Hawaiian Volcano Observatory

Frequently Asked Questions about Mauna Loa

1. What does the name "Mauna Loa" mean?

The Hawaiian name "Mauna Loa" means "Long Mountain." This name is fitting, because the subaerial (above sea level) part of the volcano extends about 120 km (75 mi) from the southern tip of the Island of Hawaiʻi across the volcano's summit to the eastern coastline near Hilo. Mauna Loa lava flows have also advanced to the north-northwest, reaching the ocean at Kīholo and Puakū on the North Kona coast of the island.

Mauna Loa
2. How big is Mauna Loa?
Maunaloa Mauna Loa, the largest active volcano on Earth, rises about 4,170 m (13,680 ft) above the Pacific Ocean. But the submarine part of the volcano descends an additional 5,000 m (16,400 ft) to the sea floor, which is depressed by Mauna Loa's enormous mass another 8,000 m (26,250 ft). So, from its base to its summit, Mauna Loa is more than 17,000 m (56,000 ft) high.

Mauna Loa encompasses more than half the area of the Island of Hawaiʻi. It is larger than all the rest of the Hawaiian Islands combined.

3. Is Mauna Loa an active volcano? Will it erupt again?

Mauna Loa is an active volcano and it will erupt again.

4. How often has Mauna Loa erupted?

During the past 3,000 years, Mauna Loa has erupted lava flows, on average, every 6 years. Since 1843, Mauna Loa has erupted 33 times, averaging one eruption every 5 years.

Lava flows erupted from Mauna Loa since 1843 are depicted in red on the map at right. Dates, locations, durations, and other facts about Mauna Loa eruptions are compiled in "Summary of Historical Eruptions, 1843-Present."

5. Where on Mauna Loa is an eruption likely to occur?

Eruptions on Mauna Loa typically occur within Mokuʻāweoweo, a caldera (large oval depression) at the summit of the volcano, along one of its two rift zones (Northeast and Southwest), or from radial vents located on the north and west flanks, outside the caldera and rift zones. These features are shown on the map at right (click on map to enlarge it).

According to the USGS Fact Sheet, Mauna Loa—History, Hazards, and Risk of Living with the World's Largest Volcano:

Most of Mauna Loa's eruptions begin with lava fountains from a series of fissure vents in the summit region and then often migrate to vents down either rift zone.

All historically recorded Mauna Loa eruptions [33 since 1843] started in the summit area, and approximately half have stayed in the summit. Seventeen continued from vents in the volcano's rift zones, producing lava flows that covered broad areas on the lower slopes of the volcano. Seven flows from the Southwest Rift Zone reached the ocean along the west coast of Hawaiʻi within a matter of hours. In 1855-56 and 1880-81, lava from Mauna Loa's Northeast Rift Zone did not reach the ocean but covered land now within the city limits of Hilo.

6. When was the most recent eruption of Mauna Loa?

Mauna Loa erupted most recently in March-April 1984. Following more than two years of increased seismicity and summit inflation, the eruption began at 1:30 a.m., HST, on March 25, when a fissure opened in Mokuʻāweoweo, the volcano's summit caldera. By 4:00 a.m., the eruption had migrated into Mauna Loa's upper Northeast Rift Zone, where active fissures eventually reached the 2,835-m (9,300-ft) elevation. Fast-moving ʻaʻā flows advanced downslope, and, in a matter of days, lava was within 6 km (4 miles) of Hilo city limits. Fortunately, the eruption ended on April 15 before lava reached Hilo.

A more detailed narrative of Mauna Loa's "1984 Eruption: March 25-April 15" is posted on HVO's website.

7. Can HVO scientists forecast a Mauna Loa eruption?

Volcanoes often show signs of unrest—increased seismicity (earthquakes), deformation (inflation) of the volcano's summit and flanks, and emission of volcanic gases—days to months in advance of an eruption. For example, Mauna Loa exhibited inflation and elevated seismicity prior to its two most recent eruptions, with increased rates of seismicity beginning one year before Mauna Loa erupted in 1975 and two years before it erupted in 1984.

USGS Hawaiian Volcano Observatory scientists can detect and track these signs of volcanic unrest, but cannot forecast exactly when or exactly where lava will erupt on Hawaiian volcanoes until an eruption is about to happen. We do know, however, that all Mauna Loa eruptions since 1843 have started in the summit area of the volcano and then sometimes moved down one of its rift zones (see question #5 for more info).

From Mauna Loa—History, Hazards, and Risk of Living with the World's Largest Volcano: The USGS Hawaiian Volcano Observatory (HVO) has recently upgraded its monitoring networks to improve its ability to detect early unrest. Numerous seismic, GPS, and tilt stations across the flanks of Mauna Loa keep a vigilant eye on the mountain 24 hours a day.

8. What kinds of instruments are used to monitor Mauna Loa and other Hawaiian volcanoes?

The USGS Hawaiian Volcano Observatory has an extensive network of more than 200 ground-based instruments to monitor volcanic activity on Hawaiʻi's active volcanoes. These instruments include:

  • seismometers to record earthquakes and tremor
  • tiltmeters to track changes in slope and GPS receivers to track changes in elevation and position of the ground surface as the volcano deforms (in response to magma movement)
  • gas sensors to measure the quantity and composition of volcanic gas emissions
  • webcams, thermal cameras, and time-lapse cameras to record images of volcanic activity, often in remote locations
  • gravimeters and other geophysical tools to detect subsurface processes

HVO scientists also use space-based technology to supplement ground-based techniques to monitor Hawaiian volcanoes. Satellites orbiting Earth provide data that can be used to identify and monitor thermal energy (heat) sources, discern and measure surface deformation, and detect and track the distribution of eruption plumes (ash and gases). Some of these technologies include Global Positioning System (GPS), Interferometric Synthetic Aperture Radar (InSAR), and NASA Earth Observing 1 (EO-1) Satellite imagery.

HVO is also exploring the use of infrasound sensors and other tools to help us evaluate changes in the volcanoes.

The evolution of HVO's monitoring tools and techniques is summarized in The Story of the Hawaiian Volcano Observatory—A Remarkable First 100 Years of Tracking Eruptions and Earthquakes.

9. How can I stay informed about the status of Mauna Loa?

Go to the Mauna Loa Status Reports posted on HVO's website. At this time, these reports are posted monthly. But, if unrest on Mauna Loa increases, status reports and updates will be posted more frequently.

The Mauna Loa Status Reports include links to "Current Monitoring" and "Long Term Monitoring" pages where you can view recent and previous deformation (GPS and tilt) and seismic data and plots.

The plot above shows vertical motion of a GPS station on the southeast side of Mauna Loa's summit caldera from June 2014 to June 2015. For up-to-date plots, please go to Current Monitoring.

10. Is Mauna Loa expected to erupt soon?

No — an eruption of Mauna Loa is NOT imminent at this time.

If the status of Mauna Loa changes, the USGS Hawaiian Volcano Observatory will elevate the Volcano Alert Level and Aviation Color Code for the volcano (see next question for more information about these levels and codes), in addition to issuing public notices through news media and HVO's website.

11. What do the USGS Volcano Alert Levels and Aviation Color Codes mean?

The USGS uses a standardized alert-notification system for characterizing the level of unrest and eruptive activity at U.S. volcanoes for people on the ground and in the air (aviation). The Volcano Alert Levels used by USGS volcano observatories are intended to inform people on the ground about a volcano's status. NORMAL indicates that a volcano is in a background, or non-eruptive state ADVISORY indicates that a volcano is exhibiting signs of unrest above known background levels but does not indicate an eruption is either likely or certain. WATCH indicates a volcano is showing heightened or escalating unrest with increased potential of eruption; it can also mean that an eruption is underway but poses only limited hazards. WARNING indicates a hazardous eruption is imminent, underway, or suspected to be occurring (when visual observations cannot verify an eruption in progress).

Aviation Color Codes are used in conjunction with the Volcano Alert Levels to provide information about volcanic-ash hazards in the atmosphere for the aviation sector (for example, airlines, dispatchers, air-traffic controllers, and pilots).

12. Under what circumstances will the Volcano Alert Level for Mauna Loa be upgraded from NORMAL to ADVISORY?

There are two main reasons why USGS scientists change the Volcano Alert Level from Normal to Advisory: (1) increased seismicity (earthquake activity) and (2) deformation of the volcano above typically quiet, or background levels. Such increases mean that changes are occurring within the volcano's magma storage system.

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Updated: 23 June 2015 (pnf)