USING SMALL SHIELD EDIFICES TO GAIN INSIGHT INTO THE VOLCANIC HISTORY OF IDUNN MONS, A POTENTIALLY ACTIVE VOLCANO ON VENUS

Idunn Mons (46.5°S, 215°E) is a ~200 km diameter large shield volcano on the eastern edge of Imdr Regio on Venus that has shown evidence for a thermal anomaly consistent with recent volcanism (Smrekar et al., 2010). Erupted materials here have predominantly manifested themselves as extensive, radiating lava flows and small shield edifices. Maximizing the scientific return of any data collected for Idunn Mons via a future Venus mission requires constraining stratigraphic relations as determined from the highest spatial resolution images currently available (i.e., Magellan SAR data). Here, we use the morphologic properties of small shields exposed on this volcano’s flanks to help determine gross stratigraphic relations. Specifically, following the methodologies of Kreslavsky and Head (1999) and Nypaver et al. (2018), we calculated radii, heights, and volumes for 17 small shields on the upper and distal flanks on the eastern side of Idunn Mons. Our results show there is an overall increase in all three properties moving away from the volcano’s summit. Specifically, edifice bases on the volcano’s upper flanks are roughly a factor of two smaller than those present on the distal flanks (i.e., ~1 to 1.5 km versus ~1.5 to 3 km, respectively). Edifice volumes near Idunn Mons’ summit are >>1 km³ whereas edifice volumes near Idunn Mons’ base range from >>1 km³ to ~8 km³. The difference in small shield properties is noticeable and, although it could be due to smaller edifices being constructed on the upper flanks of Idunn Mons (perhaps also a more explosive eruption style due to lower atmospheric pressure?), the noticeable abundance of large outpourings of magma from the summit suggest these edifices could also be partially buried. The additional observation that upper flank edifices have less distinct bases (i.e., more subtle radar backscatter changes) compared to those on the distal eastern flanks is consistent with the idea that upper flank shields are partially buried. This suggests multiple episodes of waxing and waning volcanic activity at this volcano where periods of volcanism that formed the small shields pre-dated at least some of the youngest eruptive episodes exposed at Idunn Mons. This suggests it is possible that more of these smaller edifices formed at Idunn Mons, but have been mostly to completely buried by subsequent volcanism.