Volcanic island
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Geologically, a volcanic island is an island of volcanic origin. The term high island can be used to distinguish such islands from low islands, which are formed from sedimentation or the uplifting of coral reefs (which have often formed on sunken volcanos).[1]
Formation[edit]
In terms of plate movement theory: Due to plate movement, lava flows overflowing from the demise boundaries of colliding plates and growth boundaries between plates on the seafloor gradually rise upwards later to form submarine volcanoes. Submarine volcanoes continue to grow upwards during eruptions, and will be exposed to the sea surface to form volcanic islands. Submarine volcanoes begin as lava flows along the rift valleys of the ocean floor and gradually rise upward. Most of the magma from undersea volcanoes is cooled by seawater before it reaches the surface and is no longer active. Therefore, people have never really seen undersea volcanic eruptions. At best, they just see lava springs at the bottom of the ocean bubbling up with new magma to form new igneous rocks. Two members of an American diving expedition once risked their lives to explore the Hawaiian Islands volcanoes. At a depth of 100 feet below the surface of the water, they photographed rivers of lava constantly flowing out of undersea craters, rushing down the slopes of the volcano towards the deeper seabed while the temperature of the surrounding sea water was heated up to more than 100 degrees Celsius. Undersea volcanoes continue to grow upwards in eruptions and will expose themselves to the sea to form volcanic islands.
Volcanic islands are not formed only by volcanic eruptions in the ocean, but also by land-based volcanic eruptions. Inside some large crater lakes on land, some lava domes will form, and when these lava domes grow taller, they will poke out of the lake, similar to the case of the Elf Island in the Mezama Crater Lake.
Definition and origin[edit]
There are a number of volcanic islands that rise no more than 1 metre (3 ft 3 in) above sea level, often classified as islets or rocks, while some low islands, such as Banaba, Henderson Island, Makatea, Nauru, and Niue, rise over 50 metres (160 ft) above sea level.
The two types of islands are often found in proximity to each other, especially among the islands of the South Pacific Ocean, where low islands are found on the fringing reefs that surround most volcanic islands. Volcanic islands normally rise above a hotspot.
Habitability[edit]
Volcanic islands usually range in size between 1 and 104 square kilometres (0.4 and 40 sq mi).[2] Islands above a certain size usually have fresh groundwater, while low islands often do not, so volcanic islands are more likely to be habitable.
Many volcanic islands emerge from the deep abyss of the ocean, and feature rough or mountainous landscapes in their interiors and a diverse array of summit elevations. Researchers have observed that the island will often be covered by dense tropical forest. These limit settlement on the interior of many islands, forcing communities to develop along the coast.[3] Larger islands may have rivers, resulting in flood hazards. Rivers deliver sediment downstream, which can dominate the shape of the coast and contribute to erosion. Tall volcanic islands are often surrounded by protective fringing or barrier reefs, creating lagoons.[3]
The unique geological and geographical characteristics of volcanic islands make them prone to many natural hazards, which are expected to worsen due to climate change. These include volcanic eruptions, earthquakes, tsunamis, landslides, and severe weather events like hurricanes or typhoons. Studies have highlighted the importance of implementing effective risk mitigation plans that include nature-based solutions to improve societal safety on these islands. These involve leveraging natural processes and ecosystems to reduce hazard impacts. This can include the restoration of natural barriers like mangroves or coral reefs that protect against tsunamis and storm surges or the maintenance of natural water catchments that can mitigate flood risks.[4]
See also[edit]
- Archipelagic apron – Fan-shaped gently sloping region of sea floor found around oceanic islands
- Atoll – Ring-shaped coral reef
- Canary Islands – Spanish archipelago and region in the Atlantic Ocean
- Galápagos Islands – Ecuadorean archipelago and protected area
- Guyot – Isolated, flat-topped underwater volcano mountain
- Krakatoa Archipelago – Archipelago of volcanic islands in Indonesia
- Seamount – Mountain rising from the ocean seafloor that does not reach to the water's surface
- Submarine landslide – Landslides that transport sediment across the continental shelf and into the deep ocean
- Volcanic arc – Chain of volcanoes formed above a subducting plate
References[edit]
- ^ Murphy, Raymond E. (July 1949). ""High" and "Low" Islands in the Eastern Carolines". Geographical Review. 39 (3). American Geographical Society: 425–439. Bibcode:1949GeoRv..39..425M. doi:10.2307/210643. JSTOR 210643.
- ^ Condie, Kent C. (2022-01-01), Condie, Kent C. (ed.), "Chapter 2 – The crust", Earth as an Evolving Planetary System (Fourth Edition), Academic Press, pp. 9–37, ISBN 978-0-12-819914-5, retrieved 2023-12-28
- ^ a b Velmurugan, Ayyam (2008-01-01), Sivaperuman, Chandrakasan; Velmurugan, Ayyam; Singh, Awnindra Kumar; Jaisankar, Iyyappan (eds.), "Chapter 1 – The Nature and Characters of Tropical Islands", Biodiversity and Climate Change Adaptation in Tropical Islands, Academic Press, pp. 3–30, ISBN 978-0-12-813064-3, retrieved 2023-12-28
- ^ López-Saavedra, Marta; Martí, Joan; Planagumà, Llorenç (2023). "How Effective Risk Assessment and Management Is the Key to Turning Volcanic Islands into a Source of Nature-Based Solutions". Land. 12 (3): 686. doi:10.3390/land12030686. ISSN 2073-445X.
External links[edit]
- Micronesian culture: High island and low island cultures at Britannica.com. Retrieved 2011-09-22.