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A shield volcano is a type of volcano named for its low profile, resembling a warrior's shield lying on the ground. It is formed by the eruption of highly fluid lava, which travels farther and forms thinner flows than the more viscous lava erupted from a stratovolcano. Repeated eruptions result in the steady accumulation of broad sheets of lava, building up the shield volcano's distinctive form.
The geology of the Lassen volcanic area presents a record of sedimentation and volcanic activity in the area in and around Lassen Volcanic National Park in Northern California, U.S. The park is located in the southernmost part of the Cascade Mountain Range in the Pacific Northwest region of the United States. Pacific Oceanic tectonic plates have plunged below the North American Plate in this part of North America for hundreds of millions of years. Heat from these subducting plates has fed scores of volcanoes in California, Oregon, Washington and British Columbia over at least the past 30 million years, including these in the Lassen volcanic area.
Belknap Crater is a shield volcano in the Cascade Range in the U.S. state of Oregon. Located in Linn County, it is associated with lava fields and numerous subfeatures including the Little Belknap and South Belknap volcanic cones. It lies north of McKenzie Pass and forms part of the Mount Washington Wilderness. Belknap is not forested and most of its lava flows are not vegetated, though there is some wildlife in the area around the volcano, as well as a number of tree molds formed by its eruptive activity.
Masaya is a caldera located in Masaya, Nicaragua, 20 km south of the capital Managua. It is Nicaragua's first and largest national park, and one of 78 protected areas of Nicaragua. The complex volcano is composed of a nested set of calderas and craters, the largest of which is Las Sierras shield volcano and caldera. Within this caldera lies a sub-vent, which is Masaya Volcano sensu stricto. The vent is a shield type composing of basaltic lavas and tephras and includes a summit crater. This hosts Masaya caldera, formed 2,500 years ago by an 8-km³ basaltic ignimbrite eruption. Inside this caldera a new basaltic complex has grown from eruptions mainly on a semi-circular set of vents that include the Masaya and Nindiri cones. The latter host the pit craters of Masaya, Santiago, Nindiri and San Pedro. Observations in the walls of the pit craters indicate that there have been several episodes of cone and pit crater formation.
Bazman is a dormant stratovolcano in a remote desert region of Sistan and Baluchestan Province in south-eastern Iran. A 500-m-wide crater caps the summit of the dominantly andesitic-dacitic volcano, the flanks of which are covered by monogenetic centres especially to the northwest. Bazman is a geologically young volcano which formed mainly in the Quaternary, with the oldest dated rocks being 11.7 million years old and the youngest 0.6 million years. Although no historic eruptions have been reported from Bazman, it does contain fumaroles. Thus Bazman may be regarded as dormant, rather than extinct. Its satellite cones have been the source of basaltic lava flows.
Mount Hasan is a volcano in Anatolia, Turkey. It has two summits, the 3,069 metres (10,069 ft) high eastern Small Hasan Dagi and the 3,253 metres (10,673 ft) high Big Hasan Dagi, and rises about 1 kilometre (0.62 mi) above the surrounding terrain. It consists of various volcanic deposits, including several calderas, and its activity has been related to the presence of several faults in the area and to regional tectonics.
Lava lakes are large volumes of molten lava, usually basaltic, contained in a volcanic vent, crater, or broad depression. The term is used to describe both lava lakes that are wholly or partly molten and those that are solidified.
The Itcha Range, also known as the Itchas, is a small isolated mountain range in the West-Central Interior of British Columbia, Canada. It is located 40 km (25 mi) northeast of the community of Anahim Lake. With a maximum elevation of 2,375 m (7,792 ft), it is the lowest of three mountain ranges on the Chilcotin Plateau extending east from the Coast Mountains. Two mountains are named in the Itcha Range; Mount Downton and Itcha Mountain. A large provincial park surrounds the Itcha Range and other features in its vicinity. More than 15 animal species are known to exist in the Itcha Range area, as well as a grassland community that is limited only to this location of British Columbia. The Itcha Range is within territory which has been occupied by aboriginal peoples for millennia. This area has a relatively dry environment compared to the Coast Mountains in the west.
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.
Level Mountain is a large volcanic complex in the Northern Interior of British Columbia, Canada. It is located 50 kilometres north-northwest of Telegraph Creek and 60 kilometres west of Dease Lake on the Nahlin Plateau. With a maximum elevation of 2,164 metres , it is the second-highest of four large complexes in an extensive north–south trending volcanic region. Much of the mountain is gently-sloping; when measured from its base, Level Mountain is about 1,100 metres tall, slightly taller than its neighbour to the northwest, Heart Peaks. The lower, broader half of Level Mountain consists of a shield-like structure while its upper half has a more steep, jagged profile. Its broad summit is dominated by the Level Mountain Range, a small mountain range with prominent peaks cut by deep valleys. These valleys serve as a radial drainage for several small streams that flow from the mountain. Meszah Peak is the only named peak in the Level Mountain Range.
Alu is a system of volcanic fissures, located in Ethiopia. The fissures have produced silicic lava flows, and other fissures south of the volcano have been the source of huge youthful basaltic lava flows, which enlarge to the north as far as Lake Bakili. There is major fumarolic activity, located on parallel faults, some with 100-m uplifts.
West Crater is a small lava dome with associated lava flows in southern Washington, United States. Located in Skamania County, it rises to an elevation of 4,131 feet (1,259 m), and forms part of the Cascade Volcanic Arc. It is also part of the Marble Mountain-Trout Creek Hill volcanic field, a little-known Quaternary volcanic field in the southern Cascades of Washington state. The area can be hiked, and can be accessed by roads in the Gifford Pinchot National Forest.
The Barrier is an active shield volcano located in the north of Kenya. It is last known to have erupted in 1921.
Volcanic activity, or volcanism, has played a significant role in the geologic evolution of Mars. Scientists have known since the Mariner 9 mission in 1972 that volcanic features cover large portions of the Martian surface. These features include extensive lava flows, vast lava plains, and the largest known volcanoes in the Solar System. Martian volcanic features range in age from Noachian to late Amazonian, indicating that the planet has been volcanically active throughout its history, and some speculate it probably still is so today. Both Earth and Mars are large, differentiated planets built from similar chondritic materials. Many of the same magmatic processes that occur on Earth also occurred on Mars, and both planets are similar enough compositionally that the same names can be applied to their igneous rocks and minerals.
Mess Lake Cone is a cinder cone in northwestern British Columbia, Canada. It is polygenetic in nature, having erupted more than once throughout its eruptive history. Mess Lake Cone is one of the volcanoes that produced young basaltic lava flows in the central portion of the Mount Edziza volcanic complex in the past 10,000 years. These basaltic lava flows form a north–south trending volcanic field called the Mess Lake Lava Field.
Mount Alayta is an active shield volcano in the Afar Region of Ethiopia. It is part of the Afar Triangle, a highly active volcanic region which includes the adjacent Mount Afdera. Mount Alayta covers an area of 2,700 square kilometers southwest of Lake Afrera. A chain of younger craters are aligned along a north-northwest axis in the basaltic-to-trachytic shield along the east side of the shield volcano, which extends to the western flank of Mount Afdera. The Alayta Lavafeld was formed from a series of north-south fissures. In two areas on the southern side of the volcanic complex, fumaroles can be observed.
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.
The Canadian Cascade Arc, also called the Canadian Cascades, is the Canadian segment of the North American Cascade Volcanic Arc. Located entirely within the Canadian province of British Columbia, it extends from the Cascade Mountains in the south to the Coast Mountains in the north. Specifically, the southern end of the Canadian Cascades begin at the Canada–United States border. However, the specific boundaries of the northern end are not precisely known and the geology in this part of the volcanic arc is poorly understood. It is widely accepted by geologists that the Canadian Cascade Arc extends through the Pacific Ranges of the Coast Mountains. However, others have expressed concern that the volcanic arc possibly extends further north into the Kitimat Ranges, another subdivision of the Coast Mountains, and even as far north as Haida Gwaii.
Volcanism on the Moon is represented by the presence of volcanoes, pyroclastic deposits and vast lava plains on the lunar surface. The volcanoes are typically in the form of small domes and cones that form large volcanic complexes and isolated edifices. Calderas, large-scale collapse features generally formed late in a volcanic eruptive episode, are exceptionally rare on the Moon. Lunar pyroclastic deposits are the result of lava fountain eruptions from volatile-laden basaltic magmas rapidly ascending from deep mantle sources and erupting as a spray of magma, forming tiny glass beads. However, pyroclastic deposits formed by less common non-basaltic explosive eruptions are also believed to exist on the Moon. Lunar lava plains cover large swaths of the Moon's surface and consist mainly of voluminous basaltic flows. They contain a number of volcanic features related to the cooling of lava, including lava tubes, rilles and wrinkle ridges.
Ma Alalta is a stratovolcano in the Afar Region of Ethiopia, located well to the west of the Danakil Depression at the foot of the regional Ethiopian scarp. It has a summit elevation of 1,745 m (5,725 ft) and lies between two large horsts related to the East African Rift.
References
- ↑ Handbook of Lithium and Natural Calcium Chloride By Donald E. Garrett
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