U.S. Geological Survey
Hawaiian Volcano Observatory
P.O. Box 51, Hawaii National Park, HI 96718
Phone (808) 967-7328 FAX (808) 967-8890

Volcano Watch --- November 4, 1999

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 KilaueaŠ." 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.

Volcano Watch is a weekly feature provided by scientists at the U.S.
Geological Survey