Mauna Loa

For approximately 28 million years, the Hawaiian hotspot has belched out islands and atolls. The hotspot sits in the same position, spewing upward from the mantle, while the Pacific Plate moves above it. This combination created the string we know as the Hawaiian Islands. Eight major isles comprise the archipelago. Each was once above the hotspot, where magma plumes started underwater and slowly emerged above sea level, crafting land. As tectonics worked, an island would move away from the hotspot, making the volcanos extinct. Today, just one island features active volcanoes: the eponymous island, Hawai’i AKA The Big Island.

Five giant volcanoes formed the Big Island. The most northeastern, Kohala, is now extinct. Mauna Kea, the High Point of the state of Hawaii, is dormant, having last erupted between 4,000 and 6,000 years ago. Three volcanoes are still active: Hualālai, Kīlauea, and Mauna Loa.

Translating to “Long Mountain” in English, Mauna Loa is a beastly crag.

The five volcanoes of the Big Island - graphic by Hawaii Volcano Observatory/USGS
A diagram showing the Hawaii hotspot and the inferred underlying mantle plume in cross-section - USGS

Mauna Loa more than lives up to its moniker. As you can see in the graphic above, this volcano makes up half of the Big Island’s area. It’s so large that it equals 85% of the area of the rest of the Hawaiian Islands combined! In both mass and volume, Mauna Loa is the world’s largest subaerial (not completely underwater) volcano. Its volume is estimated to be 18,000 cubic miles!

The most strikingly recognizable volcanoes are stratovolcanoes, featuring cone-shaped appearances. Mauna Loa is a shield volcano, which means it has a low profile and relatively gentle inclines, sort of resembling a shield on its side. Shield volcanoes spew less viscous lava than stratovolcanoes, which allows the shield lava to flow farther, though less explosively. Over time, the eruptions of shield volcanoes layer onto each other, producing mountains that appear like this:

Mauna Loa - photo by J.D. Griggs/USGS

Don’t let that peaceful incline fool you. Mauna Loa is the second-highest point in the state of Hawaii, just 125 feet shorter than nearby Mauna Kea. What might appear to be a small rise in the photo above actually rises 13,679 feet above the ocean!

At the summit of Mauna Loa resides a caldera, called Mokuʻāweoweo. Named after a fish – the ʻāweoweo – whose coloration resembles lava, this series of craters is 3.9 miles wide by 1.6 miles long.

Counterintuitive to the nature of volcanoes and Hawaii, the height of Mauna Loa often leaves Mokuʻāweoweo covered in snow.

Mokuʻāweoweo, Mauna Loa's summit caldera, covered in snow

Ancient Hawaiians constructed a path, called the Ainapo Trail, from the village of Kapāpala to the summit of Mauna Loa. 35 miles long and gaining 11,000 feet, the trek took multiple days. Historians believe pilgrims undertook the expedition during eruptions to leave offerings to Pele, the Hawaiian volcano goddess. Though Pele is associated with volcanic activity in general, some myths place her abode atop Mauna Loa; most stories place her home on Kilauea, however.

Though shield volcanoes tend to kill fewer people than stratovolcanoes, Mauna Loa is listed as one of the Decade Volcanoes. These volcanoes have significant histories of recent eruptions and sit near large population centers. The lava from Hawaiian volcanoes tends to be slow – often moving at just a walking pace. Eruptions there are rarely fatal; only one documented death has occurred directly due to a volcanic eruption. Still, sometimes the explosions are not so demure. In 1950, the lava from Mauna Loa reached the ocean in just four hours, destroying the village of Hoʻokena Mauka. Hilo, the largest city on the Big Island, sits on top of lavas from eruptions in the 1880s. Future eruptions could easily impact this population center.

Some scientists believe a collapse of the volcano’s sides poses an even bigger risk than lava. Sometime between 100,000 and 200,000 years ago, the west flank of Mauna Loa crumpled into the ocean, forming Kealakekua Bay. Obviously, an event of this magnitude today would be destructive to the immediate landforms, but they also pose the possibility of creating tsunamis. At least two massive tsunamis transpired in the Hawaiian islands due to landslides of this form, one of which reached over 1,000 feet in height before it smashed into the island of Lānaʻi.

Hazard zones of an eruption by Mauna Loa; the lower the number, the higher than danger - USGS
Lava flows during the 1984 eruption of Mauna Loa - photo by R.W. Decker

Historically, Mauna Loa’s activity level is very high. According to the United States Geological Survey, since the first well-documented eruption in 1843 and the last activity in 1984, the world’s largest above-ground volcano discharged 33 times. The lava in 1984 reached a spot just 4.5 miles from Hilo. In that period, the mountain erupted on average every four or five years, making the 38 years since 1984 an elongated period of calmness.

The USGS, however, needs to update its numbers.

On 27 November 2022, Long Mountain rumbled awake. Starting in the summit caldera, an eruption created three fissures in the Northeast Rift Zone. To date, flows have not yet reached any major highways or population centers. Based on the topography of current activity, volcanologists believe this eruption might completely spare human property.

Though short on potential human destruction, this eruption is filled with ineffable beauty, including lava fountains that reach 200 feet:

The peak of Mauna Loa resides in Hawaii Volcanoes National Park, which also houses Kīlauea. Though not as occupied with observatories as Mauna Kea, if one were to hike the Long Mountain, one would encounter the Mauna Loa Solar Observatory, the NOAA Mauna Loa Observatory, and the Yuan-Tseh Lee Array for Microwave Background Anisotropy.

Few spots on our planet highlight the intricate dance between destruction and creation as the volcanoes of Hawaii. The lava flows are simultaneously obliterators and cleansers, annihilators and composers, terrifying and enrapturing. Just like the constant ouroboros of life and death for which Mauna Loa is a pristine metaphor, this volcano will one day join the ranks of the extinct. Sometime between 500,000 and one million years in the future, the Pacific Plate will have nudged Mauna Loa past the hotspot, leaving only a warrior’s shield on its side.

Mauna Loa from Hilo Bay, 38 miles away - photo by Kaleodu
Mauna Loa from the Onizuka Center for International Astronomy - photo by Madereugeneandrew

Further Reading and Exploration

Mauna Loa – United States Geological Survey

Frequently Asked Questions about Mauna Loa Volcano/Questions about the Mauna Loa eruption – USGS

Mauna Loa – National Parks Service

Hawaii’s Mauna Loa volcano erupts for first time in nearly 40 years – Reuters

Hawaii Center for Volcanology – Official Website

Mauna Loa Solar Observatory – Official Website

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