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97-555: The crater was formed some 75,000 to 100,000 years ago during the secondary activity of the Honolulu Volcanic Series . A crater resulted from the ejection of hot lava through cracks in the old coral reefs which, at the time, extended to the foot of the Koʻolau Mountain Range . The volcano is most likely a monogenetic volcano , meaning that it only erupted once. Although there are various translations of

194-560: A depleted mantle component along with a mantle plume "Kalihi" component, with additional material contributed from the margins of the mantle plume. Magma may have remained in the crust for months or years before erupting. Groundwater contained in Honolulu Volcanics rocks, while not voluminous, is important in some areas such as Maunawili Valley. Moreover, impermeable tuff layers can hold groundwater in rock layers above them. However, Koʻolau volcanic rocks contain most of

291-423: A mantle wedge above the descending slab. The slab releases water vapor and other volatiles as it descends, which further lowers the melting point, further increasing the amount of decompression melting. Each tectonic setting produces basalt with its own distinctive characteristics. The mineralogy of basalt is characterized by a preponderance of calcic plagioclase feldspar and pyroxene . Olivine can also be

388-493: A basalt is diagnostic of how and where it erupted—for example, whether into the sea, in an explosive cinder eruption or as creeping pāhoehoe lava flows, the classic image of Hawaiian basalt eruptions. Basalt that erupts under open air (that is, subaerially ) forms three distinct types of lava or volcanic deposits: scoria ; ash or cinder ( breccia ); and lava flows. Basalt in the tops of subaerial lava flows and cinder cones will often be highly vesiculated , imparting

485-584: A city of the living. Fifty years later, Congress authorized a small appropriation to establish a national cemetery in Honolulu with two provisions: that the location be acceptable to the War Department , and that the site would be donated rather than purchased. In 1943, the governor of Hawaii offered the Punchbowl for a national cemetery. The $ 50,000 appropriation proved insufficient, however, and

582-442: A distinctive pillow shape, through which the hot lava breaks to form another pillow. This "pillow" texture is very common in underwater basaltic flows and is diagnostic of an underwater eruption environment when found in ancient rocks. Pillows typically consist of a fine-grained core with a glassy crust and have radial jointing. The size of individual pillows varies from 10 cm up to several metres. When pāhoehoe lava enters

679-757: A first during the Kahipa highstand, a second during the Kaʻena and Lāʻie highstands, a third during the Waipiʻo and Waimānalo highstands and a fourth after the Waimānalo highstand. In turn, the Waimānalo stage was correlated to the last interglacial / Sangamonian interstadial and the Kaʻena highstand to an interglacial 600,000 ± 100,000 years ago. First dating efforts yielded ages of Pleistocene-Holocene based on sea level variations, while potassium-argon dating has yielded ages ranging between 800,000 and 60,000 years old. However,

776-427: A flow can shrink in the vertical dimension without fracturing, it cannot easily accommodate shrinking in the horizontal direction unless cracks form; the extensive fracture network that develops results in the formation of columns . These structures, or basalt prisms , are predominantly hexagonal in cross-section, but polygons with three to twelve or more sides can be observed. The size of the columns depends loosely on

873-909: A group of volcanoes which form a volcanic field on the island of Oʻahu , Hawaiʻi , more specifically in that island's southeastern sector and in the city of Honolulu from Pearl Harbor to the Mokapu Peninsula . It is part of the rejuvenated stage of Hawaiian volcanic activity, which occurred after the main stage of volcanic activity that on Oʻahu built the Koʻolau volcano. These volcanoes formed through dominantly explosive eruptions and gave rise to cinder cones , lava flows , tuff cones and volcanic islands . Among these are well known landmarks such as Diamond Head and Punchbowl Crater . Volcanic activity began less than one million years ago and occurred at between 40 and 30 separate volcanic vents, some of which are submarine. Sea level varied during

970-465: A high content of plagioclase; these are sometimes described as leucobasalts . It can be difficult to distinguish between lighter-colored basalt and andesite , so field researchers commonly use a rule of thumb for this purpose, classifying it as basalt if it has a color index of 35 or greater. The physical properties of basalt result from its relatively low silica content and typically high iron and magnesium content. The average density of basalt

1067-416: A large section of the volcano has sunk below sea level. This volcano constitutes the tholeiitic stage of Hawaiian volcanism, and developed possibly during Miocene to Pleistocene time. Before Koʻolau volcano was active, between 3.5 and 2.74 million years ago, Waiʻanae volcano formed the western part of Oʻahu. Koʻolau volcano appears to be unrelated to the Honolulu Volcanics, which are considered to be

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1164-621: A lightweight "frothy" texture to the rock. Basaltic cinders are often red, coloured by oxidized iron from weathered iron-rich minerals such as pyroxene . ʻAʻā types of blocky cinder and breccia flows of thick, viscous basaltic lava are common in Hawaiʻi. Pāhoehoe is a highly fluid, hot form of basalt which tends to form thin aprons of molten lava which fill up hollows and sometimes forms lava lakes . Lava tubes are common features of pāhoehoe eruptions. Basaltic tuff or pyroclastic rocks are less common than basaltic lava flows. Usually basalt

1261-623: A lower total content of alkali oxides than trachybasalt and most basanites and tephrites. Basalt generally has a composition of 45–52 wt% SiO 2 , 2–5 wt% total alkalis, 0.5–2.0 wt% TiO 2 , 5–14 wt% FeO and 14 wt% or more Al 2 O 3 . Contents of CaO are commonly near 10 wt%, those of MgO commonly in the range 5 to 12 wt%. High-alumina basalts have aluminium contents of 17–19 wt% Al 2 O 3 ; boninites have magnesium (MgO) contents of up to 15 percent. Rare feldspathoid -rich mafic rocks, akin to alkali basalts, may have Na 2 O + K 2 O contents of 12% or more. The abundances of

1358-507: A phenocryst, and when present, may have rims of pigeonite. The groundmass contains interstitial quartz or tridymite or cristobalite . Olivine tholeiitic basalt has augite and orthopyroxene or pigeonite with abundant olivine, but olivine may have rims of pyroxene and is unlikely to be present in the groundmass . Alkali basalts typically have mineral assemblages that lack orthopyroxene but contain olivine. Feldspar phenocrysts typically are labradorite to andesine in composition. Augite

1455-525: A prominent promontory east of Honolulu. Inland from Diamond Head lie the Kaimukī and Mauʻumae cones, which appear to come from a shared fissure . Mauʻumae features a lava flow and Kaimukī is an unusual lava cone with a summit crater. Its slopes are gentle and lava ponded against topographical obstacles. The Kaimukī and Kaʻau cinder cones together with Mauʻumae and Diamond Head form the Kaʻau or Kaimukī rift zone;

1552-469: A separate volcanic system; sometimes the "Kokohead Volcanics" are split off from the Honolulu Volcanics. The Honolulu Volcanics constitute a late stage of volcanism which in Hawaiʻi is known as the rejuvenated stage and the third stage of a typical Hawaiian volcano. They have a much smaller volume than the Koʻolau volcano even though their lava flows are usually thicker; the unconformity that separates

1649-456: A series of volcanoes in the southeastern sector of Oʻahu and includes dikes , lava flows , spatter cones , tephra deposits, tuff cones , and mesas where the surrounding terrain has been eroded away. Vents span the area southeast of a line between Mokapu Peninsula and Pearl Harbor , and extend from the ridges of Koʻolau volcano to below sea level and to the coast plain of southern Oʻahu. The system takes its name from Honolulu ,

1746-602: A short time such as a few hours, as has been observed in similar eruptions during historical time. The field has also seen many Surtseyan or phreatomagmatic eruptions, especially at nearshore vents, when ascending magma encountered water, such as at Mānana Island, Koko and Punchbowl; these eruptions were explosive and they are the best exposed site of Surtseyan activity in the United States. Some formed small islands when they emerged, and one vent may now be buried beneath coral deposits. At Koko Crater and Diamond Head,

1843-523: A significant constituent. Accessory minerals present in relatively minor amounts include iron oxides and iron-titanium oxides, such as magnetite , ulvöspinel , and ilmenite . Because of the presence of such oxide minerals, basalt can acquire strong magnetic signatures as it cools, and paleomagnetic studies have made extensive use of basalt. In tholeiitic basalt , pyroxene ( augite and orthopyroxene or pigeonite ) and calcium -rich plagioclase are common phenocryst minerals. Olivine may also be

1940-427: Is 2.9 g/cm , compared, for example, to granite ’s typical density of 2.7 g/cm . The viscosity of basaltic magma is relatively low—around 10 to 10 cP —similar to the viscosity of ketchup , but that is still several orders of magnitude higher than the viscosity of water, which is about 1 cP). Basalt is often porphyritic , containing larger crystals ( phenocrysts ) that formed before the extrusion event that brought

2037-435: Is about 1 kilometre (0.62 mi) wide. Hanauma Bay close to Kalanianaʻole Highway is located 13 kilometres (8.1 mi) east of Honolulu and is a 0.4 by 0.8 kilometres (0.25 mi × 0.50 mi) large, 18 metres (59 ft) deep compound crater /tuff cone with several associated dykes and lava flows- It was breached by the sea and coral reefs grow within it. Together with Kahauloa and Kalama all these vents form

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2134-541: Is about 35,000 years assuming that the younger ages for the Koko Rift are correct. Many eruptions were highly explosive , probably due to the magma being rich in gases, threw tephra high into the air, and ripped pre-existent volcanic rock and limestone out. When the rising magma intercepted water—especially close to the coast— steam explosions ensued which threw up rock debris including older rocks such as coral fragments. Lava flows were erupted mainly during

2231-401: Is also produced by some subglacial volcanic eruptions. Basalt is the most common volcanic rock type on Earth, making up over 90% of all volcanic rock on the planet. The crustal portions of oceanic tectonic plates are composed predominantly of basalt, produced from upwelling mantle below the ocean ridges . Basalt is also the principal volcanic rock in many oceanic islands , including

2328-417: Is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low- viscosity lava rich in magnesium and iron ( mafic lava) exposed at or very near the surface of a rocky planet or moon . More than 90% of all volcanic rock on Earth is basalt. Rapid-cooling, fine-grained basalt is chemically equivalent to slow-cooling, coarse-grained gabbro . The eruption of basalt lava

2425-761: Is considered a key to understanding plate tectonics , its compositions have been much studied. Although MORB compositions are distinctive relative to average compositions of basalts erupted in other environments, they are not uniform. For instance, compositions change with position along the Mid-Atlantic Ridge , and the compositions also define different ranges in different ocean basins. Mid-ocean ridge basalts have been subdivided into varieties such as normal (NMORB) and those slightly more enriched in incompatible elements (EMORB). Isotope ratios of elements such as strontium , neodymium , lead , hafnium , and osmium in basalts have been much studied to learn about

2522-481: Is defined as volcanic rock with a content of between 45% and 52% silica and no more than 5% alkali metal oxides. This places basalt in the B field of the TAS diagram. Such a composition is described as mafic . Basalt is usually dark grey to black in colour, due to a high content of augite or other dark-coloured pyroxene minerals, but can exhibit a wide range of shading. Some basalts are quite light-coloured due to

2619-435: Is likely to occur in the southeastern sector of Oʻahu and will be of small volume, involving the emplacement of cinders, lava flows and mudflows with characteristics similar to those of past Honolulu Volcanics eruptions: The Mokapu Peninsula has been prospected for the presence of geothermal power resources, but the presence of such resources was judged to be unlikely. Short-lasting volcanism typical for Honolulu Volcanics

2716-517: Is no evidence in oral tradition for eruptions during historical times. Future eruptions of Honolulu Volcanics are possible, but the likelihood of a new event in the next hundred or thousand years is considered to be so small as to be negligible; it is probably comparable to the Kohala peninsula on Hawaiʻi, the lowest risk area of the active island. Additionally, only small areas of Oʻahu are likely to be affected by an eruption. Any future eruption

2813-753: Is observed by geologists at about 20 volcanoes per year. Basalt is also an important rock type on other planetary bodies in the Solar System . For example, the bulk of the plains of Venus , which cover ~80% of the surface, are basaltic; the lunar maria are plains of flood-basaltic lava flows ; and basalt is a common rock on the surface of Mars . Molten basalt lava has a low viscosity due to its relatively low silica content (between 45% and 52%), resulting in rapidly moving lava flows that can spread over great areas before cooling and solidifying. Flood basalts are thick sequences of many such flows that can cover hundreds of thousands of square kilometres and constitute

2910-421: Is questionable. Submarine vents are also known, including a 300-metre (980 ft) high solitary cone with two ridges off northeast Oʻahu, which is covered by pillow lavas and volcaniclastic sediments. At least five cones are found off the southwestern extension of the Koko Rift where they are situated on a southwestward extending ridge. Another set of submarine vents is found south of Diamond Head. It

3007-608: Is rejuvenated volcanism on Waiʻanae volcano also, but it appears to be older than the Honolulu Volcanics. The petrology of the Honolulu Volcanics is well studied. The volcanic rocks of the Honolulu Volcanics are diverse; they include alkali basalts , melilite and nepheline basalts , basanites , melilite, nephelinite and websterite , and form an alkaline -nephelinite suite. The variations in composition reflect distinct proportions of melts produced from parent rocks. Phenocrysts include augite , labradorite , olivine and plagioclase ; additionally spinels are found in

Punchbowl Crater - Misplaced Pages Continue

3104-583: Is rich in titanium compared to augite in tholeiitic basalt. Minerals such as alkali feldspar , leucite , nepheline , sodalite , phlogopite mica, and apatite may be present in the groundmass. Basalt has high liquidus and solidus temperatures—values at the Earth's surface are near or above 1200 °C (liquidus) and near or below 1000 °C (solidus); these values are higher than those of other common igneous rocks. The majority of tholeiitic basalts are formed at approximately 50–100 km depth within

3201-402: Is suppressed. Above this depth, submarine eruptions are often explosive, tending to produce pyroclastic rock rather than basalt flows. These eruptions, described as Surtseyan, are characterised by large quantities of steam and gas and the creation of large amounts of pumice . When basalt erupts underwater or flows into the sea, contact with the water quenches the surface and the lava forms

3298-440: Is too hot and fluid to build up sufficient pressure to form explosive lava eruptions but occasionally this will happen by trapping of the lava within the volcanic throat and buildup of volcanic gases . Hawaiʻi's Mauna Loa volcano erupted in this way in the 19th century, as did Mount Tarawera , New Zealand in its violent 1886 eruption. Maar volcanoes are typical of small basalt tuffs, formed by explosive eruption of basalt through

3395-455: Is ultimately derived from Late Latin basaltes , a misspelling of Latin basanites "very hard stone", which was imported from Ancient Greek βασανίτης ( basanites ), from βάσανος ( basanos , " touchstone "). The modern petrological term basalt , describing a particular composition of lava -derived rock, became standard because of its use by Georgius Agricola in 1546, in his work De Natura Fossilium . Agricola applied

3492-457: Is unlikely to leave remnant heat resources. The only anomalously warm springs in the area are found within the Koʻolau caldera and are related to that volcanic system rather than the Honolulu Volcanics. Some evidence of geothermal activity has been found elsewhere on Oʻahu. Download coordinates as: Basalt Basalt ( UK : / ˈ b æ s ɔː l t , - əl t / ; US : / b ə ˈ s ɔː l t , ˈ b eɪ s ɔː l t / )

3589-477: Is widespread across Honolulu and originated in volcanic eruptions of the Honolulu Volcanics, and ash layers cover coral reef deposis both onshore and offshore as far as ʻEwa Beach . Ash from the Salt Lake Craters was transported by winds to Pearl Harbor and is considered to be responsible for the formation of the bay by closing off its access to the sea. Activity at specific vents: Many vents of

3686-539: The Clementine mission demonstrate that the lunar maria possess a continuum of titanium concentrations, and that the highest concentrations are the least abundant. Lunar basalts show exotic textures and mineralogy, particularly shock metamorphism , lack of the oxidation typical of terrestrial basalts, and a complete lack of hydration . Most of the Moon 's basalts erupted between about 3 and 3.5 billion years ago, but

3783-1228: The Paraná Traps in Brazil, the Siberian Traps in Russia , the Karoo flood basalt province in South Africa, and the Columbia River Plateau of Washington and Oregon . Basalt is also prevalent across extensive regions of the Eastern Galilee , Golan , and Bashan in Israel and Syria . Basalt also is common around volcanic arcs, specially those on thin crust . Ancient Precambrian basalts are usually only found in fold and thrust belts, and are often heavily metamorphosed. These are known as greenstone belts , because low-grade metamorphism of basalt produces chlorite , actinolite , epidote and other green minerals. As well as forming large parts of

3880-524: The hypabyssal and plutonic equivalents of basalt. During the Hadean , Archean , and early Proterozoic eons of Earth's history, the chemistry of erupted magmas was significantly different from what it is today, due to immature crustal and asthenosphere differentiation. The resulting ultramafic volcanic rocks, with silica (SiO 2 ) contents below 45% and high magnesium oxide (MgO) content, are usually classified as komatiites . The word "basalt"

3977-524: The lanthanide or rare-earth elements (REE) can be a useful diagnostic tool to help explain the history of mineral crystallisation as the melt cooled. In particular, the relative abundance of europium compared to the other REE is often markedly higher or lower, and called the europium anomaly . It arises because Eu can substitute for Ca in plagioclase feldspar, unlike any of the other lanthanides, which tend to only form cations . Mid-ocean ridge basalts (MORB) and their intrusive equivalents, gabbros, are

Punchbowl Crater - Misplaced Pages Continue

4074-667: The 1880s, leasehold land on the slopes of the Punchbowl opened for settlement and in the 1930s, the crater was used as a rifle range for the Hawaii National Guard . Anti-aircraft guns located there were fired during the Japanese attack December 7, 1941. The US Navy built the Nimitz Bowl in 1944 in Punchbowl Crater for USO Hawaii shows and sports. Toward the end of World War II , tunnels were dug through

4171-463: The Earth's crust, basalt also occurs in other parts of the Solar System. Basalt commonly erupts on Io (the third largest moon of Jupiter ), and has also formed on the Moon , Mars , Venus , and the asteroid Vesta . The dark areas visible on Earth's moon , the lunar maria , are plains of flood basaltic lava flows. These rocks were sampled both by the crewed American Apollo program and

4268-416: The Honolulu Volcanics are furrowed; erosion has cut gullies in the slopes of Diamond Head and Punchbowl Crater. Wavecut terraces formed in some volcanoes during sea level highstands; it is likely that wave erosion breached Hanauma Bay, flooding it, either during or after the eruption that created it. The youngest eruptions of the whole field took place either 30,000 or 76,000 years ago, making it

4365-662: The Honolulu Volcanics follow northeastward-trending alignments that are at right angles to the rift zone of the Koʻolau volcano. From northwest to southeast these are the Haʻikū Rift, the Tantalus Rift, the Kaimukī/Kaʻau Rift and the Koko Head/Koko Rift, but each rift has had eruptions at different times and with different compositions. It is not clear whether these alignments are in any way related to

4462-676: The Honolulu Volcanics from the Koʻolau Volcanic Series was already recognized in the 19th century. As Hawaiian volcanoes grow, they start to sink under their weight. As volcanism moves along the Hawaiian chain, the Hawaiian Arch moves behind the volcanism at a distance of several hundred kilometres, and appears to have passed under Oahu in geologically recent times. The tectonic effect of the Hawaiian Arch passing under

4559-572: The Honolulu Volcanics have been correlated to shorelines generated by sea level variations, which have left both drowned and emergent platforms and terraces on Oʻahu. Some volcanoes formed when sea level was lower than today and thus part of their structures are now submerged, others formed when it was higher and grew on reefs . These sea level variations are a function of glacial - interglacial changes, with higher sea levels associated with interglacials when polar glaciers expand and retreat. Thus four stages of volcanic activity have been defined,

4656-475: The Kaʻau crater lies close to the crest of the Koʻolau Range and is filled by a swamp that drains into Waimao stream. Punchbowl Crater rises north of and at the centre of Honolulu and is a good outlook to the city and its surroundings. The Mokapu peninsula was formed by Honolulu Volcanics and includes the three volcanic vents of Puʻu Hawaiʻiloa, Pyramid Rock and Ulapaʻu Head; additional vents form islets off

4753-411: The Koko Rift occurred between 100,000 and 60,000 years ago; it is not clear whether Koko Rift or Tantalus Rift erupted last, as ages of 35,000 and 85,000 years before present have been obtained on the Koko Rift while the Tantalus Rift has yielded ages of 76,000 ± 1,000 years ago, and the two rifts are clearly unrelated to each other. The average recurrence interval for eruptions in the Honolulu Volcanics

4850-489: The Koko Rift. Farther northeast lie the Kaupō lava flow and the islands of Kāohikaipu and Mānana; all these except Mānana are also in the Koko Rift. This 15 kilometres (9.3 mi) long rift includes at least 12 separate volcanic vents and its vents appear to have formed in a single eruption. Diamond Head is a 1,700-metre (5,600 ft) (rim-to-rim) wide typical tuff cone with a wide and not overly deep crater that forms

4947-521: The Punchbowl's Hawaiian name, "Pūowaina," the most common is "Hill of Sacrifice." This translation closely relates to the history of the crater. The first known use was as an altar where Hawaiians offered human sacrifices to their gods and killed violators of the many taboos. Later, during the reign of Kamehameha the Great , a battery of two cannons was mounted at the rim of the crater to salute distinguished arrivals and signify important occasions. Early in

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5044-553: The activity of the volcanic field, and some volcanic eruptions have been dated through correlation with individual sea level fluctuations. The field erupted various kinds of lavas of mostly basaltic type with a high content of xenoliths . During eruptions, ascending magma often underwent interactions with water and thus caused steam explosions and the formation of particular volcanic structures such as tuff cones. The last eruption took place 35,000 or 76,000 years ago and future hazardous eruptions are possible. The Honolulu Volcanics are

5141-523: The ages of the Koko rift. Volcanic activity occurred in two pulses, one between 800,000 and 250,000 years ago and the other in the last 120,000 years, with a hiatus in between the two pulses. Sometimes the vents of the Sugar Loaf, Tantalus Peak and Koko Rift area are classified separately from the other vents of the Honolulu Volcanics as they are usually less than 100,000 years old. Volcanic eruptions in

5238-402: The amount of water interacting with the developing volcano varied over the course of the eruption, as more water entered the vent when the eruption enlarged it. Volcanic rocks of Honolulu Volcanics include agglomerates , breccia , breccia-tuffs, scoria bombs and tuffs. Tephra takes the form of both lapilli and volcanic ash and some eruptions were followed by lahars when volcanic ash

5335-480: The basalt/andesite field of the QAPF diagram. Basalt is further distinguished from andesite by its silica content of under 52%. It is often not practical to determine the mineral composition of volcanic rocks, due to their very small grain size, in which case geologists instead classify the rocks chemically, with particular emphasis on the total content of alkali metal oxides and silica ( TAS ); in that context, basalt

5432-476: The capital of Hawaiʻi , as craters are scattered in and around the city. The volcanic system includes well-known landmarks of Honolulu such as Diamond Head , Koko Head , Punchbowl Crater , Rabbit Island , Tantalus , Hanauma Bay (notable as a snorkeling site) and the Mokapu Peninsula, which is the location of Marine Corps Base Hawaiʻi . The United States military has made use of some of

5529-478: The characteristic igneous rocks formed at mid-ocean ridges. They are tholeiitic basalts particularly low in total alkalis and in incompatible trace elements, and they have relatively flat REE patterns normalized to mantle or chondrite values. In contrast, alkali basalts have normalized patterns highly enriched in the light REE, and with greater abundances of the REE and of other incompatible elements. Because MORB basalt

5626-447: The crust, forming an apron of mixed basalt and wall rock breccia and a fan of basalt tuff further out from the volcano. Amygdaloidal structure is common in relict vesicles and beautifully crystallized species of zeolites , quartz or calcite are frequently found. During the cooling of a thick lava flow, contractional joints or fractures form. If a flow cools relatively rapidly, significant contraction forces build up. While

5723-545: The evolution of the Earth's mantle . Isotopic ratios of noble gases , such as He / He, are also of great value: for instance, ratios for basalts range from 6 to 10 for mid-ocean ridge tholeiitic basalt (normalized to atmospheric values), but to 15–24 and more for ocean-island basalts thought to be derived from mantle plumes . Source rocks for the partial melts that produce basaltic magma probably include both peridotite and pyroxenite . The shape, structure and texture of

5820-464: The formation of zeolitic palagonite; minerals included in altered rocks include analcime , aragonite , calcite, chabazite , erionite , faujasite , gonnardite , gypsum , montmorillonite , natrolite , opal , phillipsite and thomsonite . In some vents, such as Diamond Head, the rocks are so heavily altered that their original composition and texture can no longer be reconstructed. The Honolulu Volcanics rocks originate at greater depths than

5917-432: The groundwater on Oʻahu, and most Honolulu Volcanics have little significance. Some groundwater in Honolulu Volcanics rocks is saline, and has been used both as a water source for a sea-life park at Makapuʻu and for the discharge of salty wastewaters. The activity of the Honolulu Volcanics began less than one million years ago during the late Pleistocene and Holocene , after volcanic activity at Koʻolau had ceased and

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6014-462: The island may be responsible for the onset of Honolulu Volcanics volcanism, as well as of the Kōloa Volcanics on Kauaʻi and perhaps for future volcanism on Maui or Molokaʻi , but also for ongoing uplift on Oʻahu. Other proposed mechanisms are a conductive heating of the lithosphere or ongoing upwelling in the mantle plume . There is evidence that a fall in sea level at the beginning of

6111-740: The islands of Hawaiʻi , the Faroe Islands , and Réunion . The eruption of basalt lava is observed by geologists at about 20 volcanoes per year. Basalt is the rock most typical of large igneous provinces . These include continental flood basalts , the most voluminous basalts found on land. Examples of continental flood basalts included the Deccan Traps in India , the Chilcotin Group in British Columbia , Canada ,

6208-554: The last ice age triggered the last eruptions. The terrain that the volcanoes developed on includes both old volcanic rocks of the Koʻolau volcano, sediments of the coastal plains, and soils. Some Honolulu Volcanics have grown on coral deposits, Koko Head developed on limestone for example, and coral reef development was widespread during the activity of the Honolulu Volcanics. The Honolulu Volcanics are not associated with either aeromagnetic or gravimetric anomalies; only Salt Lake Crater has an associated gravity anomaly . There

6305-548: The late stage of the eruption and were typically of small dimensions; the longest flow is 7 kilometres (4.3 mi) long and the largest one at Kaimukī forms a 4 square kilometres (1.5 sq mi) lava shield or lava dome . Cinder cones form from the fallout of volcanic ejecta material, which is variously described as cinder , lava bombs , pumice and spatter and forms layered deposits. Tuff cones in addition can also contain non-magmatic ejecta. Many of these eruptions, especially that of Diamond Head, probably only lasted for

6402-523: The lava flows filled deep valleys cut into the older Koʻolau volcano and displaced streams that previously ran through these valleys; for example, water passing over a lava flow in Kamanaiki Valley forms a waterfall . Together with sediments coming down from the mountains and coral reef growth, the deposits of the Honolulu Volcanics have formed the coastal plain on which the city of Honolulu and military installations are built. The vents of

6499-604: The magma as it decompresses during its approach to the surface; the erupted lava then solidifies before the gases can escape. When vesicles make up a substantial fraction of the volume of the rock, the rock is described as scoria . The term basalt is at times applied to shallow intrusive rocks with a composition typical of basalt, but rocks of this composition with a phaneritic (coarser) groundmass are more properly referred to either as diabase (also called dolerite) or—when they are more coarse-grained (having crystals over 2 mm across)—as gabbro . Diabase and gabbro are thus

6596-458: The magma itself; isotope ratios of the rocks indicate that groundwater carbonates are the most important source, however. In Punchbowl Crater, where the rocks have been quarried, they have a brown to yellow colour. Cinders have red-black colours which can grade to yellow when they are hydrothermally altered, due to the formation of the glassy rock palagonite . Many of the erupted rocks have undergone various degrees of alteration, including

6693-416: The magma to the surface, embedded in a finer-grained matrix . These phenocrysts are usually made of augite, olivine , or a calcium-rich plagioclase, which have the highest melting temperatures of any of the minerals that can typically crystallize from the melt, and which are therefore the first to form solid crystals. Basalt often contains vesicles ; they are formed when dissolved gases bubble out of

6790-710: The mantle. Many alkali basalts may be formed at greater depths, perhaps as deep as 150–200 km. The origin of high-alumina basalt continues to be controversial, with disagreement over whether it is a primary melt or derived from other basalt types by fractionation. Relative to most common igneous rocks, basalt compositions are rich in MgO and CaO and low in SiO 2 and the alkali oxides, i.e., Na 2 O + K 2 O , consistent with their TAS classification . Basalt contains more silica than picrobasalt and most basanites and tephrites but less than basaltic andesite . Basalt has

6887-406: The most voluminous of all volcanic formations. Basaltic magmas within Earth are thought to originate from the upper mantle . The chemistry of basalts thus provides clues to processes deep in Earth's interior . Basalt is composed mostly of oxides of silicon, iron, magnesium, potassium, aluminum, titanium, and calcium. Geologists classify igneous rock by its mineral content whenever possible;

6984-461: The old shoreline of the Koʻolau volcano. The volcanic vents there include Koko Head, the Hanauma Bay craters, Kahauloa crater bay, a wave-eroded cone, Koko Crater and Kalama cinder cone; Koko Head cones are heavily eroded, and the sea has broken into one of the cones, exposing its structure in outcrops. Koko Head is the largest cone of the Honolulu Volcanics and the crater of Koko Crater

7081-410: The oldest samples are 4.2 billion years old, and the youngest flows, based on the age dating method of crater counting , are estimated to have erupted only 1.2 billion years ago. From 1972 to 1985, five Venera and two VEGA landers successfully reached the surface of Venus and carried out geochemical measurements using X-ray fluorescence and gamma-ray analysis. These returned results consistent with

7178-422: The peninsula, such as Moku Manu and Mōkōlea Rock . Puʻu Hawaiʻiloa is a cinder cone in the middle of the peninsula, Pyramid Rock at the northwestern tip is deeply eroded and probably the oldest vent in the peninsula, and Ulapaʻu Head is a crater that was breached by the sea and of which only a crescent-like western part remains. Salt Lake Crater contains a salt lake and is located east from Pearl Harbor;

7275-465: The presence of excess radiogenic argon due to the xenoliths makes dates obtained by potassium-argon dating unreliable and dates older than 800,000 years are especially questionable. Argon-argon dating has been applied to submarine vents of the Honolulu Volcanics and has yielded ages of 700,000 to 400,000 years for submarine vents northeast of Oʻahu while the southwestern submarine vents have ages clustering around 140,000 ± 50,000 years, in line with

7372-772: The project was deferred until after World War II. By 1947, Congress and veteran organizations placed a great deal of pressure on the military to find a permanent burial site in Hawaii for the remains of thousands of World War II servicemen on the island of Guam awaiting permanent burial. Subsequently, the Army again began planning the Punchbowl cemetery; in February 1948 Congress approved funding and construction began. 21°18′55″N 157°50′55″W  /  21.31528°N 157.84861°W  / 21.31528; -157.84861 Honolulu Volcanic Series The Honolulu Volcanics are

7469-475: The rate of cooling; very rapid cooling may result in very small (<1 cm diameter) columns, while slow cooling is more likely to produce large columns. The character of submarine basalt eruptions is largely determined by depth of water, since increased pressure restricts the release of volatile gases and results in effusive eruptions. It has been estimated that at depths greater than 500 metres (1,600 ft), explosive activity associated with basaltic magma

7566-411: The relative volume percentages of quartz (crystalline silica (SiO 2 )), alkali feldspar , plagioclase , and feldspathoid ( QAPF ) are particularly important. An aphanitic (fine-grained) igneous rock is classified as basalt when its QAPF fraction is composed of less than 10% feldspathoid and less than 20% quartz, and plagioclase makes up at least 65% of its feldspar content. This places basalt in

7663-402: The rim of the crater for the placement of shore batteries to guard Honolulu Harbor and the south edge of Pearl Harbor . During the late 1890s, a committee recommended that the Punchbowl become the site for a new cemetery to accommodate the growing population of Honolulu. The idea was rejected for fear of polluting the water supply and the emotional aversion to creating a city of the dead above

7760-595: The robotic Russian Luna program , and are represented among the lunar meteorites . Lunar basalts differ from their Earth counterparts principally in their high iron contents, which typically range from about 17 to 22 wt% FeO. They also possess a wide range of titanium concentrations (present in the mineral ilmenite ), ranging from less than 1 wt% TiO 2 , to about 13 wt.%. Traditionally, lunar basalts have been classified according to their titanium content, with classes being named high-Ti, low-Ti, and very-low-Ti. Nevertheless, global geochemical maps of titanium obtained from

7857-403: The rock at the landing sites being basalts, including both tholeiitic and highly alkaline basalts. The landers are thought to have landed on plains whose radar signature is that of basaltic lava flows. These constitute about 80% of the surface of Venus. Some locations show high reflectivity consistent with unweathered basalt, indicating basaltic volcanism within the last 2.5 million years. Basalt

7954-433: The rocks from Koʻolau volcano and their composition is fairly dissimilar as well, while there are substantial geochemical similarities to young volcanic rocks from East Molokaʻi , Kauaʻi and West Maui . Jackson and Wright suggested that the pyroxenite may be the source rock of the magmas, with orthopyroxene-rich rocks being leftovers from the melting process; strontium isotope ratios endorse this origin although none of

8051-434: The rocks. Xenoliths of amphibole , calcite , clinopyroxene , dunite , garnet , garnet peridotite , orthopyroxene , phlogopite , garnet pyroxenite , lherzolite and spinel have been described. The most common ones are dunite, garnet containing rocks and lherzolite and the relative prevalence of the various xenoliths is a function of the position of their source vent relative to the Koʻolau caldera. Their formation

8148-500: The salt lake formed when salty groundwater seeped into the crater and was concentrated by evaporation . A cluster of additional older vents known as ʻĀliamanu, Makalapa, ʻĀliamanu School Cone, Moanalua Cone, ʻĀkulikuli Vent and Wiliki Cone are associated with Salt Lake Crater. The Salt Lake Tuff is associated with these craters and covers an area of at least 13 square kilometres (5 sq mi); Honolulu International Airport and Hickham Air Force Base lie south and southwest from

8245-462: The sea it usually forms pillow basalts. However, when ʻaʻā enters the ocean it forms a littoral cone , a small cone-shaped accumulation of tuffaceous debris formed when the blocky ʻaʻā lava enters the water and explodes from built-up steam. The island of Surtsey in the Atlantic Ocean is a basalt volcano which breached the ocean surface in 1963. The initial phase of Surtsey's eruption

8342-503: The structure of the previous Koʻolau volcano, instead of being controlled by the crust of the Pacific Ocean , but the trends along the Koko and Tantalus Rifts are parallel to that of the flexural arch of Hawaiʻi Island . There is also a hypothetical "Diamond Head fault " that may be associated with earthquakes on Oahu that occurred in 1948, 1951 and 1961–1981, but it is not parallel to these alignments and its very existence

8439-670: The term "basalt" to the volcanic black rock beneath the Bishop of Meissen's Stolpen castle , believing it to be the same as the "basaniten" described by Pliny the Elder in AD ;77 in Naturalis Historiae . On Earth, most basalt is formed by decompression melting of the mantle . The high pressure in the upper mantle (due to the weight of the overlying rock ) raises the melting point of mantle rock, so that almost all of

8536-580: The upper mantle is solid. However, mantle rock is ductile (the solid rock slowly deforms under high stress). When tectonic forces cause hot mantle rock to creep upwards, pressure on the ascending rock decreases, and this can lower its melting point enough for the rock to partially melt , producing basaltic magma. Decompression melting can occur in a variety of tectonic settings, including in continental rift zones, at mid-ocean ridges , above geological hotspots , and in back-arc basins . Basalt also forms in subduction zones , where mantle rock rises into

8633-403: The vents respectively. Some of these vents have been identified as maars . The Honolulu Volcanics developed on the 2.3 million year old Koʻolau Volcanic Series , which forms the core of eastern Oahu and extends underwater far from the shore. Like other Hawaiian volcanoes Koʻolau is a shield volcano that grew through lava flows erupted from a rift system with a central caldera , although

8730-492: The volcanic islands that were formed by the Honolulu Volcanics. The Koko area is designated as the Koko Head Regional Park and Hanauma Bay is also a state park. Parts of this system are among the best known volcanic vents of Hawaiʻi. About 30–40 vents have been identified. Most cinder cones on Oʻahu are quite large, over 76 metres (250 ft) high and up to 0.80 kilometres (0.5 mi) wide. Some of

8827-457: The volcano been substantially eroded. The first eruptions occurred within the Koʻolau caldera and the youngest in the far southeastern part of Oʻahu, coinciding with the Koko Rift. There is otherwise little evidence for a spatial pattern in the volcanic activity, with each rift having eruptions widely spaced in time. The lava flows from Honolulu Volcanics have been used to construct a history of variations of Earth's magnetic field . Eruptions of

8924-482: The xenoliths appears to be entirely representative of the source melts. Water - and carbon dioxide -containing volatiles may have altered the source rocks of the Honolulu Volcanics melts before these actually melted. In terms of the ultimate origin of the magmas, either an origin from a mixing between MORB mantle with mantle plume rocks, the lithosphere or exclusively from lithospheric mantle have been proposed. Research published in 2007 favoured an origin from

9021-430: The youngest rejuvenated volcanism in Hawaii. Some of the youngest volcanics of Honolulu Volcanics were once considered 5,000 years old, with an age of 7,000 years attributed to a volcanic event at Hanauma Bay and another of 10,000 years to the Kaupō flow. However, radiometric dating has not yielded ages younger than 31,000–43,000 years old, and most age estimates of less than 30,000 years ago are misinterpreted. There

9118-400: Was highly explosive, as the magma was quite fluid, causing the rock to be blown apart by the boiling steam to form a tuff and cinder cone. This has subsequently moved to a typical pāhoehoe-type behaviour. Volcanic glass may be present, particularly as rinds on rapidly chilled surfaces of lava flows, and is commonly (but not exclusively) associated with underwater eruptions. Pillow basalt

9215-403: Was influenced by mantle rocks left over from the Koʻolau volcano. Coral fragments have been found in Koko and Salt Lake rocks, and metamorphic rocks included in the volcanics may be part of the basement that the magmas of the volcanoes traversed. Calcite – which in the form of crystals gives Diamond Head its name – in the volcanic rocks may come from coral reefs, groundwater or even from

9312-459: Was once proposed that some seamounts (underwater mountains) off northeastern Oʻahu such as Tuscaloosa Seamount are related to the volcanic series; today however they are considered to be fragments of the giant Nuʻuanu Slide off northeastern Oʻahu. Most of the present-day shoreline of Hawaiʻi Kai was formed by Honolulu Volcanics; the Kuapā Pond is a leftover lake between the new shoreline and

9409-472: Was swept up by streams; one such deposit is found in Pālolo Valley. During eruptions, trade winds blew material from the vent; this wind-driven material transport is responsible for the frequently asymmetric shape of the volcanoes such as at Diamond Head where the southeastern rim is the highest part of the crater rim. Drill cores in Hanauma Bay have found ash layers; a black ash known as "black sand"

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