Earthquakes and Eruptions

There are a few examples suggest a connection between large earthquakes and volcanic eruptions. The most unambiguous case of triggering is the November 29, 1975 magnitude (M) 7.2 Kalapana, Hawaii earthquake, which was immediately followed by a small, and short-lived eruption at Kulauea volcano, Hawaii. In this case, the fault plane of the earthquake was directly beneath Kulauea Volcano. Kulauea is one of the most active volcanoes in the world, and erupted frequently in the decades before and after the 1975 earthquake.

Hawaii, Kalapana Earthquake, Tsunami, Volcano, Puna Ridge.

Mechanisms might be behind volcanic triggering by large earthquakes:
- Stress changes caused by large earthquakes may either compress or expand nearby magma reservoirs. In the former case, the compression could increase the reservoir pressure, while in the latter case, the expansion could cause tensile (opening) fractures, around the reservoir. Either way, conditions promoting eruption may become more favorable after a large nearby earthquake.
- High amplitude seismic waves passing through a magma reservoir may cause the nucleation of bubbles within the magma and/or the disturbance of previously stable layers within the reservoir. Bubble creation can increase magma pressure, and layer destabilization can cause reservoir “overturn” where dense layers of relatively gas-poor magma sink forcing gas-rich magma to rise. Either of these events could prompt an eruption.
- Violent shaking during large earthquakes can create landslides, fractures, and other major ground disturbances that can affect shallow magma reservoirs, such as Kilauea’s in 1975, that are poised to erupt anyway.

Conversely, volcanic activity is known to trigger earthquakes. For example, swarms of small earthquakes, rarely larger than M5, can accompany the upward movement of magma through the Earth's crust. Also, large volumes of magma that rise from deep within the lower crust to shallower depths are thought to perturb the stress field around a volcano, possibly triggering small earthquakes up to 25 km away.

World Map of Volcanoes, Earthquakes, Impact Craters, and Plate Tectonics