110-464: The Honolulu Volcanics are 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
220-555: 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
330-580: A ghost town ) and Fourpeaked Mountain in Alaska, which, before its September 2006 eruption, had not erupted since before 8000 BCE. Crust (geology) In geology , the crust is the outermost solid shell of a planet , dwarf planet , or natural satellite . It is usually distinguished from the underlying mantle by its chemical makeup; however, in the case of icy satellites, it may be distinguished based on its phase (solid crust vs. liquid mantle). The crusts of Earth , Mercury , Venus , Mars , Io ,
440-484: A magma chamber below the surface. The process that forms volcanoes is called volcanism . On Earth, volcanoes are most often found where tectonic plates are diverging or converging , and because most of Earth's plate boundaries are underwater, most volcanoes are found underwater. For example, a mid-ocean ridge , such as the Mid-Atlantic Ridge , has volcanoes caused by divergent tectonic plates whereas
550-750: 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,
660-437: A graduated spectrum, with much overlap between categories, and does not always fit neatly into only one of these three separate categories. The USGS defines a volcano as "erupting" whenever the ejection of magma from any point on the volcano is visible, including visible magma still contained within the walls of the summit crater. While there is no international consensus among volcanologists on how to define an active volcano,
770-412: 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
880-443: A paper was published suggesting a new definition for the word 'volcano' that includes processes such as cryovolcanism . It suggested that a volcano be defined as 'an opening on a planet or moon's surface from which magma , as defined for that body, and/or magmatic gas is erupted.' This article mainly covers volcanoes on Earth. See § Volcanoes on other celestial bodies and cryovolcano for more information. The word volcano
990-512: 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
1100-450: 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 ,
1210-597: 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,
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#17327807665551320-632: A volcano is largely determined by the composition of the lava it erupts. The viscosity (how fluid the lava is) and the amount of dissolved gas are the most important characteristics of magma, and both are largely determined by the amount of silica in the magma. Magma rich in silica is much more viscous than silica-poor magma, and silica-rich magma also tends to contain more dissolved gases. Lava can be broadly classified into four different compositions: Mafic lava flows show two varieties of surface texture: ʻAʻa (pronounced [ˈʔaʔa] ) and pāhoehoe ( [paːˈho.eˈho.e] ), both Hawaiian words. ʻAʻa
1430-555: A volcano is of a conical mountain, spewing lava and poisonous gases from a crater at its summit; however, this describes just one of the many types of volcano. The features of volcanoes are varied. The structure and behaviour of volcanoes depend on several factors. Some volcanoes have rugged peaks formed by lava domes rather than a summit crater while others have landscape features such as massive plateaus . Vents that issue volcanic material (including lava and ash ) and gases (mainly steam and magmatic gases) can develop anywhere on
1540-465: A volcano that has experienced one or more eruptions that produced over 1,000 cubic kilometres (240 cu mi) of volcanic deposits in a single explosive event. Such eruptions occur when a very large magma chamber full of gas-rich, silicic magma is emptied in a catastrophic caldera -forming eruption. Ash flow tuffs emplaced by such eruptions are the only volcanic product with volumes rivalling those of flood basalts . Supervolcano eruptions, while
1650-739: Is a volcanic field of over 60 cinder cones. Based on satellite images, it has been suggested that cinder cones might occur on other terrestrial bodies in the Solar system too; on the surface of Mars and the Moon. Stratovolcanoes (composite volcanoes) are tall conical mountains composed of lava flows and tephra in alternate layers, the strata that gives rise to the name. They are also known as composite volcanoes because they are created from multiple structures during different kinds of eruptions. Classic examples include Mount Fuji in Japan, Mayon Volcano in
1760-402: 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; the salt lake formed when salty groundwater seeped into
1870-527: Is a planet's "original" crust. It forms from solidification of a magma ocean. Toward the end of planetary accretion , the terrestrial planets likely had surfaces that were magma oceans. As these cooled, they solidified into crust. This crust was likely destroyed by large impacts and re-formed many times as the Era of Heavy Bombardment drew to a close. The nature of primary crust is still debated: its chemical, mineralogic, and physical properties are unknown, as are
1980-538: 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
2090-412: Is characterized by a rough, clinkery surface and is the typical texture of cooler basalt lava flows. Pāhoehoe is characterized by its smooth and often ropey or wrinkly surface and is generally formed from more fluid lava flows. Pāhoehoe flows are sometimes observed to transition to ʻaʻa flows as they move away from the vent, but never the reverse. More silicic lava flows take the form of block lava, where
2200-444: Is debated. The anorthosite highlands of the Moon are primary crust, formed as plagioclase crystallized out of the Moon's initial magma ocean and floated to the top; however, it is unlikely that Earth followed a similar pattern, as the Moon was a water-less system and Earth had water. The Martian meteorite ALH84001 might represent primary crust of Mars; however, again, this is debated. Like Earth, Venus lacks primary crust, as
2310-565: Is derived from the name of Vulcano , a volcanic island in the Aeolian Islands of Italy whose name in turn comes from Vulcan , the god of fire in Roman mythology . The study of volcanoes is called volcanology , sometimes spelled vulcanology . According to the theory of plate tectonics, Earth's lithosphere , its rigid outer shell, is broken into sixteen larger and several smaller plates. These are in slow motion, due to convection in
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#17327807665552420-584: Is expressed using the volcanic explosivity index (VEI), which ranges from 0 for Hawaiian-type eruptions to 8 for supervolcanic eruptions. As of December 2022 , the Smithsonian Institution 's Global Volcanism Program database of volcanic eruptions in the Holocene Epoch (the last 11,700 years) lists 9,901 confirmed eruptions from 859 volcanoes. The database also lists 1,113 uncertain eruptions and 168 discredited eruptions for
2530-421: 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 the peninsula, such as Moku Manu and Mōkōlea Rock . Puʻu Hawaiʻiloa
2640-432: 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
2750-454: 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 the Koko Rift. Farther northeast lie the Kaupō lava flow and
2860-496: Is needed to create tertiary crust, and Earth is the only planet in the Solar System with plate tectonics. Earth's crust is a thin shell on the outside of Earth, accounting for less than 1% of Earth's volume. It is the top component of the lithosphere , a division of Earth's layers that includes the crust and the upper part of the mantle . The lithosphere is broken into tectonic plates that move, allowing heat to escape from
2970-512: 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
3080-537: Is one of the several tuyas in the area of the Tuya River and Tuya Range in northern British Columbia. Tuya Butte was the first such landform analysed and so its name has entered the geological literature for this kind of volcanic formation. The Tuya Mountains Provincial Park was recently established to protect this unusual landscape, which lies north of Tuya Lake and south of the Jennings River near
3190-415: 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
3300-597: 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
3410-471: Is typically low in silica, shield volcanoes are more common in oceanic than continental settings. The Hawaiian volcanic chain is a series of shield cones, and they are common in Iceland , as well. Lava domes are built by slow eruptions of highly viscous lava. They are sometimes formed within the crater of a previous volcanic eruption, as in the case of Mount St. Helens , but can also form independently, as in
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3520-480: 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: Volcanoes A volcano is a rupture in the crust of a planetary-mass object , such as Earth , that allows hot lava , volcanic ash , and gases to escape from
3630-474: 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
3740-617: The Cascade Volcanoes or the Japanese Archipelago , or the eastern islands of Indonesia . Hotspots are volcanic areas thought to be formed by mantle plumes , which are hypothesized to be columns of hot material rising from the core-mantle boundary. As with mid-ocean ridges, the rising mantle rock experiences decompression melting which generates large volumes of magma. Because tectonic plates move across mantle plumes, each volcano becomes inactive as it drifts off
3850-626: The Hawaiian hotspot is an example. Volcanoes are usually not created where two tectonic plates slide past one another. Large eruptions can affect atmospheric temperature as ash and droplets of sulfuric acid obscure the Sun and cool Earth's troposphere . Historically, large volcanic eruptions have been followed by volcanic winters which have caused catastrophic famines. Other planets besides Earth have volcanoes. For example, volcanoes are very numerous on Venus. Mars has significant volcanoes. In 2009,
3960-473: 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
4070-573: The Moon and other planetary bodies formed via igneous processes and were later modified by erosion , impact cratering , volcanism, and sedimentation. Most terrestrial planets have fairly uniform crusts. Earth, however, has two distinct types: continental crust and oceanic crust . These two types have different chemical compositions and physical properties and were formed by different geological processes. Planetary geologists divide crust into three categories based on how and when it formed. This
4180-473: The adiabatic rise of mantle causes partial melting. Tertiary crust is more chemically-modified than either primary or secondary. It can form in several ways: The only known example of tertiary crust is the continental crust of the Earth. It is unknown whether other terrestrial planets can be said to have tertiary crust, though the evidence so far suggests that they do not. This is likely because plate tectonics
4290-834: The landform and may give rise to smaller cones such as Puʻu ʻŌʻō on a flank of Kīlauea in Hawaii. Volcanic craters are not always at the top of a mountain or hill and may be filled with lakes such as with Lake Taupō in New Zealand. Some volcanoes can be low-relief landform features, with the potential to be hard to recognize as such and be obscured by geological processes. Other types of volcano include cryovolcanoes (or ice volcanoes), particularly on some moons of Jupiter , Saturn , and Neptune ; and mud volcanoes , which are structures often not associated with known magmatic activity. Active mud volcanoes tend to involve temperatures much lower than those of igneous volcanoes except when
4400-408: 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
4510-657: 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
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4620-675: 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
4730-567: 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,
4840-571: 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; the Kaʻau crater lies close to the crest of the Koʻolau Range and
4950-408: 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
5060-831: The Pacific Ring of Fire has volcanoes caused by convergent tectonic plates. Volcanoes can also form where there is stretching and thinning of the crust's plates, such as in the East African Rift , the Wells Gray-Clearwater volcanic field , and the Rio Grande rift in North America. Volcanism away from plate boundaries has been postulated to arise from upwelling diapirs from the core–mantle boundary , 3,000 kilometres (1,900 mi) deep within Earth. This results in hotspot volcanism , of which
5170-622: The Philippines, and Mount Vesuvius and Stromboli in Italy. Ash produced by the explosive eruption of stratovolcanoes has historically posed the greatest volcanic hazard to civilizations. The lavas of stratovolcanoes are higher in silica, and therefore much more viscous, than lavas from shield volcanoes. High-silica lavas also tend to contain more dissolved gas. The combination is deadly, promoting explosive eruptions that produce great quantities of ash, as well as pyroclastic surges like
5280-613: The USGS defines a volcano as active whenever subterranean indicators, such as earthquake swarms , ground inflation, or unusually high levels of carbon dioxide or sulfur dioxide are present. The USGS defines a dormant volcano as any volcano that is not showing any signs of unrest such as earthquake swarms, ground swelling, or excessive noxious gas emissions, but which shows signs that it could yet become active again. Many dormant volcanoes have not erupted for thousands of years, but have still shown signs that they may be likely to erupt again in
5390-553: 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
5500-520: 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
5610-399: 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
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#17327807665555720-510: The boundary with the Yukon Territory . Mud volcanoes (mud domes) are formations created by geo-excreted liquids and gases, although several processes may cause such activity. The largest structures are 10 kilometres in diameter and reach 700 meters high. The material that is expelled in a volcanic eruption can be classified into three types: The concentrations of different volcanic gases can vary considerably from one volcano to
5830-469: 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
5940-402: The case of Lassen Peak . Like stratovolcanoes, they can produce violent, explosive eruptions, but the lava generally does not flow far from the originating vent. Cryptodomes are formed when viscous lava is forced upward causing the surface to bulge. The 1980 eruption of Mount St. Helens was an example; lava beneath the surface of the mountain created an upward bulge, which later collapsed down
6050-439: 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
6160-423: The crust ranges between about 20 and 120 km. Crust on the far side of the Moon averages about 12 km thicker than that on the near side . Estimates of average thickness fall in the range from about 50 to 60 km. Most of this plagioclase-rich crust formed shortly after formation of the Moon, between about 4.5 and 4.3 billion years ago. Perhaps 10% or less of the crust consists of igneous rock added after
6270-799: The enormous area they cover, and subsequent concealment under vegetation and glacial deposits, supervolcanoes can be difficult to identify in the geologic record without careful geologic mapping . Known examples include Yellowstone Caldera in Yellowstone National Park and Valles Caldera in New Mexico (both western United States); Lake Taupō in New Zealand; Lake Toba in Sumatra , Indonesia; and Ngorongoro Crater in Tanzania. Volcanoes that, though large, are not large enough to be called supervolcanoes, may also form calderas in
6380-453: The entire planet has been repeatedly resurfaced and modified. Secondary crust is formed by partial melting of mostly silicate materials in the mantle, and so is usually basaltic in composition. This is the most common type of crust in the Solar System. Most of the surfaces of Mercury, Venus, Earth, and Mars comprise secondary crust, as do the lunar maria . On Earth secondary crust forms primarily at mid-ocean spreading centers , where
6490-431: The flow is covered with angular, vesicle-poor blocks. Rhyolitic flows typically consist largely of obsidian . Tephra is made when magma inside the volcano is blown apart by the rapid expansion of hot volcanic gases. Magma commonly explodes as the gas dissolved in it comes out of solution as the pressure decreases when it flows to the surface . These violent explosions produce particles of material that can then fly from
6600-460: 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
6710-610: The formation of a submarine volcano off the coast of Mayotte . Subglacial volcanoes develop underneath ice caps . They are made up of lava plateaus capping extensive pillow lavas and palagonite . These volcanoes are also called table mountains, tuyas , or (in Iceland) mobergs. Very good examples of this type of volcano can be seen in Iceland and in British Columbia . The origin of the term comes from Tuya Butte , which
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#17327807665556820-463: The formation of the initial plagioclase-rich material. The best-characterized and most voluminous of these later additions are the mare basalts formed between about 3.9 and 3.2 billion years ago. Minor volcanism continued after 3.2 billion years, perhaps as recently as 1 billion years ago. There is no evidence of plate tectonics . Study of the Moon has established that a crust can form on a rocky planetary body significantly smaller than Earth. Although
6930-585: The future. In an article justifying the re-classification of Alaska's Mount Edgecumbe volcano from "dormant" to "active", volcanologists at the Alaska Volcano Observatory pointed out that the term "dormant" in reference to volcanoes has been deprecated over the past few decades and that "[t]he term "dormant volcano" is so little used and undefined in modern volcanology that the Encyclopedia of Volcanoes (2000) does not contain it in
7040-466: The glossaries or index", however the USGS still widely employs the term. Previously a volcano was often considered to be extinct if there were no written records of its activity. Such a generalization is inconsistent with observation and deeper study, as has occurred recently with the unexpected eruption of the Chaitén volcano in 2008. Modern volcanic activity monitoring techniques, and improvements in
7150-427: 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
7260-491: The igneous mechanisms that formed them. This is because it is difficult to study: none of Earth's primary crust has survived to today. Earth's high rates of erosion and crustal recycling from plate tectonics has destroyed all rocks older than about 4 billion years , including whatever primary crust Earth once had. However, geologists can glean information about primary crust by studying it on other terrestrial planets. Mercury's highlands might represent primary crust, though this
7370-416: The interior of Earth into space. A theoretical protoplanet named " Theia " is thought to have collided with the forming Earth, and part of the material ejected into space by the collision accreted to form the Moon. As the Moon formed, the outer part of it is thought to have been molten, a " lunar magma ocean ". Plagioclase feldspar crystallized in large amounts from this magma ocean and floated toward
7480-492: The interior of a continent and lead to rifting. Early stages of rifting are characterized by flood basalts and may progress to the point where a tectonic plate is completely split. A divergent plate boundary then develops between the two halves of the split plate. However, rifting often fails to completely split the continental lithosphere (such as in an aulacogen ), and failed rifts are characterized by volcanoes that erupt unusual alkali lava or carbonatites . Examples include
7590-459: 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
7700-440: 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 a prominent promontory east of Honolulu. Inland from Diamond Head lie
7810-546: 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
7920-544: 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
8030-520: 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
8140-454: 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
8250-419: The mid-oceanic ridge is above sea level, volcanic islands are formed, such as Iceland . Subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. The oceanic plate subducts (dives beneath the continental plate), forming a deep ocean trench just offshore. In a process called flux melting , water released from the subducting plate lowers the melting temperature of
8360-551: The modelling of the factors that produce eruptions, have helped the understanding of why volcanoes may remain dormant for a long time, and then become unexpectedly active again. The potential for eruptions, and their style, depend mainly upon the state of the magma storage system under the volcano, the eruption trigger mechanism and its timescale. For example, the Yellowstone volcano has a repose/recharge period of around 700,000 years, and Toba of around 380,000 years. Vesuvius
8470-415: The most dangerous type, are very rare; four are known from the last million years , and about 60 historical VEI 8 eruptions have been identified in the geologic record over millions of years. A supervolcano can produce devastation on a continental scale, and severely cool global temperatures for many years after the eruption due to the huge volumes of sulfur and ash released into the atmosphere. Because of
8580-438: The mud volcano is actually a vent of an igneous volcano. Volcanic fissure vents are flat, linear fractures through which lava emerges. Shield volcanoes, so named for their broad, shield-like profiles, are formed by the eruption of low-viscosity lava that can flow a great distance from a vent. They generally do not explode catastrophically but are characterized by relatively gentle effusive eruptions . Since low-viscosity magma
8690-452: The next. Water vapour is typically the most abundant volcanic gas, followed by carbon dioxide and sulfur dioxide . Other principal volcanic gases include hydrogen sulfide , hydrogen chloride , and hydrogen fluoride . A large number of minor and trace gases are also found in volcanic emissions, for example hydrogen , carbon monoxide , halocarbons , organic compounds, and volatile metal chlorides. The form and style of an eruption of
8800-876: The north side of the mountain. Cinder cones result from eruptions of mostly small pieces of scoria and pyroclastics (both resemble cinders, hence the name of this volcano type) that build up around the vent. These can be relatively short-lived eruptions that produce a cone-shaped hill perhaps 30 to 400 metres (100 to 1,300 ft) high. Most cinder cones erupt only once and some may be found in monogenetic volcanic fields that may include other features that form when magma comes into contact with water such as maar explosion craters and tuff rings . Cinder cones may form as flank vents on larger volcanoes, or occur on their own. Parícutin in Mexico and Sunset Crater in Arizona are examples of cinder cones. In New Mexico , Caja del Rio
8910-549: The ocean surface as new islands or floating pumice rafts . In May and June 2018, a multitude of seismic signals were detected by earthquake monitoring agencies all over the world. They took the form of unusual humming sounds, and some of the signals detected in November of that year had a duration of up to 20 minutes. An oceanographic research campaign in May 2019 showed that the previously mysterious humming noises were caused by
9020-420: The ocean surface, due to the rapid cooling effect and increased buoyancy in water (as compared to air), which often causes volcanic vents to form steep pillars on the ocean floor. Hydrothermal vents are common near these volcanoes, and some support peculiar ecosystems based on chemotrophs feeding on dissolved minerals. Over time, the formations created by submarine volcanoes may become so large that they break
9130-471: The ocean's surface. In the deep ocean basins, the tremendous weight of the water prevents the explosive release of steam and gases; however, submarine eruptions can be detected by hydrophones and by the discoloration of water because of volcanic gases . Pillow lava is a common eruptive product of submarine volcanoes and is characterized by thick sequences of discontinuous pillow-shaped masses which form underwater. Even large submarine eruptions may not disturb
9240-542: 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 is about 1 kilometre (0.62 mi) wide. Hanauma Bay close to Kalanianaʻole Highway
9350-468: The one that destroyed the city of Saint-Pierre in Martinique in 1902. They are also steeper than shield volcanoes, with slopes of 30–35° compared to slopes of generally 5–10°, and their loose tephra are material for dangerous lahars . Large pieces of tephra are called volcanic bombs . Big bombs can measure more than 1.2 metres (4 ft) across and weigh several tons. A supervolcano is defined as
9460-425: The overlying mantle wedge, thus creating magma . This magma tends to be extremely viscous because of its high silica content, so it often does not reach the surface but cools and solidifies at depth . When it does reach the surface, however, a volcano is formed. Thus subduction zones are bordered by chains of volcanoes called volcanic arcs . Typical examples are the volcanoes in the Pacific Ring of Fire , such as
9570-619: The plume, and new volcanoes are created where the plate advances over the plume. The Hawaiian Islands are thought to have been formed in such a manner, as has the Snake River Plain , with the Yellowstone Caldera being part of the North American plate currently above the Yellowstone hotspot . However, the mantle plume hypothesis has been questioned. Sustained upwelling of hot mantle rock can develop under
9680-459: 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
9790-430: 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
9900-429: 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
10010-435: The same time interval. Volcanoes vary greatly in their level of activity, with individual volcanic systems having an eruption recurrence ranging from several times a year to once in tens of thousands of years. Volcanoes are informally described as erupting , active , dormant , or extinct , but the definitions of these terms are not entirely uniform among volcanologists. The level of activity of most volcanoes falls upon
10120-492: The same way; they are often described as "caldera volcanoes". Submarine volcanoes are common features of the ocean floor. Volcanic activity during the Holocene Epoch has been documented at only 119 submarine volcanoes, but there may be more than one million geologically young submarine volcanoes on the ocean floor. In shallow water, active volcanoes disclose their presence by blasting steam and rocky debris high above
10230-622: The solidified erupted material that makes up the mantle of a volcano may be stripped away that its inner anatomy becomes apparent. Using the metaphor of biological anatomy , such a process is called "dissection". Cinder Hill , a feature of Mount Bird on Ross Island , Antarctica , is a prominent example of a dissected volcano. Volcanoes that were, on a geological timescale, recently active, such as for example Mount Kaimon in southern Kyūshū , Japan , tend to be undissected. Eruption styles are broadly divided into magmatic, phreatomagmatic, and phreatic eruptions. The intensity of explosive volcanism
10340-500: 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
10450-444: The surface. The cumulate rocks form much of the crust. The upper part of the crust probably averages about 88% plagioclase (near the lower limit of 90% defined for anorthosite ): the lower part of the crust may contain a higher percentage of ferromagnesian minerals such as the pyroxenes and olivine , but even that lower part probably averages about 78% plagioclase. The underlying mantle is denser and olivine-rich. The thickness of
10560-406: The surrounding areas, and initially not seismically monitored before its unanticipated and catastrophic eruption of 1991. Two other examples of volcanoes that were once thought to be extinct, before springing back into eruptive activity were the long-dormant Soufrière Hills volcano on the island of Montserrat , thought to be extinct until activity resumed in 1995 (turning its capital Plymouth into
10670-434: The theory of plate tectonics. For example, some volcanoes are polygenetic with more than one period of activity during their history; other volcanoes that become extinct after erupting exactly once are monogenetic (meaning "one life") and such volcanoes are often grouped together in a geographical region. At the mid-ocean ridges , two tectonic plates diverge from one another as hot mantle rock creeps upwards beneath
10780-444: The thinned oceanic crust . The decrease of pressure in the rising mantle rock leads to adiabatic expansion and the partial melting of the rock, causing volcanism and creating new oceanic crust. Most divergent plate boundaries are at the bottom of the oceans, and so most volcanic activity on Earth is submarine, forming new seafloor . Black smokers (also known as deep sea vents) are evidence of this kind of volcanic activity. Where
10890-431: The underlying ductile mantle , and most volcanic activity on Earth takes place along plate boundaries, where plates are converging (and lithosphere is being destroyed) or are diverging (and new lithosphere is being created). During the development of geological theory, certain concepts that allowed the grouping of volcanoes in time, place, structure and composition have developed that ultimately have had to be explained in
11000-399: 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
11110-486: 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
11220-454: 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
11330-492: The volcano. Solid particles smaller than 2 mm in diameter ( sand-sized or smaller) are called volcanic ash. Tephra and other volcaniclastics (shattered volcanic material) make up more of the volume of many volcanoes than do lava flows. Volcaniclastics may have contributed as much as a third of all sedimentation in the geologic record. The production of large volumes of tephra is characteristic of explosive volcanism. Through natural processes, mainly erosion , so much of
11440-424: The volcanoes of the East African Rift . A volcano needs a reservoir of molten magma (e.g. a magma chamber), a conduit to allow magma to rise through the crust, and a vent to allow the magma to escape above the surface as lava. The erupted volcanic material (lava and tephra) that is deposited around the vent is known as a volcanic edifice , typically a volcanic cone or mountain. The most common perception of
11550-475: 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
11660-424: 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
11770-421: Was described by Roman writers as having been covered with gardens and vineyards before its unexpected eruption of 79 CE , which destroyed the towns of Herculaneum and Pompeii . Accordingly, it can sometimes be difficult to distinguish between an extinct volcano and a dormant (inactive) one. Long volcano dormancy is known to decrease awareness. Pinatubo was an inconspicuous volcano, unknown to most people in
11880-399: 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
11990-456: 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
12100-467: 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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