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June 26, 2014

A few weeks ago, a Volcano Watch article recounted the advance of Mauna Loa lavas on the town of Hilo in 1855.

Hilo was again threatened by a Mauna Loa lava flow in 1881...
A sketch by Joseph Nāwahī showing the 1881 lava flow approaching Hilo. (Courtesy of National Park Service, Hawai‘i Volcanoes National Park, HAVO 394, Volcano House Guest Register 1873 to 1885, illustration by Joseph Nāwahī, February 21, 1881.)

Titus Coan, a fervent investigator and observer of all things volcanic, was in his mid-50s at the time and walked up to the source of the flow at least 7 times between August 1855, when the eruption began, and February 1856, when the lava flow stopped. By the end of the eruption, Coan understood how lava flows advanced with a level of detail that no one else had achieved before.

Hilo was again threatened by lava during an eruption sequence that started at the summit in early May 1880. After a several-month hiatus, the sequence resumed on November 5, 1880, from vents lower on the northeast rift zone and adjacent to the 1855 vent. Over the next few days, ‘a‘ā flows advanced northeastward into the Saddle area and southward toward the KAPAPALA area on the flank of Mauna Loa.

After a month, only one flow remained active and continued to advance toward Hilo into the next year, 1881. By summer, Titus Coan said, in his autobiography, "We could hear the explosions in Hilo; it was like the noise of battle. Day and night the ancient forest was ablaze, and the scene was vivid beyond description. By the 25th of March the lava was within seven miles of Hilo, and steadily advancing. Until this time we had hoped that Hilo would not be threatened. But the stream pursued its way. By the 1st of June it was within five miles of us, and its advance, though slow, was persistent."

As the 1880-1881 flow got closer to Hilo, people visited the flow more frequently. A few brave souls also ascended the flow to its source and beyond to the volcano's summit. But at age 81, Coan was not fit for the challenge. "Were I twenty years younger, I should have been on the mountaintop also, but my time to climb such rugged heights is past," he wrote. But he was with these younger adventurers in spirit.

Many of the people who made the long, grueling hikes also made good observations of the eruption, and they confirmed Coan's ideas about lava flow development. The 1881 newspaper accounts by D.H. Hitchcock and others often described lava tunnels, viaducts, or conduits and how those internal tubes carried lava to the advancing flow front.

The advancing lava flow split into three forks at the 730-m (2,400-ft) elevation (8.5 miles from Hilo Bay), only to reunite into a single flow at the 500-m (1,600-ft) elevation (6.3 miles from the bay). The flow again split into two forks—north and south—at the 90-m (300-ft) elevation (1.6 miles from the bay).

The north branch of the flow continued down the ‘Alenaio stream bed and stopped about 70 m (225 ft) mauka (inland) of Komohana Street. The south branch advanced a bit farther, crossing Komohana Street and going down what was then known as KALANAKAM‘A‘ā Gulch (just south of Mohouli Street), then stalled near the intersection of Mohouli and Popolo Streets at a distance of 1,740 m (1.1 mi) from Hilo Bay. All activity at the flow front had stopped by August 10, 1881.

Because the 1880-1881 lava flow reached lower elevations than the 1855-1856 lava flow, and, therefore, moved closer to Hilo and deep within the watershed of the Wailuku River, the propensity for lava flows to enter and advance through stream and river channels became obvious. Several writers used this tendency to predict the exact paths that lava flowing toward Hilo would take.

This is also the idea behind our current use of steepest descent lines, calculated from digital elevation models, to forecast future paths of lava flows, because, like water, lava tends to flow downhill. With the advent of fast, cheap computers and good digital terrain models, calculations can be made quickly, ahead of an actual lava flow, even in areas where stream flow has not carved out an obvious path. This tool, an offshoot of early observations, is just one of the many that we use to keep the public informed of potential volcanic activity and hazards.


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 varied between 30 and 40 m (100–130 ft) below the rim of the Overlook crater.

On Kīlauea's East Rift Zone, the Kahauale‘a 2 flow remains active. The flow front stalled at 8.8 km (5.5 miles) northeast of its vent on Pu‘u ‘Ō‘ō in mid-May. On Tuesday, June 24, the most distant active flows were approximately 7.1 km (4.4 miles) northeast of Pu‘u ‘Ō‘ō. In addition, several small, brief lava flows erupted from spatter cones within the Pu‘u ‘Ō‘ō crater.

One earthquake was reported felt in the past week across the Island of Hawai‘i. On Friday, June 20, 2014, at 10:25 p.m., HST, a magnitude-3.1 earthquake occurred 5 km (3 mi) south-southwest of Volcano village at a depth of 3 km (2 mi).

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