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Scoria is a highly vesicular, dark colored volcanic rock that may or may not contain crystals (phenocrysts). It is typically dark in color (generally dark brown, black or purplish red), and basaltic or andesitic in composition. Scoria is relatively low in density as a result of its numerous macroscopic ellipsoidal vesicles, but in contrast to pumice, all scoria has a specific gravity greater than 1, and sinks in water. The holes or vesicles form when gases that were dissolved in the magma come out of solution as it erupts, creating bubbles in the molten rock, some of which are frozen in place as the rock cools and solidifies. Scoria may form as part of a lava flow, typically near its surface, or as fragmental ejecta (lapilli, blocks and bombs), for instance in Strombolian eruptions that form steep-sided scoria cones. Chemical analysis of scoria found in Yemen showed that it was mainly composed of volcanic glass with a few zeolites (e.g. clinoptilolite).Most scoria is composed of glassy fragments, and may contain phenocrysts. The word scoria comes from the Greek σκωρία, skōria, rust. A colloquial term for scoria is cinder.
Scoria differs from pumice, another vesicular volcanic rock, in having larger vesicles and thicker vesicle walls, and hence is denser. The difference is probably the result of lower magma viscosity, allowing rapid volatile diffusion, bubble growth, coalescence, and bursting.
As rising magma encounters lower pressures, dissolved gases are able to exsolve and form vesicles. Some of the vesicles are trapped when the magma chills and solidifies. Vesicles are usually small, spheroidal and do not impinge upon one another; instead they open into one another with little distortion.
Volcanic cones of scoria can be left behind after eruptions, usually forming mountains with a crater at the summit. An example is Maungarei in Auckland, New Zealand, which like Te Tatua-a-Riukiuta in the south of the same city has been extensively quarried. Quincan, a unique form of Scoria, is quarried at Mount Quincan in Far North Queensland, Australia.
Scoria has several useful characteristics that influence how it is used. It is somewhat porous, has a high surface area and strength for its weight, and often has striking colours. Consequently, it is often used in landscaping and drainage works.It is also commonly used in gas barbecue grills.
Scoria can be used for high-temperature insulation. It is also used on oil well sites to limit mud problems resulting from heavy truck traffic.
The quarry of Puna Pau on Rapa Nui/Easter Island was the source of a red-coloured scoria which the Rapanui people used to carve the pukao (or topknots) for their distinctive moai statues, and even to carve some moai themselves.
It is also used as a traction aid on ice- and snow-covered roads.
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.
Basalt is a mafic extrusive igneous rock formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. More than 90% of all volcanic rock on Earth is basalt. Basalt lava has a low viscosity, due to its low silica content, resulting in rapid lava flows that can spread over great areas before cooling and solidification. Flood basalt describes the formation in a series of lava basalt flows.
Tuff, also known as volcanic tuff, is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is compacted into a solid rock in a process called consolidation. Tuff is sometimes erroneously called "tufa", particularly when used as construction material, but geologically tufa is a limestone precipitated from groundwater. Rock that contains greater than 50% tuff is considered tuffaceous.
Pumice, called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough textured volcanic glass, which may or may not contain crystals. It is typically light colored. Scoria is another vesicular volcanic rock that differs from pumice in having larger vesicles, thicker vesicle walls and being dark colored and denser.
Volcanic cones are among the simplest volcanic landforms. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and size of the fragments ejected during the eruption. Types of volcanic cones include stratocones, spatter cones, tuff cones, and cinder cones.
Extrusive rock refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff. In contrast, intrusive rock refers to rocks formed by magma which cools below the surface.
Volcanic rock is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic rock is artificial, and in nature volcanic rocks grade into hypabyssal and metamorphic rocks and constitute an important element of some sediments and sedimentary rocks. For these reasons, in geology, volcanics and shallow hypabyssal rocks are not always treated as distinct. In the context of Precambrian shield geology, the term "volcanic" is often applied to what are strictly metavolcanic rocks. Volcanic rocks and sediment that form from magma erupted into the air are called "volcaniclastics," and these are technically sedimentary rocks.
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 and is also responsible for activities in the Lassen volcanic area.
Pyroclastic rocks or pyroclastics are sedimentary clastic rocks composed solely or primarily of volcanic materials. Where the volcanic material has been transported and reworked through mechanical action, such as by wind or water, these rocks are termed volcaniclastic. Commonly associated with unsieved volcanic activity—such as Plinian or krakatoan eruption styles, or phreatomagmatic eruptions—pyroclastic deposits are commonly formed from airborne ash, lapilli and bombs or blocks ejected from the volcano itself, mixed in with shattered country rock. Tephra is any sized material formed by a volcanic eruption.
A cinder is a pyroclastic material. Cinders are extrusive igneous rocks; they are fragments of solidified lava. Cinders are typically brown, black, or red depending on chemical composition and weathering. Cinders are similar to pumice.
Vesicular texture is a volcanic rock texture characterized by a rock being pitted with many cavities at its surface and inside. This texture is common in aphanitic, or glassy, igneous rocks that have come to the surface of the earth, a process known as extrusion. As magma rises to the surface the pressure on it decreases. When this happens gasses dissolved in the magma are able to come out of solution, forming gas bubbles inside it. When the magma finally reaches the surface as lava and cools, the rock solidifies around the gas bubbles and traps them inside, preserving them as holes filled with gas called vesicles.
Nazko Cone is a small potentially active basaltic cinder cone in central British Columbia, Canada, located 75 km west of Quesnel and 150 kilometers southwest of Prince George. It is considered the easternmost volcano in the Anahim Volcanic Belt. The small tree-covered cone rises 120 m above the Chilcotin-Nechako Plateau and rests on glacial till. It was formed in three episodes of activity, the first of which took place during the Pleistocene interglacial stage about 340,000 years ago. The second stage produced a large hyaloclastite scoria mound erupted beneath the Cordilleran Ice Sheet during the Pleistocene. Its last eruption produced two small lava flows that traveled 1 km to the west, along with a blanket of volcanic ash that extends several km to the north and east of the cone.
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.
Panum Crater is a volcanic cone that is part of the Mono–Inyo Craters, a chain of recent volcanic cones south of Mono Lake and east of the Sierra Nevada, in California, United States. Panum Crater is between 600 and 700 years old, and it exhibits all of the characteristics of the textbook rhyolitic lava dome.
A cinder cone is a steep conical hill of loose pyroclastic fragments, such as either volcanic clinkers, volcanic ash, or cinder that has been built around a volcanic vent. The pyroclastic fragments are formed by explosive eruptions or lava fountains from a single, typically cylindrical, vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as either cinders, clinkers, or scoria around the vent to form a cone that often is symmetrical; with slopes between 30–40°; and a nearly circular ground plan. Most cinder cones have a bowl-shaped crater at the summit.
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 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.
The geology of Ascension Island is the geologically young, exposed part of a large volcano, 80 kilometers west of the Mid-Atlantic Ridge. The island formed within the last six to seven million years and is primarily mafic rock with some felsic rock.
The Sand Mountain Volcanic Field is a volcanic field in the upper McKenzie River watershed, located in the United States in Oregon. Part of the Cascade Volcanic Arc, it lies southwest of Mount Jefferson and northwest of Belknap Crater and Mount Washington. Its highest elevation is 5,463 feet (1,665 m).
A lava balloon is a gas-filled bubble of lava that floats on the sea surface. It can be up to several metres in size. When it emerges from the sea, it is usually hot and often steaming. After floating for some time it fills with water and sinks again.