of radar-bright haloes
around impact craters, the rate of removal of blocky surfaces has
been estimated to be about 10(-2) km/Ga. Pioneer-Venus altimetry
data show that the average relative permittivity (at 17 cm radar
wavelength) of the surface is too high for exposure of soils greater-than-or-equal-to
10 cm deep, except for approximately 5% of the planet located primarily
in tessarae terrains. The tectonically disrupted tessarae terrains
may be sites of soil generation caused by tectonic disruption of
bedrock and the presence of relatively steep slopes, or they may
be terrains that serve as traps for windblown material. The overall
impression is that Venus is a geologically active planet, but one
dominated by volcanism and tectonism. On the other hand, theoretical
considerations and experimental data on weathering and transport
of surface materials suggest rather different conditions. Thermochemical
arguments have been advanced that show: (1) CO2 and SO2 incorporate
into weathering products at high elevation, (2) transport of weathered
material by the wind to lower-elevation plains, and (3) re-equilibration
of weathered material, releasing both CO2 and SO2. In addition, kinetic
data suggest a rate of anhydrite formation of 1 km/Ga, a value comparable
to the soil erosion rate on Mars, a planet with an active aeolian
environment. Experiments and theoretical studies of aeolian processes
show that measured surface winds are capable of moving sand and silt
on Venus. Assuming that there is a ready sand supply, the flux could
be as high as 2.5 x 10(-5) g/cm/s, a value comparable to desert terrains
on Earth. In an active aeolian abrasion environment, sand grains
could have lifetimes < 10(3) years. In addition, comminuted debris
may be cold-welded to surfaces at the same time as abrasion is occurring.
Magellan altimetry and SAR observations should allow assessment of
which model for venusian surface modification (active vs. inactive
surficial processes) is correct, given the global coverage, high
spatial resolution, the calibrated nature of the data, and the potential
during extended missions of acquiring multiple SAR views of the surface.
