Mauna Loa Eruption

Mauna Loa Eruption

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INSIGHTi

Mauna Loa Eruption
December 8, 2022
Mauna Loa, a volcano on the island of Hawaii, began erupting on November 27, 2022, with an outbreak
of lava at the Mokoaweoweo summit caldera at an elevation of 13,681 feet within the Hawaii Volcanoes
National Park. The eruption has caused aviation restrictions and some facilities and road closures; traffic
congestion and illegal parking on the few narrow roads to the summit by sightseers; and unhealthy air
quality. The hazards from the Mauna Loa eruption include lava flows, earthquakes, fractures and
subsidence, volcanic gas emissions, hazardous volcanic smog called vog, and explosive eruptive activity.
Congress may be interested in the U.S. Geological Survey’s (USGS’s) efforts to monitor the eruption (see
USGS Mauna Loa Eruption Updates) and reduce the risks from volcanic hazards.
Mauna Loa Eruption
Mauna Loa is a large shield volcano that dominates the central part of the island. The summit and some
southern parts of the volcano are located in the national park. Outside the national park, the volcano is
covered by areas of barren lava, forest preserves, wildlife refuges, agricultural lands, a few facilities, and
coastal communities. Early on in the eruption, lava flows along the Southwest Rift Zone extended west
and southwest. On November 28, the activity moved to the Northeast Rift Zone. Several fissures opened
and spewed volcanic gases with lava fountains followed by lava flows moving northeast down the gentle
slope of the volcano (Figure 1).
Activity at the summit and along the Southwest Rift Zone had stopped by November 28. Fissures on the
Northeast Rift Zone are now the dominant source of the largest lava flows. These flows are moving
slowly down the mountain and may block the Daniel K. Inouye Highway (Saddle Road, a major highway
between volcanoes connecting the east side and west side of the island) in the near future ( Figure 1).
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Figure 1. Mauna Loa Eruption: Map and Images
November 29 and 30, 2022

Source: Left side map - USGS, November 30, 2022 – Mauna Loa Eruption Map. Top image USGS, Mauna Loa Fissure
Erupting, November 29, 2022. Bottom image USGS, Mauna Loa Northeast Rift Zone Eruption, November 29, 2022.
Notes: Top right image shows an erupting fissure high on Mauna Loa’s Northeast Rift Zone. Fountain heights of 20-25
meters (65-82 feet) were measured by Hawaiian Volcano Observatory field crews on the morning of November 29, 2022.
Bottom right image shows an aerial view of the lava flows on the northeast flank of Mauna Loa, taken during a morning
overflight on November 29, 2022. These lava flows are moving in a northeast direction, fed by fissure vents on the
Northeast Rift Zone. For the latest, see Mauna Loa Volcano Updates and USGS Mauna Loa images of eruption, field
activity and more.
Impacts of Mauna Loa Eruption
Volcanic eruptions may affect people, property, and the environment in numerous ways. Hawaii
Volcanoes National Park has closed some roads, but the park remains open to visitors, and the National
Park Service (NPS) is working to keep visitors safe amidst eruptive activity on Mauna Loa and Kilauea.
NOAA’s Mauna Loa Observatory is closed because a lava flow blocked the observatory access road and
took out power lines to the facility. The U.S. Army Pohakuloa Training Center on the northeast slope and
the Mauna Kea Observatories and a weather center on the summit of nearby Mauna Kea are not
threatened by the current eruption, but if the lava flows continue down the volcano, the flows may block
road access to these facilities.
Most communities on the island are on or near the coasts, far from the Mauna Loa summit. Some
communities are vulnerable to unhealthy air quality depending on weather conditions and volcanic gas
emissions. USGS has provided forecasts of the lava flow hazards to communities using past eruptions
between 1843 and 1984 (the last time Mauna Loa erupted) and the likely path of new lava flows based on

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topography (Figure 2). The Hamakua and Hilo districts on the northeastern and eastern coasts,
respectively, are most at risk from hazardous lava flows from the current eruption (Figure 2). The Kona
and Kau districts on the western coast are most at risk from lava flows that start on the Southwest Rift
Zone (currently not active).
Figure 2.Mauna Loa Lava Flow Hazards

Source: USGS, Mauna Loa, Geology and History. Information about lava flow arrival times from USGS Mauna Loa
Factsheet. Modified by CRS.
Notes: The lava flow hazard zones displayed on both maps and listed in the legend include Zone 1(most hazardous)—the
summit and rift zones, where lava and volcanic gases have repeatedly erupted; Zone 2 (hazardous)—slopes of the volcano
adjacent to the summit and rift zones where recorded lava flows have repeatedly flowed down slope; Zone 3 (less
hazardous)—less likely to have lava flows because of greater distance from the summit and rift zones or because the
topography does not allow easy downslope flow; Zone 6 (no hazard)—protected from lava flows by topographic features
or barriers. The dashed red circle around the summit is the 12,000 foot elevation contour. Historic lava flows from
eruptions between 1843 and 1984 are displayed in colors with blues the oldest and oranges the youngest.

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U.S Geological Survey Hawaiian Volcano Observatory Monitoring and Alerts
The U.S. Geological Survey Hawaiian Volcano Observatory (HVO) is tracking Mauna Loa’s eruption
using a network of monitoring instruments (such as cameras, thermal (heat measuring) cameras,
seismometers, tiltmeters, geodetic instruments (Global Positioning System), and gas measuring
instruments). In addition, USGS scientists and other geoscientists are deployed in the field to sample the
lava and air and make other measurements. HVO noted heightened unrest at Mauna Loa in September
when the number of earthquakes increased and the summit began to inflate (Update 9/29/22). Since then,
HVO established a 24/7 monitoring campaign, added more cameras and other instruments to the network,
and added staff from other USGS Volcano Observatories. HVO is providing information about volcanic
hazards from the Mauna Loa eruption and the continuing Kilauea eruption to federal, state, and local
authorities. HVO is able to forecast some volcanic hazards to reduce the risks to people and property
because of research, historical data on past eruptions, and long-term monitoring. HVO forecasts that the
current Mauna Loa eruption may last a few weeks and be contained to lava flows on the Northeast Rift
Zone and northeast slope. HVO is working with the Hawaii County Civil Defense Agency, the Hawaii
Interagency Vog Information Dashboard, the Hawaii Emergency Management Agency, the Federal
Emergency Management Agency, the Federal Aviation Administration, the National Weather Service,
NPS, and others to communicate the hazards and reduce the volcanic risks.
Considerations for Congress
In 2019, Congress authorized a National Volcano Early Warning and Monitoring System (NVEWS;
Section 5001 of P.L. 116-9; 43 U.S.C. 31k, see also CRS InFocus on NVEWS) to improve monitoring and
reduce risks. In 2020, the USGS submitted a five-year plan for establishing and managing NVEWS to
Congress. The plan identified 34 very-high- or high-threat volcanoes, including Mauna Loa and Kilauea,
from the 2018 volcanic threat assessment that would be prioritized for additional monitoring. Congress
appropriated $33.3 million for the Volcanic Hazards Program (VHP) in FY2022 (see Explanatory
Statement accompanying P.L. 117-103), which included $2.2 million to begin implementation of NVEWS
and $1.8 million for an Early Warning System. In addition, Congress provided supplemental
appropriations in FY2019 to repair the volcano monitoring network and establish new HVO facilities
after the ones at Kilauea summit were destroyed by intense eruptions in 2018 (P.L. 116-20 and USGS
supplemental appropriations information). Congress may be interested in the USGS monitoring and
response to the Mauna Loa and Kilauea eruptions and could consider whether recent legislation and
appropriations are sufficient to achieve the goals of improving monitoring and reducing volcanic risks as
envisioned by the NVEWS.

Author Information

Linda R. Rowan

Analyst in Natural Resources and Earth Sciences

Disclaimer

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This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff
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