AP - Notes Volcanoes
VOLCANISM
Active volcanoes produce magma (melted rock) at the surface. Other types of volcanoes are classified as intermittent, dormant (have not erupted within recorded history), or extinct (will never erupt again).
The majority of volcanoes – 95%- occur at subduction zones (where plates collide and move past one another) and mid-oceanic ridges (where plates move away from each other). The remaining 5% occur at hot spots, areas where plumes of magma come close to the surface.
Volcanoes may produce ejecta (lava rock and/or ash), molten lava, and/or toxic gases.
Active volcanoes produce magma (melted rock) at the surface. Other types of volcanoes are classified as intermittent, dormant (have not erupted within recorded history), or extinct (will never erupt again).
The majority of volcanoes – 95%- occur at subduction zones (where plates collide and move past one another) and mid-oceanic ridges (where plates move away from each other). The remaining 5% occur at hot spots, areas where plumes of magma come close to the surface.
Volcanoes may produce ejecta (lava rock and/or ash), molten lava, and/or toxic gases.
Common gases released include: steam, carbon dioxide, sulfur dioxide, and hydrogen chloride.
Volcanoes can affect climate by introducing large quantities of sulfur dioxide (SO2) into the atmosphere that is later converted into sulfate ions (SO4) in the stratosphere. The sulfate particles reflect shorter wavelengths of solar radiation and serve as condensation nuclei for high clouds.
In 1992, the year after Mt. Pinatubo erupted, the effect of stratospheric sulfate particles decreased average global temperatures by as much as 1F by decreasing the amount of sunlight that reached the earth.
The particles settle out of the atmosphere usually within two years and contribute to acid rain.
Eruptions occur when pressure within a magma chamber forces molten magma up through a conduit (pipe) and out a vent at the top of the volcano. The type of eruption depends on the gases, the amount of silica in the magma (which determines viscosity), and how free the conduit is (whether the volcano flows or explodes). Correlation exists between seismic and volcanic activity. Benefits of volcanic eruptions include producing new landforms (Hawaiian Islands) and increased soil nutrient levels produced from erosion of lava rock.
Methods of dealing with volcanoes include:
4 major types. Vary based upon size shape, and how they are formed.
Cinder Cones
Steep, conical hill formed above a vent.
Among the most common landforms found around the world and do not cause significant loss of life.
Cones usually grow up in groups, and they often occur on the flanks of composite and shield volcanoes.
Built from lava fragments called cinders.
The lava fragments are ejected from a single vent and accumulate around the vent when they fall back to earth.
Grow rapidly and soon approach their maximum size.
Rarely exceed 800 feet (250m) in height and 1,600 feet (500m) in diameters.
Example: Paricutin in Mexico, which grew to 300 feet (90 m) in 5 days.
Volcanoes can affect climate by introducing large quantities of sulfur dioxide (SO2) into the atmosphere that is later converted into sulfate ions (SO4) in the stratosphere. The sulfate particles reflect shorter wavelengths of solar radiation and serve as condensation nuclei for high clouds.
In 1992, the year after Mt. Pinatubo erupted, the effect of stratospheric sulfate particles decreased average global temperatures by as much as 1F by decreasing the amount of sunlight that reached the earth.
The particles settle out of the atmosphere usually within two years and contribute to acid rain.
Eruptions occur when pressure within a magma chamber forces molten magma up through a conduit (pipe) and out a vent at the top of the volcano. The type of eruption depends on the gases, the amount of silica in the magma (which determines viscosity), and how free the conduit is (whether the volcano flows or explodes). Correlation exists between seismic and volcanic activity. Benefits of volcanic eruptions include producing new landforms (Hawaiian Islands) and increased soil nutrient levels produced from erosion of lava rock.
Methods of dealing with volcanoes include:
- Modeling and data analysis for better volcanic activity predictions.
- Better evacuation plans.
- Study if precursors such as changes in the cone.
- Measuring changes in the temperature and gas composition
- Magnetic changes
- Changes in seismic activity.
4 major types. Vary based upon size shape, and how they are formed.
Cinder Cones
Steep, conical hill formed above a vent.
Among the most common landforms found around the world and do not cause significant loss of life.
Cones usually grow up in groups, and they often occur on the flanks of composite and shield volcanoes.
Built from lava fragments called cinders.
The lava fragments are ejected from a single vent and accumulate around the vent when they fall back to earth.
Grow rapidly and soon approach their maximum size.
Rarely exceed 800 feet (250m) in height and 1,600 feet (500m) in diameters.
Example: Paricutin in Mexico, which grew to 300 feet (90 m) in 5 days.
Composite (Strato)
Formed from alternating layers of lava and rock fragments. Constructed along subduction zones, and often form impressive, snow capped peaks that often exceed 1.5 miles (2,500 m) in height.
Between eruptions they are often so quite they seem extinct.
When a viscous magma rises to the surface it usually clogs the crater pipe. Gases build up pressure and results in an explosive eruption.
Examples: Mount Hood, Mount Rainier, Mount Shasta, Mount Pinatubo, Mount Fuji, and Mount Vesuvius
Formed from alternating layers of lava and rock fragments. Constructed along subduction zones, and often form impressive, snow capped peaks that often exceed 1.5 miles (2,500 m) in height.
Between eruptions they are often so quite they seem extinct.
When a viscous magma rises to the surface it usually clogs the crater pipe. Gases build up pressure and results in an explosive eruption.
Examples: Mount Hood, Mount Rainier, Mount Shasta, Mount Pinatubo, Mount Fuji, and Mount Vesuvius
Lava domes are a principle structural feature of a composite cone. The large amount of silica in the lava does not allow the lava to flow far from the vent. Lava domes grow slowly and steadily for month or years. When part of the lava dome collapses while it still contains molten rock or gases, it produces a pyroclastic flow – a lethal event.
Spatter Cones
When hot, erupting lava contains just enough explosive gas to prevent the formation of a lava flow but not enough to shatter it into small fragments, the lava is torn by expanding gases into fluids and hot clots. These range in size from half and inch (1cm) to 20 inches (50cm) across are called spatter. Because spatter is not fully solid when it lands, the spatter welds itself together. Spatter cones are typical of volcanoes with highly fluid magma, such as those found in the Hawaiian Islands.
Spatter Cones
When hot, erupting lava contains just enough explosive gas to prevent the formation of a lava flow but not enough to shatter it into small fragments, the lava is torn by expanding gases into fluids and hot clots. These range in size from half and inch (1cm) to 20 inches (50cm) across are called spatter. Because spatter is not fully solid when it lands, the spatter welds itself together. Spatter cones are typical of volcanoes with highly fluid magma, such as those found in the Hawaiian Islands.
Shield
Are very large and are built by many layers of runny lava flows. As the very fluid lava spills out of a central vent or group of vents, a broad-shaped, gently sloping cone is formed. Shield volcanoes may be produced by hot spots that lie away from the edges of tectonic plates. Shield volcanoes also occur along mid-oceanic ridges, where seafloor spreading is in progress, and along subduction-related volcanic arcs. Examples: Mauna Loa and Kilauea in Hawaii.
Are very large and are built by many layers of runny lava flows. As the very fluid lava spills out of a central vent or group of vents, a broad-shaped, gently sloping cone is formed. Shield volcanoes may be produced by hot spots that lie away from the edges of tectonic plates. Shield volcanoes also occur along mid-oceanic ridges, where seafloor spreading is in progress, and along subduction-related volcanic arcs. Examples: Mauna Loa and Kilauea in Hawaii.
FACTS
Mount Saint Helens: Located in Washington State. Erupted in 1980. Earthquake removed trees, increased soil erosion, destroyed wildlife, and polluted the air with gases and ash. Other affects included mudflows, melting of glacial snow and ice, and clogged rivers that caused flooding. 57 people killed.
Mount Pinatubo: Part of a chain of composite volcanoes on the west cast of the island of Luzon in the Philippines. June 1991, it erupted for 9 hours, disgorged a cubic mile of volcanic debris, and vented 180 million metric tons of sulfur dioxide into the atmosphere that encircled the earth in three weeks after reaching the stratosphere. It was the largest sulfur dioxide cloud to date. The sulfate aerosols formed in the stratosphere increased reflection of solar radiation and within 3 years caused over a 2 F (1C) overall cooling of Earth.
At this point - Proceed to the next topic: Geology - Mineral Identification and Usage
Mount Saint Helens: Located in Washington State. Erupted in 1980. Earthquake removed trees, increased soil erosion, destroyed wildlife, and polluted the air with gases and ash. Other affects included mudflows, melting of glacial snow and ice, and clogged rivers that caused flooding. 57 people killed.
Mount Pinatubo: Part of a chain of composite volcanoes on the west cast of the island of Luzon in the Philippines. June 1991, it erupted for 9 hours, disgorged a cubic mile of volcanic debris, and vented 180 million metric tons of sulfur dioxide into the atmosphere that encircled the earth in three weeks after reaching the stratosphere. It was the largest sulfur dioxide cloud to date. The sulfate aerosols formed in the stratosphere increased reflection of solar radiation and within 3 years caused over a 2 F (1C) overall cooling of Earth.
At this point - Proceed to the next topic: Geology - Mineral Identification and Usage