Shield volcano

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Mauna Loa, a shield volcano in Hawaii Mauna Loa Volcano.jpg
Mauna Loa, a shield volcano in Hawaii
An Ancient Greek warrior's shield-its circular shape and gently sloping surface, with a central raised area, is a shape shared by many shield volcanoes Bronze votive shield.JPG
An Ancient Greek warrior's shield–its circular shape and gently sloping surface, with a central raised area, is a shape shared by many shield volcanoes

A shield volcano is a type of volcano usually composed almost entirely of fluid lava flows. It is named for its low profile, resembling a warrior's shield lying on the ground. This is caused by the highly fluid (low viscosity) lava erupted, which travels farther than lava erupted from a stratovolcano, and results in the steady accumulation of broad sheets of lava, building up the shield volcano's distinctive form.

Contents

Etymology

Shield volcanoes are built by effusive eruptions, which flow out in all directions to create a shield like that of a warrior. [1] The word "shield" has a long history, and is derived from the Old English scield or scild, which is in turn taken from the Proto-Germanic *skelduz, and related to the Gothic skildus, meaning "to divide, split, or separate". Shield volcano itself is taken from the German term Schildvulkan. [2]

Geology

Structure

Diagram of the common structural features of a shield volcano

Shield volcanoes are distinguished from the three other major volcanic archetypes stratovolcanoes, lava domes, and cinder cones by their structural form, a consequence of their unique magmatic composition. Of these four forms shield volcanoes erupt the least viscous lavas: whereas stratovolcanoes and especially lava domes are the product of highly immotile flows and cinder cones are constructed by explosively eruptive tephra, shield volcanoes are the product of gentle effusive eruptions of highly fluid lavas that produce, over time, a broad, gently sloped eponymous "shield". [3] [4] Although the term is generally ascribed to basaltic shields it has also at times been appended to rarer scutiform volcanoes of differing magmatic compositionprincipally pyroclastic shields, formed by the accumulation of fragmental material from particularly powerful explosive eruptions, and rarer felsic lava shields formed by unusually fluid felsic magmas. Examples of pyroclastic shields include Billy Mitchell volcano in Papua New Guinea and the Purico complex in Chile; [5] [6] an example of a felsic shield is the Ilgachuz Range in British Columbia, Canada. [7] Shield volcanoes are also related in origination to vast lava plateaus and flood basalts present in various parts of the world, generalized eruptive features which occur along linear fissure vents and are distinguished from shield volcanoes proper by the lack of an identifiable primary eruptive center. [3]

Active shield volcanoes experience near-continuous eruptive activity over extremely long periods of time, resulting in the gradual build-up of edifices that can reach extremely large dimensions. [4] With the exclusion of flood basalts, mature shields are the largest volcanic features on Earth: [8] the summit of the largest subaerial volcano in the world, Mauna Loa, lies 4,169 m (13,678 ft) above sea level, and the volcano, over 60 mi (100 km) wide at its base, is estimated to contain about 80,000 km3 (19,000 cu mi) of basalt. [1] [4] The mass of the volcano is so great that it has slumped the crust beneath it a further 8 km (5 mi); [9] accounting for this subsidence and for the height of the volcano above the sea floor, the "true" height of Mauna Loa from the start of its eruptive history is about 17,170 m (56,000 ft). [10] Mount Everest, by comparison, is 8,848 m (29,029 ft) in height. [11] In September 2013 a team led by the University of Houston's William Sager announced the singular origination of Tamu Massif, an enormous extinct submarine shield volcano of previously unknown origin which, approximately 450 by 650 km (280 by 400 mi) in area, dwarfs all previously known volcanoes on the planet. The research has not yet been confirmed. [12]

Shield volcanoes feature a gentle (usually 2° to 3°) slope that gradually steepens with elevation (reaching approximately 10°) before eventually flattening near the summit, forming an overall upwardly convex shape. In height they are typically about one twentieth their width. [4] Although the general form of a "typical" shield volcano varies little worldwide regional differences exist in their size and morphological characteristics. Typical shield volcanoes present in California and Oregon measure 3 to 4 mi (5 to 6 km) in diameter and 1,500 to 2,000 ft (500 to 600 m) in height; [3] shield volcanoes in the central Mexican Michoacán–Guanajuato volcanic field, by comparison, average 340 m (1,100 ft) in height and 4,100 m (13,500 ft) in width, with an average slope angle of 9.4° and an average volume of 1.7 km3 (0.4 cu mi). [13]

Rift zones are a prevalent feature on shield volcanoes that is rare on other volcanic types. The large, decentralized shape of Hawaiian volcanoes as compared to their smaller, symmetrical Icelandic cousins[ citation needed ] can be attributed to rift eruptions. Fissure venting is common in Hawaiʻi; most Hawaiian eruptions begin with a so-called "wall of fire" along a major fissure line before centralizing to a small number of points. This accounts for their asymmetrical shape, whereas Icelandic volcanoes follow a pattern of central eruptions dominated by summit calderas, causing the lava to be more evenly distributed or symmetrical. [1] [4] [14] [15]

Eruptive characteristics

Hawaiian Eruption-numbers.svg
Diagram of a Hawaiian eruption. (key: 1. Ash plume 2. Lava fountain 3. Crater 4. Lava lake 5. Fumaroles 6. Lava flow 7. Layers of lava and ash 8. Stratum 9. Sill 10. Magma conduit 11. Magma chamber 12. Dike) Click for larger version.

Most of what is currently known about shield volcanic eruptive character has been gleaned from studies done on the volcanoes of Hawaiʻi island, by far the most intensively studied of all shields due to their scientific accessibility; [16] the island lends its name to the slow-moving, effusive eruptions typical of shield volcanism, known as Hawaiian eruptions. [17] These eruptions, the calmest of volcanic events, are characterized by the effusive emission of highly fluid basaltic lavas with low gaseous content. These lavas travel a far greater distance than those of other eruptive types before solidifying, forming extremely wide but relatively thin magmatic sheets often less than 1 m (3 ft) thick. [1] [4] [14] Low volumes of such lavas layered over long periods of time are what slowly constructs the characteristically low, broad profile of a mature shield volcano. [1]

Also unlike other eruptive types, Hawaiian eruptions often occur at decentralized fissure vents, beginning with large "curtains of fire" that quickly die down and concentrate at specific locations on the volcano's rift zones. Central-vent eruptions, meanwhile, often take the form of large lava fountains (both continuous and sporadic), which can reach heights of hundreds of meters or more. The particles from lava fountains usually cool in the air before hitting the ground, resulting in the accumulation of cindery scoria fragments; however, when the air is especially thick with clasts, they cannot cool off fast enough due to the surrounding heat, and hit the ground still hot, accumulating into spatter cones. If eruptive rates are high enough, they may even form splatter-fed lava flows. Hawaiian eruptions are often extremely long-lived; Puʻu ʻŌʻō, a cinder cone of Kīlauea, erupted continuously from January 3, 1983 until April 2018. [14]

Flows from Hawaiian eruptions can be divided into two types by their structural characteristics: pāhoehoe lava which is relatively smooth and flows with a ropey texture, and ʻaʻā flows which are denser, more viscous (and thus slower moving) and blockier. These lava flows can be anywhere between 2 and 20 m (10 and 70 ft) thick. ʻAʻa lava flows move through pressure the partially solidified front of the flow steepens due to the mass of flowing lava behind it until it breaks off, after which the general mass behind it moves forward. Though the top of the flow quickly cools down, the molten underbelly of the flow is buffered by the solidifying rock above it, and by this mechanism, ʻaʻa flows can sustain movement for long periods of time. Pāhoehoe flows, in contrast, move in more conventional sheets, or by the advancement of lava "toes" in snaking lava columns. Increasing viscosity on the part of the lava or shear stress on the part of local topography can morph a pāhoehoe flow into an a'a one, but the reverse never occurs. [18]

Although most shield volcanoes are by volume almost entirely Hawaiian and basaltic in origin, they are rarely exclusively so. Some volcanoes, like Mount Wrangell in Alaska and Cofre de Perote in Mexico, exhibit large enough swings in their historical magmatic eruptive characteristics to cast strict categorical assignment in doubt; one geological study of de Perote went so far as to suggest the term "compound shield-like volcano" instead. [19] Most mature shield volcanoes have multiple cinder cones on their flanks, the results of tephra ejections common during incessant activity and markers of currently and formerly active sites on the volcano. [8] [14] One prominent such parasitic cones is Puʻu ʻŌʻō on Kīlauea [15] continuous activity ongoing since 1983 has built up a 2,290 ft (698 m) tall cone at the site of one of the longest-lasting rift eruptions in known history. [20]

The Hawaiian shield volcanoes are not located near any plate boundaries; the volcanic activity of this island chain is distributed by the movement of the oceanic plate over an upwelling of magma known as a hotspot. Over millions of years, the tectonic movement that moves continents also creates long volcanic trails across the seafloor. The Hawaiian and Galápagos shields, and other hotspot shields like them, are both constructed of oceanic island basalt. Their lavas are characterized by high levels of sodium, potassium, and aluminium. [21]

Features common in shield volcanism include lava tubes. [22] Lava tubes are cave-like volcanic straights formed by the hardening of overlaying lava. These structures help further the propagation of lava, as the walls of the tube insulates the lava within. [23] Lava tubes can account for a large portion of shield volcano activity; for example, an estimated 58% of the lava forming Kīlauea comes from lava tubes. [22]

In some shield volcano eruptions, basaltic lava pours out of a long fissure instead of a central vent, and shrouds the countryside with a long band of volcanic material in the form of a broad plateau. Plateaus of this type exist in Iceland, Washington, Oregon, and Idaho; the most prominent ones are situated along the Snake River in Idaho and the Columbia River in Washington and Oregon, where they have been measured to be over 1 mi (2 km) in thickness. [1]

Calderas are a common feature on shield volcanoes. They are formed and reformed over the volcano's lifespan. Long eruptive periods form cinder cones, which then collapse over time to form calderas. The calderas are often filled up by future eruptions, or formed elsewhere, and this cycle of collapse and regeneration takes place throughout the volcano's lifespan. [8]

Interactions between water and lava at shield volcanoes can cause some eruptions to become hydrovolcanic. These explosive eruptions are drastically different from the usual shield volcanic activity, [8] and are especially prevalent at the waterbound volcanoes of the Hawaiian Isles. [14]

Distribution

Shield volcanoes are found worldwide. They can form over hotspots (points where magma from below the surface wells up), such as the Hawaiian–Emperor seamount chain and the Galápagos Islands, or over more conventional rift zones, such as the Icelandic shields and the shield volcanoes of East Africa. Many shield volcanoes are found in ocean basins, such as Tamu Massif, the world's largest, although they can be found inland as wellEast Africa being one example of this. [24]

Hawaiian Islands

The largest and most prominent shield volcano chain in the world is the Hawaiian Islands, a chain of hotspot volcanoes in the Pacific Ocean. The Hawaiian volcanoes are characterized by frequent rift eruptions, their large size (thousands of km3 in volume), and their rough, decentralized shape. Rift zones are a prominent feature on these volcanoes, and account for their seemingly random volcanic structure. [4] They are fueled by the movement of the Pacific Plate over the Hawaii hotspot, and form a long chain of volcanoes, atolls, and seamounts 2,600 km (1,616 mi) long with a total volume of over 750,000 km3 (179,935 cu mi). The chain contains at least 43 major volcanoes, and Meiji Seamount at its terminus near the Kuril–Kamchatka Trench is 85 million years old. [25] [26] The volcanoes follow a distinct evolutionary pattern of growth and death. [27]

The chain includes the second largest volcano on Earth, Mauna Loa, which stands 4,170 m (13,680 ft) above sea level and reaches a further 13 km (8 mi) below the waterline and into the crust, approximately 80,000 km3 (19,000 cu mi) of rock. [22] Kīlauea, meanwhile, is one of the most active volcanoes on Earth, with the current ongoing eruption having begun in January 1983. [1]

Galápagos Islands

The Galápagos Islands are an isolated set of volcanoes, consisting of shield volcanoes and lava plateaus, about 1,100 km (680 mi) west of Ecuador. They are driven by the Galápagos hotspot, and are between approximately 4.2 million and 700,000 years of age. [21] The largest island, Isabela Island, consists of six coalesced shield volcanoes, each delineated by a large summit caldera. Española, the oldest island, and Fernandina, the youngest, are also shield volcanoes, as are most of the other islands in the chain. [28] [29] [30] The Galápagos Islands are perched on a large lava plateau known as the Galápagos Platform. This platform creates a shallow water depth of 360 to 900 m (1,181 to 2,953 ft) at the base of the islands, which stretch over a 174 mi (280 km)-long diameter. [31] Since Charles Darwin's visit to the islands in 1835 during the Second voyage of HMS Beagle, there have been over 60 recorded eruptions in the islands, from six different shield volcanoes. [28] [30] Of the 21 emergent volcanoes, 13 are considered active. [21]

Blue Hill is a shield volcano on the south western part of Isabela Island in the Galápagos Islands and is one of the most active in the Galapagos, with the last eruption between May and June 2008. The Geophysics Institute at the National Polytechnic School in Quito houses an international team of seismologists and volcanologists [32] whose responsibility is to monitor Ecuadors numerous active volcanoes in the Andean Volcanic Belt and the Galapagos Islands. La Cumbre is an active shield volcano on Fernandina Island in the Galapagos that has been erupting since April 11, 2009. [33]

The Galápagos islands are geologically young for such a big chain, and the pattern of their rift zones follows one of two trends, one north-northwest, and one east–west. The composition of the lavas of the Galápagos shields are strikingly similar to those of the Hawaiian volcanoes. Curiously, they do not form the same volcanic "line" associated with most hotspots. They are not alone in this regard; the Cobb–Eickelberg Seamount chain in the North Pacific is another example of such a delineated chain. In addition, there is no clear pattern of age between the volcanoes, suggesting a complicated, irregular pattern of creation. How exactly the islands were formed remains a geological mystery, although several theories have been proposed. [34]

Iceland

Skjaldbreidur is a shield volcano in Iceland, whose name means broad shield in Icelandic. It is eponymous for all shield volcanoes Skjaldbreidur Herbst 2004.jpg
Skjaldbreiður is a shield volcano in Iceland, whose name means broad shield in Icelandic. It is eponymous for all shield volcanoes

Another major center of shield volcanic activity is Iceland. Located over the Mid-Atlantic Ridge, a divergent tectonic plate in the middle of the Atlantic Ocean, Iceland is the site of about 130 volcanoes of various types. [15] Icelandic shield volcanoes are generally of Holocene age, between 5,000 and 10,000 years old, except for the island of Surtsey, a Surtseyan shield. The volcanoes are also very narrow in distribution, occurring in two bands in the West and North Volcanic Zones. Like Hawaiian volcanoes, their formation initially begins with several eruptive centers before centralizing and concentrating at a single point. The main shield then forms, burying the smaller ones formed by the early eruptions with its lava. [31]

Icelandic shields are mostly small (~15 km3 (4 cu mi)), symmetrical (although this can affected by surface topography), and characterized by eruptions from summit calderas. [31] They are composed of either tholeiitic olivine or picritic basalt. The tholeiitic shields tend to be wider and shallower than the picritic shields. [35] They do not follow the pattern of caldera growth and destruction that other shield volcanoes do; caldera may form, but they generally do not disappear. [4] [31]

East Africa

East Africa is the site of volcanic activity generated by the development of the East African Rift, a developing plate boundary in Africa, and from nearby hotspots. Some volcanoes interact with both. Shield volcanoes are found near the rift and off the coast of Africa, although stratovolcanoes are more common. Although sparsely studied, the fact that all of its volcanoes are of Holocene age reflects how young the volcanic center is. One interesting characteristic of East African volcanism is a penchant for the formation of lava lakes; these semi-permanent lava bodies, extremely rare elsewhere, form in about nine percent of African eruptions. [36]

The most active shield volcano in Africa is Nyamuragira. Eruptions at the shield volcano are generally centered within the large summit caldera or on the numerous fissures and cinder cones on the volcano's flanks. Lava flows from the most recent century extend down the flanks more than 30 km (19 mi) from the summit, reaching as far as Lake Kivu. Erta Ale in Ethiopia is another active shield volcano, and one of the few places in the world with a permanent lava lake, which has been active since at least 1967, and possibly since 1906. [36] Other volcanic centers include Menengai, a massive shield caldera, [37] and Mount Marsabit, near the town of Marsabit.

Extraterrestrial volcanoes

Scaled image showing Olympus Mons, top, and the Hawaiian island chain, bottom. Martian volcanoes are far larger than those found on Earth. Olympus Mons and Hawaii to scale.png
Scaled image showing Olympus Mons, top, and the Hawaiian island chain, bottom. Martian volcanoes are far larger than those found on Earth.

Volcanoes are not limited to Earth; they can exist on any rocky planet or moon large or active enough to have a molten core, and since probes were first launched in the 1960s, volcanoes have been found across the solar system. Shield volcanoes and volcanic vents have been found on Mars, Venus, and Io; cryovolcanoes on Triton; and subsurface hotspots on Europa. [38]

The volcanoes of Mars are very similar to the shield volcanoes on Earth. Both have gently sloping flanks, collapse craters along their central structure, and are built of highly fluid lavas. Volcanic features on Mars were observed long before they were first studied in detail during the 1976–1979 Viking mission. The principal difference between the volcanoes of Mars and those on Earth is in terms of size; Martian volcanoes range in size up to 14 mi (23 km) high and 370 mi (595 km) in diameter, far larger than the 6 mi (10 km) high, 74 mi (119 km) wide Hawaiian shields. [39] [40] [41] The highest of these, Olympus Mons, is the tallest known mountain on any planet in the solar system.

Venus also has over 150 shield volcanoes which are much flatter, with a larger surface area than those found on Earth, some having a diameter of more than 700 km (430 mi). [42] Although the majority of these are long extinct it has been suggested, from observations by the Venus Express spacecraft, that many may still be active. [43]

See also

Related Research Articles

A caldera is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber/reservoir in a volcanic eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is lost. The ground surface then collapses downward into the emptied or partially emptied magma chamber, leaving a massive depression at the surface. Although sometimes described as a crater, the feature is actually a type of sinkhole, as it is formed through subsidence and collapse rather than an explosion or impact. Only seven caldera-forming collapses are known to have occurred since 1900, most recently at Bárðarbunga volcano, Iceland in 2014.

Volcano rupture in the crust of a planetary-mass object that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface

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 a magma chamber below the surface.

Mauna Loa Volcano on the island of Hawaii in Hawaii, United States

Mauna Loa is one of five volcanoes that form the Island of Hawaii in the U.S. state of Hawaiʻi in the Pacific Ocean. The largest subaerial volcano in both mass and volume, Mauna Loa has historically been considered the largest volcano on Earth, dwarfed only by Tamu Massif. It is an active shield volcano with relatively gentle slopes, with a volume estimated at approximately 18,000 cubic miles (75,000 km3), although its peak is about 125 feet (38 m) lower than that of its neighbor, Mauna Kea. Lava eruptions from Mauna Loa are silica-poor and very fluid, and they tend to be non-explosive.

Kīlauea Active volcano in Hawaii

Kīlauea is an active shield volcano in the Hawaiian Islands that last erupted between 1983 and 2018. Historically, Kīlauea is the most active of the five volcanoes that together form the island of Hawaiʻi. Located along the southeastern shore of the island, the volcano is between 210,000 and 280,000 years old and emerged above sea level about 100,000 years ago.

National Park of American Samoa United States national park in American Samoa

The National Park of American Samoa is a national park in the United States territory of American Samoa, distributed across three islands: Tutuila, Ofu, and Ta‘ū. The park preserves and protects coral reefs, tropical rainforests, fruit bats, and the Samoan culture. Popular activities include hiking and snorkeling. Of the park's 13,500 acres (5,500 ha), 9,000 acres (3,600 ha) is land and 4,500 acres (1,800 ha) is coral reefs and ocean. The park is the only American National Park Service system unit south of the equator.

Evolution of Hawaiian volcanoes Processes of growth and erosion of the volcanoes of the Hawaiian islands

The fifteen volcanoes that make up the eight principal islands of Hawaii are the youngest in a chain of more than 129 volcanoes that stretch 5,800 kilometres (3,600 mi) across the North Pacific Ocean, called the Hawaiian-Emperor seamount chain. Hawaiʻi's volcanoes rise an average of 4,572 metres (15,000 ft) to reach sea level from their base. The largest, Mauna Loa, is 4,169 metres (13,678 ft) high. As shield volcanoes, they are built by accumulated lava flows, growing a few meters/feet at a time to form a broad and gently sloping shape.

Hawaiian eruption Type of volcanic eruption

A Hawaiian eruption is a type of volcanic eruption where lava flows from the vent in a relatively gentle, low level eruption; it is so named because it is characteristic of Hawaiian volcanoes. Typically they are effusive eruptions, with basaltic magmas of low viscosity, low content of gases, and high temperature at the vent. Very small amounts of volcanic ash are produced. This type of eruption occurs most often at hotspot volcanoes such as Kīlauea on Hawaii's big island and in Iceland, though it can occur near subduction zones and rift zones. Another example of Hawaiian eruptions occurred on the island of Surtsey in Iceland from 1964 to 1967, when molten lava flowed from the crater to the sea.

Fissure vent Linear volcanic vent through which lava erupts

A fissure vent, also known as a volcanic fissure, eruption fissure or simply a fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is often a few metres wide and may be many kilometres long. Fissure vents can cause large flood basalts which run first in lava channels and later in lava tubes. After some time the eruption builds up spatter cones and may concentrate on one or some of them. Small fissure vents may not be easily discernible from the air, but the crater rows or the canyons built up by some of them are.

Types of volcanic eruptions Basic mechanisms of eruption and variations

Several types of volcanic eruptions—during which lava, tephra, and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed. Some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series.

Volcanology of Canada

Volcanology of Canada includes lava flows, lava plateaus, lava domes, cinder cones, stratovolcanoes, shield volcanoes, submarine volcanoes, calderas, diatremes, and maars, along with examples of more less common volcanic forms such as tuyas and subglacial mounds. It has a very complex volcanological history spanning from the Precambrian eon at least 3.11 billion years ago when this part of the North American continent began to form.

Anahim hotspot

The Anahim hotspot is a volcanic hotspot located in the West-Central Interior of British Columbia, Canada. One of the few hotspots in North America, the Anahim plume is responsible for the creation of the Anahim Volcanic Belt. This is a 300 km (190 mi) long chain of volcanoes and other magmatic features that have undergone erosion. The chain extends from the community of Bella Bella in the west to near the small city of Quesnel in the east. While most volcanoes are created by geological activity at tectonic plate boundaries, the Anahim hotspot is located hundreds of kilometres away from the nearest plate boundary.

Geology of the Pacific Northwest geology of Oregon and Washington (United States) and British Columbia (Canada)

The geology of the Pacific Northwest includes the composition, structure, physical properties and the processes that shape the Pacific Northwest region of North America. The region is part of the Ring of Fire: the subduction of the Pacific and Farallon Plates under the North American Plate is responsible for many of the area's scenic features as well as some of its hazards, such as volcanoes, earthquakes, and landslides.

Hawaii hotspot A volcanic hotspot located near the Hawaiian Islands, in the northern Pacific Ocean

The Hawaii hotspot is a volcanic hotspot located near the namesake Hawaiian Islands, in the northern Pacific Ocean. One of the best known and intensively studied hotspots in the world, the Hawaii plume is responsible for the creation of the Hawaiian–Emperor seamount chain, a 6,200-kilometer (3,900 mi) mostly undersea volcanic mountain range. Four of these volcanoes are active, two are dormant; more than 123 are extinct, most now preserved as atolls or seamounts. The chain extends from south of the island of Hawaiʻi to the edge of the Aleutian Trench, near the eastern coast of Russia.

Chain of Craters Road

Chain of Craters Road is a 19-mile (31 km) long winding paved road through the East Rift and coastal area of the Hawaii Volcanoes National Park on the island of Hawaii, in the state of Hawaii, United States. The original road, built in 1928, connected Crater Rim Drive to Makaopuhi Crater. The road was lengthened to reach the tiny town of Kalapana in 1959. As of 2018, the road has had parts covered by lava in 41 of the past 53 years, due to eruptions of Kīlauea volcano.

Mount Edziza volcanic complex mountain in Canada

The Mount Edziza volcanic complex is a large and potentially active north-south trending complex volcano in Stikine Country, northwestern British Columbia, Canada, located 38 kilometres (24 mi) southeast of the small community of Telegraph Creek. It occupies the southeastern portion of the Tahltan Highland, an upland area of plateau and lower mountain ranges, lying east of the Boundary Ranges and south of the Inklin River, which is the east fork of the Taku River. As a volcanic complex, it consists of many types of volcanoes, including shield volcanoes, calderas, lava domes, stratovolcanoes, and cinder cones.

Lava Molten rock expelled by a volcano during an eruption

Lava is molten rock generated by geothermal energy and expelled through fractures in planetary crust or in an eruption, usually at temperatures from 700 to 1,200 °C. The structures resulting from subsequent solidification and cooling are also sometimes described as lava. The molten rock is formed in the interior of some planets, including Earth, and some of their satellites, though such material located below the crust is referred to by other terms.

Volcanology of Northern Canada

Volcanology of Northern Canada includes hundreds of volcanic areas and extensive lava formations across Northern Canada. The region's different volcano and lava types originate from different tectonic settings and types of volcanic eruptions, ranging from passive lava eruptions to violent explosive eruptions. Northern Canada has a record of very large volumes of magmatic rock called large igneous provinces. They are represented by deep-level plumbing systems consisting of giant dike swarms, sill provinces and layered intrusions.

Volcanic history of the Northern Cordilleran Volcanic Province

The volcanic history of the Northern Cordilleran Volcanic Province presents a record of volcanic activity in northwestern British Columbia, central Yukon and the U.S. state of easternmost Alaska. The volcanic activity lies in the northern part of the Western Cordillera of the Pacific Northwest region of North America. Extensional cracking of the North American Plate in this part of North America has existed for millions of years. Continuation of this continental rifting has fed scores of volcanoes throughout the Northern Cordilleran Volcanic Province over at least the past 20 million years and occasionally continued into geologically recent times.

Volcanoes of the Galápagos Islands

The Galápagos Islands are an isolated set of volcanoes, consisting of shield volcanoes and lava plateaus, located 1,200 km (746 mi) west of Ecuador. They are driven by the Galápagos hotspot, and are between 4.2 million and 700,000 years of age. The largest island, Isabela, consists of six coalesced shield volcanoes, each delineated by a large summit caldera. Española, the oldest island, and Fernandina, the youngest, are also shield volcanoes, as are most of the other islands in the chain. The Galápagos Islands are perched on a large lava plateau known as the Galápagos Platform, which creates a shallow-water depth of 360 to 900 m at the base of the islands, which stretch over a 174 mi (280 km)-long diameter. Since Charles Darwin's famous visit to the islands in 1835, over 60 recorded eruptions have occurred in the islands, from six different shield volcanoes. Of the 21 emergent volcanoes, 13 are considered active.

North Arch volcanic field

North Arch volcanic field is an underwater volcanic field north of Oahu, Hawaii. It covers an area of about 25,000 square kilometres (9,700 sq mi) and consists of large expanses of alkali basalt, basanite and nephelinite that form extensive lava flows and volcanic cones. Some lava flows are longer than 100 kilometres (62 mi).

References

Citations

  1. 1 2 3 4 5 6 7 Topinka, Lyn (28 December 2005). "Description: Shield Volcano". USGS. Retrieved 21 August 2010.
  2. Douglas Harper (2010). "Shield". Online Etymology Dictionary. Douglas Harper. Retrieved February 13, 2011.
  3. 1 2 3 John Watson (1 March 2011). "Principal Types of Volcanoes". United States Geological Survey. Retrieved 30 December 2013.
  4. 1 2 3 4 5 6 7 8 "How Volcanoes Work: Shield Volcanoes". San Diego State University. Retrieved 30 December 2013.
  5. "Purico Complex". Global Volcanism Program . Smithsonian Institution . Retrieved 30 December 2013.
  6. "Billy Mitchell". Global Volcanism Program . Smithsonian Institution . Retrieved 30 December 2013.
  7. Wood, Charles A.; Kienle, Jürgen (2001). Volcanoes of North America: United States and Canada. Cambridge, England: Cambridge University Press. p. 133. ISBN   0-521-43811-X.
  8. 1 2 3 4 "Shield Volcanoes". University of North Dakota. Archived from the original on 8 August 2007. Retrieved 22 August 2010.
  9. J.G. Moore (1987). "Subsidence of the Hawaiian Ridge". Volcanism in Hawaii. Geological Survey Professional Paper. 1350.
  10. "How High is Mauna Loa?". Hawaiian Volcano Observatory – United States Geological Survey. 20 August 1998. Retrieved 5 February 2013.
  11. Navin Singh Khadka (28 February 2012). "Nepal in new bid to finally settle Mount Everest height". BBC News. Retrieved 10 December 2012.
  12. Brian Clark Howard (5 September 2013). "New Giant Volcano Below Sea Is Largest in the World". National Geographic. Retrieved 31 December 2013.
  13. Hasenaka, T. (October 1994). "Size, distribution, and magma output rate for shield volcanoes of the Michoacán-Guanajuato volcanic field, Central Mexico". Journal of Volcanology and Geothermal Research . 1. Elsevier. 63 (2): 13–31. Bibcode:1994JVGR...63...13H. doi:10.1016/0377-0273(94)90016-7.
  14. 1 2 3 4 5 "How Volcanoes Work: Hawaiian Eruptions". San Diego State University. Retrieved 27 July 2014.
  15. 1 2 3 World Book: U  · V  · 20. Chicago: Scott Fetzer. 2009. pp. 438–443. ISBN   978-0-7166-0109-8 . Retrieved 22 August 2010.
  16. Marco Bagnardia; Falk Amelunga; Michael P. Poland (September 2013). "A new model for the growth of basaltic shields based on deformation of Fernandina volcano, Galápagos Islands". Earth and Planetary Science Letters . Elsevier. 377–378: 358–366. Bibcode:2013E&PSL.377..358B. doi:10.1016/j.epsl.2013.07.016.
  17. Regelous, M.; Hofmann, A. W.; Abouchami, W.; Galer, S. J. G. (2003). "Geochemistry of Lavas from the Emperor Seamounts, and the Geochemical Evolution of Hawaiian Magmatism from 85 to 42 Ma". Journal of Petrology. Oxford University Press. 44 (1): 113–140. Bibcode:2003JPet...44..113R. doi:10.1093/petrology/44.1.113.
  18. "How Volcanoes Work: Basaltic Lava". San Diego State University. Retrieved 2 August 2010.
  19. Gerardo Carrasco-Núñeza; et al. (30 November 2010). "Evolution and hazards of a long-quiescent compound shield-like volcano: Cofre de Perote, Eastern Trans-Mexican Volcanic Belt". Journal of Volcanology and Geothermal Research . 1. Elsevier. 197 (4): 209–224. Bibcode:2010JVGR..197..209C. doi:10.1016/j.jvolgeores.2009.08.010.
  20. "Summary of the Pu'u 'Ō 'ō-Kupaianaha Eruption, 1983-present". United States Geological Survey - Hawaii Volcano Observatory. 4 October 2008. Retrieved 5 February 2011.
  21. 1 2 3 Bill White & Bree Burdick. "Volcanic Galapagos: Formation of an Oceanic Archipelago". University of Oregon. Retrieved 23 February 2011.
  22. 1 2 3 "VHP Photo Glossary: Shield volcano". USGS. 17 July 2009. Retrieved 23 August 2010.
  23. Topinka, Lyn (18 April 2002). "Description: Lava Tubes and Lava Tube Caves". USGS. Retrieved 23 August 2010.
  24. James S. Monroe; Reed Wicander (2006). The changing Earth : exploring geology and evolution (5th ed.). Belmont, CA: Brooks/Cole. p. 115. ISBN   978-0-495-55480-6 . Retrieved February 22, 2011.
  25. Watson, Jim (5 May 1999). "The long trail of the Hawaiian hotspot". United States Geological Survey. Retrieved 13 February 2011.
  26. Regelous, M.; Hofmann, A.W.; Abouchami, W.; Galer, S.J.G. (2003). "Geochemistry of Lavas from the Emperor Seamounts, and the Geochemical Evolution of Hawaiian Magmatism from 85 to 42 Ma" (PDF). Journal of Petrology . Oxford University Press. 44 (1): 113–140. Bibcode:2003JPet...44..113R. doi:10.1093/petrology/44.1.113. Archived from the original (PDF) on 19 July 2011. Retrieved 13 February 2011.
  27. "Evolution of Hawaiian Volcanoes". Hawaiian Volcano Observatory - United States Geological Survey. 8 September 1995. Retrieved 28 February 2011.
  28. 1 2 "How Volcanoes Work: Galapagos Shield Volcanoes". San Diego State University. Retrieved 22 February 2011.
  29. "Volcanoes". Galapagos Online Tours and Cruises. Archived from the original on 23 July 2001. Retrieved 22 February 2011.
  30. 1 2 "Volcanoes of South America: Galápagos Islands". Global Volcanism Program . Smithsonian National Museum of Natural History. Retrieved 22 February 2011.
  31. 1 2 3 4 Ruth Andrews & Agust Gudmundsson (2006). "Holocene shield volcanoes in Iceland" (PDF). University of Göttingen. Archived from the original (PDF) on 11 June 2007. Retrieved 21 February 2011.
  32. Institute for Geophysics at National Polytechnic School
  33. "Galapagos volcano erupts, could threaten wildlife". October 22, 2015. Archived from the original on 2009-04-15.
  34. Bailey, K. (30 April 1976). "Potassium-Argon Ages from the Galapagos Islands". Science . American Association for the Advancement of Science. 192 (4238): 465–467. Bibcode:1976Sci...192..465B. doi:10.1126/science.192.4238.465. PMID   17731085.
  35. Rossi, M. J. (1996). "Morphology and mechanism of eruption of postglacial shield volcanoes in Iceland". Bulletin of Volcanology . Springer. 57 (7): 530–540. Bibcode:1996BVol...57..530R. doi:10.1007/BF00304437.
  36. 1 2 Lyn Topinka (2 October 2003). "Africa Volcanoes and Volcanics". United States Geological Survey. Retrieved 28 February 2011.
  37. "Menengai". Global Volcanism Program . Smithsonian National Museum of Natural History. Retrieved 28 February 2011.
  38. Heather Couper & Nigel Henbest (1999). Space Encyclopedia . Dorling Kindersley. ISBN   978-0-7894-4708-1.
  39. Watson, John (February 5, 1997). "Extraterrestrial Volcanism". United States Geological Survey. Retrieved February 13, 2011.
  40. Masursky, H.; Masursky, Harold; Saunders, R. S. (1973). "An Overview of Geological Results from Mariner 9". Journal of Geophysical Research . 78 (20): 4009–4030. Bibcode:1973JGR....78.4031C. doi:10.1029/JB078i020p04031.
  41. Carr, M.H., 2006, The Surface of Mars, Cambridge, 307 p.
  42. "Large Shield Volcanoes". Oregon State University. Retrieved April 14, 2011.
  43. Nancy Atkinson (8 April 2010). "Volcanoes on Venus May Still Be Active". Universe Today . Retrieved April 14, 2011.