Lowland Plains on Venus
The Venusian surface, masked by thick cloud cover, remained a mystery until the utilization of radar. Applying Synthetic Aperture Radar (SAR), the Magellan mission imaged 98% of Venus. Data revealed volcanism as the dominant process, as well as a terrain with interesting intermittent high standing regions, surrounded by the less dramatic lowland plains. Attention immediately centered on the highland regions, while the lowlands were relatively ignored. Dr. Zimbelman determined the flow field stratigraphy around Sekmet Mons Volcano, in Kawelu Planitia exposes a more complex and diverse lowlands landscape than initially thought and sheds light on this previously overlooked expansive region of Venus.
Dr. Zimbelman's work goes one step farther than simply mapping the Venusian low land surface; it involves deciphering the relationship between features including their relative geologic ages, as well as their direction and mode of formation. The area of study encompasses 30° – 50° latitude and 230° – 260° longitude (see Figure 1) where Sekmet Mons Volcano is the largest landform, measuring ~ 240 km in diameter and a height of ~ 2 km1. The heart of the study, however, focuses on discovering the relative age, texture, and source of the surrounding plains that exhibited lobe-like morphology, called the lobate plains, to better understand the region as a whole.
The lobate plains are the second youngest feature, preceded only by a few impact craters, of the investigated area. It was determined that the flows trend from the SW to the NE. Instead of just one volcanic source, the plains have multiple source areas: Seket Mons, Venilia Mons, which is another volcanic construct, and the intersections of major fracture zones1. The diversity of sources may reflect variations in eruptive style or represent different stages in a continuum of related volcanism1. The ambiguity regarding the situation represents a topic that needs further investigation.
Radar reveals the plains to be composed of pahoehoe, smooth or billowy basaltic lava, in contrast to the rougher textured a'a lava. Knowing the texture, researchers can refer to similar settings on Earth, called analogs, to define constraints for the lava flow conditions and make inferences on the lava flow rates and amounts. In this case, comparisons are made with Carrizozo flow in New Mexico that also has comparably large pahoehoe lava flows lava2. Using the history and knowledge of Carrizozo, it is hypothesized that the plains are more likely a result of moderate output of 50 to 500 m3/s over a long period of time, ranging between 14,000 and 1400 Earth years1. Applying these Kawelu Planitia-specific rates to the entire northern plains portion of the planet yields a resurfacing in 1.4 million to 140 thousand Earth years at the rate of 50 to 500 m3/s1. This estimate is consistent with the generally accepted concept, derived by various superposition studies and crater counts, that the current Venusian surface is relatively young compared to the other inner planets like Mercury and Mars.
1. Zimbelman, J.R., 2003. Flow field stratigraphy surrounding Sekmet Mons volcano, Kawelu Planetia, Venus. J. Geophys. Res. - Planets 108, E5, doi: 10.1029/2002JE001965.
2. Crumpler, L.S., Aubele, J.C., Zimbelman, J.R., 2007. Volcanic features of New Mexico analogous to volcanic features on Mars. In The Geology of Mars (M. Chapman, Ed.), pp. 95-125, Cambridge Univ. Press, Cambridge, UK.
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