DOCSLIB.ORG

Contributions to the Petrography and Geochronology of Volcanic Rocks from the Leeward Hawaiian Islands

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Contributions to the Petrography and Geochronology of Volcanic Rocks from the Leeward Hawaiian Islands G. BRENT DALRYMPLE MARVIN A. LANPHERE J- U.S. Geological Survey, 345 Middlefteld Road, Menlo Park, California 94025 EVERETT D. JACKSON } Contributions to the Petrography and Geochronology of Volcanic Rocks from the Leeward Hawaiian Islands ABSTRACT the Pacific lithospheric plate moves over a fixed melting spot in the mantle, now centered near the island of Hawaii, from which magma is Petrographic and chemical analyses of basalt from Nihoa Island, supplied. Most of these hypotheses predict that the rate of propaga- Necker Island, French Frigate Shoals, and Midway Atoll, all in the tion of volcanism along the chain will be a direct function of the leeward part of the Hawaiian chain, confirm that these islands are relative motion between the Pacific plate and the asthenosphere. This subaerial remnants of tholeiitic shield volcanoes similar to those that melting-spot hypothesis recently was extended to include the Em- form the principal Hawaiian Islands. Chemistry suggests that Gard- peror Seamount chain, which on the basis of bathymetry (Chase and ner Pinnacles may be part of the alkalic cap on a tholeiitic shield. others, 1970; Jackson and others, 1972) appears to be a continuation Weighted mean potassium-argon ages of 7.0 ± 0.3 m.y. for Nihoa, of the Hawaiian chain of shield volcanoes, possibly bent northward 10.0 ± 0.4 m.y. for Necker, 11.7 ± 0.4 m.y. for French Frigate, and by a change in the direction of motion of the Pacific plate during 17.9 ± 0.6 m.y. for Midway demonstrate that the ages of these vol- Tertiary time (Morgan, 1972a, 1972b). Morgan proposed that the canoes increase northwestward, continuing the trend of increasing Hawaiian-Emperor, the Austral-Marshall, and the Line-Tuamoto age away from the active volcano of Kilauea shown by the main chains were all formed by motion of the Pacific plate over three fixed islands. The increase in age with distance along the chain, however, "plumes" in the mantle that convect upward at rates of ~2 m per appears to be nonlinear. The results support the general hypothesis yr and that supply heat to the volcanoes and provide the force that that the volcanoes of the Hawaiian chain have a common origin and drives the Pacific plate (Morgan, 1971). were formed as the Pacific plate moved northwestward over a melting McDougall (1971) suggested that the melting spot results from spot in the mantle. Key words: Hawaiian Islands, geochronology, diapiric upwelling of mantle material into a propagating fracture. potassium-argon, volcanic chain, melting spot, Pacific plate, petrog- According to his model, the melting spot is not fixed but moves at raphy, chemical analyses, basalt. about the same velocity as the Pacific plate but the opposite direction. Recent paleomagnetic data, however, indicate that Midway Atoll INTRODUCTION was formed at lat. 15° ± 4° N., which is significantly south of both its The Hawaiian Islands lie at the southeast end of a quasi-linear chain present latitude and the latitude predicted by McDougall's moving- of more than 50 shield volcanoes that trends west-northwest ~4,000 spot hypothesis, but is not significantly different from the present km across the Pacific Ocean (Fig. 1 A). Except for a few small islands latitude of Hawaii (Gromme and Vine, 1972). and atolls, most of the volcanoes west of the island of Kauai are now Shaw (1973) proposed that the Hawaiian melting spot is caused by completely below sea level. Jackson and orhers (1972) showed that viscous shear between the lithosphere and asthenosphere. His model the alignment of volcanoes in the chain is r..ot exactly linear but that includes a thermal feedback mechanism that results in episodes of individual volcanoes lie on short, sigmoidal loci that may reflect ex- melting and eruption, and cyclic irregularities in the volcanic tensional strain (Fig. IB). propagation rates that do not directly reflect the over-all rate of On the basis of the relative degrees of erosion, early workers pre- plate motion. More recently, Shaw and Jackson (1973) proposed dicted that the shield volcanoes of the Hawaiian chain increase in age that the Hawaiian melting spot is geographically stabilized by a northwestward from the active volcano of Kilauea on the island of gravitational anchor — a dense, downwelling residium that is Hawaii (Dana, 1849,1890; Stearns, 1946,1966). This prediction has formed as a result of the shear melting process. been quantitatively confirmed by K-Ar age measurements One corollary of the general melting-spot hypothesis is that the (McDougall, 1964; Funkhouser and others, 1968; Dalrymple, 1971; ages of the volcanoes in the Hawaiian-Emperor chain should in- McDougall and Swanson, 1972; Doell and Dalrymple, 1973). crease to the northwest and north. A second corollary of Wilson's Recent hypotheses for the origin of the Hawaiian chain are based (1963), Morgan's (1971), and McDougall's (1971) hypotheses is on the suggestion by Wilson (1963) that the volcanoes are formed as that all of the volcanoes in the chain should be of similar (or re- Geological Society of America Bulletin, v. 85, p. 727-738,4 figs., May 1974 727 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/85/5/727/3418286/i0016-7606-85-5-727.pdf by guest on 01 October 2021 728 DALRYMI'LE AND OTHERS Figure 1. (A) Index map of the north Pacific showing the location of the Hawaiian and Emperor chains. (B) Loci (curved lines) of shield volcanoes in the Hawaiian and southernmost Emperor chains. Crosses mark major topographic highs that are presumably coincident with major volcanic centers (after Jackson and others, 1972). Bathymetry is schematic after Chase and others (1970). (C) K-Ar age of tholeiitic volcanism relative to distance from Kilauea for the Hawaiian-Emperor chain. Circles are based on ages published by McDougall (1964) for Haleakala, West Maui, East Molokai, West Molokai, Koolau, and Kauai volcanoes; Doell and Dalrymple (1973) for Koolau and Waianae volcanoes; McDougall and Swanson (1972) for Kohala Mountain; Clague and Dalrymple (1973) for Koko Seamount; and Jackson and others (1972) for Niihau. Dots are data from Table 1. lated) type and chemistry; the lava must also be derived from the two samples from Nihoa and Necker Islands, respectively. K-Ar ages mantle. This second condition is true for the principal Hawaiian of 15.7 ± 0.9 m.y. and 16.6 ± 0.9 m.y. on two Midway samples, Islands, and although the other islands and seamounts in the chain obtained in a prelimina ry stage of this study, were: quoted by Ladd and appear to be shield volcanoes of the Hawaiian type, petrologic and others (1967), who discounted the data because of an apparent chemical data are too few to be certain. The models of Shaw (1973) conflict with fossil evidence; this conflict is discussed below. Using a and Shaw and Jackson (1973) also include a mantle source for the variety of rock types, Clague and Dalrymple (15'73) obtained an age lava but provide more latitude for petrologic and chemical diversity of 46.4 ± 1.1 m.y. tor Koko Seamount, 300 km north of the if the mantle is laterally inhomogeneous. Thus, the geochronology Hawaiian-Emperor bend. Ozima and others (1970) reported K-Ar and petrology of individual volcanoes in the chain are a critical test ages of 41.8, 40.4, and 21.2 m.y. on three volcanic rocks from Suiko of the general hypothesis that the Hawaiian-Emperor chain is Seamount, 800 km north of the bend. According to their description, caused by movement of the Pacific plate over a melting spot in the however, the samples are badly altered and the ages probably are at mantle and also are important in deciding between several pro- best minimum values for the age of the seamount. posed mechanisms. Petrologic data on the islands and seamounts leeward of Kauai are Jackson and others (1972) haveshown that the westward increase equally scarce. Palmer (1927) collected and desc :ibed flows and dikes in age of volcanoes of the main Hawaiian Islands is not linear. The rate of basalt from Nihoa and Necker Islands and La Perouse Pinnacle on of tholeiitic volcanism along the two most recent loci, which include French Frigate Shoals and concluded that these islands were rem- all of the volcanoes from Kauai to Kilauea, has been accelerating. nants of larger basaltic volcanoes. Chemical analyses (Washington Beyond Kauai, few age data are available. Funkhouser and others and Keyes, 1926; Palmer, 1927) and petrographic examination (1968) reported K-Ar ages of 7.5 ± 0.4 m.y. and 11.3 ± 0.6 m.y. on (Palmer, 1927; Macdonald, 1949) indicate that the samples col- Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/85/5/727/3418286/i0016-7606-85-5-727.pdf by guest on 01 October 2021 161" 56' 161° 55 164° 42' 30" I64°42 00 23° 1 35' 1 00 NIHOA ISLAND NECKER ISLAND y Tanager Peak (- Millers Peak 23° ' Ail 3d 1 Z^' /1 Shark Boy \ ! (C Annexation Peal^^^y—S \ \L — ' \ 23° / 34' 30' „ Summit Hill / \ \ ^0.5 KM \ 0 0.5 KM 23? N 1 1 03) - J OCf B I 1 I66°30 I66°20' 166° 10 I66°00 177°25 177° 20 1 1 1 i FRENCH FRIGATE MIDWAY ATOLL s SHOALS V>s s f Tern lsland -^~~^ V !,'V'P" < ' ' 1 ! -.y—x < v \ S 23° - i / \ 50 1 i \ / i \ \ \ I i \ 28° \ ' \ ^ vJ" \\ 15' i! ; v ->,/\East Island V, \ ¡\ La Perouse » I'Vi \\ ¡ I ] Pinnacle \ O \ \ \ \ \ Vx ) 1 S / j 1 w\ \ o / \ \ / \ V ?<> / \ \ •è'7 \ \ 1 / <\? r\ 23' ¿i*-J L ' 11 40 — ? # 1 // , 28° 0 5 10 KM 10 1 i i jyy C 1 1 , ^ 1 Figure 2.
Load more

Recommended publications
  • Relationships Among Native and Alien Plants on Pacific Islands with and Without Significant Human Disturbance and Feral Ungulates
    RELATIONSHIPS AMONG NATIVE AND ALIEN PLANTS ON PACIFIC ISLANDS WITH AND WITHOUT SIGNIFICANT HUMAN DISTURBANCE AND FERAL UNGULATES Mark D. Merlin and James 0. Juvik ABSTRACT The native plants of remote tropical islands have been frequently characterized as poor competitors against seemingly more aggressive alien species.. Does this "weak competitor" characterization relate to some real adaptive consequences of island isolation and endemism, or does the generally concurrent presence of introduced ungulates and other forms of recurrent human disturbance also act to encourage alien plant dominance? A comparison of tropical islands with and without introduced ungulates suggests that some insular plant species competitively resist alien displacement in the absence of ungulates. INTRODUCTION For millions of years remote tropical islands in the Pacific Ocean have provided a variety of ecological opportunities for plant species that reached them through long-distance dispersal mechanisms. Many species that successfully established themselves on far-flung oceanic islands gave rise to extraordinary endemic forms, examples of adaptive radiation, and unusual adaptive shifts. Evolutionary developments occurred on isolated islands largely because of the limited numbers and kinds of colonizing taxa and varying environmental diversity within islands or groups of islands. Among the structural and physiological adaptations that frequently occur in remote island environments is the disappearance of typical defensive mechanisms such as poisons, strong odors, thorns, deep tap roots, and tough stems and branches in insular plant species. Some of these adaptations left many species especially vulnerable to a variety of alien ungulates introduced in the historic period (Fosberg 1965; Mangenot 1965; Mueller-Dombois 1975). In the Hawaiian Islands, for example, only a very small fraction of the endemic species of plants produce poisons, thorns, or other defensive strategies against herbivory (Carlquist 1974, 1980).
    [Show full text]
  • Handbook Publication.Pub
    Table of Contents Maui County’s Landscape and Gardening Handbook Xeriscaping in Maui County ................................................................. 1 Planning and Design................................................................................................................. 1 Hydro-zones.............................................................................................................................. 1 Plant Selection and the Maui jkCounty Planting Zones............................................................ 2 Soil Preparation ........................................................................................................................ 4 Mulching.................................................................................................................................... 5 Irrigation .................................................................................................................................... 5 Maintenance ............................................................................................................................. 7 Other Interesting Techniques for the Ambitious ..................................... 8 Xeriscape Ponds....................................................................................................................... 8 Aquaponics in the Backyard ..................................................................................................... 9 Water Polymer Crystals ...........................................................................................................
    [Show full text]
  • Geology of Hawaii Reefs
    11 Geology of Hawaii Reefs Charles H. Fletcher, Chris Bochicchio, Chris L. Conger, Mary S. Engels, Eden J. Feirstein, Neil Frazer, Craig R. Glenn, Richard W. Grigg, Eric E. Grossman, Jodi N. Harney, Ebitari Isoun, Colin V. Murray-Wallace, John J. Rooney, Ken H. Rubin, Clark E. Sherman, and Sean Vitousek 11.1 Geologic Framework The eight main islands in the state: Hawaii, Maui, Kahoolawe , Lanai , Molokai , Oahu , Kauai , of the Hawaii Islands and Niihau , make up 99% of the land area of the Hawaii Archipelago. The remainder comprises 11.1.1 Introduction 124 small volcanic and carbonate islets offshore The Hawaii hot spot lies in the mantle under, or of the main islands, and to the northwest. Each just to the south of, the Big Island of Hawaii. Two main island is the top of one or more massive active subaerial volcanoes and one active submarine shield volcanoes (named after their long low pro- volcano reveal its productivity. Centrally located on file like a warriors shield) extending thousands of the Pacific Plate, the hot spot is the source of the meters to the seafloor below. Mauna Kea , on the Hawaii Island Archipelago and its northern arm, the island of Hawaii, stands 4,200 m above sea level Emperor Seamount Chain (Fig. 11.1). and 9,450 m from seafloor to summit, taller than This system of high volcanic islands and asso- any other mountain on Earth from base to peak. ciated reefs, banks, atolls, sandy shoals, and Mauna Loa , the “long” mountain, is the most seamounts spans over 30° of latitude across the massive single topographic feature on the planet.
    [Show full text]
  • Important Bird Areas in Hawaii Elepaio Article
    Globally Important Bird Areas in the Hawaiian Islands: Final Report Dr. Eric A. VanderWerf Pacific Rim Conservation 3038 Oahu Avenue Honolulu, HI 96822 9 June 2008 Prepared for the National Audubon Society, Important Bird Areas Program, Audubon Science, 545 Almshouse Road, Ivyland, PA 18974 3 of the 17 globally Important Bird Areas in Hawai`i, from top to bottom: Lehua Islet Hanawī Natural Area Reserve, Maui Hanalei National Wildlife Refuge, Kauai All photos © Eric VanderWerf Hawaii IBAs VanderWerf - 2 INTRODUCTION TO THE IMPORTANT BIRD AREAS PROGRAM The Important Bird Areas (IBA) Program is a global effort developed by BirdLife International, a global coalition of partner organizations in more than 100 countries, to assist with identification and conservation of areas that are vital to birds and other biodiversity. The IBA Program was initiated by BirdLife International in Europe in the 1980's. Since then, over 8,000 sites in 178 countries have been identified as Important Bird Areas, with many national and regional IBA inventories published in 19 languages. Hundreds of these sites and millions of acres have received better protection as a result of the IBA Program. As the United States Partner of BirdLife International, the National Audubon Society administers the IBA Program in the U.S., which was launched in 1995 (see http://www.audubon.org/bird/iba/index.html). Forty-eight states have initiated IBA programs, and more than 2,100 state-level IBAs encompassing over 220 million acres have been identified across the country. Information about these sites will be reviewed by the U.S. IBA Committee to confirm whether they qualify for classification as sites of continental or global significance.
    [Show full text]
  • Nihoa Manawai Holoikauaua Pearl & Hermes Atoll Kapou Papa'āpoho Lisianski Island Kamole Kauō Laysan Island Kamokuokamohoali'i Ko'anako'a Maro Reef
    175°E 180° 175°W 170°W 165°W 160°W 155°W 150°W 35°N 35°N North America Japan Map Area Photo by Dan Clark/USFWS Hawaiian Islands Photo by Na‘alehu Anthony P a c i f i c Seabird Refuge A Living Hawaiian Culture O c e a n The monument is home to over 14 million seabirds 30°N Hiryū USS Yorktown Equator representing 23 species. This includes the world's Traditional Hawaiian accounts describe largest colonies of Laysan and black-footed Papahānaumokuākea as a sacred area from which Rapa Sōryū albatross. Pictured above is the world's oldest life first emerged and to which spirits return after Nui Australia known bird in the wild – a Laysan albatross named 30°N death. Akagi Wisdom! Banded in 1956 when she was at least five Kaga years old, Wisdom may have hatched more than 36 New Zealand chicks in her lifetime. Hōlanikū Manawai Unnamed Holoikauaua Mokupāpapa Seamount Kure Atoll Pearl & Hermes Atoll 582,578 square miles, only six square miles of land Helsley Seamount Ladd Seamount Kamole Kauō ‘Ōnūnui, ‘Ōnūiki Photo by Mark Sullivan/NOAA Laysan Island Photo by NOAA/OER Endemic Sanctuary Pūhāhonu New Discoveries The monument is home to many species found Kuaihelani Gardner Pinnacles The majority of the seafloor in the Northwestern nowhere else on Earth and is a critically important Pihemanu Salmon Hawaiian Islands lies at depths below 10,000 feet nesting ground for green sea turtles and breeding Bank (3,000 meters). Using advanced technologies like ground for Hawaiian monk seals.
    [Show full text]
  • NATIVE HAWAIIAN PRACTICES Permit Application
    Papahānaumokuākea Marine National Monument Permit Application – Native Hawaiian Practices OMB Control # 0648-0548 Page 1 of 14 Papahānaumokuākea Marine National Monument NATIVE HAWAIIAN PRACTICES Permit Application NOTE: This Permit Application (and associated Instructions) are to propose activities to be conducted in the Papahānaumokuākea Marine National Monument. The Co-Trustees are required to determine that issuing the requested permit is compatible with the findings of Presidential Proclamation 8031. Within this Application, provide all information that you believe will assist the Co-Trustees in determining how your proposed activities are compatible with the conservation and management of the natural, historic, and cultural resources of the Papahānaumokuākea Marine National Monument (Monument). ADDITIONAL IMPORTANT INFORMATION: • Any or all of the information within this application may be posted to the Monument website informing the public on projects proposed to occur in the Monument. • In addition to the permit application, the Applicant must either download the Monument Compliance Information Sheet from the Monument website OR request a hard copy from the Monument Permit Coordinator (contact information below). The Monument Compliance Information Sheet must be submitted to the Monument Permit Coordinator after initial application consultation. • Issuance of a Monument permit is dependent upon the completion and review of the application and Compliance Information Sheet. INCOMPLETE APPLICATIONS WILL NOT BE CONSIDERED Send Permit
    [Show full text]
  • 1 NIHOA ISLAND TRIP REPORT, 21-29 SEPTEMBER 2013 To
    NIHOA ISLAND TRIP REPORT, 21-29 SEPTEMBER 2013 To: U.S. Fish and Wildlife Service, Hawaiian Islands National Wildlife Refuge, Honolulu, Hawai‘i. From: Sheldon Plentovich, Chris Farmer, Joshua Fisher, Holly Freifeld, and Rachel Rounds Recommended Citation: Plentovich, S., C. Farmer, J. Fisher, H. Freifeld, and R. Rounds. 2013. Nihoa Island biological monitoring and management, 21-29 September 2013. Unpublished report to the U.S. Fish and Wildlife Service. EXECUTIVE SUMMARY We conducted Variable Circular Plot surveys for Nihoa Millerbird (Acrocephalus familiaris) and the Nihoa Finch (Telespiza ultima) 23-28 September 2013 at 60 points. There were 270 Millerbird and 569 Nihoa Finch detections, with a range of 0 - 6 and 1 - 9 respectively. The detection rate of Millerbirds increased sharply between 2012 and 2013, suggesting there might have been an increase in this species. Conversely, the detection rate of Nihoa Finches declined, suggesting this species might have declined. The U.S. Geological Survey Biological Resources Division is completing a report that will compare population estimates from the distance-based strip-transect and variable circular plot methods performed in 2012. Six banded Nihoa Millerbirds were resighted. Fourteen seabird species were observed on Nihoa and 13 of the 14 were nesting or had fledglings. Three species of migratory shorebirds were observed. Fifteen native plant species were found and appeared healthy. A total of 25 grey bird locusts (Schistocerca nitens) were observed during passerine surveys. A single non-native sandbur (Cenchrus echinatus) was detected and removed. The plant was located down slope from Cluster 2, about 100 meters above our campsite, with a little bit of green growth still present.
    [Show full text]
  • Data Book 2019 Table Number Table Name
    Table Number Table Name (Click on the table number to go to corresponding table) (To return to this "Titles" worksheet, you must select this worksheet again) Narrative 01.01 Population of Counties: 1831 to 2010 01.02 Characteristics of the Population: 1831 to 2010 01.03 Resident Population, by Military Status: 2010 to 2019 01.04 Resident and De Facto Population, by Residence Status: 2000 to 2019 01.05 Resident Population of Islands: 1970 to 2014-2018 01.06 Resident Population, by County: 2000 to 2019 01.07 Percentage Change in Resident Population, by County: 2000 to 2019 01.08 County Population as a Share of the State Total: 2000 to 2019 01.09 De Facto Population, by County: 2000 to 2019 01.10 Population, Land Area and Population Density, by County and Island: 2010 01.11 Resident Population of Counties and Judicial Districts: 1990 to 2014-2018 01.12 Resident Population and Number of Households, by Island and Census Designated Place: 2014-2018 01.13 Population and Percentage Change Rankings: 2010 and 2019 01.14 Resident Population for Oahu Neighborhoods: 2010 and 2014-2018 01.15 Population Characteristics of Oahu Neighborhoods: 2014-2018 01.16 Resident Population and Households, by Island and Census Tract: 2014-2018 01.17 Resident Population of Hawaiian Home Lands, by Island: 2014-2018 01.18 Resident Population, by Island and Zip Code Tabulation Area: 2014-2018 01.19 Resident and De Facto Population and Employed Persons, for Waikiki: 1970 to 2010 01.20 Urban and Rural Areas, by County: 2010 01.21 Centers of Population, by County: 1990 to
    [Show full text]
  • Ka Moolelo O Kauai O Kukona Ka Mo’I O Ke Aupuni O Kauai, Huiia Me Kaula, Niihau, a Me Lehua I Na KA MOOLELO KAUA‘I’S Makahiki 1400
    Ka Moolelo o Kauai O Kukona ka mo’i o ke aupuni o Kauai, huiia me Kaula, Niihau, a me Lehua i na KA MOOLELO KAUA‘I’S makahiki 1400. Noloko mai no o Kukona kekahi lalani alii nana i hoomalu maluna o ka aina a hiki ia Kaumualii (hanauia 1778 a make 1824) a lilo ke aupuni ia Kamehameha i ka makahiki 1810 ma ke kuikahi mawaena o ke aupuni o Kauai a O KAUAI HERITAGE me ke aupuni o Kamehameha. O Manokalanipo ke keiki a Kukona. Oia ka mo’i i mele nui ia’i iloko o na mele e like me Nani Waialeale a me Kauai Beauty. O ke kumu o kona mele nui ia ana, no ka Holomua ka Naauao A Growing Society mea, oia ka mo’i o ka aina nei nana i kukulu i kona aupuni me ka hoonohonoho pono ana i na mahele aina like ole he moku a he ahupuaa me ka hoonoho ana i Ua holomua loa ka naauao o kanaka mamuli o ke akamai Kānaka Maoli (native Hawaiians) have lived in the area na alii maluna o kela me keia na lakou e lawelawe no ka pono o ka lahui. Mamuli o o ka noho alii ana o Manokalanipo. I kona wa i kukuluia’i surrounding Kānei‘olouma for several centuries. Upon keia papa hana, ua lako ka aina a lako ka ai a me ka i’a na kanaka. Ma ia hope mai na loko ia e like me ka mea kamaaina i keia au nei, a peia settling the area, Kānaka Maoli organized their system ikeia ka laha loa o ka maluhia maluna o ka aina a ua nui ke alohaia o ua mo’i nei.
    [Show full text]
  • Necker Island Reserve Preservation Area
    Necker Island Reserve Preservation Area MAP The reserve preservation area in this section is approximated using fathoms (fm) but shall be represented in future maps by the Secretary using straight- line boundaries in longitude and latitude coordinates to clearly encompass the reserve preservation area and to provide clarity and ease of identification. RESERVE PRESERVATION AREA The Reserve Preservation Area for Necker Island includes the waters and submerged lands from the seaward boundary of Hawaii state waters out to a mean depth of 100 fathoms, provided that commercial bottomfishing and trolling for pelagic species by recreational fishers and commercial bottomfishers shall be allowed to continue seaward of a mean depth of 25 fathoms, unless and until the Secretary determines otherwise after adequate public review and comment. ENVIRONMENT Necker Island is a hook-shaped dry volcanic island that includes about 45 acres of land. More than 380,000 acres of coral reef habitat are associated with the island. With regard to reef and coral development, Necker Island resembles Nihoa Island in several respects. Necker is a small island unable to buffer the impacts of strong waves that can break along the submerged shorelines from any direction. The effects of scour (surge combined with sand and other sediments) Northwestern Hawaiian Islands Hawaiian Northwestern is evident from the wave-cut bench in West Cove and the deeply cut sand channels and chasms at several locations in deeper water. The concentration of living corals on elevated surfaces is a manifestation of corals surviving better in less scour-prone environments. Although Necker is smaller than Nihoa, deeper coral reef shelf habitat surrounding Necker is more extensive.
    [Show full text]
  • Northwestern Hawaiian Islands/Kure Atoll Assessment and Monitoring Program
    Northwestern Hawaiian Islands/Kure Atoll Assessment and Monitoring Program Final Report March 2002 Grant Number NA070A0457 William j. Walsh1, Ryan Okano2, Robert Nishimoto1, Brent Carman1. 1 Division of Aquatic Resources 1151 Punchbowl Street Rm. 330 Honolulu, HI 96813 2 Botany Department University of Hawai`i Mānoa Honolulu, HI 96822 2 INTRODUCTION The Northwest Hawaiian Islands (NWHI) consist of 9,124 km2 of land and approximately 13,000 km2 of coral reef habitat. They comprise 70% of all coral reef areas under U.S. jurisdiction. This isolated archipelago of small islands, atolls, reefs and banks represent a unique and largely pristine coral reef ecosystem. The islands support millions of nesting seabirds and are breeding grounds for the critically endangered Hawaiian monk seal and threatened green sea turtle. The reefs include a wide range of habitats and support a diverse assemblage of indigenous and endemic reef species, many of which have yet to be described. Kure Atoll, located at the northwestern end of the NWHI chain (approximately 28º 25’ N latitude and 178º 20’ W longitude) is the northernmost atoll in the world. The atoll is located 91 km northwest of Midway Islands and nearly 1,958 km northwest of Honolulu. It is a nearly circular atoll with a diameter of 10 km (6mi). The outer reef is continuous Figure 1. IKONOS satellite image of Kure Atoll 3 and almost encircles the atoll’s lagoon except for passages to the southwest (Fig. 1). An emergent rock ledge consisting primarily of coralline algae and algally bound and encrusted coral is present along some sections of the reef crest.
    [Show full text]
  • The Hawaiian Islands –Tectonic Plate Movement
    Plate Tectonics Worksheet 2 L3 MiSP Plate Tectonics Worksheet #2 L3 Name _____________________________ Date_____________ THE HAWAIIAN ISLANDS – TECTONIC PLATE MOVEMENT Introduction: (excerpts from Wikipedia and http://pubs.usgs.gov/publications/text/Hawaiian.html) The Hawaiian Islands represent the last and youngest part of a long chain of volcanoes extending some 6000 km across the Pacific Ocean and ending in the Aleutian Trench off the coast of Alaska. This volcanic chain consists of the small section Hawaiian archipelago (Windward Isles, and the U.S. State of Hawaii), the much longer Northwestern Hawaiian Islands (Leeward Isles), and finally the long Emperor Seamounts. The Leeward Isles consist mostly of atolls, atoll islands and extinct islands, while the Emperor Seamounts are extinct volcanoes that have been eroded well beneath sea level. This long volcanic chain was created over some 70 million years by a hot spot that supplied magma, formed deep in the earth’s interior (mantle), that pushed its way through the earth’s surface and ocean cover forming volcanic islands. As the Pacific Plate was moved by tectonic forces within the Earth, the hot spot continually formed new volcanoes on the Pacific Plate, producing the volcanic chain. The direction and rate of movement for the Pacific Plate will be determined with the help of the approximate age of some of the Hawaiian volcanoes and distances between them. Procedure 1: 1. Using the data provided in Table 1 , plot a graph on the next page that compares the age of the Hawaiian Islands and reefs to their longitude. 2. Label the island (reef) name next to each plotted point.
    [Show full text]