The origin of the lowland plains remains a compelling question for Venus, and has only been made more so by the possibility of global resurfacing and by the presence of canali and large volcanic flow fields suggestive of extremely voluminous eruptions. A number of workers have suggested that some lowland plains such as Atlanta and Lavinia Planitia are current loci of mantle downwelling, citing such features as their bowl-shaped topography, the presence of ridge belts and other tectonic features suggestive of shortening, a distinct scarcity of volcanic constructs and coronae, and relatively large negative gravity anomalies and large ADC's [ Zuber, 1990; Bindschadler et al., 1990, 1992; Phillips et al., 1991; Squyres et al., 1992]. But many of the plains regions of Venus are not so easily characterized and require further investigation.
It may be that most, if not all, of the plains regions on Venus
are the result of a rapid volcanic resurfacing that occurred
m.y. ago. The possibility of such an ``event'' (which
may have occurred over several millions of years) presents a
challenge to our understanding of the mechanics of the eruption
and emplacement of magma, as well as the interior dynamics
required to create and extrude these plains lavas.