Mini volcanoes are spotted

Almost 10 years ago, an unmanned submersible in the Japan Trench picked up a chemically curious sample of young alkali basalt. Further sampling and investigations of this and another site by Naoto Hirano of the Tokyo Institute of Technology and Scripps Institution of Oceanography in La Jolla, Calif., suggest to him and his colleagues that they may have discovered a previously unrecognized type of volcano. They call them "petit spots" (Science, DOI: 10.1126/sci ence.1128235). These tiny volcanoes are away from tectonic plate boundaries or midocean ridges. Furthermore, their lava appears chemically different from that of "hot-spot" volcanoes, such as ones from which the Hawaiian islands emerged. Geoscientists have long theorized that hot-spot volcanoes form from rising plumes of magma originating in the deep mantle. Trace elements and isotopic composition data from the petit spots, however, indicate that their lava comes from shallower, more diffused reservoirs of magma reaching the surface through flex-induced fractures in the plate.