From Paul Vidanovich
The largest volcano in the solar system, Alba Mons on Mars, is diametrically on the opposite side of the planet from the very large crater Hellas Planitia. There are similarly good correlations for most of Mars’s other volcanoes. These observations may have a bearing on the coincidence of volcanic events with suspected meteor craters that were the subject of Matt Kaplan’s recent article (5 June, p 38).
Over the past few years, two large impact structures, one in Western Australia, the other in Antarctica, have been identified and roughly dated to the late Permian, a time when the land masses were connected, forming the southern part of the Pangaea supercontinent. This places these two craters very close together and antipodal to the Siberian traps that Kaplan mentions.
One possible explanation is that the impact generates waves that travel through the Earth’s crust and converge on the far side of the planet, where they cause both cracking in the crust and initial volcanic activity. Slower waves move through the Earth’s interior, where the changes in pressure they elicit will cause melting in those parts of the mantle where the rock is close to its melting point. These slower waves begin to converge at the core-mantle boundary and travel towards a point antipodal to the impact. This creates a conduit for the resulting plume of molten rock to follow.
Numerical modelling to test these ideas would be extremely interesting to see.
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