Introduction
Mauna Loa, meaning "Long Mountain" in Hawaiian, is the largest active volcano on Earth. Its summit stands 4,169 meters above sea level on Hawaii's Big Island, but measured from its base on the ocean floor, the mountain rises approximately 9,170 meters, making it taller than Mount Everest from base to peak.
Mauna Loa's massive volume of roughly 75,000 km³ makes up more than half of the Big Island. Its enormous weight has actually depressed the ocean floor beneath it by another 8 kilometers, meaning the true height of the volcanic pile from its depressed base exceeds 17,000 meters.
Geology & Scale
- Type: Shield volcano
- Summit Elevation: 4,169 m (13,681 ft)
- Height from Ocean Floor: ~9,170 m
- Volume: ~75,000 km³
Mauna Loa is a shield volcano, characterized by its broad, gently sloping profile built up by countless thin lava flows over hundreds of thousands of years. It formed over the Hawaiian hotspot and has been building for approximately 700,000 years, with the oldest exposed rocks dating to about 200,000 years ago.
The volcano covers approximately 5,271 km² of the Big Island's surface, roughly half the island. Its flanks slope gently at only 4-8 degrees, making its massive scale difficult to appreciate from ground level despite being visible from space.
Eruption History
- Eruptions Since 1843: 33
- Last Eruption: November-December 2022
- Previous Eruption: 1984
- Typical Style: Effusive lava flows
Mauna Loa has erupted 33 times since 1843 when written records began. Its eruptions typically produce fast-moving lava flows that can reach populated areas on the coast. The 1950 eruption sent lava flows to the ocean in just three hours.
The most recent eruption in November-December 2022 ended a 38-year quiet period. Lava flowed from the summit caldera (Mokuaweoweo) and the Northeast Rift Zone, coming within a few miles of the Saddle Road, the main highway connecting the east and west sides of the island. The 1984 eruption sent flows to within 7 km of Hilo, the island's largest city.
Mokuaweoweo Caldera
- Length: 6 km
- Width: 2.5 km
- Depth: 183 m
- Formation: Repeated summit collapses
The summit caldera, Mokuaweoweo, is one of the largest calderas on any active volcano. It formed through repeated collapses as magma drained from beneath the summit during rift zone eruptions on the flanks.
The caldera contains several pit craters and is often partially filled with lava during summit eruptions. Snow frequently caps the caldera in winter, creating a surreal landscape of ice and volcanic rock above the tropical Pacific.
Scientific Importance
- CO₂ Monitoring: Mauna Loa Observatory (est. 1958)
- Keeling Curve: Iconic CO₂ record
- Climate Science: Baseline atmospheric data
The Mauna Loa Observatory, established in 1958, has been continuously measuring atmospheric carbon dioxide. The resulting Keeling Curve is one of the most important datasets in climate science, documenting the steady rise of CO₂ from 315 ppm to over 420 ppm.
The observatory's location at 3,400 meters on the north slope of Mauna Loa provides clean, well-mixed air samples free from local pollution sources. It serves as a global baseline for atmospheric monitoring.
Key Facts
- Mauna Loa is the largest active volcano on Earth by volume (75,000 km³).
- Measured from the ocean floor, it exceeds 9,000 meters in height.
- It has erupted 33 times since 1843, most recently in 2022.
- The volcano makes up more than half of Hawaii's Big Island.
- The Mauna Loa Observatory has tracked atmospheric CO₂ since 1958.
Fun Facts
- If you include the depression of the ocean floor from its weight, Mauna Loa's volcanic pile exceeds 17,000 meters.
- The 1950 eruption's lava flows reached the ocean in just three hours, the fastest in Mauna Loa's recorded history.
- Mauna Loa is so massive that it visibly depresses the Pacific oceanic crust beneath it.
- The summit gets enough snow in winter for skiing, despite being in the tropics.
Final Thoughts
Mauna Loa is Earth's largest active volcano in every measurable dimension. Its sheer scale, prolific eruption history, and role in climate science through the Mauna Loa Observatory make it one of the most significant volcanoes on the planet, both geologically and scientifically.
