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BERKELEY, Calif., Sept. 5 () -- U.S. scientists say they've made a discovery that helps explain Earth's "hot spot volcanoes" that give birth to island chains such as Hawaii and Tahiti.Unlike volcanoes that emerge at collision zones between tectonic plates, hot spot volcanoes form in the middle of the plates.Most current theories assume a single upwelling of hot, buoyant rock rises vertically as a plume from deep within Earth's mantle -- the layer found between the planet's crust and core -- and supplies the heat to feed volcanic eruptions, the researchers said.However, some hot spot volcano chains are not easily explained by this simple model, suggesting a more complex interaction between plumes and the upper mantle is at play, researchers at the University of California, Berkeley, said.The Berkeley scientist detected previously unknown channels of slow-moving seismic waves in Earth's upper mantle that may provide an important piece of the puzzle in the formation of these hot spot volcanoes and other observations of unusually high heat flow from the ocean floor, a university release said Thursday.Using seismic data to create computer models of the Earth's interior, the researchers found channels where seismic waves traveled unusually slowly."We know that seismic velocity is influenced by temperature, and we estimate that the slowdown we're seeing could represent a temperature increase of up to 200 degrees Celsius [392 degrees F],[url=http://www.tymarc.com/]christian louboutin sale[/url]," study lead author Scott French, a UC Berkeley graduate student in earth and planetary sciences,[url=http://www.ksacinc.com/cheapgucci/?]cheap gucci bags[/url], said.Such seismic channels have been theoretically suggested to affect plumes in Earth's mantle, he said."We believe that plumes contribute to the generation of hot spots and high heat flow, accompanied by complex interactions with the shallow upper mantle," French said. "The exact nature of those interactions will need further study, but we now have a clearer picture that can help us understand the 'plumbing' of Earth's mantle responsible for hot spot volcano islands like Tahiti, Reunion and Samoa."