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July 6, 2000

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

Mauna Loa and Kilauea: lighthouses of the Pacific?

A TV crew doing a documentary on lighthouses in Hawai`i recently asked HVO if erupting Kilauea and Mauna Loa could have served as natural beacons for Polynesian wayfarers. Stromboli, a constantly active volcano in the Aeolian Islands north of Sicily, has been known for more than 2,000 years as the "lighthouse of the Mediterranean." Might Kilauea and Mauna Loa have served as "lighthouses of the Pacific" for past navigators?

Given their remarkable navigational skills, Polynesians voyaging to or within Hawai`i would hardly have needed a lighthouse to guide them. Nonetheless, it is always comforting to see familiar sights, and a stable lighthouse might have aided beginners and provided confirmation to the masters.

A lighthouse has to be turned on to be of any use. How often in the past 2,000 years were Mauna Loa and Kilauea turned on?

Mauna Loa has erupted more than 213 times in the past 2,000 years, an average of once every 9.4 years. Not every flow is known or dated, so the true frequency of eruption is greater. Each eruption probably lasted several weeks or longer. During the first 1,100 years, eruptions were concentrated at the summit, with many overflows from Moku`aweoweo caldera. By analogy with Kilauea, such summit activity may have persisted from months to years. A year-long eruption every 9.4 years is 10 percent of the time. Certainly Mauna Loa was not persistently active, but the frequency of its activity may have been enough to help guide voyagers occasionally.

We know little about Kilauea between about 1,000 and 2,000 years ago, because most lava flows of that age have been buried by younger flows. Since then, Kilauea had several long-lived eruptions, mainly from its summit, between about A.D. 1000 and 1500. The eruptions probably lasted years, with the `Aila`au eruption lasting about 60 years (A.D. 1410-1470). Just as for Mauna Loa, Kilauea's activity was not persistent but may have been sufficiently frequent to have helped in navigation.

Both Mauna Loa and Kilauea are high enough to have produced a glow visible for scores of kilometers (tens of miles) at sea. Kilauea is higher than Stromboli, and its most persistent eruptions have come from its summit or high on its rift zones. Mauna Loa is one of the world's highest oceanic volcanoes, and most of its eruptions also take place at the summit or high on the rift zones. Today, glow reflected by the rising steam plume at an ocean entry can be seen for a long distance from shore. Add several hundred meters (several thousand feet) in elevation, and a similar glow could be seen much farther away.

For example, Henry Bianchini, while sailing from San Diego to Hilo in August 1969, observed a glow on three consecutive nights from Mauna Ulu, at 1,000 m (3,300 feet) elevation on Kilauea. He first noted a glow (caused by a lava flow and low lava fountains) when 100-150 nautical miles at sea; two days later, he saw what turned out to be a 400-m-high (1,300-foot-high) fountain.

The great exploration and migration voyages of the 10th-14th centuries would have brought Polynesians within sight of Mauna Loa and Kilauea during periods when both volcanoes were rather active, likely from months to years at a time. Would a glow seen from afar have been viewed as Pele welcoming or warning the voyagers? One could ask a similar question about today's lighthouses, since they both welcome you to land and warn you of the danger in getting there.

Were erupting Mauna Loa and Kilauea useful beacons for Polynesians in Hawai`i? We will probably never know for sure, though there may be information in chants that could shed light (pun intended) on this question. Please contact HVO if you are aware of any mention in a chant or mo`olelo of volcanic glow helping to guide ancient travelers.

Eruption Update

Eruptive activity of Kilauea Volcano continued unabated during the past week. Lava is erupting from Pu`u `O`o and flowing through a network of tubes toward the coast near the eastern boundary of Hawai`i Volcanoes National Park. Surface flows from breakouts of the tube system are seen occasionally in the coastal flats and on Pulama pali. Lava is entering the ocean mainly at two locations: Waha`ula and Kamokuna. A third entry, located 500 m (550 yards) to the east of Waha`ula, is erratic and wispy. The public is reminded that the ocean-entry areas are extremely hazardous, with explosions accompanying sudden collapses of the new land. The active lava flows are hot and have places with very thin crust. The steam clouds are highly acidic and laced with glass particles.

No earthquake was reported felt during the week ending on July 6, 2000.

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Updated: 10 July 2000