A powerful 1975 earthquake caused Hawaii's Kilauea Volcano to erupt.
Volcanoes produce seismic activity as well as being affected by seismic events such as earthquakes. The question of which comes first --- an eruption or a quake --- can be as puzzling as the old chicken-vs.-the egg mystery. Furthermore, not all earthquakes incite or are related to volcanic action. But the Pacific Disaster Center notes a strong relationship between the two.
Releasing Magma
Maps of earthquake locations throughout the world show volcanoes in close proximity, the Pacific Disaster Center says. They both occur at the edges of tectonic plates, which are huge slabs of the earth's crust --- both on land and under the ocean --- that slide, bump into each other and pull apart again.
When the plates move, pressure is released from inside the earth, creating earthquakes. Volcanoes form from magma (molten rock also called lava) that breaks through the earth's crust at plate boundaries. Movement of magma within existing volcanoes is one cause for many of the world's earthquakes, but usually small ones with a magnitude of 3 or less. The United States Geological Service (USGS) says that sometimes these earthquakes are the only sign that a volcano "is becoming restless."
Predicting Eruptions
An instrument called a seismometer is used to measure both earthquake and volcanic movement. By locating numerous seismometers within 12 miles of a volcano's vent, scientists can detect small earthquakes related to the volcano. These quakes are caused by shifting crust under the volcano and around its base as well as from the movement of magma within its cone. Almost all volcanic eruptions in Hawaii are preceded by an increase in earthquakes, according to the USGS. If sizeable enough, an earthquake can also cause an eruption. Hawaii's magnitude 7.2 earthquake in November 1975 not only created "remarkable ground movement," the USGS says, but also a tsunami and the eruption of Kilauea Volcano.
Producing Champagne Effect
Earthquakes can shake up the magma in volcanoes, creating a pop-the-cork explosion that scientists affiliated with Oxford University refer to as the "champagne effect." Their 2008 study was titled "The Influence of Great Earthquakes on Volcanic Eruption Rate Along the Chilean Subduction Zone." A report about the study in the "The Sunday Times" of London says that "volcanoes erupt up to four times more often after a large earthquake than they would without the seismic agitation." The Oxford research team based this conclusion on historical records of eruptions occurring over 150 years in southern Chile.
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