Mauna Loa Volcano, Hawai`i Long Term Monitoring Data

Long-term Monitoring Data
| deformation | seismicity | gas |

Early morning view of lava erupting 
from Mauna Loa's northeast rift zone on July 6, 1975.

Detailed monitoring data is available only for Mauna Loa's last two eruptions, which occurred in 1975 and 1984. Earlier eruptions of the volcano preceded the invention and deployment of modern volcano- monitoring instruments.

The 1975 eruption was preceded by more than 12 months of irregular, but increased, seismic unrest and notable inflation of the summit magma reservoir. Late in 1974, HVO alerted Hawai`i residents to the possibility of a Mauna Loa eruption through extensive media reports. The volcano erupted in July 1975.

Prior to the 1984 eruption, the rate of intermediate-depth seismicity began to increase as early as 1980. This unrest led HVO scientists to forecast in 1983 that Mauna Loa was likely to erupt within the next two years. The eruption began in March 1984.

Since 1984, HVO's capability to detect unrest on Mauna Loa has increased markedly. Monitoring instruments on the volcano now include digital seismic stations, Global Positioning System (GPS) receivers, electronic tiltmeters, an ultraviolet spectrometer, fumarole temperature sensor, SO2 and CO2 gas sensors, and webcams. These remotely located instruments transmit real-time data via radio signals to HVO 24 hours a day, seven days a week.




Deformation


The plot below shows changes in distance across Mokuʻāweoweo, Mauna Loa's summit caldera, since 1974, as measured by continuously recording GPS stations. Increases in distance often indicate increased pressure in the magma reservoir beneath the summit area (inflation). For more information about the inflation-deflation cycles of magma chambers, see How Hawaiian Volcanoes Work.

Distance changes and earthquake counts in the summit area

Distance changes 
across the summit caldera of Mauna Loa. Red lines indicate eruptions in 1975 and 1984. 
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Distance changes across the summit caldera of Mauna Loa, as measured between MOKP and MSLP GPS stations (see map inset). Vertical thin red lines indicate eruptions in 1975 and 1984. Monthly earthquake rates are shown in black. Plots will be updated as necessary.

The large extensions associated with the 1975 and 1984 eruptions were caused by magma rising from the summit reservoir to the volcano's surface and accompanied by increased rates of seismicity. During the 1984 eruption, the summit area contracted and subsided rapidly as magma left the reservoir to feed the eruption along the northeast rift zone. When the eruption stopped, the summit magma reservoir immediately began to re-inflate. The inflation ceased in 1993; distances across the caldera decreased and the ground surface subsided from then until 2002.

In May 2002, years of slow contraction and subsidence abruptly changed to extension and uplift. GPS measurements and remote imaging revealed patterns of ground-surface motion that indicated renewed influx of magma into a complex shallow magma system below. The extension and uplift rates increased dramatically in July 2004, as a swarm of very deep earthquakes started. The high rates of inflation slowed dramatically in 2005 and continued to slow until completely ceasing by mid-2013. Inflation resumed in mid-2014. For information on the current status of Mauna Loa click here.

Spatial pattern of deformation

Horizontal velocities of ground motion
 on Mauna Loa from 2004-2005 measured with GPS.
This map shows horizontal velocities measured with GPS from 2004 to 2005, a period of rapid motion similar to 2014-2015. The arrows represent the speed (proportional to length) and direction of motion at both continuously recording and survey GPS stations on Mauna Loa. The ellipses at the arrow tips provide information about the uncertainty associated with the measurements. The pattern results from inflation of a complex magma reservoir beneath Mauna Loa's summit area.

InSAR image of 
ground surface motion near the summit of Mauna Loa during 2004-2005.  Each cycle of colored 
fringes represents about 3 cm of 
motion toward the satellite. The butterfly-shaped pattern of fringes centered on 
Mokuʻāweoweo indicates inflation of a complex magma reservoir beneath Mauna Loa.
Interferometric Synthetic Aperture Radar (InSAR) measurements capture the motion of the ground surface associated with the infilling of the magma reservoir from 2004-2005 in exceptional spatial detail. Each cycle of colored fringes represents about 3 cm of motion toward the satellite. The butterfly- shaped pattern of fringes centered on Mokuʻāweoweo indicates inflation of a complex magma reservoir beneath Mauna Loa.




Seismicity


Prior to Mauna Loa's most recent eruptions in 1975 and 1984, HVO's seismic network recorded significant changes in seismicity. In both instances a change from years with no earthquakes occurring beneath the volcano to a systematic and steady increase in the rate and magnitude of earthquakes beneath Mauna Loa took place. Both times the increased seismicity culminated in eruption.

Cumulative numbers of located earthquakes beneath Mauna Loa

Cumulative numbers of located earthquakes
beneath Mauna Loa, in the same area
as the maps below, since 1970. The graphs, from top
to bottom, show earthquakes that occurred in three depth ranges:  shallow (0 to
5 km deep), intermediate (5 to 15 km deep), and deep (more than 15 km deep).
Note the increase in shallow and intermediate depth seismicity preceding the
1975 and 1984 eruptions. The current network of seismometers provide greater
sensitivity than was possible in the past, so in order to directly compare the
rates of seismicity, these graphs plot only earthquakes with magnitudes greater
than 1.8.
Cumulative numbers of located earthquakes beneath Mauna Loa, in the same area as the maps below, since 1970. The graphs, from top to bottom, show earthquakes that occurred in three depth ranges: shallow (0 to 5 km deep), intermediate (5 to 15 km deep), and deep (more than 15 km deep). Note the increase in shallow and intermediate depth seismicity preceding the 1975 and 1984 eruptions. The current network of seismometers provide greater sensitivity than was possible in the past, so in order to directly compare the rates of seismicity, these graphs plot only earthquakes with magnitudes greater than 1.8. Plots will be updated as necessary.

In April 1974, following more than two decades of quiet at Mauna Loa, HVO seismologists recognized and reported increasing numbers of earthquakes beneath the volcano. In August 1974 a swarm of earthquakes occurred northwest of Mokuʻāweoweo, centered at intermediate depths of 5 to 8 km. In December 1974, a shallower earthquake swarm (depths less than 5 km) occurred beneath Mauna Loa's summit. In February 1975, after a brief lull in seismicity, the intermediate source region that had been the center of activity in August became active again, and the numbers of earthquakes steadily rose until an eruption began on July 5, 1975.

Mauna Loa was quiet for 3 years following the July 1975 eruption. Then in 1978, regional seismic activity resumed, with rates of seismicity at both shallow and intermediate depths gradually increasing in areas that were seismically active before the 1975 eruption. Seismicity rates ratcheted up in 1981 and then increased again in 1983. Shallow earthquake activity dramatically increased beneath the summit caldera in March 1984, three weeks before the eruption started on March 25.

Between April 1984 and 2004, seismicity returned to background levels and HVO only located approximately 30 earthquakes per year beneath the summit and upper flanks of Mauna Loa, with the exception of a swarm of small, deep earthquakes that occurred beneath the volcano's summit in late April 2002.

In July 2004, the numbers of earthquakes beneath Mauna Loa increased markedly. From July through December 2004, about 1,700 very deep, long-period earthquakes occurred beneath Mauna Loa. These earthquakes were located over 40 km below the surface, and was a different type of seismic swarm than had ever before been recorded beneath Mauna Loa. This swarm coincided with an increased rate of deformation interpreted as magma influx into the shallower reservoir about 4 km beneath the summit area. The increased rate of inflation continued for another year after the deep seismic swarm ended at the end of 2004. An eruption never occurred at this time and the seismic swarm and deformation were attributed to an intrusion of magma into the volcano.

Since 2005, seismic activity was near background levels until HVO started recording swarms of very small earthquakes in 2013. These earthquakes were initially occurring in the intermediate depth region northwest of Mokuʻāweoweo that first saw activity in August 1974, though they were below previous detection levels thanks to advances in the seismic network since that time. The rate of activity continued to increase through 2014 and 2015 with earthquakes mostly recorded beneath the summit and upper southwest rift.

For more information on current seismicity, see our pages on recent earthquakes in Hawai`i. For information on the current status of Mauna Loa click here.

Locations of earthquakes 
with magnitudes greater than 1.7. During the two years preceding the 1975 (top left) 
and 1984 (top right) Mauna Loa eruptions, shallow seismicity beneath Mokuʻāweoweo, 
the summit caldera, greatly increased. A cluster of 
intermediate-depth earthquakes northwest of the caldera also occurred prior to 
both eruptions. Recently (bottom plot), 
shallow and intermediate-depth seismicity indicative of an impending eruption has not 
occurred beneath Mauna Loa.  For more information on current seismicity, go to 
our pages on recent earthquakes in Hawai`i.
Locations of earthquakes with magnitudes greater than 1.7. During the two years preceding the 1975 (top left) and 1984 (top right) Mauna Loa eruptions, shallow seismicity beneath Mokuʻāweoweo, the summit caldera, greatly increased. A cluster of intermediate-depth earthquakes northwest of the caldera also occurred prior to both eruptions. Recently (bottom plot), the strength of shallow (less than 5 km deep) and intermediate (5-10 km)-depth seismicity to the last two eruptions has not occurred beneath Mauna Loa as of mid-2015. For more information on current seismicity, see our pages on recent earthquakes in Hawai`i . Plots will be updated as necessary.




Gas Monitoring


Monitoring volcanic gases can provide clues about the internal workings of an active volcano. In 2005, HVO installed gas monitoring systems to track changes in gas release from Mauna Loa.

A real-time ambient gas monitoring station located in Mokuʻāweoweo, (see photo below), measures fumarole (volcanic gas vent) and ambient air temperatures, as well as sulfur dioxide (SO2) and carbon dioxide (CO2) concentrations adjacent to the fumarole. Changes in gas emissions can signal a change in eruptive status; gathering SO2 and CO2 data as Mauna Loa activity increases can help track the movement of magma within the volcano.For information on the current status of Mauna Loa click here.

A real-time ambient gas 
monitoring station.
A real-time ambient gas monitoring station.