Just more than a month ago, the Hawaiian Volcano Observatory raised the curtain on its new website. The change was part of an overall update to how the U.S. Geological Survey’s Volcano Hazards Program (https://volcanoes.usgs.gov) provides information to 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 Kilauea eruptions and current unrest on Mauna Loa. Other Hawaiian volcanoes also are featured on the website, including the island chain’s youngest and still submarine volcano, Lo‘ihi.
Somewhat coincident with the debut of HVO’s updated website, eagle-eyed web surfers noticed recent increases in earthquake activity at Lo‘ihi. Although we have no seismic stations near Lo‘ihi, which is centered 40 kilometers (24 miles) southeast of Pahala in the Ka‘u District, HVO has tracked earthquake activity there from land-based seismic stations for more than 50 years.
Indeed, since the end of February 2017, HVO seismic analysts noted a slight uptick in the number of earthquakes near Lo‘ihi. From January 2015 through February of this year, there was, on average, one located Lo‘ihi earthquake per month. Since then, the rate of earthquakes gradually increased. This month alone (as of June 22), there have been 51 located earthquakes in the Lo‘ihi region.
Without permanent seismic stations at Lo‘ihi — because the highest point of the volcano is still a kilometer (0.6 mile) underwater — it is not possible to locate earthquakes there as accurately as we can at Kilauea or Mauna Loa. However, we can state that the June earthquakes appear to be clustered roughly 10-12 kilometers (6-7 miles) below sea level and extend from beneath the summit region of Lo‘ihi to the south.
Interestingly, the roughly 170 earthquakes located in the area of Lo‘ihi between 2010 and 2016 occurred away from the summit region. They were primarily beneath the northern flanks of Lo‘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 Lo‘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 Lo‘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 Lo‘ihi occurred in 1996. That year, an energetic earthquake swarm began in July and quickly intensified, motivating a scientific expedition to Lo‘ihi to seize an unprecedented opportunity to possibly observe a submarine eruption. Thousands of earthquakes, including more than 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 Lo‘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 Lo‘ihi is still so deep beneath the ocean’s surface, the USGS regards Lo‘ihi as a low- to very low-threat volcano. Thus, there are no immediate plans for additional monitoring instruments and our views of Lo‘ihi for the foreseeable future will be strictly seismological.
Volcano activity updates
This past week, Kilauea Volcano’s summit lava lake fluctuated in concert with summit inflation and deflation, with levels ranging 22-40 meters (72-130 feet) below the vent rim. On the East Rift Zone, the 61g flow remained active, with lava entering the ocean near Kamokuna. The new lava delta is approximately 3.2 acres in size, extending about 100 meters (328 feet) from the sea cliff. Scattered surface breakouts continue on the upper flow field just downslope of Pu‘u ‘O‘o. The 61g flows do not pose an immediate threat to nearby communities.
Mauna Loa is not erupting. During the past week, only a few small-magnitude earthquakes occurred beneath the volcano, primarily in the south caldera and upper Southwest Rift Zone at depths less than 5 kilometers (3 miles). A few earthquakes also occurred on the west flank of the volcano at depths of 0-13 kilometers (0-8 miles). GPS measurements continue to show deformation related to inflation of a magma reservoir beneath the summit and upper Southwest Rift Zone. No significant changes in volcanic gas emissions were measured.
Two earthquakes were reported felt on Hawaii Island during the past week. At 10:09 a.m. June 21, a magnitude-4.5 earthquake occurred 28 kilometers (17 miles) southeast of Hawaiian Ocean View at a depth of 38 kilometers (24 miles). At 6:43 a.m. June 19, a magnitude-2.5 earthquake occurred 9 kilometers (6 miles) southeast of Leilani Estates at 0 kilometer (0 mile) depth.
Visit the HVO website (https://volcanoes.usgs.gov/hvo) for past Volcano Watch articles, Kilauea daily eruption updates, Mauna Loa weekly updates, volcano photos, recent earthquakes info, and more. Call for summary updates at 808-967-8862 (Kilauea) or 808-967-8866 (Mauna Loa). Email questions to askHVO@usgs.gov.
Volcano Watch (http://hvo.wr.usgs.gov/volcanowatch/) is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists.
