Regional Geology of Maui Nui

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Regional Geology of Maui Nui
The island of Maui comprises two major volcanoes,
West Maui and East Maui (Haleakala). But Maui
itself is one of four islands that form the
once-great island of Maui Nui. The other islands
are Kahoolawe, Lanai, and Molokai. The extent
of these islands and the shallow flooded platform
that connects them is easily seen in the
accompanying bathymetric map, which shows the
southeastern part of the Hawaiian Island chain.
Maui Nui--roughly coincident with the four
islands of Maui County--probably was similar in
extent to today's Big Island. The submergence of
Maui Nui resulted from the complex interplay of
diminished volcanic upbuilding and continued
subsidence as the island complex moved away from
the Hawaiian hot spot. A similar fate awaits the
Big Island. As the Pacific plate moves
relentlessly northwestward, at about 10 cm per
year, the Big Island volcanoes will lose their
eruptive vigor. Without the benefit of rapid
volcanic construction, subsidence will dominate
the sea will slowly encroach on the flanks of the
separate volcanoes, then flood the saddles that
separate them, creating smaller islands
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The four islands of Maui, Molokai, Lanai, and
Kahoolawe were once all connected as a vast
landmass known as Maui Nui, literally "big Maui."
This concept was first proposed 60 years ago by
geologist Harold Stearns, who recognized the
geologic evidence for repeated episodes of island
submergence and reemergence. Recently, Jonathan
Price of the Smithsonian Institution modeled the
area's submergence history using a computer-based
geographic information system (GIS). The model
examines the effects of global sea-level change,
age of volcanism, and likely rates of volcano
subsidence. Using Price's model, we can watch the
response of Maui Nui to subsidence and sea-level
change as we move the clock forward or back
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Maui Nui in its heyday, about 1.2 million years
ago, encompassed about 14,600 square kilometers
(5,640 sq mi), larger by 50 percent than today's
Big Island of Hawaii. Included in this landmass
was Penguin Bank, a broad shoal west of Molokai.
Penguin Bank originated as a volcano that
completed its shield-building stage about 2.2
million years ago, when it was briefly connected
to Oahu. Now bearing a thick coral cap and lying
in water shallower than 200 m, the once-emergent
volcano covered an area eight times that of
present-day Kahoolawe. From Penguin Bank on the
west, Maui Nui reached 250 km (160 mi) eastward,
its distant shore lying 70 km (40 mi) east of
today's Maui village of Hana.
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Maui Nui, the large island that once included
today's separate islands of Maui, Moloka'i,
Lana'i and Koho'olawe, as well as Penguin Bank,
was made up of seven volcanoes. Haleakala is the
youngest of these volcanoes. Earth scientists say
it's probable that Haleakala will erupt again
within the next several hundred years.Scientists
say that Kaho'olawe is extinct. West Maui and
East Moloka'i are finished, too, as both show
evidence of having had rejuvenation stages long
ago. East Maui is at the post-shield stage and
could conceivably erupt anew in a rejuvenation
period. Penguin Bank is extinct and is now under
water, covered with coral deposits (and research
for this article was unable to uncover any
association of Penguin Bank with penguins). Maui
Nui, the one great island, gave way to subsidence
and erosion 300,000 to 400,000 years ago,
creating two islands. One of the islands was made
up of Penguin Bank, Moloka'i and Lana'i. The
other consisted of Kaho'olawe and Maui.Then,
100,000 to 200,000 years ago, erosion and
subsidence separated Kaho'olawe from Maui, and
after that, Lana'i from Moloka'i. Penguin Bank
slipped beneath the sea within the past few
hundred thousand years. The scientists say that
if today's rates of erosion and subsidence
continue, Haleakala and West Maui will become two
separate islands in about 15,000 years.
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Lanai is the sixth largest of the eight main
Hawaiian Islands with an area of 36,520 ha. Lanai
Island is the emergent portion of a single
volcano. The highest point is Lanaihale Peak at
1020 m (3370 ft). Island slopes on the easterly
side are steep and cut by gulches. Western slopes
are gentler. The south central portion of the
island between elevations of 300 m and 600 m is a
flat plain known as the Palawai Basin, which was
the major pineapple-growing region of the island
until recently
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The Island of Molokai is the fifth largest of the
eight main Hawaiian Islands. The joining of two
ancient volcanoes formed Molokai Mauna Loa to
the west and Kamakou to the east. Erosion,
deposition, slumping and secondary volcanic
events modified the topography. The resulting
shape of the island is elongated in the east-west
direction, much in the shape of a peanut. The
crest of the eastern volcano is named Kamakou,
the highest peak on Molokai (1515 m or 4970 ft).
Steep mountain slopes that are deeply eroded and
cut by numerous gorges characterize East Molokai.
In contrast, West Molokai is a barren tableland
that reaches only 400 m (1200 ft) in elevation.
West Molokai supports plantations, ranches and
small farms