11/30/2022 0 Comments Johnston atoll![]() While the volcano is near sea level, a coral reef can develop that will attempt to keep growing near sea level. ![]() As such a volcano moves further away from the hotspot, eventually volcanic activity stops, and the once hot volcano cools down causing subsidence, while it also erodes to sea level. In the hotspot volcanism model, a tectonic plate moves over the top of a stable hotspot, creating a trail of volcanoes as the hotspot burns into the plate overhead. Most of the young islands were created by hotspot volcanism. The atolls were originally also young volcanic islands that subsequently experienced millions of years of subsidence and erosion. ![]() This type of island is known as an atoll, the volcanic base is entirely submerged and covered in coral and coral debris (including sand). Instead, these islands commonly consist of white coral sand islands in the shape of a large ring, surrounding a central lagoon. Others islands are tens of millions of years old, and these islands are usually no longer clearly volcanic in origin. Some of these islands are geologically young, such as the Hawaiian Islands, and include features such as volcanic craters and cones. These islands generally were built as volcanoes on the Pacific Ocean floor, growing from three miles deep to the ocean surface or further. The central Pacific Ocean basin contains only a few islands, and they are spaced apart over large distances. Image courtesy of the NOAA Office of Ocean Exploration and Research. Two guyots just south of Johnston Atoll in the monument that have cone features on their summits. ![]()
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