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).
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, as uplifted coral islands, 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 arise above a hotspot.
The size of volcanic islands usually ranges between 1 and 104 square kilometres (0.4 and 40 sq mi).  Volcanic 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, featuring rough or mountainous landscapes in their interiors and displaying a diverse array of summit elevations. Researches observed that the island will often be covered by dense tropical forest. The forests limit the use of the lands for settlement on many islands, therefore Communities, roads and houses were limited to develop along the coaster margin, as a result suffering from coastal hazards. On larger islands rivers can flow, resulting in flood hazards and delivering sediment, which can dominate coastal morphology. Tall volcanic islands are often surrounded by protective fringing or barrier reefs, creating lagoons.
A study focused on the vulnerability of volcanic islands to multi-risk natural hazards, which are expected to worsen due to climate change. These include not just volcanic eruptions, but also earthquakes, tsunamis, landslides, and severe weather events like hurricanes or typhoons. The unique geological and geographical characteristics of volcanic islands make them prone to these diverse hazards. The research highlighted the importance of implementing effective risk mitigation plans that include nature-based solutions to improve societal safety on these islands. These solutions 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.