Bob 2009-12-28 10:54:14
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
Lee meyerson 2009-12-28 10:54:29
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
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 akuta 2009-12-28 10:54:49
The wag remarking that Mauna Loa base is positioned in a large
while that of Mauna Kea is situated on a high plateau wouldn’t be
all, given Lee’s interpretation. Which goes to say that the sea
not the same sea floor all around!
Mainland dan 2009-12-28 10:54:52
Also, if you are looking for references, here are two pages that
“When one considers that the flanks of Mauna Loa sit on sea floor
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.”
Alvin e. toda 2009-12-28 10:55:15
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 2009-12-28 10:55:22
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.
Alvin e. toda 2009-12-28 10:55:25
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 2009-12-28 10:55:40
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 2009-12-28 10:55:55
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.
Palms, Etc.: Tropical Plant Seeds – Hand-made Jewelry – Plants & Lilikoi
– fresh Spiderlily/Crinum Asiaticum seeds available –
Lawrence akuta 2009-12-28 10:55:58
ie, reality bites…again.
Mother Nature has this peculiar propensity to disregard wishes and
as well as could-have-beens and should-have-beens. She centers on
Jefferson Clinton’s comments not withstanding) what *is*. A spin
definitely is not.
Bob 2009-12-28 10:56:24
three ways to measure the heights of Mauna Kea and Mauna Loa. To most
people, it is the height above sea level that really matters. But to
others, it is the height from the ocean floor to the top. And to still
others (geologists mainly) it is the height measured from the base of
mountain, which because of its enormous weight may be suppressed
ocean floor. If you take a rock and put it in a bucket of mud, some
of that rock will probably sink below the surface of the mud. To
the real size of the rock, you would need to look at the subsurface
not just the part that is above the surface of the mud. And if you
water to the bucket on top of the mud, you would roughly have the
of the three types of measurement. Somewhat related to this thread
article in this morning’s San Francisco Chronicle that says that the Big
Island (and others) is sinking and in 80 million years well be
sea level, so check your insurance policies!
Gerard fryer 2009-12-28 10:56:26
On 2006-10-13 17:25:01 -1000, Just Another
That’s basically what these mountains do. Mauna Loa is as high as it’s
ever going to get: it will keep erupting, but it will keep sinking. I
suspect no Hawaiian volcano ever reaches much above 4 km elevation at
Want proof that these island’s sink? Download the bathy map at
http://geopubs.wr.usgs.gov/i-map/i2809/ Look at the terraces west of
Kohala towards Mahukona Seamount. Each of those steps is a fossil
shoreline. They go down over 2 km. Right now, Kohala is sinking at
almost 3mm/year. That’s over an inch a decade!
Alvin e. toda 2009-12-28 10:56:37
I believe you that they sink, but at the beginning of
this thread I get the impressions that Mauna Kea arizes
from an undersea plateau not a depression. That’s why
the numbers indicate a smaller mountain.
Can’t help but suspect that Mauna Loa formed on the
slope of Mauna Kea, and the undersea environment
rapidly cooled the lava from Mauna Loa forming an
undersea dike or tube which caused the lava from Mauna
Loa to flow towards Mauna Kea, fill up the sink
depression of Mauna Kea and even form the plateau under
Razzbar 2009-12-28 10:56:45
I think it’s funny that Hawaii’s big mountains are the “tallest on
earth when measured from …”. But nobody ever measures other mountains
that way. How high would Everest be when measured from “the base”?
Measure ’em all the same way. Fair’s fair. Mauna Loa and Mauna Kea are
still very impressive. They don’t need any special help.
I had some old encyclopedia that had a graphic showing different
mountains of the world in outline, superimposed on one another. Mauna
Loa was unbelieveable not by its height but its width and overall size.
Brandy 2010-01-04 04:13:00
Many thanks for the link to the bathynetric map ( have ordered a
plus $5 sh).
The presence of terraces suggests that the subsidence process is
discontinuous in time and I wonder is: are there are any explanations
Cheers – Carl
Alvin e. toda 2010-01-04 04:13:20
”high” has usually got a base from “sea level”. But
Size… now that’s a different story.