البراكين في كندا
أنماط الثوران والتكوينات البركانية

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| Hawaiian eruptions | Hawaiian eruption: 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 | Hawaiian eruptions are passive eruptions characterized by effusive emission of highly fluid basalt lavas with low gas contents. Like other Hawaiian eruptions, the relative volume of ejected pyroclastic material is less than that of all other eruption types. The main phenomenons during Hawaiian eruptions is steady lava fountaining and the production of thin lava flows that eventually build up into large, broad shield volcanoes. Eruptions are also common in central vents near the summit of shield volcanoes, and along linear volcanic vents radiating outward from the summit area. Lava advances downslope away from their source vents in lava channels and lava tubes.  Eve Cone, one of the best preserved cinder cones in Canada. In Canada, cinder cones form when lava fountains release fragments of lava that harden in the air and fall around a linear volcanic vent. The rock fragments, often known as cinder or scoria, are glassy and contain gas bubbles "frozen" into place as magma exploded into the air and then cooled quickly. Some of the lava is not fragmented and flows from the vent as a lava flow. Cinder cones are also called pyroclastic cones and are found in volcanic fields, on the flanks of shield volcanoes, stratovolcanoes and calderas. For example, geologists have identified at least 30 young cinder cones on the Mount Edziza volcanic complex, a large shield volcano in northwestern British Columbia with an area of 1,000 كيلومتر مربع (390 ميل2). Eve Cone, on the northern end of the Mount Edziza volcanic complex, is one of the best preserved cinder cones in Canada, due to its undeformed and symmetrical shape. During other Hawaiian eruptions, fluid basaltic lava may pond in vents, craters, or broad depressions to produce lava lakes. As lava lakes solidify, they create a grey-silver crust that is usually only a few centimeters thick. Active lava lakes comprise young crust that is repeatedly destroyed and regenerated. Convective motion of the underlying lava causes the crust to break into slabs and sink. This then exposes new lava at the surface that cools into a new crustal layer which will again fracture into slabs and be recycled into the circulating lava beneath the crust. |
| Phreatic and phreatomagmatic eruptions | Phreatic eruption: 1: water vapor cloud, 2: magma conduit, 3: layers of lava and ash, 4: stratum, 5: water table, 6: explosion, 7: magma chamber | Phreatic eruptions occur when rising magma makes contact with ground or surface water. The extreme temperature of the magma causes near-instantaneous evaporation, resulting in an explosion of steam, water, ash, rocks and volcanic bombs. The temperature of the rock fragments can range from cold to incandescent. If magma is included, the term phreatomagmatic may be used. Phreatomagmatic eruptions occasionally create broad, low-relief volcanic craters called maars. These explosion craters are interpreted to have formed above rubble-filled volcanic pipes called diatremes; deep erosion of a maar presumably would expose a diatreme. Maars range in size from 61 to 1,981 متر (200–6,499 قدم) across and from 9 to 198 متر (30–650 قدم) deep and are commonly filled with water to form a crater lake. Fiftytwo Ridge at the southeastern end of Wells Gray Provincial Park in southeastern British Columbia is an example of a volcano containing lake-filled maars. Most maars have low rims composed of a mixture of loose fragments of volcanic rocks and rocks torn from the walls of the diatreme. Phreatic explosions can be accompanied by carbon dioxide or hydrogen sulfide gas emissions. |
| Subglacial eruptions | Subglacial eruption: 1: water vapor cloud, 2: lake, 3: ice, 4: layers of lava and ash, 5: strata, 6: pillow lava, 7: magma conduit, 8: magma chamber, 9: dike | Subglacial eruptions occur when lava erupts under large portions of glacial ice. As lava erupts under a large glacier, the heat of the lava would immediately start to melt the overlying glacial ice to produce meltwater. The resulting meltwater would quickly harden the lava to produce pillow-shaped masses called pillow lava. In places, the pillow lava will fracture to create other types of volcanic deposits called pillow breccia, tuff breccia, and hyaloclastite. If magma intruded and melted a vertical pipe through the overlying glacier, the partially molten mass would cool as a large block with gravity flattening its upper surface to form a flat-topped, steep-sided subglacial volcano called a tuya. The term tuya originates from Tuya Butte in far northern British Columbia. While still in graduate school in 1947, Canadian geologist William Henry Mathews coined the term "tuya" to refer to these distinctive volcanic formations and was one of the first people on Earth to describe in detail these types of subglacial volcanoes. Tuya Butte is the first such landform analyzed in the geological literature, and its name has since become standard worldwide among volcanologists in referring to and writing about tuyas. Other subglacial volcanoes, including subglacial mounds, are formed when the erupted magma is not hot enough to melt through the overlying glacial ice. Once the glaciers melt away, the tuyas and subglacial mounds would reappear with a distinctive shape as a result of their confinement within glacial ice.  Because volcanic activity in Western and Northern Canada was contemporaneous with the ebb and flow of past glaciations, other volcanoes display ice-contact features. Mount Garibaldi in southwestern British Columbia is the only major volcano in North America known to have formed upon a regional ice sheet during the last glacial period, which began 110,000 years ago and ended between 10,000 and 15,000 years ago. Hoodoo Mountain in northern British Columbia was contained within basins thawed in the ice and assumed the flat-topped, steep-sided form of a tuya. Pyramid Mountain, in the Shuswap Highland of east-central British Columbia, was formed under more than 1,000 متر (3,300 قدم) of glacial ice to assume the form of a subglacial mound. The Fort Selkirk Volcanic Field in central Yukon contains volcanic features that were erupted subglacially when the large Cordilleran Ice Sheet existed in this area between 0.8 and one million years ago. |
| Submarine eruptions | Submarine eruption: 1: water vapor cloud, 2: water, 3: stratum, 4: lava flow, 5: magma conduit, 6: magma chamber, 7: dike, 8: pillow lava | Submarine eruptions are eruptions that occur underwater. The appearance of these eruptions is different from those that occur on land. When lava erupts it will be quickly cooled by the unlimited supply of water surrounding a submarine volcano, creating pillow lava. Explosive fragmentation of lavas forms hyaloclastites. Deep-sea submarine eruptions usually occur where the ocean floor is being pulled apart by plate tectonic movements called mid-ocean ridges, where about 75% of the Earth's magmatic eruptions occur. Shallow submarine eruptions can cause explosions of steam and volcanic ash called Surtseyan eruptions, named for the island of Surtsey off the southern coast of Iceland. Explosive submarine eruptions usually eject large quantities of very light volcanic rock called pumice. This very light volcanic rock can initially float on water, forming long-lived rafts of floating pumice carried long distances from the volcano by ocean currents. Lava flows entering water can cause explosions that form piles of ash and rubble similar to cinder cones, although they were formed from rootless vents not located above a magma conduit.  The deformed volcanic sequences that form greenstone belts in the Canadian Shield contain hyaloclastite and pillow lavas, indicating these areas were once below sea level and the lava was rapidly cooled underwater. Pillow lavas more than two billion years old indicate large submarine volcanoes existed during the early stages of the Earth's formation. |
| Pelèan eruptions | Peléan eruption: 1: ash plume, 2: volcanic ash rain, 3: lava dome, 4: volcanic bomb, 5: pyroclastic flow, 6: layers of lava and ash, 7: strata, 8: magma conduit, 9: magma chamber, 10: dike | Peléan eruptions are violent eruptions characterized by fast-moving streams of hot volcanic gas and rock called pyroclastic flows or nuées ardentes. Named for the stratovolcano Mount Pelée on the island of Martinique in the Caribbean Sea, Peléan eruptions occur when thick magma, typically of rhyolite، dacite and andesite type, is involved, and share some similarities with another type of explosive eruption known as Vulcanian eruptions. The thick magma associated with Peléan eruptions can form lava domes and lava spines in the volcano's vent or on the volcano's summit. Lava domes are steep-sided lava masses frequently circular in plan view and spiny, rounded, or flat on top. If a lava dome is created, it may later collapse, forming an ash column and sending flows of ash and hot volcanic blocks down the volcano's flanks. Lava spines are upright cylindrical masses of lava caused by the upward squeezing of pasty lava inside a volcanic vent. |
| Plinian eruptions | Plinian eruption: 1: ash plume, 2: magma conduit, 3: volcanic ash rain, 4: layers of lava and ash, 5: stratum, 6: magma chamber | Plinian eruptions are large explosive eruptions that form pyroclastic flows and enormous dark columns of tephra and gas that commonly rise into the second layer of the Earth's atmosphere. Named for Roman natural philosopher Pliny the Younger, these spectacularly explosive eruptions are associated with magmas of high viscosity and gas content such as dacite and rhyolite and typically occur at calderas and stratovolcanoes. The duration of these eruptions is highly variable, ranging from hours to days, and they commonly occur at volcanic arcs where the Earth's tectonic plates are moving towards one another, with one sliding underneath the other called a subduction zone. Although Plinian eruptions typically involve magma with high levels of silica, such as dacite and rhyolite, they can occasionally occur at volcanoes characterized by passive basaltic eruptions, including shield volcanoes, when the magma chambers become differentiated and zoned to create a siliceous top. In some cases, a basaltic shield volcano may have periods of explosive activity to form a stratovolcano mounted on top of the shield volcano. An example of this activity includes the massive Level Mountain shield volcano in northwestern British Columbia, which is capped by a 860 كيلومتر مكعب (206 ميل3) dissected stratovolcano.  Plinth Peak of the Mount Meager massif in southwestern British Columbia is the source for a large-scale Plinian eruption that occurred 2,350 years ago, sending ash as far as Alberta Following massive Plinian eruptions, temperatures may decrease to cause volcanic winters. Volcanic winters are caused by volcanic ash and droplets of sulfuric acid obscuring the sun's light, usually after a volcanic eruption. A massive (VEI-7) Plinian eruption in 1815 from Mount Tambora on the island of Sumbawa، Indonesia expelled more than 150 كيلومتر مكعب (36 ميل3) of volcanic ash around the Earth, causing particularly long, dark and harsh volcanic winters in Eastern Canada from 1816 to 1818. The result of this was the large amount of volcanic ash blocking out the sun's light, causing the Earth's temperature and visibility to decrease. The first volcanic winter in 1816, known as the Year Without a Summer, affected the Canadian province of Newfoundland and Labrador. In February 1816, a fire swept through St. John's, leaving 1,000 people homeless and in May during the following year, frost killed most of the crops that had been planted. In June, two large winter storms occurred throughout Eastern Canada, resulting in several casualties. The cause was limited amount of food supplies, and further deaths from those who, in a hunger-weakened state, then succumbed to disease. Nearly a foot of snow was observed in Quebec City. Rapid, dramatic temperature swings were common, with temperatures sometimes reverting from normal or above-normal summer temperatures as high as 35 °C to near-freezing within hours. In November 1817, two more fires swept through St. John's, leaving another 2,000 people poor. Many who had somewhere to live had low amounts of food or fuel for heating. The volcanic winters were also felt in the Maritime provinces, which includes Nova Scotia، New Brunswick and Prince Edward Island. |