Transcript Koloa Volcanic Series

Island of Kaua‘i
• Kaua‘i, one of the older islands in the chain, is also
the most complex structurally.
• Generally thought of as a single-volcano island,
some isotopic data challenge that interpretation.
Consequently, Kaua‘i provides many opportunities to
substantially broaden our understanding of how oceanisland volcanoes develop.
• Kaua‘i is the fourth largest island.
Geology of Kaua‘i
• Kaua’i consists of perhaps a single shield volcano
formed 5 million years ago. Wai‘ale‘ale Volcano.
• Like the Ko’olau Volcano on O‘ahu, only has shield
stage and rejuvenation stage without the postcaldera alkalic cap
– Lacks well-defined rift zones like O‘ahu volcanoes
• This volcano has experienced significant faulting
and has the largest known caldera of any Hawaiian
volcano
• This volcano has also passed through the erosion
and coral reef growing stages
– Erosion also affected by faulting: Waimea Canyon
Kaui's Volcanoes Revealed
Prominent terraces (shown in orange and yellow)
illustrate the larger size of the islands in the past.
in particular, are mere vestiges of their former extent
160°W
North Kaua‘i
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22°N
Kaua‘i
Ka‘ula
Ni‘ihau
South Kaua‘i
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Oahu
Deep
Kaua‘i Volcano, Shield Stage
• Shield-stage rocks are called the Waimea Canyon
Volcanic Series
– Na Pali Member (5.10 to 4.30 Ma)
• shield-forming rocks outside of the caldera
• thin, inclined flows
• tholeiitic basalt
– Olokele and Makaweli Members (4.16-3.6 Ma)
• fill the caldera and the Makaweli graben (normal falut-bounded
valley), respectively
• thick, flat-lying flows
• tholeiitic basalt, alkalic basalt, and hawaiite
– Haupu Member (unknown age)
• lavas filling a small caldera on the southeastern flank of the
volcano
Shield building
Stage
Rejuvenated Stage
Kaua‘i Volcano, Rejuvenation Stage
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Called the Koloa Volcanic Series
Age: 2.3 to 1.0 Ma
~40 vents, spatter and cinder cones, and a tuff cone
Koloa lavas cover about half of the surface of the
eastern part of the island
– floor the Lihue Basin
– Mt. Kilohana and flows
• Interbedded with the Koloa Volcanic Series is the
Palikea Formation, consisting of conglomerates
and breccias, coarse sedimentary rocks produced
by mass wasting-style erosion
Rejuvenated Stage Volcanic Eruptions on Kaui
Kaua‘i Volcano, Rejuvenation Stage
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Called the Koloa Volcanic Series
Age: 2.3 to 1.0 Ma
~40 vents, spatter and cinder cones, and a tuff cone
Koloa lavas cover about half of the surface of the
eastern part of the island
– floor the Lihue Basin
• Interbedded with the Koloa Volcanic Series is the
Palikea Formation, consisting of conglomerates
and breccias, coarse sedimentary rocks produced
by mass wasting-style erosion
Sedimentary Rocks
• Extensive deposits of colluvium (mass
wasting deposits) and alluvium
(stream erosion deposits)
• Cemented sand dunes and beach rock
• Sediments can form coastal plains
Two Shield Volcanoes or one?: The two-volcano
hypothesis remains a topic worthy of pursuit.
An alternative interpretation has been suggested on the
basis of strontium isotopic analyses from late-shield
strata of the Waimea Canyon Basalt on the west and
east sides of the island, which differ sufficiently to
suggest that two magma-supply systems were erupting
during the growth of Kaua‘i.
An additional rationale offered in support of a twovolcano hypothesis is the possibility of numerous rift
zones radiating outward in as many as five directions
(Holcomb et al, 1997). A two-volcano, five-zone rift
system was depicted in a simplified map figure by
Island of Ni‘ihau
• Ni‘ihau, covering 187 km2 , is the westernmost of the
Hawaiian Islands.
• Ni‘ihau is the eroded remnant of a single shield
volcano.
• It is third smallest of the major Hawaiian islands,
larger only than Kaho‘olawe and Lāna‘i.
• Its land is held privately, and access is controlled;
consequently it is one of the least visited and least
studied of the Hawaiian islands.
•Offshore, a fringing wave-cut shelf extends out 5–10
km, beyond which the slopes plunge steeply to abyssal
depth.
Geology of Island of Ni‘ihau
• Lies off of main trend of Hawaiian Islands, a “cross trend”
• Topographically it comprises a central highland built almost
entirely of shield-stage pāhoehoe lava flows (Pānī‘au
Basalt).
• A deeply eroded remnant of a shield volcano fringed by a
platform composed of rejuvenation stage volcanic rocks
• Ni‘ihau’s rejuvenated-stage lava - A late vent, Ka‘eo, stands
about 60 m above the surrounding surface. Possibly a
product of postshield-stage activity.
• More than 23 percent of this platform’s area is mantled by
alluvium and dune deposits with well-developed calcareous
dune deposits.
Ni‘ihau Volcanic Rocks
• Shield Stage
– Paniau Volcanic Series, 5.5 to 4.8 Ma
– tholeiitic and olivine-rich basalts, dikes and lavas
• evolving towards alkalic postsheild stage?
– caldera and summit are gone, only a rift zone remains
• erosion? faulting?
• Rejuvenation Stage
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Ki‘eki‘e Volcanic Series, 2.2 to -0.3 Ma
9 vents, including Lehua Island
all are dry eruptions except for 2 tuff cones
produced lavas that cover a wave-cut terrace
• alkalic olivine basalt, not as low in silica as rejuvenation
stages on other islands
Geology of Island of Ni‘ihau – Rift Zones
Island of Lehua
•Lehua island is a tiny Ki‘eki‘e Basalt tuff cone, only
1.1 km2 in area, that lies 1 km north of Ni‘ihau .
•Undated, it is fairly youthful, to judge from its
landform. Ash from its eruptions carried across much
of Ni‘ihau, forming weakly consolidated dunes on the
northern part of the island.
•These deposits are 1–5 m thick where mapped on
Pakeho‘olua cone, a small Ki‘eki‘e shield vent
emplaced about 0.52 Ma that now forms the northern
quarter of Ni‘ihau.