Hawaiian Volcano Observatory

Frequently Asked Questions about Mauna Loa

13. How will HVO scientists respond to a change in the Volcano Alert Level for Mauna Loa?

USGS Hawaiian Volcano Observatory scientists closely track Mauna Loa's seismicity, deformation activity, and gas emissions at the summit caldera through the HVO monitoring network, and they are prepared to deploy additional monitoring instruments on the volcano as needed. These might include additional seismometers, GPS receivers, webcams, and gas-measuring stations. HVO will also continue to provide information about Mauna Loa's status to Hawaiʻi County Civil Defense, Hawaiʻi Volcanoes National Park, and the public.

14. Does an ADVISORY Alert level mean that Mauna Loa is about to erupt?

At the ADVISORY level, an eruption of Mauna Loa is NOT considered likely or certain in the near future. When scientists declare an ADVISORY level for Mauna Loa, they will have determined that earthquake activity and changes in ground deformation (for example, ground tilt and spreading across the volcano's flanks) are occurring at rates above background levels. At the ADVISORY level, continued increases in earthquake and deformation activity are by no means certain—the level could return to NORMAL without an eruption.

15. Why do HVO scientists think that a Mauna Loa eruption is NOT imminent at this time?

Recent earthquakes beneath Mauna Loa have been smaller in magnitude and fewer in number than those that occurred prior to the volcano's two most recent eruptions in 1975 and 1984.

Prior to Mauna Loa's 1975 and 1984 eruptions, shallow earthquakes significantly increased in number and frequency over a period of 1-2 years, clearly indicating that pressure was building within the volcano.

The locations of recent shallow earthquakes (green circles on map below) are similar to those prior to the 1975 and 1984 Mauna Loa eruptions, but other precursory signals are missing. These signals include stronger intermediate depth earthquakes and increasing rates of deformation (inflation) and seismicity.

The distinct clusters of intermediate depth earthquakes (red circles) located northwest of Mokuʻāweoweo prior to the 1975 and 1984 eruptions (maps above) have not been observed in recent years (map at right).

If seismicity and deformation rates increase above background levels, the Volcano Alert Level for Mauna Loa will be elevated from NORMAL to ADVISORY. However, an ADVISORY alert level does not mean that an eruption is likely to occur. See questions 11-14 for more information about Volcano Alert Levels.

Mauna Loa Status Reports include links to "Current Monitoring" and "Long Term Monitoring" pages, which include up-to-date deformation (GPS and tilt) and seismic data plots, as well as monitoring data from Mauna Loa's 1975 and 1984 eruptions.

16. Are Mauna Loa eruptions similar to Kīlauea eruptions?

Mauna Loa tends to erupt more lava more quickly than Kīlauea—in other words, large volumes of lava erupt at higher effusion rates—so Mauna Loa produces voluminous, fast-moving lava flows. For comparison, during the 1984 eruption, Mauna Loa produced as much lava in 20 minutes as Kīlauea erupts in a day (at Kīlauea's eruption rate in 2015).

The slopes of Mauna Loa, especially on its southwest flank, are also quite steep compared to much of Kīlauea. These steep slopes also contribute to the speed of advancing Mauna Loa lava flows. Mauna Loa is similar to Kīlauea in that both volcanoes can produce ʻaʻā lava or tube-fed pāhoehoe flows that can travel long distances from an active vent.

17. What kinds of volcanic hazards will a Mauna Loa eruption pose?

    Volcanic hazards associated with a Mauna Loa eruption include:
  • voluminous, fast-moving lava flows
  • potentially large and destructive earthquakes and ground motion due to vertical and horizontal movements of the volcano's flanks as it inflates
  • volcanic gas emissions and dense vog (volcanic smog) that can be a nuisance or potential health hazard to people downwind of the vent
  • possible explosive eruptions and associated ashfall that can impact air traffic

The USGS Fact Sheet, Mauna Loa—History, Hazards, and Risk of Living with the World's Largest Volcano, provides more detailed information about these hazards.

18. What are the possible impacts of a Mauna Loa eruption?

A Mauna Loa eruption could disrupt communication, traffic, and people's lives—disruptions that could be further complicated by the influx of large numbers of residents and visitors wanting to see lava flows. These spectators could add to the congestion of roadways and other infrastructure already impacted by the eruption.

It's important to note that these impacts will likely be far-reaching. In other words, the impacts will not necessarily be restricted to the immediate area of the eruption or only to the Island of Hawaiʻi. For example, during the 1984 Mauna Loa eruption, vog (volcanic smog) blanketed much of the State of Hawaii.

19. How much time will I have to respond to a Mauna Loa eruption?

Mauna Loa erupts lava at a much higher rate than any other Hawaiian volcano, even the highly active Kīlauea volcano. This results in fast-moving and long-travelled lava flows, which can require quick responses in order to protect life and property.

How long you have to respond to a Mauna Loa eruption depends on your proximity to the eruptive vent, how steep the slope is between you and the vent, and the rate at which lava is being erupted. If you are in close proximity to, or on a steep (more than 15 degrees) hillside downslope of, an erupting vent on Mauna Loa, you could have precious little time to respond or evacuate—perhaps only hours.

The Districts of Kaʻū and South Kona on the Island of Hawaiʻi are at significant risk during a Mauna Loa Southwest Rift Zone (SWRZ) eruption due to the steep slopes and proximity of developed areas relative to the rift zone. During most historic SWRZ eruptions (1868, 1887, 1919, 1950), lava flows reached the ocean in less than a day. In fact, during the 1950 Mauna Loa eruption, one lava flow traveled from the vent at an elevation of about 3,050 m (10,000 ft) to the sea in about 3 hours.

On the other hand, the District of Hilo is relatively far from the most active part of Mauna Loa's Northeast Rift Zone (NERZ) and the slopes above the town are fairly gentle. NERZ eruptions can certainly threaten Hilo (for example, the 1855-56 and 1881 lava flows covered land that is now within Hilo city limits), but the lead time for response and potential evacuation during a NERZ eruption is likely to be substantially longer (days to weeks) than for SWRZ eruptions (hours).

20. How will I find out about a Mauna Loa eruption?

USGS Hawaiian Volcano Observatory scientists closely monitor Mauna Loa around the clock. If an eruption is likely, or is in progress, HVO will immediately notify Hawaiʻi County Civil Defense, Hawaiʻi Volcanoes National Park, and other emergency managers responsible for public safety. HVO will also issue public notifications through news media, and will post updates and status reports on the HVO website.

You can sign up to receive Volcano Activity Notices (updates, status reports, information statements, and alerts) via email for Mauna Loa and other Hawaiian volcanoes by signing up for the free USGS Volcano Notification Service at

HVO currently records a Mauna Loa update message that can be accessed by calling (808) 967-8866. This message is a summary of the Mauna Loa Status Report posted on the HVO website. The status report and telephone message are both are updated monthly while Mauna Loa is at a NORMAL Alert Level, but will be updated more frequently if the Volcano Alert Level is elevated.
21. What can I do to prepare for a Mauna Loa eruption?

Preparing for an eruption can help you prepare for other emergencies, such as severe storms and earthquakes, so it's a good thing to do! Learn about the hazards that you might face during an eruption and how to evacuate from your home. Prepare an emergency kit and make a family plan. Know how to get information about the volcano should it become significantly restless or erupt.

Agencies that provide information on preparing for natural disasters and other emergencies include Hawaiʻi Emergency Management Agency and the American Red Cross. FEMA offers a webpage that provides information specific to preparing for volcanic eruptions.

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Updated: 23 June 2015 (pnf)