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 ocean-island 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 post-caldera 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 http://pubs.usgs.gov/of/2007/1089/

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 Slide 22°N Kaua‘i Ka‘ula Ni‘ihau South Kaua‘i Slide 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 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 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 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 two-volcano 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 Clague (1996).

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 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.