(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)
Seismologists are often asked the question, “Can large earthquakes trigger volcanic eruptions?” The short answer is yes, earthquakes and volcanic processes are closely linked, as suggested by the existence of the “ring of fire” of active volcanoes and earthquakes circling the Pacific Ocean.
A volcanic eruption occurs when the force of the magma plumbing system exceeds the force holding the rock together between the magma chamber and the surface. For earthquakes that are relatively close to an active volcano, the displacement of the earthquake itself can change the stresses around the magma chamber, possibly bringing the volcano closer to an eruption. Depending on the type of earthquake and the geometry of the fault, different areas around the earthquake source area may be subject to increased compression or relaxation. A nearby magma chamber that experiences relaxation of the crust above the chamber as a result of a large nearby earthquake would be more likely to erupt because less force would be required from within to push the crust apart.
In principle, large, distant earthquakes, like the magnitude-9 (M9) quake in Japan in March 2011, send seismic waves across the globe. Much like shaking up a soda pop can, passing seismic waves can induce bubble formation, density and/or viscosity changes, increasing the pressure within the magma chamber and possibly increasing the likelihood of an eruption of a distant volcano. Since the actual forces imparted on the magma chamber from distant earthquake waves are generally low with respect to the force imparted by the magma chamber itself, the magma chamber must already be poised for an eruption.
Globally, we see ample evidence for both types of triggering. In regions that have experienced a M9 earthquake or larger in the last 75 years (Kamchatka, Chile, Alaska, Indonesia), several nearby volcanoes in areas of relaxation from the earthquake erupted in the weeks to months after the earthquake. Mount Merapi, Indonesia, showed significant changes in activity following two local earthquakes (M6.3 in 2001, M6.3 in 2006). After the M7.9 Denali earthquake in Alaska, no volcanic eruptions were triggered, but earthquake swarms occurred at several distant volcanoes (Mount Rainier, Washington; Long Valley Caldera, California; and Yellowstone Caldera, Wyoming), suggesting a change in the respective magma systems in response to the passing seismic waves.
In Hawai`i, interplay between earthquakes and volcanic activity has been observed, but the details of the cause-and-effect are complex. M4-5 earthquakes are common under the south flank of Kilauea after intrusions within the Upper East Rift Zone. The 1868 M6.1, M7.0, and M7.9 earthquakes were likely triggered by the eruption of Mauna Loa that was occurring at the time. In contrast, the 1975 and 1984 eruptions of Mauna Loa were both preceded by moderate earthquakes (>M5) months in advance; however, it is unclear whether these events induced a magmatic intrusion or were triggered by an existing magmatic intrusion. The 1975 M7.2 Kalapana earthquake, which occurred on a fault patch under the entire Kilauea Summit and East Rift Zone area, was followed within hours by a short eruption at the summit of Kilauea. In addition, many of the patterns in activity within the magmatic system of Kilauea irreversibly changed after the earthquake, suggesting significant changes within the magmatic system.
Seismic waves from large, distant earthquakes (such as the Japanese earthquake) have produced few obvious changes in the magmatic systems of Kilauea or Mauna Loa. One exception was the cessation of a deep intrusion under Mauna Loa in 2004 after the passage of seismic waves from the 2004 M9.3 Sumatra earthquake.
When looking at whether eruptions are triggered by earthquakes, it seems clear that both large local earthquakes and large distant earthquakes can bring a volcano closer to eruption. If a volcano is already poised to erupt, the changing stress patterns may result in an eruption. More commonly, large earthquakes simply goose the magma plumbing system, producing earthquake swarms or changing the behavior of the magma plumbing system, but not triggering an eruption. Our understanding of the complex interaction between volcanism and seismicity will improve through the continued study of both seismology and deformation over a long period of time.
For a list of recent Hawaii earthquakes visit: tux.wr.usgs.gov/Quakes/quakes0…