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November 4, 1999

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

Is Mauna Loa older or younger than Kilauea?

In 1916, Thomas Jaggar, renowned scientist and founder of HVO, wrote, in a foreword to "Hawaiian Legends of Volcanoes" by Westervelt, that "Everything indicates that Kilauea is older than Mauna Loa. Mauna Loa with its flows is tending through the ages to bury up Kilauea?." But for at least the past 40 years, volcanologists have unanimously agreed that Kilauea is younger, not older, than Mauna Loa. What occasioned this remarkable about-face, and how secure is today's interpretation?

Jaggar was no dummy. He didn't develop his ideas out of thin air. He looked at the much greater lava-flow activity of Mauna Loa than of Kilauea during the preceding 100 years and reasoned that Kilauea was waning and Mauna Loa waxing. He thought that Mauna Loa had formed in a "long spoon-shaped valley between [Hualalai and Kilauea]."

But careful observations by Polynesian settlers of Hawai`i had noted that the islands become younger toward the southeast. J.D. Dana, a leading 19th-century naturalist, had concluded similarly on the basis of geologic evidence. Rather than building on these concepts and suggesting that Kilauea was younger than its northwestern neighbor, Mauna Loa, Jaggar concluded that Mauna Loa must be younger because of its greater activity in the previous 100 years.

Since Jaggar wrote his words for Westervelt, the concepts and supporting data for plate tectonics and hot spots have changed the way that scientists view the earth. The case has been strongly made that the Pacific plate is moving northwestward over an immobile (or only slightly mobile) hot spot carrying magma up from the earth's mantle. A volcano begins to form as a point on the plate nears the hot spot; the volcano flourishes as it passes over the hot spot and slowly dies as it moves northwestward away from the spot. In this way the Hawaiian Islands in general---and each volcano on each island in particular---become younger toward the southeast. These concepts are supported by isotopic dating, landform development, and much other information. The Polynesians and Dana were right by modern thinking, and Jaggar wrong.

But what about the details of specific volcanoes? What is the "hard" evidence that Mauna Loa is older than Kilauea? We cannot see the earliest lava flows erupted by each volcano; they are deeply buried. No geophysical techniques are capable of telling which volcano is on top of the other at depths of several kilometers. There are no deep drill holes that penetrate the two volcanoes to show that one started before the other. Even with such holes, it might be tough to distinguish flows from the two volcanoes; they don't talk to you and aren't color coded. Indirect geochemical methods would be needed to develop ways to tell old Mauna Loa flows from old Kilauea flows.

You can, in places, see Mauna Loa flows on top of Kilauea flows, and vice versa. These relations, however, simply tell us what we already know; the two volcanoes have each erupted many times in the past thousand years. The relations do not tell which volcano started first, some 100,000 or more years ago.

And so we're stuck. We really can't find proof that Mauna Loa began erupting before Kilauea, yet all our concepts demand it, and there is no evidence against it. We disagree strongly with Jaggar, and, put to the test of a civil lawsuit, we would surely win a majority vote of the jury. Yet there is really no smoking gun. It is simply not possible, on the basis of what we know today, to say with absolute certainty that Mauna Loa is older than Kilauea.

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 tube to the southeast in the direction of the sea coast. The lava pond within Pu`u `O`o occasionally drains, and gases jet from the vents with a loud roar. Lava leaves Pu`u `O`o and flows through a tube southeastward to the 620-m (2050-ft) elevation, near the top of Pulama pali. There lava wells out to form a low shield with a perched pond on top. Since October 22, breakouts from the south side of the shield have been feeding a flow that has descended to the base of Pulama pali and spread part way across the coastal flat. By November 4, the distal end of the flow is about 1.6 km (1.0 mi) from the sea coast just west of the old Kamoamoa campground.

Two earthquakes were reported felt by a resident of Leilani Estates during the week ending on November 4. The first earthquake was at 10:06 p.m. on Sunday, October 31, and the second was at 12:28 p.m. on Monday, November 1. Both earthquakes were located 3 km (1.8 mi) south of Pu`ulena Crater at a shallow depth. The magnitudes of the two earthquakes were 2.2 and 2.5, respectively.

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Updated: 15 Nov 1999