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72-534: The significant Late Neolithic and Early Bronze Age Cycladic culture is best known for its schematic, flat sculptures carved out of the islands' pure white marble centuries before the great Middle Bronze Age Minoan civilization arose in Crete to the south. (These figures have been looted from burials to satisfy a thriving Cycladic antiquities market since the early 20th century.) A distinctive Neolithic culture amalgamating Anatolian and mainland Greek elements arose in

144-886: A mid-ocean ridge , such as the Mid-Atlantic Ridge , has volcanoes caused by divergent tectonic plates whereas 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

216-462: A brisk trade in forgeries arose. The context for many of these Cycladic figurines has thus been mostly destroyed; their meaning may never be completely understood as a result. It has been suggested that around 90% of the figures we know of were looted or removed from their original locations in a unscientific manner, resulting in the loss of context with which to build a proper historical narrative. Between 2009 and 2010, scholars were able to meet with

288-437: 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,

360-401: A large part of the artifacts we have, especially in context, from Cycladic culture. Pottery has played a large role in sectioning Cycladic chronology into different periods. This is due to shifts in style and materials over time. Pottery was also hugely important to Cycladic culture in the context of their maritime activities. Evidence suggests that pottery was a primary good traded to and from

432-424: A man they simply identified as "the forger", and obtained inside information about the illicit process of funneling artifacts and forgeries to collectors, as well as how these forgeries were being produced. This has helped archaeologists and scholars to properly identify forgeries with more accuracy, as well as to trace certain artifacts back to their original locations more accurately. Volcano A volcano

504-443: 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

576-442: A ship, which is indicative of the importance of seafaring to Cycladic peoples. This also gives us a good idea of how Cycladic ships would have been constructed. There were likely two kinds of ships, a small boat meant to be managed by one person or a very small crew, and a longboat that could support a crew of at least twenty five people. Studies of Cycladic culture have faced significant difficulties due to artifact looting . Since

648-632: 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

720-555: 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

792-465: 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

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864-739: 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

936-445: 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. 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,

1008-412: 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

1080-565: 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

1152-584: 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

1224-864: Is known as the Helladic period . In recent decades the Cyclades have become popular with European and other tourists, and as a result there have been problems with erosion , pollution, and water shortages. The Cyclades includes about 220 islands, the major ones being Amorgos , Anafi , Andros , Antiparos , Delos , Ios , Kea , Kimolos , Kythnos , Milos , Mykonos , Naxos , Paros , Folegandros , Serifos , Sifnos , Sikinos , Syros , Tinos , and Thira or Santoríni . There are also many minor islands (the Lesser Cyclades ) including Donousa , Eschati , Gyaros , Irakleia , Koufonisia , Makronisos , Rineia , and Schoinousa . The name "Cyclades" refers to

1296-537: 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

1368-470: Is that of the Cycladic frying pans . More accurate archaeology has revealed the broad outlines of a farming and seafaring culture that had emigrated from Anatolia c.  5000 BCE . Early Cycladic culture evolved in three phases, between c. 3300 – 2000 BCE, when it was increasingly swamped in the rising influence of Minoan Crete. The culture of mainland Greece contemporary with Cycladic culture

1440-471: 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

1512-701: The British School at Athens and by Christos Tsountas , who investigated burial sites on several islands in 1898–1899 and coined the term "Cycladic civilization". Interest lagged, and then picked up in the mid-20th century, as collectors competed for the modern-looking figures that seemed so similar to sculpture by Jean Arp or Constantin Brâncuși . Sites were looted and a brisk trade in forgeries arose. The context for many of these Cycladic figurines has been mostly destroyed and their meaning may never be completely understood. Another intriguing and mysterious object

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1584-617: 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

1656-804: The core–mantle boundary , 3,000 kilometres (1,900 mi) deep within Earth. This results in hotspot volcanism , of which 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,

1728-834: 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

1800-439: The 1880s, undertaken by antiquaries such as Theodore Bent , were followed by systematic work by the British School at Athens and by Christos Tsountas , who investigated burial sites on several islands in 1898–99 and coined the term "Cycladic civilization". Interest then lagged, but picked up in the mid-20th century, partially to collectors taking an interest in owning artifacts from Early Cycladic cemeteries. Pottery makes up

1872-644: The Cyclades via boats, especially during the Early Cycladic period. While there are no discovered surviving boats from this time and place, other types of archaeological finds have helped historians piece together evidence of a rich seafaring practice in Cycladic culture. Discoveries include the Cycladic frying pans , whose original functions remain unknown. Despite the mysteries that come with them, Cycladic frying pans offer insight into Cycladic culture through their imagery. The pan pictured in this section, as well as others that archaeologists have found, depicts

1944-646: The Orthodox Cathedral in Chora, where the archaeological site of Grotta is located today. Naxos has been continuously inhabited since at least the fourth millennium BC. Study of the island's toponyms asserts that Naxos has never been abandoned. Cycladic culture in the Middle Bronze age went through some geographical shifts, as archaeologists have found artifacts and communities that point towards an expansion of Cycladic culture's influence, including on

2016-622: 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

2088-613: 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

2160-510: 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

2232-402: 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

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2304-404: The early 1900s, private collectors have coveted Cycladic figures and other artifacts, leading to a huge illicit trade in these items. These figures have typically been stolen from burials to satisfy the Cycladic antiquities market. This really began as collectors competed for the modern-looking figures that seemed so similar to a sculpture by Jean Arp or Constantin Brâncuși . Sites were looted and

2376-799: 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

2448-431: 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

2520-610: 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

2592-585: 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

2664-466: 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

2736-492: 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

2808-421: The islands forming a circle ("circular islands") around the sacred island of Delos. Most of the smaller islands are uninhabited. Ermoupoli on Syros is the chief town and administrative center of the former prefecture. The islands are peaks of a submerged mountainous terrain, with the exception of two volcanic islands , Milos and Santorini. The climate is generally dry and mild, but with the exception of Naxos,

2880-872: The islands' pure white marble. It was roughly contemporaneous with the Middle Bronze Age (" Minoan ") culture that arose in Crete , to the south. A distinctive Neolithic culture amalgamating Anatolian and mainland Greek elements arose in the western Aegean in the third millennium BC based on emmer and wild-type barley, sheep and goats, pigs, and tuna that were apparently speared from small boats (Rutter). Excavated sites include Chalandriani , Phylakopi , Skarkos , Saliagos , Amorgos , Naxos and Kephala (on Kea ), which showed signs of copper-working. Early Cycladic culture evolved in three phases, between c. 3100 and 2300 BC. Excavations at Knossos on Crete reveal an influence of Cycladic civilization upon Knossos in

2952-500: The last of these retained its archaic reputation as a sanctuary through the period of Classical Greek civilization (see Delian League ). The chronology of Cycladic civilization is divided into three major sequences: Early, Middle and Late Cycladic. The early period, beginning c. 3100 BC, segued into the archaeologically murkier Middle Cycladic c. 2000 BC. By the end of the Late Cycladic sequence (c. 1000 BC), there

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3024-484: The mainland and Crete. Walls that appear to date to this period show expansion from older Cycladic walls in many areas. One of the main pieces of evidence we have for this period of Cycladic history is pottery. Likewise, graves serve as a primary source of information for this period. Transitions in pottery styles have helped historians pin down a more accurate date range for the Middle Cycladic period. Each of

3096-419: 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

3168-551: 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

3240-415: 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

3312-438: 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

3384-452: 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

3456-876: 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

3528-549: 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

3600-420: 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

3672-471: 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

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3744-468: 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

3816-425: 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

3888-471: The period 3400 to 2000 BC as evidenced from pottery finds at Knossos. Kea is the location of a Bronze Age settlement at the site now called Ayia Irini , which reached its height in the Late Minoan and Early Mycenaean eras (1600–1400 BC). The Mycenaean town of Naxos (around 1300 BC) covered the area from today's city to the islet of "Palatia." Part of it was discovered under the square in front of

3960-619: 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

4032-678: The prefecture was abolished, and its territory was divided into nine regional units of the South Aegean region: The prefecture was subdivided into the following municipalities and communities. These have been reorganised at the 2011 Kallikratis reform as well. Note: Provinces no longer hold any legal status in Greece . Local specialities of the Cyclades include: 37°00′N 25°10′E  /  37.000°N 25.167°E  / 37.000; 25.167 Cycladic culture Cycladic culture (also known as Cycladic civilisation )

4104-435: 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

4176-492: 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

4248-450: The scattered communities (Rutter), and when the highly organized palace-culture of Crete arose, the islands faded into insignificance, with the exception of Delos, which retained its archaic reputation as a sanctuary throughout antiquity and until the emergence of Christianity. The first archaeological excavations of the 1880s, undertaken by antiquaries such as Theodore Bent at Antiparos in early 1884, were followed by systematic work by

4320-458: The small Cycladic islands could support no more than a few thousand people, though Late Cycladic boat models show that crews of twenty-five oarsmen could be assembled from the scattered communities. When the highly organized palace-culture of Crete arose, the islands became relatively less significant. This occurred when Cycladic culture was increasingly submerged in the rising influence of Minoan Crete. Exceptions to this were Kea, Naxos and Delos ;

4392-473: The soil is not very fertile; agricultural produce includes wine, fruit, wheat, olive oil , and tobacco. Lower temperatures are registered in higher elevations and these areas do not usually see wintry weather. The Cyclades are bounded to the south by the Sea of Crete . The Cyclades Prefecture ( Greek : Νομός Κυκλάδων ) was one of the prefectures of Greece . As a part of the 2011 Kallikratis government reform ,

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4464-622: 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

4536-406: 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

4608-434: 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

4680-444: 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

4752-431: 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

4824-492: 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

4896-424: 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

4968-455: The western Aegean before 4000 BCE, based on emmer and wild-type barley, sheep and goats, pigs, and tuna that were apparently speared from small boats (Rutter). Excavated sites include Chalandriani , Phylakopi , Skarkos , Saliagos and Kephala (on Kea ) with signs of copperworking, Each of the small Cycladic islands could support no more than a few thousand people, though Late Cycladic boat models show that fifty oarsmen could be assembled from

5040-617: Was a Bronze Age culture (c. 3100–c. 1000 BC) found throughout the islands of the Cyclades in the Aegean Sea . In chronological terms, it is a relative dating system for artifacts which is roughly contemporary to Helladic chronology (mainland Greece) and Minoan chronology (Crete) during the same period of time. The significant Late Neolithic and Early Bronze Age Cycladic culture is best known for its schematic flat female (and, rarely, male) figurines of uncertain purpose carved out of

5112-421: 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

5184-478: Was essential convergence between the Cycladic and Minoan civilizations. There is some disagreement between the dating systems used for Cycladic civilization, one "cultural" and one "chronological". Attempts to link them lead to varying combinations. A prominent scholarly attempt to do this, as proposed by Oliver Dickinson, can be found below: * Indicates this space is left intentionally blank due to lack of scholarly data. The initial archaeological excavations of

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