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Weathering & Erosion
After volcanic mountains reach the surface, they are subject to the effects of erosion; unless lava continues to flow, the whole mass could wear away. In the early stages of erosion, a fringing reef will fasten to the shore. In Hawaii, this happened to the Waikiki Beach in Honolulu. These fringing reefs eventually become separated from the shore by lagoons. This forms a barrier reef. Eventually erosion or submergence(Like at a sumbergent plate boundry) might completely overcome the island and the barrier reef might form an atoll. A atoll is a ring-shaped coral island forming a lagoon. When the top is completely worn away, it leaves a sandbar cutting across the volcanic cone deep below sea level.
Hawaii is able to ward off erosions easily because when volcanoes erupt,they are usually followed by a series of earthquakes that open fissures and allow magma to reach the surface. Initially, lava fountains, known as "curtains of fire," shoot streams of lava hundreds of feet into the air from many points along the fissure. Hawaiian flows are are not as powerful as others becuase the lava is extremely fluid, and the gases escape easily without the disruption of the lava into ash or cinders. Large floods of lava then flow down the mountainside, replacing the land that was eroded. Eruptions can last from a few days to ten months. Then they are often followed in two to three years by a flank eruption.
Stages Of Eroding Volcanoes