The Ring of Fire, Explained

What it is

The Ring of Fire is a nearly continuous, roughly 40,000-km belt of tectonic activity that follows the edges of the Pacific Ocean. It runs from the southern tip of South America up the west coasts of the Americas, across the Aleutian Islands, and down through Kamchatka, Japan, the Philippines, Indonesia and the southwest Pacific to New Zealand.

It is not a single fault or a single plate boundary. It is the combined edge of the Pacific Plate and several smaller plates (Nazca, Cocos, Juan de Fuca, Philippine Sea) against the continents and plates around them.

Why it exists

Almost the entire rim of the Pacific is subduction zone: dense oceanic crust bending down and sliding beneath the plate next to it. Subduction does three things at once. It locks the boundary fault (the megathrust) so that stress builds until it releases in a large earthquake. It drags the descending slab deep into the mantle, producing earthquakes as far down as 700 km. And it carries water down with the slab, which lowers the melting point of the overlying mantle and feeds a line of volcanoes — the “fire” in the name.

The stretches that are not subduction zones are transform faults, such as the San Andreas in California and the Alpine Fault in New Zealand, where plates grind horizontally past each other and produce their own large, shallow earthquakes.

What you can see on the map

Set “Show” to “everything up to here” and “Min magnitude” to 4.5. The Ring of Fire appears as a dense, unbroken line. Now raise the minimum magnitude to 7 or 8: almost every remaining dot is still on the Ring. Every earthquake of magnitude 9 or greater in the record — Chile, Alaska, Kamchatka, Sumatra, Japan — sits on it.

Switch the colour by looking at depth. Along the deep-ocean trenches the earthquakes are shallow and red; move inland from the trench and they get deeper — yellow, then blue, then violet — tracing the subducting slab as it sinks beneath South America, Japan, Tonga and the Sunda arc.

Does the Ring of Fire produce more earthquakes over time?

No. The rate of large earthquakes around the Pacific has been roughly steady over the century-plus of instrumental records. Clusters of great earthquakes — such as 2004–2011, or 1952–1965 — happen by chance in a process that is random on human timescales, and they are followed by quieter stretches. What has genuinely changed is our ability to detect and report earthquakes, not the earthquakes themselves.