Volcano Watch — Mauna Loa's 1984 eruption taught us much about how lava flows work

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The eruption began at about 1:30 a.m., HST, on March 25, 1984, after only a few hours of precursory seismic activity. The initial curtain of fire occupied the entire summit caldera and eventually migrated into the upper southwest rift zone. Within a few hours, however, the activity made a U-turn—magma began migrating into the northeast rift zone. By 5:00 a.m., the northeast rift zone vents had become the focus of eruptive activity. The eruption lasted for three weeks, feeding lava flows that reached within 6.5 km (4 mi) of the outskirts of Hilo.

The 1984 activity was the first (and, so far, the only) Mauna Loa eruption to have been well monitored scientifically (which is why it is the only Mauna Loa eruption that we will cover in this month's series of articles). HVO scientists were able to reach the northeast rift zone vents within hours of the eruption's onset and collected detailed observations of lava flow activity over the ensuing three weeks. The work was motivated by the need to assess the threat to Hilo but resulted in a wealth of scientific insights and a better understanding of how lava flows work.

Mauna Loa eruptions differ from those of Kīlauea because they are usually much more vigorous. The eruption rate of lava during typical Mauna Loa eruptions is generally several times that of a typical Kīlauea eruption. In fact, the amount of lava emitted during Mauna Loa's 22-day-long eruption was equivalent to about two years of output from Kīlauea!

During the eruption, HVO and collaborating scientists made repeated observations at points along the lava channels that fed the flows moving toward Hilo. Data collected included lava velocity, temperature, density, chemical composition, eruption rate, channel width, and, most importantly, changes in these parameters over time. In fact, volcanologists from all over the world descended on the Big Island to study the eruption (lots of tourists showed up too!).

What resulted from this intensive study was an understanding of how channelized lava flows grow and what factors control flow morphology, including the transition from pāhoehoe to ‘a‘ā. In fact, the comprehensive data collected from lava flows during the 1984 Mauna Loa eruption and the resulting insights into the behavior of ‘a‘ā flows, especially, have been used to construct models that forecast how long a lava flow will extend and what path it will follow. The 1984 Mauna Loa lava flows now serve as a standard for the interpretation of older flows and for the development of flow models. It seems fitting that an eruption that posed such a significant threat to Hilo now provides the data needed to help better evaluate—and protect against—lava flow threats in Hawai‘i and elsewhere around the world.

Next week, in the third part of our series on scientifically important eruptions in Hawai‘i, we will focus our attention the 1969–1974 eruption of Mauna Ulu, on Kīlauea's east rift zone.

Meanwhile, check out the Volcano Awareness Month activities that HVO has scheduled for this week by visiting our Web site or by calling 808-967-8844.

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Volcano Activity Update

A lava lake within the Halema‘uma‘u Overlook vent produced nighttime glow that was visible from the Jaggar Museum overlook and via HVO's Webcam during the past week. The lake reached to within 26 m (85 ft) of the floor of Halema‘uma‘u before dropping slightly back down. This is not as high as the level reached during October 2012, but it is very close. There were several collapses from the rim and walls of the Overlook crater with the high levels. The Overlook crater is now 160 m (525 ft) wide from the viewpoint of the Jaggar overlook, and is about 200 m (656 ft) long.

On Kīlauea's east rift zone, surface lava flows remain active near the coast and are feeding weak ocean entries scattered along the sea cliff on both sides of the Hawai‘i Volcanoes National Park boundary. Within Pu‘u ‘Ō‘ō, the lava level has reached to a high level and flows have been spilling from the crater onto the northeastern flank of the Pu‘u ‘Ō‘ō cone. This is the highest level of activity at Pu‘u ‘Ō‘ō since September 2011.

There were four felt earthquakes in the past week on the Island of Hawai‘i. On January 13, 2013, at 4:28 a.m., a magnitude-3.2 earthquake occurred 4 km (3 mi) southeast of Kīlauea summit at a depth of 3 km (2 mi). On January 15 at 5:15 p.m., a magnitude-2.7 earthquake occurred 4 km (3 mi) south of Volcano at a depth of 3 km (2 mi). Later that same day at 11:50 p.m., a magnitude-2.1 earthquake occurred 4 km (3 mi) west of Kailua-Kona at a depth of 10 km (7 mi). On January 16 at 10:33 a.m., a magnitude-2.6 earthquake occurred 13 km (8 mi) south of Kapoho at a depth of 10 km (7 mi).