bob

At one point I say that Mauna Loa is 56,000 feet above the ocean floor; on
another page I say that Mauna Kea is 32,000 feet above the ocean floor. I
went back to try to find my sources and came across two websites: USGS
website says Mauna Loa is "about 17 km (56,000 ft) above its base!" But UH
Institute for Astronomy's website says Mauna Kea "rises 9,750 meters (32,000
ft) from the ocean floor" and is the highest island-mountain in the world.
Both seem to be reputable sources, but the two statements seem at odds with
one another. I need a geologist! I'm just a mere historian. Anyone know
the answer?

Bob

lee meyerson

The answer lies in the terms used. Mauna Loa is the tallest mountain when
measured from its base. Being an extremely massive mountain, the weight of
Mauna Loa depresses the crust. Thus the height above its base is greater
than its height above the sea floor, because it depresses the crust beneath
it.

The quote for Mauna Kea uses the sea floor as a reference point and does not
account for the depressions of the crust. If it did, since it is less
massive than Mauna Loa, the total height of Mauna Kea would be less than
Mauna Loa, even though it is higher above sea level.

lawrence akutagawa

The wag remarking that Mauna Loa base is positioned in a large
depression
while that of Mauna Kea is situated on a high plateau wouldn't be
wrong at
all, given Lee's interpretation. Which goes to say that the sea
floor is
not the same sea floor all around!

mainland dan

Also, if you are looking for references, here are two pages that
give
specifics:

http://www.soest.hawaii.edu/mauna_loa/intro.html

http://www.soest.hawaii.edu/GG/HCV/maunaloa.html

"When one considers that the flanks of Mauna Loa sit on sea floor
that is
about 16,400 ft (5,000 M) deep, the "height" of this volcano relative to
neighboring land (the sea floor) is more like 30,080 ft (9,170 m)! Mauna
Loa is the largest active volcano in the world.
....All large land masses (such as mountains) also push down upon the
Earth's crust due to their enormous weight. So, directly beneath Mauna
Loa, the sea floor on which it sits is depressed by and additional
26,000 ft (8000 m). Thus, if one wanted to say how thick (at its center)
is the lava pile that makes up Mauna Loa, one would need to add its
above sea level height, its sea floor to sea level height, and the
thickness of its depression in the Pacific sea floor. These total 56,080
ft (17,170 m). For more details about estimation of the actual thickness
of Mauna Loa volcano, see the write up on "How high is Mauna Loa
volcano" at the HVO website."

http://hvo.wr.usgs.gov/volcanowatch/1998/98_08_20.html

Thanks, Dan

alvin e. toda

I just find it hard to believe that the sea floor is so
uneven. And if you were to drive up from sea level
Mauna Kea would be higher than Mauna Loa not lower.
There's probably a better explanation for these
figures. Can't help but feel that somebody's reporting
the wrong units of length.

BTW, Mauna Kea's the dormant one, and probably older.
It's probably why Mauna Kea is taller. So Mauna Loa's
flow would cover Mauna Kea's. Can't help but feel that
there would be a depression under Mauna Kea if there is
one under Mauna Loa.

lee meyerson

There is a depression under Mauna Kea, however since Mauna Kea is not as
massive as Mauna Loa, the depression is not as great.

In the original post the quote used two different reference points, hence
the discrepancy. The base of the mountain and the general depth of the sea
floor are two very different reference points. One takes into account the
depression of the sea floor and the other does not.

Lee

alvin e. toda

Well since Mauna Loa is a more recent flow, perhaps
part of that Mauna Kea depression has been filled in by
the Mauna Loa flow. If we really wanted to compare the
sizes of the two, then we should find a suitable point
on the base of Mauna Kea on the side opposite to Mauna
Loa-- the same for Mauna Loa. It could be that Mauna
Kea is still the bigger volcano. It might just be that
much of it's depression is filled in by Mauna Loa.
Perhaps Mauna Loa originated on the slope of Mauna Kea.

just another

The depression is caused by the weight; if you try to "fill in" the
depression, you'll increase it, by increasing the weight.

maren purves

OK, I understood this that way too.
It's comparing apples and oranges.


Height and size are two different animals.
Size is 3 dimensional, height being one of them.
While Mauna Kea is only slightly higher than Mauna
Loa as measured from wea level, the upper slopes of
Mauna Kea are rather steep, and even if its length
and width at the base were similar, Mauna Loa's
volume would still be bigger. You're comparing
a very flat cone (Mauna Loa) to a much steeper
one (at least at the higher elevation, Mauna Kea),
i.e. no matter what the height, Mauna Loa's volume
(and thus probably mass, unless the denisities are
vastly different) is much bigger (probably causing
a deeper depression in the mantle).

Can't help it, sometimes the physics takes over.

Maren
Palms, Etc.: Tropical Plant Seeds - Hand-made Jewelry - Plants & Lilikoi
http://www.jach.hawaii.edu/~maren/palms_etc/
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lawrence akutagawa

ie, reality bites...again.

Mother Nature has this peculiar propensity to disregard wishes and
desires
as well as could-have-beens and should-have-beens. She centers on
(William
Jefferson Clinton's comments not withstanding) what *is*. A spin
maker she
definitely is not.