GL102 Lecture Notes - Lecture 11: Mid-Ocean Ridge, Subduction, Frederick Vine
Document Summary
The ridge crest, with sea floor moving away from it on either side, has been called a spreading axis (or spreading center). The sliding of the seafloor beneath a continent or island arc is termed subduction. The seafloor moves at a rate of 1 to 24 cm per year. Although this may seem to be quite slow, it is rapid compared to most geologic processes: hess"s original hypothesis was that seafloor spreading is driven by deep mantle convection. Convection is a circulation pattern driven by the rising of hot material and/or the sinking of cold material. Hot material has a lower density, so it rises; cold material has a higher density and sinks. If convection drives seafloor spreading, then hot mantle rock must be rising under the mid- oceanic ridge. Hess showed how the existence of the ridge and its high heat flow are caused by the rise of this hot mantle rock.
