Laboratory Studies - Dune Worlds: How Windblown Sand Shapes Planetary Landscapes - page 204

Fig. 17.16 Results of the flume experiments on barchan morphology,
showing the grading from the classic barchans at the bottom,up
through more teardrop and triangle/linear forms as the wind angle
diverges more, until the wing shapes (sometimes with two slip faces

dash see also Fig. 6.25 ) appear in reversing winds. Hooked barchans at
left form when one wind prevails much more than another. Image
courtesy of K. Taniguchi

sand grain hit the surface was also varied while holding
other variables constant. All of the experiments could be
reproduced under either terrestrial or planetary atmospheric
pressure conditions. The experimental runs produced a large
matrix of results that represented the first well controlled
documentation of both impacting grain and target condi-
tions for a variety of atmospheric conditions (Greeley et al.
1982; Greeley and Iversen 1985, pp. 112-118).
The results of the experiments demonstrated that sus-
ceptibility is directly proportional to both the cube of the
sand grain diameter and to the square of the velocity for the
impacting particles, which in turn means that the mass loss
from the target is directly proportional to the kinetic energy
of the impacting particle (Greeley et al. 1982; Greeley and
Iversen 1985, p. 115). This conclusion was in agreement
with earlier experiments by Dietrich (1977) that explored

the abrasion of natural materials by windblown dust. The
damage done to the target is thus primarily a function of the
energy that the impacting particle can impart at the point of
impact, but the resulting damage is also governed by the
strength of bonds present between the atoms that comprise
the target minerals (Dietrich 1977). The sand-slinging
experiment also demonstrated that the angle of impact
played a significant role in the amount of material abraided
from the target, consistent with inferences about the abra-
sion of rocks to form wind-shaped features called

'ventifacts'.
Some related experiments were performed by Marshall
et al. (1991) to explore the strength and adhesion of basalt
particles at Venus-like temperatures (see Sect. 14.6 ). Sim-
ilar experiments might usefully be performed on Titan
analog materials.