Since 1983 Kaj Hoernle has been studying a couple of hot spots: the Canary and Madeira Islands, two volcanic chains located in the Atlantic southwest of Gibraltar. Like other hot spots--Hawaii, for instance--these islands are thought to have been formed by narrow, pipe-shaped plumes of hot rock rising from deep in Earth’s mantle. Hoernle, a geochemist at GEOMAR, a marine geology institute in Kiel, Germany, has been measuring the chemical fingerprints of rocks on the islands. Last March he reported some bizarre results: those supposedly distinctive fingerprints look much like the ones of rocks found far away--on Mount Etna in Sicily, for instance, and as far off as Germany.
If the Madeiras and Canaries were formed by isolated plumes of mantle rock, why should their ratios of lead, strontium, and neodymium isotopes resemble ratios seen thousands of miles away? Hoernle has an idea: he thinks the hot spots are really ...
