Frequently Asked Questions about Mauna Loa Volcano

By Mauna Loa

Frequently asked questions about Mauna Loa, including the most recent eruption.

Color graphic showing the Island of Hawaiʻi and Mauna Loa structural features — Island of Hawai‘i map, showing Mauna Loa and the other four volcanoes that make up the island. Mauna Loa structural features include summit caldera, rift zones, radial vents, and historical lava flows. (Public domain.)

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

Yes, Mauna Loa is active and it will erupt again.

Where on Mauna Loa is an eruption likely to occur?

Eruptions on Mauna Loa typically occur within Moku‘āweoweo, 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.

How often does Mauna Loa erupt?

Since 1843, Mauna Loa has erupted 34 times. Most eruptions occurred prior to 1950, averaging 3.5 years between eruptions. Since 1950, there have only been three eruptions; a summit eruption 25 years later in 1975, a rift eruption 9 years later in 1984, and a summit/Northeast Rift Zone eruption 38 years later in 2022. The 38 years between the 1984 and 2022 eruptions was the longest quiet period on record.

Color graphic showing an the Island of Hawaiʻi with red polygons showing lava flow areas — Map of lava flows that have erupted on Mauna Loa Volcano from 1843-1984. (Public domain.)

During the past 3,000 years, Mauna Loa has erupted lava flows, on average, every 6 years. Geologic mapping of Mauna Loa shows that, in the past 150 years, 14 percent (276 square miles) of the volcano’s surface was covered by new lava flows. As much as 35 percent to 40 percent (695 to 795 square miles)—an area equal to or greater than O‘ahu or Maui—was covered in the past 1,000 years.

Dates, locations, durations, and other facts about Mauna Loa eruptions are compiled in "Geology & History."

When was the most recent eruption of Mauna Loa?

Mauna Loa erupted most recently from November-December 2022. From vents on the Northeast Rift Zone, lava flows extended 12 miles (19 km) north/northeast, coming within 1.7 miles (2.8 kilometers) of the Daniel K. Inouye Highway (Saddle Road). rior to that, an eruption in March-April 1984 generated fast-moving ‘a‘ā flows that advanced downslope; in a matter of days, lava was within 6 km (4 miles) of Hilo city limits. Fortunately, the 1984 eruption ended on April 15 before lava reached Hilo.

Read a more detailed narrative of Mauna Loa's 1984 Eruption: March 25-April 15.

Additional info about past Mauna Loa eruptions:

How does a typical Mauna Loa eruption progress?

All of the 34 recorded eruptions on Mauna Loa started within Moku‘āweoweo caldera at the summit of the volcano and we expect future eruptions to follow this pattern. About half of the eruptions remain confined to summit area and did not pose a threat to surrounding communities.

However, nearly half of Mauna Loa eruptions have migrated from the summit down either the Southwest Rift Zone toward Hawaiian Ocean View Estates or the Northeast Rift Zone towards Hilo. Rare eruptions can also occur from “radial” vents on the west and north sides below Mauna Loaʻs summit.

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

A fast-moving ‘s‘ā flow erupted from Mauna Loa in 1950 as it advanc... — Aerial photograph shows the Ka‘apuna lava flow erupted from Mauna Loa in 1950 as it advanced through the forest at about 3,000 feet elevation on the morning of June 2. This rapidly moving ‘A‘ā lava flow traveled from the Southwest Rift Zone vent to the ocean in about 17 hours. Earlier flows from this same eruption reached the ocean in as little as three hours. (Public domain.)

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.

Additional information:

Celebrating colossal Mauna Loa with a "Hi-yo, Silver!" (about vog)
Mauna Loa's 1984 eruption taught us much about how lava flows work
USGS Volcano Hazards Program – Types of Volcano Hazards
Explosive Eruptions from Mauna Loa's Summit
How fast does Hawaiian lava flow?

What are the possible impacts of a Mauna Loa eruption?

Lava flows from the 1984 eruption of Mauna Loa loom above the town ... — Lava flows from the 1984 eruption of Mauna Loa loom above the town of Hilo. Photograph taken near the Hilo airport on April 4. (Credit: Little, David. Credit photographer.)

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 Hawai‘i. For example, during the 1984 Mauna Loa eruption, vog (volcanic smog) blanketed much of the State of Hawaii.

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

Lava flow on Mauna Loa — Aerial view of Mauna Loa summit with Lua Hou in the foreground followed by Lua Hohonu, South Pit, and Mokuʻāweoweo summit caldera. A small dusting of snow covers the ground east of the summit. The steaming fissure was active during the beginning of the eruption, but this morning the lava in the summit caldera had already cooled to a black color. The white plume in the background is rising from the fissures in the Northeast Rift Zone. USGS photo J. Schmith

Subscribe to the Volcano Notification Service and change your settings to receive status updates for Mauna Loa. All current reports are available on HVO website, and past reports can be searched on the Volcano Hazards Program website. Residents with questions about emergency response and resources that may be available to assist those at risk should consult https://hawaii-county-volcano-hazards-hawaiicountygis.hub.arcgis.com/.

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 is updated as frequently as the status reports are released, which varies with alert level.

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

Alert levels and aviation color code icons for volcanoes within the... — Alert levels and aviation color code icons for volcanoes within the USGS area of responsibility.(Public domain.)

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).

Additional information can also be found in our fact sheet: U.S. Geological Survey's Alert-Notification System for Volcanic Activity

What can I do to prepare for a potential 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 Hawai‘i Emergency Management Agency and the American Red Cross. FEMA offers a Ready.gov webpage that provides information specific to preparing for volcanic eruptions.

Has Mauna Loa's Northeast Rift Zone erupted in the past?

Since the mid-19th century, Mauna Loa’s Northeast Rift Zone has erupted nine times: in 1843, 1852, 1855–1856, 1880–1881, 1899, 1935–1936, 1942, 1984, and 2022. Lava flows from the Northeast Rift Zone can travel swiftly in north, west, northwest, south, and southwest directions to eventually threaten property, roads, and communities. Hilo has been threatened by seven Mauna Loa lava flows.  These flows, and the distance each one reached relative to Hilo’s current Komohana Street, include: 

1852 – 14.5 km (9 mi) 
1855-56 – 9.7 km (6 mi)

1880-81 – neg 0.6 km (neg 0.4 mi) – reached intersection of Mohouli and Popolo Streets 
1899 – 28.2 km (17.5 mi) 
1935-36 – 26.6 km (16.5 mi) 
1942 – 14.5 km (9 mi) 
1984 – 15.3 km (9.5 mi) – [it is often said that the 1984 flow reached to within 4 miles of Hilo city limits, but this depends on how you define the city limits] 
2022 –19 km (12 mi)

Mauna Loa typically erupts lava at a very high rate, similar to the 2018 eruption of Kīlauea. High eruption rates combined with the steep slopes of Mauna Loa results in fast-moving and long-travelled lava flows, which can require a quick response.

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).

What does the name "Mauna Loa" mean?

Color photograph showing the summit of a shield volcano capped with snow — Snow adorns the upper 1.5 km (5,000 ft) of Mauna Loa Volcano. Rarely does snow reach so far down the mountain. This panorama photograph was taken from the summit area of Kīlauea's caldera near HVO. (Public domain.)

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 Hawai‘i 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 PUAKU on the North Kona coast of the island.

How big is Mauna Loa?

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 Hawai‘i. It is larger than all the rest of the Hawaiian Islands combined.

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 (HVO) 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. 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.

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

Color photograph showing a geologist in a yellow shirt working on a web camera at the summit of a volcano — An HVO geologist performs a routine check of the thermal camera and webcam at the summit of Mauna Loa. (Public domain.)

The USGS Hawaiian Volcano Observatory has an extensive monitoring network of more than 100 field stations, each with multiple ground-based instruments to monitor volcanic activity in Hawaii. These instruments monitor for changes in:

Number and size of earthquakes – Seismometers detect earthquakes and tremor.
Deformation of the ground surface – Tiltmeters track changes in slope and GPS receivers track changes in elevation and position of the ground surface as the volcano deforms (in response to magma movement).
Volcanic gas – Gas sensors measure the quantity and composition of volcanic gas emissions.
Volcanic activity and eruption behavior – Webcams, thermal cameras, and time-lapse cameras record images of volcanic activity, often in remote locations.
Subsurface processes – Gravimeters and other geophysical tools 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.

Mauna Loa Volcano monitoring map including earthquakes and instruments
Mauna Loa Volcano: Current Monitoring Plots
Mauna Loa Webcams
An Analysis of Three New Infrasound Arrays around Kīlauea Volcano

Are Mauna Loa eruptions similar to Kīlauea eruptions?

Aa lava flows erupting from Mauna Loa.... — Aa lava flows erupting from Mauna Loa. (Public domain.)

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 ‘a‘ā lava or tube-fed pāhoehoe flows that can travel long distances from an active vent.

Is Mauna Loa expected to erupt soon?

An eruption of Mauna Loa is not imminent at this time.

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