Volcanoes are openings on the surface of a terrestrial object where materials from its interior can escape. On Earth, most volcanoes are found near tectonic plate boundaries, where interactions create openings for magma—melted rock, crystals, and gases—to emerge from the mantle. Others are found over hot spots, which may result from unusually hot plumes of magma in the mantle breaking through thinner regions of the lithosphere.
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Magma usually stays underground because of a balance between its upward pressure, the weight of the Earth’s crust above, and the crust’s rock strength. Landslides can reduce crust weight, while built-up gas pressure can strengthen magmastatic pressure.
Active volcanoes may be in the process of erupting or expected to erupt in the future, having done so within the past 11,650 years. Dormant volcanoes have no short-term eruption history, but are expected to erupt in the future, while extinct volcanoes lack the history and expectation.
Thin, runny flows spread quickly before cooling, producing expansive layers that build over time into wide shield volcanoes. The ejection and fast hardening of thicker lava flows and pyroclastic material create steep slopes and the characteristic cone shape of composite volcanoes.
Silicate-rich magma contains extensive molecular chains that trap dissolved gases like water and carbon dioxide. These gases build pressure until they violently escape, creating explosive eruptions. Low-silica magmas produce gentler eruptions categorized as effusive.
At converging oceanic-continental plate boundaries, the subduction of the oceanic plate introduces seawater that reduces the melting temperature of the overlying mantle. This causes it to melt into less dense magma, which can rise to fuel more volcanic activity.
The three major types of volcanoes—cinder cone, composite, and shield—each exhibit unique, lesser-known subterranean and surface features, including lava bombs, lahars, and spatter. Other types of volcanoes include lava domes, calderas, fissure volcanoes, and Maars and tuff rings.
The Natural Hazards Viewer allows users to map the locations of major natural hazards from 2150 BCE to the present. Advanced filters allow for various refinement methods, including volcano morphology, earthquake magnitude, tsunami height, deaths, and damage.
Abnormally hot magma rose through the crust and emerged from the seafloor, where it cooled and piled onto layers that became tall enough to form an island. As the plate moved, the existing island moved away and a new one formed over the hot spot, repeating for each Hawaiian island.
Reaching temperatures up to 1,000°C, these “clouds” carry thousands of kilograms of volcanic ash, gas, and rock near the ground away from volcanoes. Research shows these flows achieve speeds as high as 700 kilometers per hour by moving above a lubricating layer of gas.
These abrasive particles are hazardous to aircraft. They can melt within engines and re-solidify on turbine blades, preventing forward propulsion. If inhaled, chemicals within ash can be toxic, and the particles can embed themselves into the lungs' ducts, causing suffocation.
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