react with water to form hydrated minerals.14 The hydration process in the downward moving slabs leads to production of a talc layer that reduces and stabilizes the sliding friction between adjoining plates. A just-right level of lubrication permits efficient movement of one tectonic plate under another. At these subduction zones, some basaltic slabs become hydrated. The newly hydrated minerals—silicates—are lighter than their nonhydrated cousins, and they have a lower melting point. Once these silicates