Introduction to Volcanic Arc systems highlights the importance of understanding how subduction zones operate. For example, many of the Earth's most active ' Decade Volcanoes ' are associated with subduction zones. In addition, siesmicity associated with subduction zones may result in significant earthquake and tsunami hazards in contiguous areas.
Volcanism commonly is associated with the first two types of margins.
An example of the first type is the currently active Axial Seamount which lies on the Juan de Fuca Ridge off the coast of Washington. This web page focuses primarily on convergent margins. Topographic relief maps - surficial expression of convergence Background information . Use of satellite altimetry to predict global seafloor topography provides unprecedented morphological detail of the seafloor. Incipient oceanic spreading is evident in the Red Sea and Gulf of Aden .