Mauna Loa Volcano: Geological Formation, Historical Eruptions, Monitoring Efforts, Hazards, and Cultural Significance Explained

Mauna Loa Volcano: Geological Formation, Historical Eruptions, Cultural Significance, Monitoring, Hazards, and Future Outlook

Mauna Loa, whose name means "Long Mountain" in Hawaiian, is the largest active volcano on Earth by both mass and volume. Located on the Big Island of Hawaiʻi, it is a quintessential shield volcano, characterized by broad, gently sloping sides formed by highly fluid basaltic lava flows. Rising 13,681 feet (4,170 meters) above sea level and extending 30,000 feet (9,144 meters) from its base on the ocean floor, Mauna Loa surpasses Mount Everest in total height when measured from its underwater foundation. This colossal volcano has played a pivotal role in shaping the Hawaiian archipelago and continues to be a focal point for geological research, cultural significance, and volcanic hazard monitoring.

Geological Formation and Structure

Mauna Loa was formed by the Hawaiian hotspot, a plume of molten rock rising from deep within the Earth’s mantle. As the Pacific tectonic plate moved northwestward over this stationary hotspot, a chain of volcanic islands was created, with Mauna Loa being one of the youngest and most active. The volcano likely began erupting underwater around 700,000 years ago and emerged above sea level approximately 400,000 years ago.

The structure of Mauna Loa is dominated by its summit caldera, Mokuʻāweoweo, which spans 6.2 by 2.5 km (3.9 by 1.6 mi) and consists of three overlapping pit craters. The caldera floor lies between 50 and 170 meters (164–558 feet) below its rim and has undergone multiple collapses and refilling events over millennia. The volcano also features two primary rift zones—the Northeast Rift Zone (NERZ) and the Southwest Rift Zone (SWRZ)—which extend from the summit and serve as conduits for magma during eruptions.

Mauna Loa’s magma is silica-poor and highly fluid, resulting in effusive (non-explosive) eruptions that produce extensive lava flows rather than violent explosions. However, historical evidence suggests that explosive eruptions did occur between 300 and 1,000 years ago, likely due to interactions between magma and groundwater.

Historical Eruptions and Impact

Mauna Loa has erupted 34 times since 1843, with an average interval of about five years between eruptions. However, the period between its 1984 and 2022 eruptions—38 years—was the longest recorded quiescence in its documented history.

Notable Eruptions:

• 1868 Eruption – One of the most destructive in Hawaiian history, this event began with summit activity on March 27, followed by a massive M7.9 earthquake on April 2, which triggered landslides, a tsunami, and significant damage. Lava flows from the Southwest Rift Zone reached the ocean in just 3.5 hours, covering 9 square miles (24 km²) of land. New research suggests that the summit caldera may have collapsed during this eruption, similar to Kīlauea’s 2018 collapse, though historical records are limited.

• 1950 Eruption – This SWRZ eruption produced fast-moving lava flows that reached the sea within hours, destroying villages in South Kona.

• 1984 Eruption – Lava flows advanced toward Hilo but stopped just 4 miles short of the city.

• 2022 Eruption – After 38 years of dormancy, Mauna Loa erupted on November 27, 2022, with fissures opening in Mokuʻāweoweo before migrating to the NERZ. Lava flows traveled 12.1 miles (19.5 km) and covered 16.5 square miles (42.7 km²), stopping 1.7 miles short of Saddle Road (Daniel K. Inouye Highway). The eruption lasted until December 13, 2022, and was closely monitored due to its potential threat to infrastructure, including the Mauna Loa Observatory, which lost power when lava cut its access road.

Monitoring and Hazards

The USGS Hawaiian Volcano Observatory (HVO) has monitored Mauna Loa since 1912, using a network of seismometers, tiltmeters, GPS stations, and satellite radar (InSAR) to detect magma movement and ground deformation.

Key Monitoring Observations from the 2022 Eruption:

• Seismic Activity: A swarm of shallow earthquakes beneath the summit began around 10:20 p.m. on November 27, signaling magma ascent.

• Ground Deformation: Tiltmeters recorded over 100 microradians of inflation at the summit before rapid deflation once the eruption began.

• Summit Subsidence: GPS data showed the caldera floor sank nearly 40 cm (16 inches) as magma drained from the summit reservoir.

Mauna Loa’s eruptions pose significant hazards due to their potential for fast-moving lava flows, which can threaten communities like Hilo and Hawaiian Ocean View Estates. Additionally, volcanic gases (e.g., sulfur dioxide) and ash emissions can impact air quality.

Cultural and Ecological Significance

Mauna Loa holds deep cultural importance in Hawaiian traditions as the domain of Pele, the goddess of fire and volcanoes. The volcano’s lava flows have also shaped Hawaiʻi’s ecosystems, creating new land while burying forests and altering landscapes.

The Mauna Loa Observatory, located near the summit, is a critical facility for atmospheric research, particularly in tracking global CO₂ levels via the Keeling Curve. The 2022 eruption disrupted these measurements temporarily, forcing scientists to relocate instruments to Maunakea until power was restored.

Future Eruptions and Long-Term Outlook

Mauna Loa will undoubtedly erupt again, given its history of frequent activity. While the volcano is currently in a period of recovery and magma recharge, HVO continues to monitor for signs of renewed unrest.

In the long term (over millions of years), Mauna Loa will eventually drift away from the Hawaiian hotspot, becoming extinct like its neighbors Kohala and Mauna Kea. Erosion will gradually reduce its height, transforming it into a deeply dissected island similar to Kauaʻi.

Conclusion

Mauna Loa is a dynamic and awe-inspiring force of nature, embodying the raw power of volcanic activity. Its eruptions have shaped the Hawaiian landscape, influenced scientific understanding of volcanism, and posed both risks and opportunities for local communities. As monitoring technology advances, scientists can better predict future activity, but the volcano’s unpredictability ensures that it will remain a subject of fascination and respect for generations to come.

For those visiting Hawaiʻi, Mauna Loa offers unparalleled opportunities to witness geology in action—from hiking its rugged slopes to observing the aftermath of its latest eruption. Whether viewed as a scientific marvel or a cultural icon, Mauna Loa stands as a testament to the ever-changing nature of our planet.

Photo from: iStock

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