Volcanoes may either never be active enough to break the surface of the ocean or be sufficiently active to break the surface and form an island. The island may also be so heavy that it eventually sinks and forms a seamount. Thousands of these seamounts have been discovered and studied worldwide to help provide evidence of past and current tectonic processes. In this investigation, students analyze Hawaiian and Alaskan seamount/island chain maps and data tables, plus a demonstration to develop an explanation to the phenomenon: How do seamounts and island chains form in the middle of the ocean?