No. 88: Jul-Aug 1993
Hotspots are isolated areas of the earth's crust where there is an unusually large amount of basaltic volcano activity. At present, over 120 hotspots are recognized by geophysicists -- and they are not distributed randomly about the globe. In fact, many seem to be diametrically opposite one another, as described by M.R. Rampino:
"The observed number of antipodal hotspot pairs depends on the maximum allowable deviation from exact antipodality, At a maximum deviation of 700 km, 26% to 37% of hotspots form antipodal pairs in the published lists examined here, significantly more than would be expected from the general hotspot distribution. Two possible mechanisms that might create such a distribution include: (1) symmetry in the generation of mantle plumes; and (2) melting related to antipodal focusing of seismic energy from large-body impacts."
(Rampino, Michael R.; "Antipodal Hotspot Pairs on the Earth," Geophysical Research Letters, 19:2011, 1992.)
Similar Phenomenon. On the moon, the magcons (magnetic concentrations) seem to be located diametrically opposite large lunar impact basins. See ALZ3 in The Moon and the Planets. This catalog volume is described here.