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 (see map) now include digital seismic stations, Global Positioning System (GPS) receivers, electronic tiltmeters, an ultraviolet spectrometer, fumarole temperature sensor, SO2 and CO2 gas sensors, and a Web camera. These remotely located instruments transmit real-time data via radio signals to HVO 24 hours a day, seven days a week.

Mauna Loa Monitoring Network

Continuously recording instruments monitor deformation and seismicity on 
Mauna Loa. In addition to these sites, many other benchmarks are used in GPS 
surveys; they are reoccupied yearly or whenever necessary.
Continuously recording instruments monitor deformation and seismicity on Mauna Loa. In addition to these sites, many other benchmarks are used in GPS surveys; they are reoccupied yearly or whenever necessary.

Deformation

Summit deformation since 1974

The plot below shows changes in distance across Moku`aweoweo, Mauna Loa's summit caldera, since 1974, as measured by continuously recording GPS stations. The distance changes usually correspond to changes in pressure in the magma reservoir beneath the summit area. Distance increases with inflation (magma reservoir pressure rises) and decreases with deflation (magma reservoir pressure declines). For more information about the inflation-deflation cycles of summit magma chambers, see
How Hawaiian Volcanoes Work.

Distance across Moku`aweoweo

Distance changes 
across the summit caldera of Mauna Loa, as measured between MOKP and MSLP GPS stations (see map inset). 
 Red lines indicate eruptions in 1975 and 1984.
Distance changes across the summit caldera of Mauna Loa, as measured between MOKP and MSLP GPS stations (see map inset). Red lines indicate eruptions in 1975 and 1984.

The huge extensions associated with the 1975 and 1984 eruptions were caused by magma rising from the summit reservoir to the volcano's surface. 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, the slow contraction and subsidence abruptly changed to extension and uplift. GPS measurements and remote imaging revealed patterns of motion that indicated renewed influx of magma into a complex shallow magma system. The extension and uplift rates increased dramatically in July 2004, as a swarm of very deep earthquakes started. The high rates of inflation leveled off by 2009 and appear to have stopped by mid-2013.

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, the period of fastest motion since re-inflation began in 2002. The arrows represent the speed 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 radial velocity pattern results from inflation of a complex magma reservoir beneath Mauna Loa's summit area.

Interferometric Synthetic Aperture Radar (InSAR) measurements capture the motion of the ground surface associated with the infilling of the magma reservoir in the mid 2000's in exceptional spatial detail, as shown below.

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 
Moku`aweoweo indicates inflation of a complex magma reservoir beneath Mauna Loa.
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 Moku`aweoweo indicates inflation of a complex magma reservoir beneath Mauna Loa.

Seismicity

HVO's seismic network recorded significant changes in seismicity before the Mauna Loa eruptions in 1975 and 1984. Our short-term forecasts of these eruptions were based in large part on such precursory seismicity.

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 Moku`aweoweo and 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 August 1974 source region became active again, and the numbers of earthquakes steadily rose until the eruption began on July 5, 1975.

A period of quiescence followed the July 1975 eruption. Regional seismic activity gradually resumed, and in 1978, rates of seismicity at both shallow and intermediate depths increased. A swarm of intermediate-depth earthquakes that occurred in the same region as the August 1974 earthquake swarm was possibly the strongest indicator of volcanic unrest. Shallow earthquake activity dramatically increased beneath the summit caldera in March 1984, three weeks before the eruption started on March 25.

After the 1984 eruption, HVO located approximately 30 earthquakes per year beneath the summit and upper flanks of Mauna Loa until late April 2002, when a swarm of small, deep earthquakes occurred beneath the volcano's summit. Following this swarm, seismicity returned to low levels until July 2004, when the numbers of earthquakes increased markedly.

From July through December 2004, about 1,700 locatable earthquakes occurred beneath Mauna Loa. These long-period earthquakes were very deep-greater than 40 km below the surface-and created a type of seismic swarm that had never before been recorded beneath Mauna Loa. This swarm coincided with the increased rate of magma influx into the shallower (about 4 km deep) reservoir beneath the summit area. The increased inflation rate continued for another year after the deep seismic swarm ceased at the end of 2004.

Since 2005, seismic activity was near background levels until we started recording swarms of very small earthquakes in 2013. Before Mauna Loa's next eruption becomes imminent, we expect that rates of shallow seismicity will elevate to levels much higher than those currently observed. For more information on current seismicity, see our pages on recent earthquakes in Hawai`i .

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.

Locations of earthquakes 
with magnitudes greater than 1.8. During the two years preceding the 1975 (top left) 
and 1984 (top right) Mauna Loa eruptions, shallow seismicity beneath Moku`aweoweo, 
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 1.8. During the two years preceding the 1975 (top left) and 1984 (top right) Mauna Loa eruptions, shallow seismicity beneath Moku`aweoweo, 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, see our pages on recent earthquakes in Hawai`i .

Gas Monitoring

Monitoring volcanic gases can provide clues about the internal workings of an active volcano. In 2005, HVO installed two gas monitors atop Mauna Loa: a fixed-view ultraviolet spectrometer system and a real-time ambient gas monitor.

The fixed-view spectrometer "looks" south along the 1984 fissure within Moku`aweoweo, Mauna Loa's summit caldera. Continuous, real-time data from this instrument is telemetered to HVO. The small amount of SO2 currently released from Mauna Loa's summit area is below the detection limit of the instrument.

A real-time ambient gas monitoring station (see photo below), also in Moku`aweoweo, measures fumarole (volcanic gas vent) and ambient air temperatures, as well as sulfur dioxide (SO2) and carbon dioxide (CO2) concentrations adjacent to the fumarole. Because changes in gas emissions can signal a change in eruptive status, gathering SO2 and CO2 data while Mauna Loa is quiet is important to establish normal background levels for gases emitted from the volcano.

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