This volcanic field appears to be somehow related to the Hawaii hotspot, although the exact mechanisms are debated. Similar volcanic units are also found on the adjacent islands, such as the Honolulu Volcanics on Oahu. The volcanic field was formed through effusive and explosive eruptions between 1.5 and 0.5 million years ago, although eruptions before and after these dates also took place.
Geography and geomorphology
The North Arch volcanic field lies 200–400 kilometres (120–250 mi)[5] north of Oahu at 3,900–4,380 metres (12,800–14,370 ft) depth;[2] within the Exclusive Economic Zone of the Hawaiian Islands. The existence of lava flows in this geological region was already postulated in 1964, but it was GLORIA sidescan sonar eventually identified an anomalously reflective seafloor that constitutes the North Arch volcanic field;[6] the discovery was first published in 1968[7] and rock samples taken in 1988.[6] The volcanic field lies on the Hawaiian Arch[b][2] and on its southern slope.[10]
The volcanic field covers an area of about 25,000 square kilometres (9,700 sq mi)[2][c] and consists of about 100 observed volcanic cones with associated lava flows. The volcanic cones range from shield-like to steep[11] to lava dome-like and long ridges[12] and lava flows range from lava lakes forming flat-topped cones[10] to over 100 kilometres (62 mi) long lava flows despite the flat terrain;[11] small hills in the lava flows may be vents.[8] The average thickness of the lava flows probably amounts to either less than 10 metres (33 ft)[13] or about 40–50 metres (130–160 ft).[14]Fissure vents also occur in the field; one of these has been the source of a 3,600 square kilometres (1,400 sq mi) lava flow.[15] Owing to the sizes of the lava flows, the field has also been called a flood basalt in analogy to its usually much larger continent-based counterparts.[4] The volcanoes are located among Cretaceousseamounts and sediment-covered seafloor, which forms kipukas between the lava flows.[16] In turn, lava flows are covered with over 1 metre (3 ft 3 in) thick sediments.[8] A noticeable swell where clusters of volcanic cones occur may reflect the presence of sills.[10] The total volume of the volcanic field is about 1,250–1,000 cubic kilometres (300–240 cu mi),[16] much less than a typical Hawaiian shield stage volcano,[17] and rocks occur in the form of e.g. glass shards, pillow lavas, scoria and volcaniclastic material.[11] A seismic velocity anomaly at depth appears to be associated with the North Arch volcanic field.[18][19]
Geology
The bulk of the volcanism of a Hawaiian volcano is made up by the shield stage during which tholeiitic lavas are erupted.[20] This stage is after between 250,000 – 2,500,000 years followed by a "post-erosional" or "rejuvenated" stage during which lavas of alkali basalt, melilitite and nephelinite composition; such volcanism has been observed on Koolau, Kauai and Niihau[2] and covers large parts of the Hawaiian Islands even though it makes up less than one percent of their volume.[1] The North Arch volcanic rocks resemble the composition of these rejuvenated stage volcanics of Hawaii such as the Honolulu Volcanics,[21] and another unit of these volcanics forms the South Arch volcanic field[20] 200 kilometres (120 mi) south of Kilauea,[22] and have been deemed "peripheral lavas" of the Hawaii hotspot.[23] In fact, it has been proposed that the rejuvenated volcanics of Niihau, Kauai, Oahu and Molokai might actually be part of the North Arch volcanic field.[24] Other volcanic units of a probably similar nature have been found between Oahu and Kauai.[25]
Origin
While the shield stage volcanics of Hawaii are linked to the mantle plume, the origin of volcanism in the North Arch volcanic field is debated:[1]
The flexure of the crust under the weight of the Hawaiian volcanoes forms the Hawaiian Arch, where the crust breaks up and melts can concentrate; this would provide both pathways and sources for magma to ascend to the surface.[26]
The volcanism of the North Arch volcanic field might nevertheless have a common cause as the rejuvenated stage volcanism of Hawaiian Islands.[13] Volcanic units interpreted similarly to the North Arch volcanic field are also known from Kerguelen.[30]
Volcanism on the North Arch volcanic field occurred during the Plio-Pleistocene[16] between 1.5 million years ago[d] and less than 500,000 years ago, at the same time as the Honolulu Volcanics[1] although even younger flows have been found.[15] The timing of volcanic activity has been inferred from the thicknesses of palagonite and sediment layers as well as the stratigraphy[8] and overlaps with rejuvenated volcanism on Oahu, Kauai and Niihau.[9] In contrast, the South Arch volcanic field was emplaced in the last 10,000 years.[41]
Apparently the central part of the field was emplaced first, with the surrounding parts forming later; in addition, lava flows which make up the surrounding parts appear to preferentially originate at the foot of Cretaceous ridges and seamounts;[42] perhaps these ridges and seamounts can act as pathways for magma to reach the surface.[43] Total magma production is about 0.001 cubic kilometres per year (0.00024 cu mi/a).[44]
The North Arch volcanic field has been the site of voluminous lava effusion[10] and the formation of shallow magma chambers which gave rise to pit craters when they collapsed.[15] Despite the great depth of the North Arch volcanic field, traces of explosive eruptions has been found there[16] such as steep and low volcanic cones and deposits from fire fountaining;[45] the formation of bubbles from volatile substances in the magma[45] and processes involving supercritical fluids and magma-water interaction are probably involved in the explosive volcanism there.[46]
^The Hawaiian Arch is a 0.2 kilometres (0.12 mi) high ridge that formed through the flexure induced by the weight of the Hawaiian Islands[8] and is accompanied by a trough.[9]
^In turn, it appears to be part of an even larger field that covers 150,000 square kilometres (58,000 sq mi).[7]
^One eruption may have occurred over 1.6 million years ago[8] and some flows are buried beneath sediments generated by the 1.8 – 2.7 million years old Nuanuu landslide on Koolau volcano, Oahu.[40]
^ abcdHirano, N.; Clague, D.; Takahashi, E.; Hirata, T.; Coombs, M.; Eakins, B. (1 December 2003). "Eruptive style and geochemistry of North Arch lavas". AGU Fall Meeting Abstracts. 22: V22C–0593. Bibcode:2003AGUFM.V22C0593H.
^ abcClague, David A.; Uto, Kozo; Satake, Kenji; Davis, Alicé S. (2002). "Eruption style and flow emplacement in the Submarine North Arch Volcanic Field, Hawaii". Hawaiian Volcanoes: Deep Underwater Perspectives. Geophysical Monograph Series. Vol. 128. pp. 65–84. doi:10.1029/GM128p0065. ISBN0-87590-987-6.
^Kani, T.; Hanan, B. B.; Kingsley, R.; Schilling, J. (1 December 2005). "Constraints on the Source Components Involved in the Magmatism of North Arch Volcanic Field and South Arch Volcanic Field, Hawaii". AGU Fall Meeting Abstracts. 51: V51A–1470. Bibcode:2005AGUFM.V51A1470K.
^Uto, K.; Ishizuka, O.; Garcia, M. O.; Clague, D. A.; Naka, J. (1 December 2002). "Reconsideration of evolutionary model of the Hawaiian-type volcano: 40Ar/39Ar ages for lavas from deep interior of Oahu Island and alkali basalts from the North Arch volcanic field". AGU Fall Meeting Abstracts. 62: T62A–1284. Bibcode:2002AGUFM.T62A1284U.
^Mahoney, John J.; Clague, David A.; Guillou, Hervé; Zander, Iris van der; Pyle, Douglas; Tardona, Mary; Eason, Deborah E.; Sinton, John M. (1 September 2014). "Ka'ena Volcano—A precursor volcano of the island of O'ahu, Hawai'i". GSA Bulletin. 126 (9–10): 11. Bibcode:2014GSAB..126.1219S. doi:10.1130/B30936.1. ISSN0016-7606.
^Kani, T.; Uto, K. (1 December 2001). "Geochemical Characteristics of Mantle Sources of North Arch Alkalic Volcanism, Hawaii". AGU Fall Meeting Abstracts. 12: V12B–0961. Bibcode:2001AGUFM.V12B0961K.
Bianco, Todd Anthony; Ito, Garrett; Becker, Janet M.; Garcia, Michael O. (2005). "Secondary Hawaiian volcanism formed by flexural arch decompression: SECONDARY HAWAIIAN VOLCANISM". Geochemistry, Geophysics, Geosystems. 6 (8). doi:10.1029/2005GC000945. S2CID85508354.
Clague, David A.; Holcomb, Robin T.; Sinton, John M.; Detrick, Robert S.; Torresan, Michael E. (May 1990). "Pliocene and Pleistocene alkalic flood basalts on the seafloor north of the Hawaiian islands". Earth and Planetary Science Letters. 98 (2): 175–191. Bibcode:1990E&PSL..98..175C. doi:10.1016/0012-821X(90)90058-6.
Davis, Alicé S.; Clague, David A. (18 October 2005). "Volcaniclastic deposits from the North Arch volcanic field, Hawaii: explosive fragmentation of alkalic lava at abyssal depths". Bulletin of Volcanology. 68 (3): 294–307. doi:10.1007/s00445-005-0008-7. S2CID129822788.
Le, Ba Manh; Yang, Ting; Morgan, Jason P. (November 2022). "Seismic Constraints on Crustal and Uppermost Mantle Structure Beneath the Hawaiian Swell: Implications for Plume-Lithosphere Interactions". Journal of Geophysical Research: Solid Earth. 127 (11). Bibcode:2022JGRB..12723822L. doi:10.1029/2021JB023822.