Knowra Ring of Fire Ring of Fire A horseshoe-shaped belt of subduction zones around the Pacific Ocean holding about three-quarters of Earth's active volcanoes and most of its strong earthquakes.
Subduction : The sinking of a dense oceanic plate beneath another plate at a convergent boundary, recycling crust into the mantle. Every segment of the Ring of Fire is a subduction zone; the whole belt is the rim of subducting Pacific seafloor.
1815 eruption of Mount Tambora : The largest historical eruption, on Sumbawa in 1815, which caused the 1816 year without a summer. The ring's most violent event, produced by subduction beneath the Sunda Arc.
Mid-Atlantic Ridge : The divergent boundary where seafloor spreading builds new oceanic crust down the center of the Atlantic. Divergent volcanism is gentle and effusive, the opposite of the ring's explosive convergent eruptions.
Pacific Tsunami Warning System : The international warning network established in 1949 after a Hawaiian tsunami, now tracking the whole Pacific rim. Megathrust quakes on the ring generate tsunamis that cross the ocean, demanding shared forecasting.
Plate tectonics : The theory that Earth's outer shell is broken into moving plates whose boundary interactions drive earthquakes and volcanism. Before 1967 the ring was a pattern without a cause; plate tectonics explained why the rim burns.
Benioff zone : The inclined plane of earthquake foci tracing a descending slab from the trench down into the mantle. Deep earthquakes under Japan and South America outline exactly where Pacific plates descend.
1960 Valdivia earthquake : The largest earthquake ever recorded, magnitude 9.5, where the Nazca Plate subducts beneath Chile. Shows the ring's capacity for megathrust rupture along the Peru–Chile margin.
Hotspot volcanism : Volcanism from mantle plumes fixed relative to the plate above, as at Hawaii, far from any plate boundary. Hawaii sits inside the Pacific ring but owes its volcanoes to a plume, not subduction.
Earthquake engineering : The design of structures to withstand seismic shaking, codified most strictly in ring nations like Japan and Chile. Cities on the ring built their seismic codes around the recurring megathrusts beneath them.
Alexander von Humboldt : The Prussian naturalist who in the early 1800s noticed volcanoes clustered in belts around the Pacific. The first observation that Pacific volcanism forms a connected ring.
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