The Pacific Ring of Fire: Source of Major Earthquakes and Volcanic Activity

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Volcanoes such as this one in Alaska are typical of subduction zones. Image credit: US Fish and Wildlife Service

Volcanic Activity Along the Pacific Ring of Fire

Two types of volcanic activity occur around the margins of the Pacific plate. At constructive margins, low-level submarine volcanism occurs through volcanic vents on the ocean floor. The volcanic material comes directly from the earth’s mantle and is typically dense, made of a rock called basalt. This creates additional oceanic crust.

At destructive margins, the heat and pressure of the subduction process melts the descending rock, which then rises to the surface to supply long chains of volcanoes in the over-riding plate. These volcanoes are made from recycled crustal rocks and are typically much more explosive than the volcanic vents found at constructive margins. In the Pacific, these zones generate the volcanic belts of the Aleutian Islands, Kuril Islands Japan, Philippines and the South Pacific/Northern New Zealand.

Earthquakes Along the Pacific Ring of Fire

The Pacific Ring of Fire is not only characterised by the presence of many of the earth’s most active volcanoes; it is also the location for around 80% of the world’s earthquakes according to National Geographic. And earthquakes along subduction zones are not just commonplace.

These zones are, in the words of geologist Roger Musson, “the only places where monster earthquakes can occur.”  Several of the largest earthquakes on record have occurred along the Pacific margin; most recently the 2011 Tohoku-oki ‘quake which struck with devastating effect off Japan. Smaller swarms of earthquakes also occur along mid-ocean ridges.

The aftermath of the San Francisco earthquake of 1906. Image credit: USGS

Although conservative margins are not characterised by significant volcanic activity, the immense strains which build up through lateral movement between plate boundaries will, when released, generate earthquakes – sometimes major ones. It was a rupture of the conservative margin which formed the western edge of the Ring of Fire — the San Andreas Fault zone, that caused the destructive M7.8 earthquake which devastated San Francisco in 1906 (USGS).

Pacific Ring of Fire

Given the configuration of plates and their relative rates of movements, the margins of the Pacific Ocean will continue to be afflicted by major earthquakes –  the USGS list of major earthquakes for 2012 shows 15 of at least M7.0. And the great lengths of the fault margins which are under water mean that areas even at great distance from the epicentre of a major earthquake are vulnerable to resulting tsunamis.

Sources

Musson, R. The Million Death Quake. Macmillan 2012.

National Geographic. Earthquakes. Accessed 11 March 2013.

Open University. How Plate Tectonics Work. (1997).

Smithsonian Institute. This Dynamic Planet – World Map of Volcanoes, Earthquakes, Impact Craters, and Plate Tectonics. Accessed 11 March 2013.

Tilling, R.I., Heliker, C. and Swanson, D. A. Eruptions of Hawaiian Volcanoes: Past, Present, and Future. Department of the Interior/U.S. Geological Survey Publication.  Accessed 11 March 2013.

USGS. Earthquake information for 2012. Accessed 11 March 2013.

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