Volcano Watch — The next Hualālai eruption

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What will the next eruption of Hualālai be like? The first step in answering that question is to find out what the last several eruptions were like. That doesn't sound so hard - we should be able to look in some book or on the Worldwide Web. After all, Kīlauea and Mauna Loa erupted a bunch of times in the last couple of centuries and there is plenty of information on those eruptions available.

What will the next eruption of Hualālai be like? The first step in answering that question is to find out what the last several eruptions were like. That doesn't sound so hard - we should be able to look in some book or on the Worldwide Web. After all, Kīlauea and Mauna Loa erupted a bunch of times in the last couple of centuries and there is plenty of information on those eruptions available.

Alas, it's not that easy. The last eruptions of Hualālai occurred sometime between the late 1700s and 1801. This is a period of Hawaiian history that is not well documented and, although one can find many references to the eruption, most are contradictory. For example, twenty-three references (mostly diaries or trip reports) give a specific date for these eruptions varying from 1774 to 1811. We currently accept that they occurred in 1800 and 1801 but we cannot be certain. We have found no first-hand descriptions and only four second-hand accounts (interviews with eye-witnesses).

By the process of matching these historical accounts with information we get from studying the actual lavaflows, we have been able to piece together a little of the story of these eruptions. The flows erupted from six different vents on the northwest rift zone of Hualālai. That's why we're talking about the last `eruptions' and not the last `eruption.' The two largest and best known of these flows are the Ka`upulehu flow, which went into the ocean between the Kona Village Resort and Kiholo Bay, and the Hu`ehu`e flow upon which most of the Keahole airport is built. We don't know how long these eruptions lasted, but we're pretty sure that the Hu`ehu`e flow, was erupted last in 1801. Its vents were less than 6 km (4 miles) from the coast at that time and the lavas probably reached the sea quickly.

Eye-witness John Young, a western advisor to Kamehameha, reported that the eruption was very loud and sent lava crusts into the air (probably at the ocean entry). The ocean entry was so hot that it could not be approached in a canoe closer than 50 yards. The coastal waters were heated to the point that numerous fish were killed and canoes in the water were softened.

The Hu`ehu`e flow was particularly devastating because it destroyed a very valuable fishpond named Pa`aiea that belonged to Kamehameha. Pa`aiea was reported to be 5 km (3 miles) long and 1 km (0.5 mile) wide. It is now completely covered by the flow. In addition, agricultural and habitation areas around the fishpond were inundated.

A story is told about how Kamehameha stopped the flow with a lock of his hair thrown into a raging channel full of lava. We now know that the final phase of the Hu`ehu`e flow was a slowly emplaced pahoehoe that is very similar to the pahoehoe produced by Kīlauea during the latest eruption. The earlier phases of the Hu`ehu`e were emplaced through large, wide channels. Kamehameha may have committed his sacrifice to stop the earlier, channelized pahoehoe.

When Hualālai next erupts (about a 30% chance in the next century), look for similar types of flows which will probably advance rapidly down the steep slopes. Considerably more coastal areas are developed now than in 1801 around Hualālai. Destruction will be difficult to avoid if the flows last long enough to get to the ocean. Neither can we hope that a lock of anyone's hair will be useful in altering the course of the eruption as it is said to have been during the previous activity.

Volcano Activity Update

Kīlauea's east rift zone eruptive activity is limited to a sustained lava pond within the Pu`u `O`o Crater.