Electrical properties of eolian sand and silt

A review of observed and theoretically expected electrical properties of eolian sand, silt and dust reveals that little attention has been directed by geologists and geophysicists toward sand and silt even though much research on dust has demonstrated the importance of electrical charging. Potential mechanisms for non-uniform charging and/or polarization of sand and silt particles include (1) polarization by Earth's atmospheric electric field, (2) triboelectrification, (3) contact electrification, (4) cleavage/fractoelectrification, (5) radiation (X-rays, gamma rays, UV and visible) and charged particle bombardment electrification, (6) pyroelectrification and (7) piezoelectrification. Electrical charges may have significant effects upon sand and silt behavior during transport, deposition and, subsequently, at rest. These effects include greater mobility during particle repulsion, aggregation and greater stability after particle deposition. Charged particles in Earth's electromagnetic field also may add or subtract from the effect of Earth's gravitational field, depending on net sign of charge. Electric charge retention among grains at rest may be much greater than intuitive inference suggests and may be a major factor in explaining larger angles of repose in ancient sediments compared to present sediments. Although light and acoustical emissions during sand and silt transport have long been recognized and at times inferred to be due to electric discharging of grains, no scientific models or explanations have been proposed which adequately explain these phenomena. Charges on individual grains are expected to range from 10 −1 to 10 2 pC, but never have been measured under field conditions. During a sand storm, field strength arising from the cumulative effect of grain charges can be expected to range from 10–30 kV/m. Many additional data need to be accumulated and more detailed research performed before an adequate electrical model for sand behavior during transport and deposition, as well as at rest, can be formulated. All major empirical observations, including relative contributions by various charging mechanisms and associated light and acoustical emissions, should be predicted accurately by an acceptable model for electrical charging of eolian sand and silt.