Morphology of the island of Hawaii

Abstract

Digital elevation data for the island of Hawaii from the U.S. Geographical Survey gridded at 30 m spacing was used to generate a slope map, a shaded relief map, and plots that compare slope and elevation for each of the five volcanoes that compose the island.These computer- generated products are useful in analyzing the morphology of the sland. The volcanoes become steeper with increasing age. The five volcanoes, in order of increasing age, are Kilauea, Mauna Lao, Hualalai, Mauna Kea and Kohala; their average slopes are 3.3, 5.4, 6.6, 7.0, and 11.3, respectively. This relation apparently results from growth of the late, steeper alkali cap on the older volcanoes that include more viscous, thicker flows, flows that are smaller hence tend to pile up more near the summit vents, and volatile- rich lavas that commonly produce steep sided cinder cones at summit vents. The cause of the gentler slopes of younger volcanoes include the high proportion of exposed fluid lava flows from the shield building stage, the ponding of lava against earlier volcanoes, and the grading of lava to sea level; subsidence of the older volcanoes have cause these gently dipping near-seas-level lava flows to subside below the sea. Finally, steep erosional canyons have developed in large areas of the older volcanoes (notably Kohala). Virtually all of the major fault systems on the sland appear to be related to the upper parts of giant landslides, most of which are hidden below sea level on the submarine flanks of the volcanoes. These are generally normal faults in the tensional regime at the heads and upper parts of the landslides Subtle changes in slope hint at buried landslide related faults scarps that have been covered by subsequent lava flows. Major erosional canyons are present in only two places, each presumed to be in the amphitheaters of the major landslides. The probably formed in this setting because steam erosion is favored by the steep sloped generated at the heads of landslides. The slope map clearly displays two bands of steep slope on Mauna Kea that mark the terminal moraines at the edges of the last two advances of the Pleistocene ice cap.