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O‘ahu
Landsat Image, courtesy of NASA Hawai‘i Informart Project
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About when Wai‘anae was pau, Ko‘olau
begins to grow above sea level.
Submarine portion
Submarine portion
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Diagram by G.P.L. Walker
Dense rocks (e.g., solidified magma chambers) produce a stronger
pull of gravity,
measured at the surface as a positive gravity anomaly
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SPOT satellite image
approximate
boundary of old caldera
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Mt. Ka‘ala, an essentially undissected remnant of post-shield
alkalic lavas
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Lualualei valley – essentially the eroded-out old caldera
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Pu‘u Ma‘ili‘ili: erosional remnant exposing flat-lying,
intra-caldera flows -
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Wai‘anae volcano viewed essentially up-rift from Kapolei
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Main tholeiite shield flows exposed above the road to Ka‘ena
Point (to the left)
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Ka‘ena Point viewed from the West
(from
http://www.soest.hawaii.edu/coasts/data/oahu/oblique_north.xml)
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View from above Ka‘ena Pt.
eastward towards Mokule‘ia. Cliffs at right are wave-cut,
and narrow coastal plain consists of coral now 2-3 m
above sea level.
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Makua valley -
Ridge consists of many
many dikes, marking the axis of a rift zone (arrow)
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The axis of one of the Wai‘anae Volcano rift zones is exposed in
the cliff at Kaneana. -
Farrington Hwy.
Makua cave -
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Planezes of original Ko‘olau shield surface, accentuated by
expensive houses
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Planar remnants of the original Ko‘olau shield surface,
accentuated by sugar cane
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Planar remnants of the original Ko‘olau shield surface,
accentuated by pineapples
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Konahuanui, the highest point
on Ko‘olau
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Most of Honolulu sits on alluvium washed out of large
amphitheater-headed valleys that is
interbedded with old coral reefs and rejuvenation-stage lavas
and pyroclastics.
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Waikiki sits on reclaimed marshland, and the highrises are
supported by piles driven down to stronger layers of coral and/or
rejuvenation-stage lava flows.
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Sand channels indicate where streams used to enter the ocean
(coral doesn’t like fresh H2O)
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Ni‘u “peninsula” is an old Hawaiian
fishpond that was filled in
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Another view of Ni‘u Peninsula
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Palolo Valley -
alluvium
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On the Ko‘olau side of Ko‘olau, there is original shield
material remaining, but essentially no original shield surface
remaining.
original shield remnants
approximate trace
of giant avalanche scar
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Photo from Volcanoes in the Sea
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View inland from Mokulua Islands: the hills in the foreground
are intra-caldera lavas, and those behind are flank lavas dipping
away (i.e., towards Honolulu).
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The Honolulu Volcanic Series, Ko‘olau Volcano’s rejuvenation
stage
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Ozawa et al. (2005)
Recent, precise age-dating work is starting to sort-of unravel
the Honolulu Volcanics
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There appear to have been
two pulses of rejuvenation, with a break from ~0.36 Ma
to ~0.24 Ma. Maybe this represents two different
processes going on?
Heating of the lithosphere by
the dragged-along plume might explain the early part
(~0.84-~0.36 Ma), and then the lithospheric flexure
process might explain the
most recent activity.
Ozawa et al. (2005)
Kaimuk
Koko rift M noa,
Tantalus
Puowaina
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Famous landmarks: Le‘ahi (foreground) and Koko Rift (background)
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Aliamanu (bird salt pond) crater, a place where Pele and her
family lived for a while. “When they left, Pele dropped some salt,
and the pet bird of Hi‘iaka, Pele’s favorite sister, escaped…”
(Pukui et al., 1974 Place Names of Hawai‘i)
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Aliapa‘akai (salt pond) crater - known as Salt Lake today. Pele
dug the crater, and some salty mucus from her eye fell here (Pukui
et al., 1974 Place Names of Hawai‘i)
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The Koko Rift,
probably 30-40 thousand years
old
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Rejuvenation
Rejuvenation
Main Shield remnants
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Ka‘au Crater
Mau‘umae Cone
THREE LESSER-KNOWN HONOLULU VOLCANIC SERIES VENTS
Kaimuki Shield -
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Traced from Volcanoes in the Sea
