Ocean Island Volcanoes: Genesis, Evolution and Impact

Book excerpt: Ocean island volcanoes constitute some of the most prominent and rapidly-formed features on Earth, and yet they cannot be explained by conventional plate tectonics. Although typically associated with intraplate settings (hotspots), these volcanoes also occur in different geodynamic settings (near mid-ocean ridges). The nature of ocean island magmatism is still the subject of intense debate within the geological community. Traditionally it has been linked to the presence of mantle plumes at depth (e.g. Hawaii), although the interaction with plate tectonics is also recognized to play a significant role (e.g. Azores, Galápagos). Magma compositions may range from basaltic to more differentiated, which consequently is accompanied by striking changes in the eruption style from effusive-dominated to highly explosive volcanism. Understanding how these magmas evolve and how volcanic processes act at ocean island volcanoes are key issues of modern volcanology. Moreover, the growth of ocean island volcanoes from their rise on the seafloor as seamounts, to island emergence and subsequent formation of shield volcanoes (and in some cases large caldera volcanoes) is governed by multiple interrelated changes. It is well known that competing processes model ocean island volcanoes during alternating and/or coeval periods of construction and destruction. The geological evolution of these volcanoes results from the balance among volcanism, intrusions, tectonics, subsidence/uplift, mass wasting, sedimentation, and subaerial and wave erosion. A better knowledge of the interplay between these processes is crucial to obtain a more comprehensive understanding of the evolution of such volcanoes, and to the eventual formulation of a unified model for ocean island evolution. Ocean islands are especially vulnerable to volcanic eruptions and other geological hazards on account of their typical small size, rough topography and isolation, which make risk management and evacuation difficult. Volcanic eruptions, in particular, may have a significant impact on local populations, infrastructures, economy and even on the global climate. It is therefore fundamental to monitor these volcanoes with complementary geophysical, geodetic and geochemical techniques in order to forecast future eruptions and their impacts. However, the assessment of volcanic hazards on ocean islands is challenging due to the large variety of phenomena involved (e.g. lava flows, tephra fallout, pyroclastic density currents, lahars, gas emissions). Different approaches are used to assess volcanic hazards, either based on empirical methods or sophisticated numerical models, focusing on a single phenomenon or the combination of different hazards. This Frontiers Research Topic aims to promote discussion within the scientific community, representing an important step forward in our knowledge of ocean island volcanoes in order to serve as a reference for future research.