Nine in ten quakes crowd a 40,000-kilometre Pacific belt
The Ring of Fire—also Rim, Girdle, or Circum-Pacific belt—is a tectonic horseshoe of quakes and volcanoes about 40,000 kilometres long and up to 500 wide around most of the Pacific. It holds roughly 750 to 915 active or dormant volcanoes, about two-thirds of the world total, and hosts some ninety percent of Earth’s earthquakes.
It is not one structure but a chain of subduction zones: the Antarctic, Nazca and Cocos plates sinking beneath South America, the Pacific and Juan de Fuca plates beneath North America, the Philippine plate beneath Eurasia, and further arcs elsewhere. The belt in its present form is more than 35 million years old, though some segments have been subducting far longer, which is why extinct cones also sit inside the ring.
More than 350 of its volcanoes have erupted in historical times, and the four largest eruptions of the Holocene all happened here. Most of the active volcanoes above sea level are stratovolcanoes such as Mount St. Helens, built up from alternating layers of explosive debris and lava, often rich in andesite.
People noticed the pattern early. In 1825 the volcanologist G. P. Scrope described chains of volcanoes around the Pacific rim, and an account of the Perry Expedition to Japan in 1852 to 1854 placed the Japanese islands on a vast volcanic circle reaching from Tierra del Fuego to the Moluccas. Scientific American outlined the phenomenon in 1878, and in 1912 the geologist Patrick Marshall drew an Andesite Line through the south-west Pacific separating islands with different volcanoes and lavas, a boundary later extended and found to track the ring closely.
The name itself is a fossil. From Greek and Roman times until the late eighteenth century, volcanoes were thought to be caused by fires burning underground, and the label kept that idea even though nothing actually burns. Only with plate tectonics, developed from the early 1960s, did scientists explain why earthquakes and volcanoes cluster along the Pacific margins.
Source: Ring of Fire
