Kaʻū News Briefs Thursday, June 21, 2018

     The volcano alert level was raised to Advisory and the aviation color code to Yellow in September 2015. It was noted that the increase in alert level did not mean an eruption was imminent or that progression to an eruption was certain. This episode of unrest lasted several years without progressing to an eruption, similar to the period of unrest from 2004 to 2009.
     Since late 2017, rates of earthquake occurrence and of ground motion related to inflation of shallow magma reservoirs have slowed to near background levels. Seismicity has continued to be low during the current activity on Kīlauea volcano. Recent motions recorded by GPS instruments on Mauna Loa are due to the M6.9 Kīlauea south flank earthquake on May 4 and subsidence at the summit Kīlauea Volcano, according to HVO. None of the activity on Kīlauea volcano has produced a detectable effect on Mauna Loa’s magmatic system.

Mauna Loa is quieter and hikeable for experienced explorers, with permits from Hawaiʻi Volcanoes National Park. USGS photo

     In the history of Mauna Loa, the largest active volcano on Earth, eruptions typically start at the summit. Within minutes to months of eruption onset, about half of the eruptions migrate into either the Northeast or Southwest Rift Zones. Since 1843, the volcano has erupted 33 times,  with intervals between eruptions ranging from months to decades. Mauna Loa last erupted 34 years ago, in 1984. Mauna Loa eruptions tend to produce voluminous, fast-moving lava flows that can impact communities on the east and west sides of the Island of Hawaiʻi. Since the mid-19th century, the city of Hilo in east Hawaiʻi has been threatened by seven Mauna Loa lava flows. Mauna Loa lava flows have reached the south and west coasts of the island eight times: 1859, 1868, 1887, 1926, 1919, and three times in 1950.
     HVO will suspend weekly updates on Mauna Loa and instead issue them monthly. Should volcanic activity change significantly, an update will be issued. Regularly scheduled updates are posted at hvo.wr.usgs.gov. Stay informed about Mauna Loa by following volcano updates and tracking current monitoring data on the HVO web page at hvo.wr.usgs.gov/activity/maunaloastatus.php or by signing up to receive updates by email at this site at volcanoes.usgs.gov/vns.

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     Even with all the activity, sulfur dioxide emissions from the volcano's summit have dropped to levels that are about half those measured prior to the onset of the current episode of eruptive activity. This gas and minor amounts of ash are being transported downwind, with small bursts of ash and gas accompanying intermittent explosive activity.

     For forecasts of where ash would fall under forecast wind conditions, consult the Ash3D model output here: volcanoes.usgs.gov/observatories/hvo/ash_information.html