HVO/USGS Volcanic Activity Notice http://hvo.wr.usgs.gov/activity/maunaloastatus.php Volcano: Mauna Loa (VNUM #332020) Current Volcano Alert Level: ADVISORY Previous Volcano Alert Level: NORMAL Issued: Friday, September 18, 2015, 5:12 PM PDT (20150919/0012Z) Source: Hawaiian Volcano Observatory Notice Number: 2015/H2 Location: N 19 deg 28 min W 155 deg 36 min Elevation: 13681 ft (4170 m) Area: HI Hawaii and Pacific Ocean Volcanic Activity Summary: HVO seismic stations continue to record elevated rates of shallow, small-magnitude earthquakes beneath Mauna Loa’s summit, upper Southwest Rift Zone, and west flank. For at least the past year, the rate of shallow earthquakes has varied but overall has remained above the long-term average. During this same time period, HVO has measured ground deformation consistent with recharge of the volcano’s shallow magma storage system. Together, these observations indicate the volcano is no longer at a background level of activity. Accordingly, HVO is elevating the Mauna Loa alert level to ADVISORY and the aviation color code to YELLOW. This increase in alert level does not mean that an eruption is imminent or that progression to an eruption is certain. Shallow earthquakes are occurring in locations similar to those that preceded Mauna Loa's two most recent eruptions in 1975 and 1984; however, the energy release of the recent earthquakes remains comparatively low. The current rate and pattern of ground deformation is similar to that measured during inflation of Mauna Loa in 2005, an episode of unrest that did not end in an eruption. It is possible that, as in 2005, the present heightened activity will continue for many months, or even years, without progressing to an eruption. It is also possible that the current unrest is a precursor to an eruption, as was the case prior to eruptions in 1975 and 1984. At this early stage of unrest, we cannot determine which of these possibilities is more likely. HVO continues to monitor the volcano closely and will report any significant changes. Stay informed about Mauna Loa by following volcano updates and tracking current monitoring data on the HVO web page (http://hvo.wr.usgs.gov/activity/maunaloastatus.php) or by signing up to receive updates by email at this site: http://volcanoes.usgs.gov/vns/ Recent Observations: [Volcanic cloud height] NIL [Other volcanic cloud information] NIL Remarks: Mauna Loa is the largest active volcano on Earth. Eruptions typically start at its summit and, 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 eruptions tend to have large eruption rates compared to Kīlauea, producing voluminous, fast-moving lava flows that can impact communities on the east and west sides of the Island of Hawai`i. Since the mid-19th century, the city of Hilo in east Hawai‘i 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. Improvements to the USGS monitoring networks under the American Recovery and Reinvestment Act (ARRA) have significantly improved HVO’s ability to detect unrest.

• published: 19 Sep 2015
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