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Encircling the Pacific Ocean is a 25,000-mile horseshoe-shaped arc called the “Ring of Fire.” It’s an apt nickname—more than 75 percent of the world’s volcanoes can be found here. The Ring of Fire is also where 90 percent of earthquakes occur.
What makes the area so seismically restless? It’s because subduction is happening, where one tectonic plate is descending beneath another. It’s a process that also gives birth to volcanoes. The Ring of Fire, where more than ten plates interact in a series of subduction zones, is one long volcano factory.
Creating Volcanoes
 How does subduction cause volcanoes to form? Where a plate meets another plate, it can descend—or subduct—beneath it. As the seafloor plunges into Earth’s mantle, seawater causes the surrounding rock to melt, forming magma.
The lighter magma rises, some of it hardening within the crust. But some continues to rise, forming and filling magma chambers beneath Earth’s crust. As magma accumulates, pressure grows. If the pressure gets high enough, the crust can crack and the magma can spew in the form of a volcano.
Monitoring Volcanoes
Many of the 1,500 or so volcanoes active in the recent past could erupt again. Twenty are probably erupting right now. Fortunately, these days, eruptions rarely come as a surprise. Geologists use technologies to monitor whether magma is rising beneath a volcano—a sign that it could erupt.
GPS (Global Positioning System) and satellite radar technology can signal if rising magma is causing a volcano’s shape to change. Seismometers can detect earthquakes that rising magma can trigger. By monitoring a restless volcano 24 hours a day, geologists can determine if an area should be evacuated to keep people safe.
Continue to Types of Volcanoes. >>
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