Volcano Watch — The 1855–1856 Mauna Loa lava flow nearly devastated Hilo

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On the evening of August 11, 1855, Mauna Loa erupted from a location described as 1,000 to 2,000 ft below the summit of the volcano. This was the sixth eruption of Mauna Loa—and the second to send a lava flow advancing toward Hilo—since the Waiakea Mission Station (the east Hawai‘i base for Protestant missionaries) was established in Hilo in 1824.

The eruption was reported to be vigorous and its fountain and massive flow cast a bright light on the island from the first night. Lava rushed down the north slope of Mauna Loa and, in a few days, reached the Saddle between Mauna Loa and Mauna Kea, where it was obscured from Hilo's view by a forest belt around the town.

Hilo residents became worried as the flow slowly advanced toward Hilo Bay, and some began packing and making plans to relocate. Sarah Lyman, who had lived in Hilo since the early 1830s wrote in her diary for November 25: "The lava is advancing gradually and may soon be flowing through our beautiful town. I confess to a feeling of nervousness and have laid out suits for myself and children, so that we can flee at a moment's warning." Groups in Hilo, around the island, and around the state prayed for Hilo to be spared.

Through early 1856, the lava flow continued downslope, getting close to the Wailuku River and slowly cutting off its tributaries. Reverend Titus Coan, the missionary who also studied Hawaiian volcanoes, said, "…the water of the Wailuku is greatly reduced and rendered for the present unfit for use." He also reported that a man died after "…falling into the boiling water near the fused lava stream," although this was never confirmed.

The first good news came in February 1856, when Reverend Coan wrote, "The lava stream has ceased to advance towards Hilo. There is still much smoke, in the top of the mountain, and fusion bursts up here and there on the hardened stream several miles above its terminus. Hilo is spared and we should be thankful." After 6 months, the flow front stalled 6 miles from Hilo Bay (just above what is now Kaumana City subdivision) although the eruption at the vent continued.

Likewise, the smoke (or "vog," as it's now called), mentioned by Coan continued with unabated intensity. A Honolulu resident wrote in August 1856, "Permit me to call the attention of your readers to the smoky condition of the atmosphere, which … obscures the outlines of our nearest hill and hides the distant mountains entirely from our eye…. The natives do not consider its occurrence very uncommon, and from the fact that they call it 'uahi a Pele,' appear to trace it to volcanic action." The vog continued until the eruption ended in late October 1856.

By the time of the 1855–1856 eruption, Reverend Coan, who had also described the 1843 and 1852 Mauna Loa eruptions, had already recognized the importance of lava tubes in the long-distance advancement of lava flows. He wrote, "Surface lava exposed to the atmosphere crusts over before running very far, unless it is moving with great velocity, as down steep descents. This process of refrigeration so protects the liquid below that it flows onward at white-heat … until obstructed, when it gushes out on the margins, or bursts up vertically. On plains where the movement is slow the obstructions are more numerous and the force required to overcome them is less."

Stalling of the Mauna Loa lava flow in 1856 is somewhat analogous to the current stalled state of the Kahauale‘a 2 flow from the Pu‘u ‘Ō‘ō vent on Kīlauea. We are now able to acquire vastly more information about the condition of Hawai‘i's volcano and lava flows than was possible in 1856. Through this, we interpret that the current stalled flow on Kīlauea is due to a lower eruption rate—the Kahauale‘a 2 flow probably won't advance far beyond its current length if the eruption rate doesn't increase.

A waning eruption rate was likely responsible for stalling the 1856 lava flow and saving Hilo. Let's hope that the eruption rate from Pu‘u ‘Ō‘ō continues to wane and that the Kahauale‘a 2 flow remains stalled.

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Volcano Activity Update

A lava lake within Halema‘uma‘u produced nighttime glow that was visible via HVO's Webcam during the past week. The lava lake level peaked with summit inflation early last week, and then dropped again with deflation. On June 5, the lava level was 48 m (157 ft) below the rim of the Overlook crater.

On Kīlauea's East Rift Zone, the Kahauale‘a 2 flow remains active but has diminished in vigor. The flow front stalled at 8.8 km (5.5 miles) northeast of its vent on Pu‘u ‘Ō‘ō in mid-May. The most distant active flows are now just over 6 km (4 miles) from Pu‘u ‘Ō‘ō and are relatively weak. Several small spatter cones within the Pu‘u ‘Ō‘ō crater continue to produce glow.

There were no earthquakes reported felt in the past week within the State of Hawaii.