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Mauna
Loa is massive. Geologists call it the largest volcano
on earth. It covers half of the surface area of the Big
Island. Besides it size, Mauna Loa is one of the best-studied
mountains on earth. It is also one of the most active
volcanoes on the planet. While Kilauea continues to pump
out the magma and capture the headlines, the giant Mauna
Loa quietly inflates and readies itself for another show.
With its mass, history of monitoring and study, and its
very active eruptive rate, Mauna Loa is the superlative
Hawaiian volcano.
Mauna
Loa's immensity is difficult to comprehend. Though it
rises 13,680 feet above sea level, Mauna Loa begins its
rise from the ocean floor some 16,400 feet down. So the
mountain is over 30,000 feet high, taller than Mt. Everest.
For sheer mass it is unequalled. The volcano covers an
area roughly the size of all the other Hawaiian Islands
combined. I've heard one geologist call it "the largest
projected landmass between Mars and the Sun." Another
oft-quoted statement is that the entire Sierra Nevada
mountain range in California could fit within Mauna Loa.
Or how about the fact that Manhattan Island could fit
within its summit caldera Mokuaweoweo.
Mauna
Loa |
Mauna
Loa |
Recently,
the staff of Hawaii Volcano Observatory printed in the
weekly Volcano Watch a fantastic description of Mauna
Loa's true vertical relief. One reason the ocean is so
deep here in Hawaii is because of the downward flexing
of the Pacific Plate. The weight of Hawaii's volcanoes
is pushing down the oceanic crust. With new technologies
geologists have been able to view with an almost X-ray
vision inside the bottom of Mauna Loa. As the volcano
has built up, it has also depressed a mirror image of
itself down into the sea floor. This depression extends
26,000 feet down from the ocean floor. Therefore, the
complete height of Mauna Loa from its true base to the
summit is 56,000 feet!
Satelite
photo showing various flows on Mauna Loa.
(Click image for larger rendering) |
Scientists
have been studying and monitoring Mauna Loa since 1843.
The new images of Mauna Loa's great depth are an example
of remarkable technology and research. Just as remarkable
are the studies that have mapped the surface of the volcano.
With nearly a million acres of lava fields, some barren,
but many covered with thick vegetation, geologists such
as John Lockwood have spent years identifying and dating
the different lava fields that cover the mountain. Their
efforts, encompassing very nearly the entire surface of
the mountain, have led to the best-documented chronology
of eruptive activity of any volcano on earth. From their
studies they've calculated that every 1000 years Mauna
Loa covers 40% of her surface area with new lava. The
first flow from Mauna Loa that was documented historically
was in 1843. Since then the mountain has erupted 33 times.
This eruptive record is one of the most active on earth.
Mauna
Loa last erupted in 1984. The previous flow to that was
1975. Before both the 1975 and the 1984 eruptions, geologists
measured an inflation of Mauna Loa. Magma charges the
mountain swelling it like a balloon and with varying technologies
this deformation can be measured. They also recorded increased
seismic activity two years prior to the eruptions associated
with the magma movement. Since the 1984 flow the volcano
has inflated from magma storage underground. Mauna Loa
has inflated 20 inches since then. Geologists believe
that more magma has charged the mountain since the '84
eruption, than did previous to it. The '84 flow was not
a small eruption. It produced "220 million cubic
meters of lava, the third largest volume this century."
Geologists tell us it was putting out enough lava every
hour to build a sidewalk from Honolulu to New York City.
That flow made it within a few miles of Hilo. Though the
mountain continues to swell, currently there is no increased
earthquake activity suggesting an imminent eruption. But
you can be sure Mauna Loa will erupt again.
When
the eruption occurs it will add more mass to the big mountain.
And it will offer the students and researchers another
chance to observe and learn. Mauna Loa's lessons extend
beyond geology of course. It is not just a mountain of
volcanic rock. It contains a wide variety of terrain and
ecosystems all organized very nicely among differing ages
of well cataloged and dated substrates. This marriage
of earth and life sciences makes Mauna Loa a model system
for ecological research. As the noted biologist Peter
Vitousek says, "To biologists as well [as geologists],
Mauna Loa is a place of global significance-not for rocks,
but for the organisms and ecosystems that occupy it's
surface." Mauna Loa is swelling with magma, sinking
with weight, and offering us glimpses into some of the
life's lessons.
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