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What will the next eruption of Hualālai be like?

August 23, 2013

View of the volcano Hualālai from Kaloko-Honokohau National Historical Park, on the Kona side of the Big Island of Hawaii. (Photo used by permission)

The following is this week’s installment of Volcano Watch from the USGS Hawaiian Volcano Observatory:

Hualālai, looming majestically above Kailua-Kona, is Hawaiʻi’s third most active volcano (http://hvo.wr.usgs.gov/volcanowatch/archive/2009/09_10_01.html). The U.S. Geological Survey classifies it as a “high threat” volcano, based on its frequency of eruptions and the proximity of its vents to developed areas.

We can’t say when Hualālai will next erupt, but we can offer clues about the nature of its next eruption.

We get these clues from Hualālai’s past behavior. The geologic map of its volcanic deposits (http://pubs.er.usgs.gov/publication/i2213) shows that ash deposits are found around vents along the volcano’s rift zones and summit but rarely along coastal areas. The dominant features of the map are the several hundred lava flows covering the volcano’s surface, about 35 of which have been dated from the past 25,000 years. About 200 eruptions produced lava flows within the last 10,000 years. From this, we conclude that the predominant threat from Hualālai is lava flows.

Hualālai lava flows of 1801.

Hualālai lava flows of  1800-1801.

It appears that Hualālai’s eruptions are clustered in time, separated by centuries of inactivity. The most recent cluster of activity included eruptions that ended in 1801 from six different vents within the volcano’s northeast rift zone. Lava flows from the largest of these eruptions—the Kaʻūpūlehu (to the northwest) and the Huʻehuʻe (Kona airport) flows—have been examined in detail, and the results are surprising.

The Kaʻūpūlehu flow erupted from the second highest vent, and the Huʻehuʻe flow came from the lowest two vents. Both eruptions produced complex lava flows in phases that started with channelized ʻaʻā flows and ended with pāhoehoe flows.

The Kaʻūpūlehu lava flow is similar in character to the flow produced by Mauna Loa’s 1984 eruption. If the comparison is correct, then, by analogy, the eruption rate of the two flows should be similar. Using this logic, we assume the eruption rate of the Kaʻūpūlehu flow to be about 300 cubic meters per second (4 million gallons per minute). Using this eruption rate and the volume of the Kaʻūpūlehu flow—estimated to be about 160 million cubic meters (130,000 acre-feet)—the eruption must have lasted more than a week.

What we call the “Huʻehuʻe flow” is actually two flows. The earlier one progressed from ʻaʻā to pāhoehoe, while the later flow was entirely pāhoehoe. This later pāhoehoe flow is very similar to today’s active flows on Kīlauea’s coastal plain, suggesting, by analogy, that the Huʻehuʻe flows advanced similar distances to the ocean over several days to weeks.

We can further use the analogy with Mauna Loa to estimate possible advance rates of future lava flows from Hualālai.

The initial lava flow that erupted from Mauna Loa in 1984 had advanced 15 km (9 mi) in little more than 20 hours. So, if Hualālai’s next eruption produces lava flows similar to the Kaʻūpūlehu or the Huʻehuʻe flows, we speculate that they could reach the ocean in less than a day.

Because developed coastal areas are 15 km (9 mi) or less from the vents on Hualālai’s summit and northeast rift zone, our next question is, will we be able to detect any eruption precursors?

We have only one possible example from which to draw conclusions: an earthquake swarm that was interpreted to be an intrusion or a failed eruption. Starting on September 19, 1929, more than 6,200 earthquakes were recorded over the span of a month. Many of the earthquakes were strongly felt, especially near the Puʻuwaʻawaʻa cone, and two had magnitudes estimated at more than 6. The earthquakes alone produced “hundreds of thousands of [1929] dollars in damage.” But no eruption occurred.

The Volcanoes of Hawaii Island. (USGS)

The Kaʻūpūlehu flow offers another possible clue about the duration of precursory signals: abundant, large xenoliths (rocks dragged up from depth with the ascending magma). From the size, shape, and mass of these xenoliths and the viscosity of the magma, we can estimate how fast the magma must have risen to carry these heavy rocks to the surface. Calculations suggest that the magma ascent was extremely rapid (hours to days), which, in turn, suggests a short period of precursory signals.

These are the reasons why the Hawaiian Volcano Observatory closely monitors Hualālai, even when there are no apparent changes on the volcano. Should any occur, we will immediately let you know.

One Comment leave one →
  1. Flo Kalawa Tabag permalink
    August 23, 2013 8:46 pm

    ALOHA INO!!!

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