USGS: Slope map of Mauna Loa, including lava flows that have erupted since 1823 (gray), showing the estimated number of hours or days it took before the flow from the outlet space to the ocean or the maximum reach of a flow progressed. One stream moving down the steep slopes on the western flank of Mauna Loa reached the ocean within just three hours after the opening began to erupt in 1950. The fat numbers (for example 12Mm3 / d) are the average rate of lava effusion (lava eruption) in millions of cubic meters per day. Note: the west flank has the steepest slopes (red-orange areas), the shortest distance from the air to the ocean and the highest average effusion rate during eruptions, resulting in precious little time to warn residents during an eruption from the Southwest Rift Area of Mauna Loa.
(BIVN) A few days ago we reported that scientists were noticing a “slight increase” in deformation and seismicity at the Mauna Loa volcano. The USGS Hawaiian Volcano Observatory has followed up this detailed Volcano Watch article on the subject:
“When will Mauna Loa erupt next?” It was the title of a video presentation on Volcano Awareness Month released by the USGS Hawaiian Volcano Observatory (HVO) in January 2021. It was also the subject of discussion among HVO scientists last week after detecting minor changes in soil deformation and seismicity during the summit of Mauna Loa.
Mauna Loa is not currently erupting. However, there have been signs of increased unrest over known background activities since July 2019, when HVO raised its volcano alert level to ADVICE and its aviation color code to YELLOW.
Mauna Loa is the largest active volcano on earth and covers just over half of the island of Hawaii. It rises gradually to 4,170 m (13,681 ft) above sea level, and its long submarine flanks descend 5 km (3 miles) below sea level to the ocean floor.
Mauna Loa, like Kīlauea, has a top caldera and two active ravines stretching from its crest. Eruptions range from short to long in life and occur on the crest, on the southwestern or northeastern rift regions, or on the northern and western sides of the volcano.
History has shown that Mauna Loa eruptions can start with very little warning and produce high volume lava flows that cover long distances in short periods of time, affecting communities on the flanks of the volcano.
The last eruption of Mauna Loa began at its summit on March 25, 1984. A series of cracks subsequently opened up along the northeastern rift zone, feeding lava flows that came within 17 km within five miles of Hilo Bay. The eruption ended on April 15.
The fastest large-scale eruption from Mauna Loa in history began on June 1, 1950, when cracks opened from the upper Southwest Rift Area, producing a lava flow that traveled 24 km (15 miles) and the ocean in less if reached 3 hours. ! During the next 23 days, lava flows descended on both sides of the rift zone, flooding the coastal town of Ho’okena-mauka and occupying three places on the Māmalahoa Highway (HWY 11).
HVO seismometers last week recorded about 271 small (mostly below magnitude 2), shallow (less than 6 km deep) earthquakes on Mauna Loa, of which 226 were below the top and top sides. This is a relative increase in activity, but within the range of fluctuations observed over the past few years.
HVO’s modern seismic network can detect much smaller earthquakes. But even with this greater sensitivity, recent earthquake counts are still lower than those observed before eruptions in the past, and have occurred in bursts with quiet time in between. We expect shallow seismic activity to be sustained and sustained prior to an eruption.
The revision of data from 1984 may help to put recent observations into perspective. An immediate precursor to the 1984 eruption was a sudden increase in the number of small earthquakes and volcanic earthquakes. HVO’s seismic network recorded hundreds to more than a thousand earthquakes every day. In the hours before the 1984 eruption, seismic activity increased to the point that the astronomical telescopes at Mauna Kea, 42 km (26 miles) away, could not be stabilized due to the constant vibration on the ground.
HVO also uses remote monitoring features that were not available in 1984. Telemetered Global Positioning System (GPS) and tilt stations record continuous measurements of soil deformation showing slow, long-term inflation, consistent with magma supply to the volcano’s shallow storage system. A slight rise in the inflation rate at the peak that began in January 2021 continues.
Current monitoring tools also include high-resolution webcams, infrared audio arrays, span meters, gas emission sensors, and access to spatial radar and thermal imaging measurements.
So, when will Mauna Loa erupt next? It is not possible to “predict” the exact date and time. Geophysical measurements indicate that Mauna Loa’s magma storage system has been recharged since the eruption in 1984, and that there have been signs of increased unrest since 2019, but the next Mauna Loa eruption does not appear to be imminent. Nevertheless, the recent slight increase in seismic and soil deformation is a reminder that Mauna Loa is a ‘sleeping giant’.
Check out the virtual presentation by HVO geologist Frank Trusdell for additional information on the past, present and possible future of Mauna Loa.