Cross-section along the southern Kermadec-Tonga Arc. Each peak is a separate volcano, formed by magma generated by heating the Pacific Plate as it sinks into the Earth below the arc. This same effect creates terrestrial volcano chains, such as the Cascades and the Andes. This plot illustrates the distribution of hydrothermal plumes by plotting the relative concentration of very fine-grained particles (measured by the optical parameter &Mac198;NTU), usually metal sulfides that have precipitated from the hydrothermal plume. Volcanoes with a high concentrations of particles have orange-red plumes above their peaks in this illustration (such as Brothers and Macauley). Volcanoes with hydrothermal plumes are named. Names in yellow are principal targets of the New Zealand American Submarine Ring of Fire 2005 expedition.