The Ring of Fire is a string of volcanoes and sites of seismic activity, or earthquakes, around the edges of the Pacific Ocean. Roughly 90 percent of all earthquakes occur along the Ring of Fire, and the ring is dotted with 75 percent of all active volcanoes on Earth.

The Ring of Fire is shaped like an approximately 40,000 kilometer (25,000-mile) horseshoe. A string of 452 volcanoes stretches from the southern tip of South America, up along the coast of North America, across the Bering Strait, down through Japan and into New Zealand. Several active and inactive volcanoes in Antarctica, however, close the ring.

Plate Boundaries?

The Ring of Fire is the result of tectonic plates, huge slabs of Earth's crust that fit together like pieces of a puzzle. The plates are constantly moving atop a layer of solid and molten rock called the mantle. Sometimes these plates collide, move apart or slide next to each other.

Convergent Boundaries

A convergent plate boundary is formed by tectonic plates crashing into each other. Convergent boundaries are often subduction zones, where the heavier plate slips under the lighter plate, creating a deep trench. This subduction changes the dense mantle material into magma or liquid rock. The magma rises through the crust to Earth's surface over millions of years, creating a series of active volcanoes known as a volcanic arc.

If you were to drain the water out of the Pacific Ocean, you would see a series of deep ocean trenches that run parallel to volcanic arcs along the Ring of Fire. The arcs create both islands and continental mountain ranges.

The Aleutian Islands in the U.S. state of Alaska, for example, run parallel to the Aleutian Trench. Both geographic features continue to form as the Pacific Plate subducts beneath the North American Plate. The Aleutian Islands have 27 of the United States' 65 historically active volcanoes.

Divergent Boundaries

A divergent boundary is formed by tectonic plates pulling apart from each other. Magma wells up as the old crust pulls itself in opposite directions, then cold seawater cools the magma, creating new crust. The upward movement and eventual cooling of this magma has created high ridges on the ocean floor over millions of years.

Transform Boundaries

A transform boundary is formed as tectonic plates slide horizontally past each other. Parts of these plates get stuck at the places where they touch, causing the rock to break or slip, suddenly pushing the plates forward and causing earthquakes. These areas of breakage or slippage are called faults. The majority of Earth's faults can be found along transform boundaries in the Ring of Fire.

The San Andreas Fault is one of the most active faults on the Ring of Fire. It lies on the transform boundary between the North American Plate and the Pacific Plate. Measuring about 1,287 kilometers (800 miles) long and 16 kilometers (10 miles) deep, the fault cuts through the western part of California. Movement along the fault caused the 1906 San Francisco earthquake, which destroyed nearly 500 city blocks.

Hot Spots

The Ring of Fire is also home to hot spots, areas deep inside Earth's mantle from which heat rises. This heat melts the rock above it. The melted rock, known as magma, often pushes through cracks in the crust to form volcanoes.

Mount Erebus, the most southern active volcano on Earth, sits over the eruptive zone of the Erebus hot spot in Antarctica. It has been consistently erupting since it was first discovered in 1841.

Active Volcanoes In The Ring Of Fire

Most of the active volcanoes on the Ring of Fire are found on its western edge. Krakatoa is an island volcano in Indonesia. Beneath Krakatoa, the denser Australian Plate is being subducted beneath the Eurasian Plate. An eruption in 1883 destroyed the entire island, sending volcanic gas, volcanic ash, and rocks as high as 80 kilometers (50 miles) in the air. A new island volcano, Anak Krakatau, has been forming with minor eruptions ever since.

Mount Fuji, Japan's tallest and most famous mountain, is an active volcano in the Ring of Fire. Mount Fuji last erupted in 1707, but recent earthquake activity suggests it could erupt again. Mount Fuji sits at a "triple junction," where three tectonic plates interact.

The Ring of Fire's eastern half also has a number of active volcanic areas. Mount St. Helens is an active volcano in Washington state. It lies on a particularly weak section of crust, which makes it more prone to eruptions. Its historic 1980 eruption lasted nine hours and covered nearby areas in tons of volcanic ash.

Popocatépetl is one of the most dangerous volcanoes in the Ring of Fire. The mountain is one of Mexico's most active volcanoes, with 15 recorded eruptions since 1519. Located close to Mexico City and Puebla, 20 million people live close enough to Popocatépetl to be threatened by a destructive eruption.