Volcano Watch — Can earthquakes trigger volcanic eruptions?

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 Kīlauea 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 Kīlauea Summit and East Rift Zone area, was followed within hours by a short eruption at the summit of Kīlauea. In addition, many of the patterns in activity within the magmatic system of Kīlauea 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 Kīlauea 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.

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Volcano Activity Update

A lava lake has been present within the Halema‘uma‘u Overlook vent over the past week, resulting in night-time glow visible from the Jaggar Museum. The lake, visible by Webcam, remains deep within the vent cavity, with minor spattering along the lake margin, and has risen slightly since last week.

After a decline in activity last weekend, effusion from vents in Pu‘u ‘Ō‘ō, on Kīlauea's east rift zone, picked up again on Monday, September 5, and began refilling Pu‘u ‘Ō‘ō's crater at a relatively rapid pace. As of this writing (Thursday, September 8), the accumulating lava had reached to within about 10 m (33 ft) of the east rim of Pu‘u ‘Ō‘ō, and appeared to be within about 5 m (16 ft) of low points on the west side of Pu‘u ‘Ō‘ō crater.

One earthquake beneath Hawai‘i Island was reported felt this past week. A magnitude-2.5 earthquake occurred at 6:13 p.m., HST, on Tuesday, September 6, 2011, and was located 10 km (6 mi) west of Mauna Kea's summit at a depth of 28 km (17 mi).