Coral Reef and Volcanic Island Formation

How do volcanic islands form? Many oceanic islands get formed as a result of underwater volcanic eruptions Many islands found around boundaries of tectonic plates (but not all) Areas of active plate tectonic movement and volcanic activity known as hot spots

Hotspot Theory Hot spots are volcanic regions thought to be fed by underlying mantle significantly hotter compared to the surrounding mantle Occurs where one of earth’s outer tectonic plates moves over a hot part of the mantle Allows magma and lava to rise through the plates Produce large volcanic eruptions Also know as “mantle plumes”

Example of Hotspots: Hawaii Hawaiian islands are good examples of volcanic islands found around hotspots Hawaii was formed as a chain of seamounts Each island or submerged seamount is successively older toward the northwest Due to the northwest motion of the oceanic plate Older seamounts were once above sea-level but went below as the oceanic plate began to sink

Geology of Coasts The geology of coasts can vary depending on the terrain of the land Some coasts are sandy; others are rocky Beaches are formed as a result of loose sediments eroding from land Waves, tides, and precipitation can erode rock on the shore

Beaches vs Rocky Coasts Beaches are composed of sand (eroded rock), rock, and shell and bone fragments Delta – a landform found at the mouth of a river, carrying sediments to an ocean shore Topographically flat Rocky coasts formation dates back to ice age as Earth warmed and carved valley where ocean filled Fjord – a long, narrow inlet of the sea between high cliffs Iceland, Norway, Chile Topographically steep Beaches Rocky Coasts

Formation of Coral Reefs Coral reefs form when free-swimming coral larvae attach to submerged rocks on the edges of islands or continents Three different types of reefs: Fringing Barrier Atoll

Formation of Coral Reefs Fringing reefs – lie a few kilometers offshore and run parallel to the mainland Water shallow on shore side; deep on ocean side Florida Keys and Caribbean Barrier reefs – lie 20 – 50 kilometers offshore and are separated from the island by a channel Atoll – a string of coral islands that form a circle with a lagoon in the middle Found in Pacific Ocean