Geology of the Hawaiian Islands

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Geology of the Hawaiian Islands

• Origin of the Hawaiian Swell
• Evolution
• Volcanic evolution
• Modification by erosion and mass wasting
• Volcanic Features

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Some islands are approximately circular
Others clearly consist of two main mountain
ranges, e.g., Waianae and Koolau on Oahu East
and West Molokai East and West Maui
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Or even 5!
Each individual mountain is a separate volcano
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Hawaiian Swell more than just the principal
islands at the SE end more than just volcanic
peaks sticking out of the water
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Arch broad feature 350 km across rises 1 km
above moat Moat (or deep) axis 100 km off
shore discontinuous at least to Gardner
Pinnacles more prominent on N. side of
ridge Ridge rises 4500-9200 m above surrounding
seafloor. Islands sit astride the ridge.
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Origin of the Swell
The swell is partly a product of thermal
expansion - From intrusion of hot material from
below
Volcanic loading on a stiff plate
And partly a product of flexure - Plate bends or
flexes downward below the volcanic load and
upward away from it.
Volcanic loading on an elastic plate
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The main Hawaiian islands represent only the SE
end of a long structure that includes both the
Hawaiian Ridge (WNW-trending islands and atolls)
and the Emperor Seamounts (N-trending collection
of submarine mountains (seamounts) The Hawaiian
Swell is present over much of this length,
although it is most evident around the SE end of
the chain.
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Irregular volume distribution along the Hawaiian
Ridge
Midway
Gardner Pinnacles
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Age Progression along the Hawaiian Ridge
Hawaiian legends Pele changed house. Arrived on
Oahu at Kaneana from Kauai, left Oahu along
Koko rift Pele resided for a time at Haleakala,
now resides at Halemaumau Crater in Kilauea
J. D. Dana, U. S. Exploring Expedition, 1849
Note that extinction age is not the same as age
of formation
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Modern approaches involve radiometric dating,
primarily using K-Ar
Age-distance plot from Clague and Dalrymple
(1989). Overall slope 86 mm/yr.
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What does it mean to have an age progression
along the Hawaiian Ridge?

• The Hawaiian-Emperor chain is the result of some
  regular process that has been fairly systematic
  for at least the last 70 m.y.
• It is a kind of clock, i.e. if you know where you
  are, you know the age of the rocks under your
  feet.

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What is moving? What changed 43 million years
ago (the age of the Hawaiian-Emperor bend?
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Plate Tectonics shows that the surface of the
Earth is in motion - driven by convection within
the underlying mantle.
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The melting anomaly (hotspot) responsible for the
Hawaiian islands must be relatively stationary
compared to the overriding plate. Hotspots may
be associated with deep-mantle convection,
possibly arising from the core-mantle boundary
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Other Linear Island Volcanic Chains on the
Pacific Plate

• Hawaii Emperor chain perhaps the most prominent
• Most associated with known hotspots (stars)
• Lineament should reflect the direction of
  absolute motion of the plate over the hotspot (if
  the hotspot location is fixed beneath the
  lithosphere)

Galápagos , Easter, Louisville, Marquesas,
Gambier, Society, Cook-Austral, Samoa, Caroline,
Cobb, Yellowstone
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Have you ever wondered..
Why Mauna Loa is so smooth and Mauna Kea so
bumpy
Hualalai
Mauna Kea
Mauna Loa
Kohala
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Why the surface of Mauna Loa is paved with young
lava flows?
and Mauna Kea with cones and older lava?
Why the summit of Mauna Loa has a summit crater
(caldera)?
and Mauna Kea has cones and telescopes and no
caldera
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According to Harold Stearns, the reason is that
Mauna Loa and Mauna Kea are in different stages
of evolution Mauna Loa is a mature volcano Mauna
Kea is older and has evolved beyond maturity
The concept of life stages of Hawaiian volcanoes
grew out of mapping of the individual volcanoes
of the Hawaiian chain. This work mainly took
place in the 1930s 1950s.
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The basis for this mapping was the distinction
between An early sequence of thin-bedded
basaltic flows and dikes (Wailuku Basalt of West
Maui)
And thick-bedded, much more massive and lighter
colored, later stage lavas (Honolua Volclanics,
West Maui). Intervening soils and oxidized flow
tops indicate infrequent eruptions in the late
stage of activity at West Maui
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Geologic map of West Maui (after Stearns and
Macdonald, 1942) - showing principal volcanic and
sedimentary units separated into mapped
formations (members) Wailuku lavas, vents,
caldera complex, dike complex and intrusive
rocks. Honolua lavas, domes and cones Lahaina
flows and cones.
U.S. Geol. Surv. Open File Report 2007-1089.
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Similar relations on East Molokai
E. Molokai, near Kamalo
Overlain by later, thicker flows that weather to
light grey
Early sequence of thin basaltic lava flows that
weather red-brown
E. Molokai viewed from the north Photo by S.
Rowland
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And in the Waianae Mts., Oahu
Later, thicker bedded, lighter colored lava flows
Early, thin-bedded lava flows
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Elsewhere volcanism clearly post-dates periods of
significant erosion.
Former shoreline
Koko Rift, SE Oahu
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Life stages of Hawaiian volcanoes according to
Stearns (1940, 1946)

• - correctly identified the characteristics of
  three primary constructional phases of Hawaiian
  volcanism that have come to be known as
• Shield Stage (his 2 3)
• Postshield Stage (his 4)
• Rejuvenation Stage (his 7)

According to this scheme - Mauna Loa is in the
shield stage - Mauna Kea is in the postshield
stage - And the Koko Rift volcanoes represent
rejuvenation
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Life Stages of Hawaiian Volcanoes
adapted from Peterson Moore (1987)
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Stages generally bear a relationship to the
position of the volcano with respect to the
underlying hotspot
S. Rowland
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Main shield stage
Calderas and rift zones Frequent eruptions of
tholeiitic basalt Volcano directly above hotspot
center Maximum volcanic productivity
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Calderas are very dynamic features Kilauea
caldera then and now
1825
1944
today
Kilauea caldera got bigger in 1979, when part of
Waldron Ledge collapsed during an earthquake.
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Magmatic plumbing system Magma rises beneath
the summit and can then travel laterally to feed
rift zone eruptions. EQs occur during this
process
Lateral transport of magma occurs in dikes,
mostly 1 m wide.
Mokulua Is., Oahu
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Dike complexes delineate the locations and
orientations of rift zones in ancient volcanoes
Koolau Dike complex showing the rift zones in
the volcano when it was active.

• note
• the axis of Koolau is now partly offshore

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- volcano moves off hotspot - magma production
declines - alkalic composition of magma -
Hualalai, Mauna Kea, East Maui
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When volcanism ceases, erosion and reef growth
dominate

• island moves off hotspot
• volcanism ceases (volcano dies)
• - erosion becomes dominant geological process
• - extensive reefs develop
• - example Kohala

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Reef development on the S. coast of East Molokai
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Sea cliffs
Oahu
River-cut valleys
River-cut valleys
Pearl Harbor (drowned river valleys estuary)
Former shore line
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Mass Wasting Mass wasting processes pose a
significant natural hazard in urban areas. Large
events near the shoreline can generate tsunamis.
Mass wasting is the principal process by which
valleys widen.
Palolo Valley, Oahu
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Mapping of the submarine flanks of Hawaiian
volcanoes shows the distribution of giant
submarine landslides
Two major types Slumps and debris avalanches
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Nuuanu Debris Avalanche
Kaena Slump
Wailau Slide
Waianae Slump
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Nuuanu Debris Avalanche

• - largest in the Hawaii region
• 23,000 km2
• 230 km long
• Traveled 140 km beyond the axis of the deep, 300
  m uphill
• Contains huge blocks, e.g., Tuscaloosa Smt 30 km
  x 17 km, with 1.8 km of relief
• Must have been a fast-moving avalanche

Axis of Hawaiian Deep
Arcuate scarp 20 km offshore is the most likely
headwall for the landslide
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Profile through E. Oahu showing landslide blocks
Landslide headwall
E. Oahu - restored
Waianae
Moore and Clague 2002

• Note
• big bulge on seaward Koolau prior to sliding
• Nuuanu pali is not the landslide headwall the
  actual headwall is 20 km farther north

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Big Island slumps and avalanche deposits can be
tied to on-land structures
Modern GPS measurements indicate southward
slumping of south Hawaii.
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The origin of palis are they related to
offshore landslides?
Nuuanu, Waianae and Molokai palis are far
inshore of the actual landslide headwalls.

• The association of extensive erosion landward of
  submarine landslide deposits suggests that
  off-shore landslides accelerate on-shore erosion.
• Over-steepening of submarine flanks
• Structural weakening of on-shore and near-shore
  regions

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Big Island Evolution
The two oldest Big Island volcanoes are Kohala
(Ko) and a submarine volcano called Mahukona
(M) Both were probably present 500,000 yrs ago
Hawaiian Swell
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Big Island Evolution
By 300,000 years ago Mahukona was extinct (?)
Kohala, Mauna Kea, and Hualalai were active
shields Kohala had undergone a major
landslide Probably Mauna Loa was also active at
this time
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Big Island Evolution
By 100,000 years ago Kohala, Mauna Kea and
Hualalai were in the postshield stage Mauna Loa
and Kilauea were active, subaerial shield
volcanoes Mauna Loa also had been modified by
major landslides
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Big Island Evolution
In the last 100,000 yrs Kohala has gone
extinct Kilauea and Mauna Loa have continued to
be active shields Major landsliding has occurred
on the south flank of Kilauea Loihi is growing
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Rejuvenation Volcanism the least well
understood aspect of Hawaiian geologic evolution
- source of magma (and explanation) under
debate - mainly very low degrees of partial
melting (very alkalic compositions) - very small
overall volume of volcano - W. Maui, Molokai
(Kalaupapa), E. Oahu, Kauai, Niihau no others
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• Rejuvenation volcanism in Honolulu
• Tuff rings from interaction with water
• Cones and flows from dry magmatic eruptions

Location of Honolulu Volcanics Vents
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Sugarloaf eruption 100 ka changed course of
Manoa stream. Ponded sugarloaf lava was
quarried in early 20th C.
Drawing by N. Witten in N. Stearns, 1935
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Nested tuff cones Koko Rift - SE Oahu
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Kalaupapa rejuvenation volcano on edge of E.
Molokai
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Not every volcano has undergone every stage
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Lanai a Hawaiian volcano that died in the
shield stage
Palawai Basin, Lanai the remnants of the old
caldera
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Continued erosion and subsidence
Nihoa Is., NW Hawaiian Is.
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Variation in depth with distance along Hawaiian
Ridge
subsidence
Most volcanoes west of Maui have subsided at
least 3 km!
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- erosion and subsidence continue - reef-building
keeps pace with subsidence - NW Hawaiian islands
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Atolls result when reef growth keeps pace with
island subsidence - As originally proposed by
Darwin (1839)
Pearl and Hermes Atoll
after Darwin, 1839
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Drowned seamounts occur when reef building cannot
keep pace with island subsidence (water too
cold) - Emperor Seamounts
Sea surface temperature (Feb., 2008)
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