ESS 101 Lecture Notes - Lecture 4: Uee, Tephra, Diorite
Document Summary
Morphology of a volcano is strongly controlled by the viscosity of the magma: the hawaiian shield volcano shown is composed of interlayered basalt flows, slope angles typically range between 7-10 for shield volcanoes. Age becomes progressively older to the northwest. The plate changed directions ~38mya from a north-south direction to a northwest-southeast direction. Hawaiian basalt flows can travel great distances from their linear vent because of the low viscosity of the flow. As the oceanic plate moves away from the hotspot, the crust begins to cool, causing its density to increase. The crust subsides causing the island to submerge relative to sea level, the volcanic island is subject to constant wave erosion as well. In tropical oceans, limestone reefs can form around the island where the water is shallow, eventually the volcano can become completely eroded leaving a fringing reef island defined as an atoll.