(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)
Just over a month ago, the Hawaiian Volcano Observatory (HVO) raised the curtain on its new website. The change was part of an overall update to how the U.S. Geological Survey’s (USGS) Volcano Hazards Program (https://volcanoes.usgs.gov) provides information to both the scientific community and the general public.
The new HVO website (https://volcanoes.usgs.gov/hvo/) provides a portal to a wide range of information about the two ongoing KÄ«lauea eruptions and current unrest on Mauna Loa. Other Hawaiian volcanoes are also featured on the website, including the island chain’s youngest and still submarine volcano, LÅ‘ihi.
Somewhat coincident with the debut of HVO’s updated website, eagle-eyed web surfers have noticed recent increases in earthquake activity at LÅ‘ihi. Although we have no seismic stations near LÅ‘ihi, which is centered 40 km (24 mi) southeast of PÄhala in Hawai‘i County’s Ka‘ū District, HVO has been tracking earthquake activity there from land-based seismic stations for over 50 years.
Indeed, since the end of February 2017, HVO seismic analysts have noted a slight uptick in the numbers of earthquakes near LÅ‘ihi. From January 2015 through February 2017, there was, on average, one located LÅ‘ihi earthquake per month. Since then, the rate of earthquakes has gradually increased. This month alone (as of June 22), there have been 51 located earthquakes in the LÅ‘ihi region.
Without permanent seismic stations at LÅ‘ihi—because the highest point of the volcano is still a kilometer (0.6 mi) under water—it is not possible to locate earthquakes there as accurately as we can at KÄ«lauea or Mauna Loa. However, we can state that the June 2017 earthquakes appear to be clustered roughly 10–12 km (6–7 mi) below sea level and extend from beneath the summit region of LÅ‘ihi to the south.
Interestingly, the roughly 170 earthquakes located in the area of LÅ‘ihi between 2010 and 2016 occurred away from the summit region. They were primarily beneath the northern flanks of LÅ‘ihi, and extended to significantly greater depths below the volcano. The significance of this difference is unclear.
As early as 1952, HVO scientists interpreted occasional earthquake swarms in the LÅ‘ihi region as reflecting active volcanism there. In fact, the earthquakes were key to recognizing that the seamount is actually an active volcano!
Earthquake activity alone does not conclusively indicate that LÅ‘ihi is erupting. But the locations of recent earthquakes directly beneath the volcano’s summit region plausibly suggest magmatic or volcanic origin, such as adjustments within the magma reservoir or volcanic edifice. We would, however, expect to see many more earthquakes associated with an eruption.
The most recent confirmed eruption of LÅ‘ihi occurred in 1996. That year, an energetic earthquake swarm began in July and quickly intensified, motivating a scientific expedition to LÅ‘ihi to seize an unprecedented opportunity to possibly observe a submarine eruption. Thousands of earthquakes, including over a dozen with magnitudes greater than 4.5, were recorded from beneath the summit and south flank of the volcano between July and September 1996.
Subsequent viewing and mapping of the LÅ‘ihi summit region showed that, consistent with magma movement from beneath the summit area, a significant portion of it had collapsed. Fresh pillow lavas and glassy fragments collected during submersible dives also confirmed the occurrence of an eruption.
Because LÅ‘ihi is still so deep beneath the ocean’s surface, the USGS regards LÅ‘ihi as a low- to very low-threat volcano. Thus, there are no immediate plans for additional monitoring instruments and our views of LÅ‘ihi for the foreseeable future will be strictly seismological.
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