Volcanoes and Volcanic Rocks
by Owen Borville
January 30, 2021
Learning, Geology, Science
A volcano is a vent at the Earth's surface through which magma (molten rock) and associated gases erupt, and also the cone built by effusive and explosive eruptions. An active volcano is one that is currently erupting, has erupted recently, or shows signs of erupting. Mauna Loa and Kilauea in Hawaii, Mount Fuji in Japan, Mount Vesuvius in Italy, Mount St. Helens in Washington State, and Mount Pinatubo in the Philippines are examples of active volcanoes. Dormant volcanoes are those that are not currently active but could become active or erupt again. Extinct volcanoes are those that scientists consider unlikely to erupt again.
Volcanic gas is released from magma into the atmosphere during eruptions. Gases are also released from magma that either remain below ground (intrusions) or rise toward the surface. In such cases, gases may escape continuously into the atmosphere from the soil, volcanic vents, fumaroles, and hydrothermal systems. The most common gas released by magma is steam (H2O), followed by CO2 (carbon dioxide), SO2 (sulfur dioxide), and HCl (hydrogen chloride).
Features of Volcanoes
Lava flows are streams of molten rock that erupt relatively non-explosively from a volcano and move slowly downslope. The distance traveled by a lava flow depends on such variables as the viscosity of the lava, the volume erupted, the steepness of the slope, and obstructions in the path of the flow.
A lava fountain is a jet of lava sprayed into the air by the rapid formation and expansion of gas bubbles in the molten rock. Lava fountains typically range from about 10 to 100 meters in height.
A pyroclastic eruption is a volcanic eruption that produces a large volume of solid volcanic fragments (pyroclastics or tephra) rather than fluid lava. This type of eruption is typical of volcanoes with high silica and viscous, gas-rich magma. Lapilli is pyroclastic material two to 64 millimeters in diameter. Pyroclastic materials greater than 64 millimeters in diameter are called bombs or blocks. Ash is pyroclastic material less than two millimeters in diameter.
A pyroclastic flow is an extremely hot mixture of gas, ash, and pumice fragments that travels down the flanks of a volcano or along the surface of the ground at speeds of 50 to 100 miles per hour. Pyroclastic surge is a turbulent, low-density cloud of hot rock debris and gases that moves over the ground surface at high speed. The surge is similar to a pyroclastic flow but of much lower density (higher gas to rock ratio).
A lahar is a rapidly flowing mixture of rock debris and water that originates on the slopes of a volcano. Lahars are also referred to as volcanic mudflows or debris flows. They form in a variety of ways including the rapid melting of snow and ice by pyroclastic flows, intense rainfall on loose volcanic rock deposits, the breakout of a lake dammed by volcanic deposits, and as a consequence of debris avalanches.
Pahoehoe is basaltic lava that has a smooth, hummocky, or ropy surface and typically advances as a series of small lobes and toes that continually break out from a cooled crust. The surface texture of pahoehoe flows varies widely. A`a (pronounced "ah-ah") is a Hawaiian term for lava flows that have a rough rubble surface composed of broken lava blocks called clinkers.
Lava tubes are natural conduits through which lava travels beneath the surface of a lava flow. Tubes form by the crusting over of lava channels and pahoehoe flows. A skylight is an opening in the roof of a lava tube and commonly forms when part of the roof collapses into the tube. However, skylights also occur where a roof failed to form over the lava channel. If the tube is active, a stream of glowing lava can be seen moving below.
Pressure ridges occur as flowing lava pressures and pushes up on the overlying solidified crust that cools quicker, commonly cracking the crust and forming a ridge.
Spatter cones are low, steep-sided hills or mounds of welded lava fragments that form along a linear fissure or around a central vent. As lava fragments erupt into the air, they often do not have time to cool completely before hitting the ground. The fragments spatter as they land and bond to the underlying lava fragments, which are still hot and sometimes oozing down the side of the cone. Spatter ramparts are lava fountains that erupt from an elongate fissure and build broad embankments of spatter along both sides of the fissure.
Columnar jointing is a phenomenon that occurs as lava contracts to form a solid. During the cooling process, polygonal prismatic shapes form to accommodate the escaping heat. The polygonal prismatic shapes extend down through the thickness of the lava flow to form columns of solid rock.
Pillow lava are mounds of elongate pillow-shaped features formed by repeated oozing and quenching of hot basalt lava erupting underwater on the sea floor.
A caldera is a large, commonly circular depression at the summit of a volcano formed when magma is withdrawn or erupted from a shallow underground magma reservoir. A crater is a circular shaped depression at the top of a volcano where gas and lava have escaped. Craters are usually smaller than calderas. A maar or maar crater is a low-relief, broad volcanic crater formed by shallow explosive eruptions. The explosions are usually caused by the heating and boiling of groundwater when magma invades the groundwater table. Maars often fill with water to form a lake.
Types of Volcanoes
Shield volcanoes are built almost entirely of fluid lava flows of basalt that pour out in all directions from a central summit vent, or group of vents. Shield volcanoes build a broad, gently sloping cone of flat, domical shape and extend for miles. Shield volcanoes form some of the largest volcanoes in the world, such as the Hawaiian Islands. Other locations for shield volcanoes include Iceland and East Africa.
A cinder cone is a volcanic cone-shaped hill built almost entirely of loose volcanic fragments, ash, and pumice. Cinder cones form when low viscosity lava with large amounts of gas erupts as liquid fountains. Lava may be spewed hundreds of feet through the air. The molten rock solidifies instantly, often preserving bubbles created by escaping gases.
A stratovolcano (stratiform or composite volcano) is a steep, conical volcano built by the eruption of viscous lava flows, tephra, and pyroclastic flows and is usually constructed over a period of tens to hundreds of thousands of years. Stratovolcanoes may erupt a variety of magma types, including basalt, andesite, dacite, and rhyolite with all but basalt commonly generating highly explosive eruptions. A stratovolcano typically consists of many separate vents, some of which may have erupted cinder cones and domes on the volcano flanks. Mount St. Helens in Washington is an example of a stratovolcano. Other stratovolcanoes include Mount Shasta in the Cascade Mountains of North America and Nevado Ojos del Salado in Chile.
Lava domes (volcanic domes) are rounded, steep-sided mounds built by very viscous or felsic magma, usually either dacite or rhyolite. Such magmas are typically too viscous (resistant to flow) to move far from the vent before cooling and crystallizing. Domes may consist of one or more individual lava flows.
Nuee ardente (French, meaning fiery cloud) is a type of volcanic activity associated with pyroclastic flows that are very hot and includes glowing clouds of gas and volcanic debris that is forcefully ejected down the sides of a volcano. Ignimbrite is a rock formed by the widespread deposition and consolidation of ash flows and Nuees Ardentes.
A fissure is a fracture or crack in rock along which there is a distinct separation. Fissures are often filled with mineral-bearing materials. On volcanoes, a fissure is an elongate fracture or crack at the surface from which lava erupts. Fissure eruptions typically dwindle to a central vent after a period of hours or days. Occasionally, lava will flow back into the ground by pouring into a crack or an open eruptive fissure, sometimes the original fissure.
Basalt rock also forms on continents as volcanic traps, or large continental sized, step-like plateaus of volcanic rock that are found around the world, such as the Siberian Traps, India's Deccan Traps, and the Parana region of Brazil along with the associated formation in Namibia-Angola. As mantle plumes and volcanic magma push upward and crack the crust open, lava pours out in large amounts to cover large portions of continents. Much of this occurred during the creation week or the Flood year.
Flood basalts also occur around the world, which are large episodes of lava spilling onto the land surface like a flood, notably at Missoula in western North America. Flood basalts are found in Washington, Idaho, Montana, Iceland, Greenland.
Hot Spots occur around the Earth, spurred by mantle plumes that push upward and crack the surface. Iceland, Hawaii, Reunion Island, and Yellowstone are known hot spots. Hot Spots are found in Iceland, Hawaii, Yellowstone, Reunion Island.
Volcanic traps are large continent scale volcanic flood basalt pours onto the surface with terraced shape, found in Siberia East of Urals, India-Deccan Plateau, East Africa, Brazil-Parana.
by Owen Borville
January 30, 2021
Learning, Geology, Science
A volcano is a vent at the Earth's surface through which magma (molten rock) and associated gases erupt, and also the cone built by effusive and explosive eruptions. An active volcano is one that is currently erupting, has erupted recently, or shows signs of erupting. Mauna Loa and Kilauea in Hawaii, Mount Fuji in Japan, Mount Vesuvius in Italy, Mount St. Helens in Washington State, and Mount Pinatubo in the Philippines are examples of active volcanoes. Dormant volcanoes are those that are not currently active but could become active or erupt again. Extinct volcanoes are those that scientists consider unlikely to erupt again.
Volcanic gas is released from magma into the atmosphere during eruptions. Gases are also released from magma that either remain below ground (intrusions) or rise toward the surface. In such cases, gases may escape continuously into the atmosphere from the soil, volcanic vents, fumaroles, and hydrothermal systems. The most common gas released by magma is steam (H2O), followed by CO2 (carbon dioxide), SO2 (sulfur dioxide), and HCl (hydrogen chloride).
Features of Volcanoes
Lava flows are streams of molten rock that erupt relatively non-explosively from a volcano and move slowly downslope. The distance traveled by a lava flow depends on such variables as the viscosity of the lava, the volume erupted, the steepness of the slope, and obstructions in the path of the flow.
A lava fountain is a jet of lava sprayed into the air by the rapid formation and expansion of gas bubbles in the molten rock. Lava fountains typically range from about 10 to 100 meters in height.
A pyroclastic eruption is a volcanic eruption that produces a large volume of solid volcanic fragments (pyroclastics or tephra) rather than fluid lava. This type of eruption is typical of volcanoes with high silica and viscous, gas-rich magma. Lapilli is pyroclastic material two to 64 millimeters in diameter. Pyroclastic materials greater than 64 millimeters in diameter are called bombs or blocks. Ash is pyroclastic material less than two millimeters in diameter.
A pyroclastic flow is an extremely hot mixture of gas, ash, and pumice fragments that travels down the flanks of a volcano or along the surface of the ground at speeds of 50 to 100 miles per hour. Pyroclastic surge is a turbulent, low-density cloud of hot rock debris and gases that moves over the ground surface at high speed. The surge is similar to a pyroclastic flow but of much lower density (higher gas to rock ratio).
A lahar is a rapidly flowing mixture of rock debris and water that originates on the slopes of a volcano. Lahars are also referred to as volcanic mudflows or debris flows. They form in a variety of ways including the rapid melting of snow and ice by pyroclastic flows, intense rainfall on loose volcanic rock deposits, the breakout of a lake dammed by volcanic deposits, and as a consequence of debris avalanches.
Pahoehoe is basaltic lava that has a smooth, hummocky, or ropy surface and typically advances as a series of small lobes and toes that continually break out from a cooled crust. The surface texture of pahoehoe flows varies widely. A`a (pronounced "ah-ah") is a Hawaiian term for lava flows that have a rough rubble surface composed of broken lava blocks called clinkers.
Lava tubes are natural conduits through which lava travels beneath the surface of a lava flow. Tubes form by the crusting over of lava channels and pahoehoe flows. A skylight is an opening in the roof of a lava tube and commonly forms when part of the roof collapses into the tube. However, skylights also occur where a roof failed to form over the lava channel. If the tube is active, a stream of glowing lava can be seen moving below.
Pressure ridges occur as flowing lava pressures and pushes up on the overlying solidified crust that cools quicker, commonly cracking the crust and forming a ridge.
Spatter cones are low, steep-sided hills or mounds of welded lava fragments that form along a linear fissure or around a central vent. As lava fragments erupt into the air, they often do not have time to cool completely before hitting the ground. The fragments spatter as they land and bond to the underlying lava fragments, which are still hot and sometimes oozing down the side of the cone. Spatter ramparts are lava fountains that erupt from an elongate fissure and build broad embankments of spatter along both sides of the fissure.
Columnar jointing is a phenomenon that occurs as lava contracts to form a solid. During the cooling process, polygonal prismatic shapes form to accommodate the escaping heat. The polygonal prismatic shapes extend down through the thickness of the lava flow to form columns of solid rock.
Pillow lava are mounds of elongate pillow-shaped features formed by repeated oozing and quenching of hot basalt lava erupting underwater on the sea floor.
A caldera is a large, commonly circular depression at the summit of a volcano formed when magma is withdrawn or erupted from a shallow underground magma reservoir. A crater is a circular shaped depression at the top of a volcano where gas and lava have escaped. Craters are usually smaller than calderas. A maar or maar crater is a low-relief, broad volcanic crater formed by shallow explosive eruptions. The explosions are usually caused by the heating and boiling of groundwater when magma invades the groundwater table. Maars often fill with water to form a lake.
Types of Volcanoes
Shield volcanoes are built almost entirely of fluid lava flows of basalt that pour out in all directions from a central summit vent, or group of vents. Shield volcanoes build a broad, gently sloping cone of flat, domical shape and extend for miles. Shield volcanoes form some of the largest volcanoes in the world, such as the Hawaiian Islands. Other locations for shield volcanoes include Iceland and East Africa.
A cinder cone is a volcanic cone-shaped hill built almost entirely of loose volcanic fragments, ash, and pumice. Cinder cones form when low viscosity lava with large amounts of gas erupts as liquid fountains. Lava may be spewed hundreds of feet through the air. The molten rock solidifies instantly, often preserving bubbles created by escaping gases.
A stratovolcano (stratiform or composite volcano) is a steep, conical volcano built by the eruption of viscous lava flows, tephra, and pyroclastic flows and is usually constructed over a period of tens to hundreds of thousands of years. Stratovolcanoes may erupt a variety of magma types, including basalt, andesite, dacite, and rhyolite with all but basalt commonly generating highly explosive eruptions. A stratovolcano typically consists of many separate vents, some of which may have erupted cinder cones and domes on the volcano flanks. Mount St. Helens in Washington is an example of a stratovolcano. Other stratovolcanoes include Mount Shasta in the Cascade Mountains of North America and Nevado Ojos del Salado in Chile.
Lava domes (volcanic domes) are rounded, steep-sided mounds built by very viscous or felsic magma, usually either dacite or rhyolite. Such magmas are typically too viscous (resistant to flow) to move far from the vent before cooling and crystallizing. Domes may consist of one or more individual lava flows.
Nuee ardente (French, meaning fiery cloud) is a type of volcanic activity associated with pyroclastic flows that are very hot and includes glowing clouds of gas and volcanic debris that is forcefully ejected down the sides of a volcano. Ignimbrite is a rock formed by the widespread deposition and consolidation of ash flows and Nuees Ardentes.
A fissure is a fracture or crack in rock along which there is a distinct separation. Fissures are often filled with mineral-bearing materials. On volcanoes, a fissure is an elongate fracture or crack at the surface from which lava erupts. Fissure eruptions typically dwindle to a central vent after a period of hours or days. Occasionally, lava will flow back into the ground by pouring into a crack or an open eruptive fissure, sometimes the original fissure.
Basalt rock also forms on continents as volcanic traps, or large continental sized, step-like plateaus of volcanic rock that are found around the world, such as the Siberian Traps, India's Deccan Traps, and the Parana region of Brazil along with the associated formation in Namibia-Angola. As mantle plumes and volcanic magma push upward and crack the crust open, lava pours out in large amounts to cover large portions of continents. Much of this occurred during the creation week or the Flood year.
Flood basalts also occur around the world, which are large episodes of lava spilling onto the land surface like a flood, notably at Missoula in western North America. Flood basalts are found in Washington, Idaho, Montana, Iceland, Greenland.
Hot Spots occur around the Earth, spurred by mantle plumes that push upward and crack the surface. Iceland, Hawaii, Reunion Island, and Yellowstone are known hot spots. Hot Spots are found in Iceland, Hawaii, Yellowstone, Reunion Island.
Volcanic traps are large continent scale volcanic flood basalt pours onto the surface with terraced shape, found in Siberia East of Urals, India-Deccan Plateau, East Africa, Brazil-Parana.