Geologically, avolcanic island is anisland ofvolcanic origin. The termhigh island can be used to distinguish such islands fromlow islands, which are formed fromsedimentation or theuplifting ofcoral reefs (which have often formed on sunken volcanoes).[1]
There are a number of volcanic islands that rise no more than 1 metre (3 ft 3 in) abovesea level, often classified asislets or rocks, while some low islands, such asBanaba,Henderson Island,Makatea,Nauru, andNiue, rise over 50 metres (160 ft) above sea level.
The two types of islands are often found in proximity to each other, especially among theislands of the South Pacific Ocean, where low islands are found on thefringing reefs that surround most volcanic islands. Volcanic islands normally rise above ahotspot orsubduction zone.
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 freshgroundwater, 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 toclimate 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]
