From Peter Slessenger
The article on volcanic hot spots and how they might be formed did not mention the effects on tectonic plates of the curvature of the Earth (8 March, p 32).
Our planet is an oblate spheroid, with a polar radius 21 kilometres less than its radius at the equator. This may not sound like much, but it means that the summits of Chimborazo, at 6310 metres above mean sea level, and Kilimanjaro, 5895 metres, which are both on the equator, are actually farther from the centre of the Earth than the top of Everest, which is 8848 metres above sea level but at 28° North.
As tectonic plates move around the globe, could the stresses caused by changes of curvature as they change latitude cause them to fracture, providing weak points for magma to reach the surface?
Reading, Berkshire, UK
