How volcanoes work: magma chambers and eruption types
Magma becomes lava at the surface, building shields like Hawaii and stratovolcanoes like Fuji.
Magma below, lava above
Magma is molten rock stored 5 to 150 kilometers deep with 700 to 1,200 degree heat. Once it erupts it is called lava. Gas bubbles drive blasts, and silica above 60 percent makes thick sticky flows.
Shield volcanoes like Hawaii pour runny basalt and grow 10 kilometers from seafloor with gentle slopes of 8 degrees. Stratovolcanoes like Fuji stack ash and lava into steep 30 degree cones that explode every 200 years.
Where eruptions strike
About 90 percent of quakes and 75 percent of volcanoes ring the Pacific Ring of Fire, a 40,000 kilometer belt. There the ocean plate sinks 100 kilometers deep and melts, feeding 450 active volcanoes.
Iceland sits directly on the Atlantic rift and erupts every 4 years from 32 active systems. Scientists forecast blasts by 6 months of quakes plus sulfur gas doubling and ground swelling 10 centimeters yearly.
- Magma deep, lava on surface
- Hawaii shield grows 10 km tall
- Fuji stratovolcano, 30 degree cone
- Ring of Fire holds 450 volcanoes
- Iceland erupts every 4 years