Comparison of the shapes and sizes of seafloor volcanoes on Earth and “pancake” domes on Venus

Abstract

The fact that flat-topped “pancake” domes observed on Venus resemble flat-topped volcanoes on Earth's seafloor suggests that volcanic processes on the seafloor and on Venus may operate to construct volcanic forms with similar characteristics. To test this, the shapes and size distributions of terrestrial submarine volcanoes (seamounts) from several magmatic and tectonic provinces are quantitatively compared with those of venusian pancake domes. Seamount heights and diameters are highly correlated suggesting that there may be a universal mechanism for their growth. The 2014-point sample mean of the height-to-diameter ratio is ξ d = 0.10 ± 0.04. In contrast, heights and diameters of 52 pancake domes exhibit no obvious trend, and values of ξ d are as much as three orders of magnitude smaller, with a 52-point sample mean of ξ d = 0.02 ± 0.03. Seamounts with basal diameters d b < 10 km have flatness values (ratio of top-to-bottom diameter) that span the entire range between 0 (pointed cone) and 1 (truncated cone). Larger-sized seamounts tend to have small values of flatness, and more pointed tops. This is not true for pancake domes which show large flatnesses at all sizes. Additionally, seamounts have distinctive profiles with their flank slopes increasing in gradient toward the summit; flank slopes of pancake domes, however, commonly increase in gradient toward the base. With respect to sizes, the diameter distributions of the different seamount populations are consistent with a model in which the number of seamounts decreases exponentially with increasing diameter. The diameter distribution of 126 pancake domes, by contrast, is more uniform. Its mean is d b = 22 ± 13 km. This size is at least an order of magnitude larger than the estimated characteristic diameters of the seamount populations. Based on the above results, I conclude that seamounts have significantly different shapes and size distributions than venusian pancake domes that have been identified and measured to date. This suggests that one or more of the variables (e.g., magma composition, crystallinity, magma volume, effusion rate, cooling rate, pre-existing topography) governing their formation differs. In terms of shapes and size distributions, the small ( d b < 20 km) volcanic edifices first identified from Venera data are good morphologic matches to seamounts, and should be the focus of future work investigating the formation of comparable volcanic features in these two different planetary environments.