Mauna Loa Ends Thirty-Eight-Year Silence

Hawai’i Volcanoes Observatory scientists estimated the height of Mauna Loa’s tallest lava fountains to be around sixty meters, or 200 feet.

After months of seismic unrest, Hawai’i’s largest volcano Mauna Loa began erupting. 

At 11:30 PM Sunday evening, the floor of Moku‘āweoweo, Mauna Loa’s enormous caldera, split open. Lava soon flooded the crater and spilled out on the mountain’s broad, rocky slopes. Scientists familiar with the truly massive volcano (33,500+ feet from seafloor to summit) knew it might happen this way. Mauna Loa has a habit of erupting unannounced, with anywhere from hours to minutes’ notice. This eruption occurred without warning.

Big Island residents witnessed the fiery orange glow from Hilo in the east to Kona out west. Multiple fissures have opened, sending lava downslope past the ten-thousand-foot mark. Lava overtook the sole roadway to the caldera’s observatory house. No other infrastructure or residences are currently under threat. As a precaution, Hawai’i Civil Defense opened shelters at old Kona Airport in Kailua Kona and Kau Gymnasium in Pahala. 

Mauna Loa, a Gentle Giant

Unlike Mount Shasta or the Long Valley Caldera here in California, Mauna Loa is a shield volcano. It won’t explode violently and bury the island in feet of hot ash. The lava it erupts is too fluid to trap the gas required to turn its magma chamber into a powderkeg. Runny lava doesn’t build steep cones. It builds a broad, slumping mound, like a shield lying in the grass. Depending on which path it takes, a flow can reach the ocean in a matter of weeks, months, or hours.

Flanking the caldera Moku‘āweoweo like a pair of shoulders are two extensive rift zones. The Northeast and Southwest Rift Zones meet in the summit crater, where this eruption originated. On Monday, November 28th, the eruption propagated into the Northeast Rift Zone. Smaller fissures opened parallel to the main line of lava fountains, contributing to the flow that cut off the observation center. Curious residents have been flocking to Saddle Road, the highway linking Kona and Hilo, for a closer view. There the danger isn’t so much lava and noxious fumes as it is speeding traffic and narrow lanes.

Why Saddle Road is Important

Travelers heading to Hilo and Kona International Airports should check with their airlines about any delays or diversions. While Mauna Loa rarely produces hazardous ash, an air travel advisory is in effect. Of the three fissures opened in the first stages of the eruption, only one was still fountaining as of Tuesday afternoon. The active fissure still feeds a flow moving east, parallel to Mauna Loa’s Northeast Rift Zone. By Tuesday night, lava had made it to just over five miles from Saddle Road. 

Saddle Road, also called Hawai’i State Route 200, is an important link between the Big Island’s two largest population centers. Beginning in downtown Hilo and ending near Waimea, Saddle Road is just over fifty miles long. The mostly one-lane highway (two-lane on dangerous hills) is the only overland route. Without it, commuters face up to two more hours on coastal roadways to reach the other side of the island. Officials may close the road if lava threatens to overtake it. Drivers, according to Hawai’i Island Mayor Mitch Roth, are “used to that” disappointment.

The Future

In Hawai’i, it can take hours to months for lava to reach a populated area. It will slow as the island’s already gradual slopes taper out. The trouble is, those areas are densely populated, with over twenty thousand residents potentially affected. Another factor is the volcano’s finicky behavior. Mauna Loa may erupt for only twenty-two more hours, as in 1975, or for 278 more days, like in 1880–81. That event sent a flow to within two miles of Hilo. The city’s modern outskirts were built on top.

Right now, property damage seems unlikely. If Saddle Road is inundated anywhere along its desolate stretch, it may take months to repave, and that’s after the lava cools. That could take years. However, just because it’s been about thirty-eight years does not guarantee a lengthy eruption. Volcanoes are infamously unpredictable. Only time will tell whether this event will continue or conclude as quickly as it started.