Why volcanoes line up along plate edges
Zoom out and the volcanoes trace the same lines as the plate boundaries. Around the Pacific they form the Ring of Fire, a chain of arcs above subduction zones where ocean floor sinks into the mantle. Water squeezed out of the sinking plate lowers the melting point of the rock above it, and that melt rises to feed volcanoes like Fuji, Merapi and Villarrica.
A second family sits on divergent boundaries: Iceland on the Mid-Atlantic Ridge and the volcanoes of the East African Rift. Most ridge volcanism is hidden on the seafloor. The rest are hotspots, such as Hawaii, Galapagos and Yellowstone, fed by plumes rising from deep in the mantle.
About this data
Volcano locations, types and last eruption dates come from the Smithsonian Global Volcanism Program's Holocene volcano list. "Erupted" years are the latest confirmed eruption in that list, so an eruption that started this week may not appear yet. For current activity, check the Smithsonian/USGS Weekly Volcanic Activity Report.