Hotspots on Venus and Earth: Topographic Comparisons

We use topographic profiles to establish well-understood terrestrial analogs to Venus' features. Specifically, using cross-correlation, we compare average profiles for terrestrial hotspots with those for uplift features, termed "regiones," on Venus. It has been proposed that terrestrial hot spots may have varying characteristics such as form of initiation, length and continuity of track, overlying plate type, rare gas isotopic ratios, and relative buoyancy. Based on the presence of these characteristics, only a minority of hotspot features are ranked as primary, or "Type I", corresponding to a deep origin. Hawaii, Reunion and Iceland fit the criteria for this primary status, but Yellowstone, picked as a representative for a continental hotspot, does not fall into this select group. Similarly, regiones have been classified based on associated features; specifically, whether they are rift-dominated (e.g. Atla, Beta), volcano-dominated (W. Eistla), or corona-dominated (Themis). Of particular interest is Imdr, which based on recent imaging by Venus Express, may actually be presently active. Using Magellan topography data for Venus, and ETOP05 for Earth, we analyze profiles for selected hotspots and regiones. For each feature studied, we form an average profile from 5 to 36 individual profiles across the feature. We cross-correlate these average profiles to determine degree of similarity between individual features and classes of features. Previously, we have considered the Hawaii, Reunion, and Iceland oceanic hotspots and Yellowstone, a hotspot beneath a continent on Earth. For Venus, we examine rift-dominated Atla and Beta regiones, and volcano-dominated W. Eistla regio. Yellowstone correlated only moderately well with the Earth's oceanic hotspots and Venus' regio, W. Eistla. Correlations of Hawaii and Reunion with Iceland are probably somewhat poorer than might be expected for a hotspot, due to the domination of the Mid-Atlantic Ridge and Iceland's proximity to Greenland. Atla and Beta correlated well with each other, but poorly with W. Eistla. The power spectra of average topographic profiles for Earth and Venus are found using Fourier analysis. As a group, the terrestrial profiles can be fit quite well with 5 or 6 Fourier components. Just 6 components are needed to fit Hawaii's average profile at the 95% level, whereas fully 16 are required to achieve the same level of fit for Atla, Venus' highest regio. Our immediate goal is to establish whether topographic analyses can reveal or confirm the proposed differences in classes of hotspots and regiones, and furthermore to establish if any similarities exist between terrestrial and venusian upwelling features. A longer-term goal will be to draw inferences as to the processes responsible for shaping Venus' surface.