Mauna Loa: The Long Mountain - The Largest Volcano on Earth & The 2022 Eruption
Explore Mauna Loa, the largest active volcano on Earth. Discover its massive size, the historic 2022 eruption, its connection to the Keeling Curve (CO2 monitoring), and its relationship with neighbor Kilauea.
Mauna Loa (Hawaiian for “Long Mountain”) is a superlative in every sense. It is the largest active volcano on Earth by both mass and volume. Rising 4,169 meters (13,679 feet) above sea level, its true size is hidden beneath the waves; measured from its base on the ocean floor, it stands over 9,000 meters (30,000 feet) tall, making it taller than Mount Everest. It is so massive that its weight depresses the Pacific tectonic plate, creating a depression in the ocean floor. For visitors to Hawaii’s Big Island, Mauna Loa is an omnipresent giant, a horizon-spanning shield that occupies more than half of the island’s landmass.
1. The 2022 Eruption: The Giant Wakes
For 38 years—the longest quiet period in recorded history—Mauna Loa slumbered. Then, shortly before midnight on November 27, 2022, the giant woke up.
A Summit Spectacle
The eruption began in Mokuʻāweoweo, the summit caldera. Residents awoke to a crimson sky as lava fountains surged from fissures on the crater floor. For the first few hours, the activity was contained within the summit, a spectacle visible from miles away but posing no immediate threat.
The Migration to the Northeast
As is typical for Mauna Loa, the magma migrated. By the next morning, the summit vents had quieted, and new fissures cracked open on the Northeast Rift Zone. This was a “best-case scenario” for the island’s population. Lava flows from the Northeast Rift Zone generally head toward unpopulated areas, unlike the Southwest Rift Zone, which can send steep, fast-moving lava into residential communities in a matter of hours.
The March to the Saddle
The eruption produced spectacular “curtains of fire” and generated a massive river of lava that flowed north toward the Daniel K. Inouye Highway (Saddle Road), the main artery connecting the east and west sides of the island. The world watched as the flow front inched closer to the highway, stalling just 1.7 miles short before the eruption abruptly ended on December 10, 2022. The event was a reminder of the volcano’s power, producing nearly 40 billion gallons of lava in just two weeks.
The 1984 Eruption: The Close Call
Before the long pause leading to 2022, the 1984 eruption was the benchmark for modern activity. Lasting three weeks, it sent fast-moving ʻaʻā flows within 4 miles of Hilo city limits. The city was illuminated by the glow of the volcano at night, and residents packed their bags, fearing the worst. The eruption stopped just in time, but it served as a wake-up call for urban planning on the island. The contrast between 1984 (threatening Hilo) and 2022 (threatening the highway) highlights the unpredictability of rift zone eruptions.
The “Secret” Eruption of 1942
One of the most bizarre chapters in Mauna Loa’s history occurred during World War II. In April 1942, just months after the attack on Pearl Harbor, Mauna Loa erupted. Fearing that the bright glow would guide Japanese bombers to the island, the US military imposed a strict news blackout. The eruption was kept secret from the public.
- The Bombing Run: When the lava flow threatened the critical Olaʻa Flume (a water source for the Mountain View sugar plantation and military sites), the Army Air Corps decided to bomb the volcano. Under the direction of geologist Thomas Jaggar, planes dropped 600-pound demolition bombs near the vent to divert the flow.
- The Result: While the bombing created craters, it failed to stop the lava. Fortunately, the eruption ended naturally shortly after. This remains one of the few instances in history where humans have attempted to fight a volcano with aerial explosives.
2. Legends of the Fire and Ice: Pele and Poliʻahu
In Hawaiian mythology, Mauna Loa is the battleground for one of the islands’ most enduring rivalries.
Although Pele dominates Kilauea, Mauna Loa is often associated with the goddess of snow, Poliʻahu.
Poliʻahu lives on the snowy summit of nearby Mauna Kea but often extends her chilly mantle of snow across the saddle to the summit of Mauna Loa. Legends tell of fierce battles where Pele throws fountains of fire at Poliʻahu, who counters with storms of ice and freezing winds. The geological reality mirrors the myth: Mauna Loa is the only place in Hawaii where you can see red-hot lava flowing over snow-capped ground.
3. A Sky Island: Biodiversity Above the Clouds
Mauna Loa is not just rock; it is a layered ecosystem.
The Silversword Alliance
High on the rocky slopes lives the Kaʻū Silversword (Argyroxiphium kauense). Related to the famous Haleakalā silversword but distinct, this rare plant looks like a metallic, spiky sphere. It lives for decades, blooms once in a spectacular tower of flowers, and then dies. It is an evolutionary marvel, adapted to the intense UV radiation and freezing temperatures of the alpine desert.
Native Birds and Insects
The lower slopes are home to ancient koa and ʻōhiʻa forests, the habitat of endangered honeycreepers like the ʻAkiapōlāʻau. Higher up, in the barren lava fields, scientists have found endemic “lavacrickets” and wolf spiders that survive by eating windblown debris. Life here hangs by a thread, isolated from the rest of the world.
4. The Science of the Sky: The Keeling Curve
High on the barren northern slope of Mauna Loa sits one of the most important scientific facilities in the world: the Mauna Loa Observatory (MLO).
Tracking the Breath of the Planet
Run by NOAA, this observatory has been tracking atmospheric conditions since the 1950s. It is famous for the Keeling Curve, a graph initiated by Charles David Keeling that plots the ongoing change in concentration of carbon dioxide in Earth’s atmosphere. Because Mauna Loa is located in the middle of the Pacific Ocean, far from major continents and pollution sources, it provides the “cleanest” air for measuring global baselines.
Volcanic Interruption
Ironically, the volcano that hosts this climate research occasionally disrupts it. The 2022 eruption cut off power lines and buried the access road to the observatory, forcing a temporary halt to the data collection that had run uninterrupted for decades. Scientists scrambled to set up a temporary station on nearby Maunakea to ensure the gap in this critical climate record was minimal.
3. Mauna Loa vs. Kilauea: A Tale of Two Volcanoes
Mauna Loa shares the Big Island with its younger, more hyperactive neighbor, Kilauea.
Distinct Magma Systems
For years, scientists debated whether the two volcanoes shared the same “plumbing.” Geochemical analysis proves they are distinct. They have different magma compositions and erupt independently. However, there is a stress link: when Mauna Loa expands with magma, it can physically squeeze Kilauea’s supply channels, and vice versa.
The 2022 Double Event
In a rare geological coincidence, the 2022 eruption of Mauna Loa occurred while Kilauea was also erupting. For roughly two weeks, visitors to Hawaii Volcanoes National Park could see two active eruptions simultaneously—the glow from Halemaʻumaʻu (Kilauea) and the lava fountains of Mauna Loa. The last time this happened was in 1984. Strangely, both volcanoes stopped erupting at almost the exact same time in December 2022, a synchronized “pause” that continues to puzzle volcanologists.
4. Understanding Hazard Zones
Because of its size and eruptive history, the USGS has mapped the Big Island into distinct Lava Flow Hazard Zones, ranging from 1 (highest risk) to 9 (lowest risk).
Zone 1 and 2
- Zone 1: Includes the summits and rift zones of Mauna Loa and Kilauea. Lava has covered significant portions of these areas in the last century.
- Zone 2: Areas adjacent to the rift zones. On Mauna Loa, this includes areas like Ocean View on the Southwest Rift. Here, the slopes are steep, and lava can reach the ocean in as little as 3 hours, giving residents very little time to evacuate.
The “Safe” Zones?
Zones 3 through 9 are farther downslope or protected by topography (like the older volcanoes of Mauna Kea and Kohala). However, Mauna Loa is capable of sending flows into Hilo (Zone 3), as it threatened to do in 1984. Its flows travel miles, covering vast distances that smaller volcanoes cannot reach.
5. Frequently Asked Questions (FAQ)
Can I hike to the summit?
Yes, but it is grueling. The Mauna Loa Trail is a long, arduous trek over jagged lava rock. Most hikers take 3-4 days to complete the round trip from the park entrance. There are cabins (Red Hill and Mauna Loa Summit Cabin), but they are rustic and require permits. The altitude (nearly 13,700 feet) makes every step a struggle against hypoxia. This is not a casual day hike; it is a serious mountaineering endeavor.
Is it safe to visit?
Yes, Mauna Loa is generally safe when not erupting. It is a massive shield volcano with gentle slopes (unlike the steep cones of stratovolcanoes). However, hikers should be prepared for extreme altitude, cold weather, and altitude sickness. The summit is often freezing, even when the beaches below are tropical. Hypothermia is a real risk, even in Hawaii.
How often does it erupt?
Historically, Mauna Loa erupted on average every 5-6 years. The 38-year gap between 1984 and 2022 was an anomaly. Geologists expect it may return to a more frequent cycle, though prediction remains an inexact science.
What is “Vog”?
Vog (volcanic smog) is a hazy mixture of sulfur dioxide gas and aerosols produced by the volcano. During the 2022 eruption, Mauna Loa pumped out 250,000 tonnes of SO2 per day. This can cause respiratory issues for people downwind.
Technical Specifications
| Feature | Data |
|---|---|
| Elevation | 4,169 m (13,679 ft) |
| Base to Summit | > 9,000 m (30,000 ft) |
| Type | Shield Volcano |
| Volume | ~75,000 cubic km |
| Last Eruption | 2022 |
| Key Danger | Fast-moving lava flows (Southwest Rift) |
| Scientific Role | Host of the Keeling Curve (CO2) |
Mauna Loa is a sleeping giant that demands humility. It is a creator of land, a driver of climate science, and a force of nature that shapes life on the Big Island.