Chapter 5, 6, 7 Study Guide

Magma Characteristics

• A magma's viscosity is directly related to its silica content.
• Magma with higher silica content has a higher viscosity.

Volcanic Eruptions

• The term "pyroclastic material" is given to any material that is ejected into the atmosphere during a volcanic eruption.
• Nuee ardente is a dangerous, fast-moving, hot, turbulent cloud of volcanic gases and fine-sized pyroclastic particles that precedes an explosive eruption.
• Lahar is a destructive volcanic mudflow.

Igneous Plutons

• Igneous plutons are classified based on their shape and relation to the host rock.
• If an igneous pluton cuts across existing rock units or structures, it is termed discordant.

Volcanic Rocks and Landforms

• Basaltic magma is the most abundant type of magma erupted at oceanic spreading centers.
• Basaltic lava flows that resemble twisted braids of rope are termed pahoehoe flows.
• These lava flows develop due to their high temperatures or as cooler lava flows begin to move over steeply sloped terrain.
• A lava tube is an opening under the Earth's surface that is formed by molten material that has flowed, in some cases a great distance from the source.
• Flood basalt refers to the production of a low-viscosity lava that can flow up to 90 miles from the eruption.

Volcanic Hazards

• Blocks are broken fragments of solid rocks; bombs are ejected as magma lumps.
• Lahars are a volcanic hazard associated with Kilauea.
• Extensive lava flows are a volcanic hazard associated with Kilauea.

Volcano Types

• Shield volcanoes are characterized by gentle slopes and are built from effusive eruptions of fluid lava flows.
• Mauna Loa and Kilauea are classified as shield volcanoes.
• Cinder cones are the smallest and are built from ejected lava fragments which form a relatively steep slope.
• Stratavolcanoes are characterized by violent/explosive eruption styles.

Volcanic Examples

• Crater Lake was produced when the summit of a volcano collapsed.
• Mount St. Helens and Mount Rainier are examples of stratavolcanoes.
• Vesuvius is an example of a stratavolcano that erupted in 79 A.D., resulting in ash and pumice completely covering the town of Pompeii.

Volcanic Features

• A crater is a steep-walled depression located at the summit of a volcano.
• A batholith is a massive and discordant body of intrusive, igneous rock.

Magma Characteristics

• A magma's viscosity is directly related to its silica content.
• Magma with higher silica content has a higher viscosity.

Volcanic Eruptions

• The term "pyroclastic material" is given to any material that is ejected into the atmosphere during a volcanic eruption.
• Nuee ardente is a dangerous, fast-moving, hot, turbulent cloud of volcanic gases and fine-sized pyroclastic particles that precedes an explosive eruption.
• Lahar is a destructive volcanic mudflow.

Igneous Plutons

• Igneous plutons are classified based on their shape and relation to the host rock.
• If an igneous pluton cuts across existing rock units or structures, it is termed discordant.

Volcanic Rocks and Landforms

• Basaltic magma is the most abundant type of magma erupted at oceanic spreading centers.
• Basaltic lava flows that resemble twisted braids of rope are termed pahoehoe flows.
• These lava flows develop due to their high temperatures or as cooler lava flows begin to move over steeply sloped terrain.
• A lava tube is an opening under the Earth's surface that is formed by molten material that has flowed, in some cases a great distance from the source.
• Flood basalt refers to the production of a low-viscosity lava that can flow up to 90 miles from the eruption.

Volcanic Hazards

• Blocks are broken fragments of solid rocks; bombs are ejected as magma lumps.
• Lahars are a volcanic hazard associated with Kilauea.
• Extensive lava flows are a volcanic hazard associated with Kilauea.

Volcano Types

• Shield volcanoes are characterized by gentle slopes and are built from effusive eruptions of fluid lava flows.
• Mauna Loa and Kilauea are classified as shield volcanoes.
• Cinder cones are the smallest and are built from ejected lava fragments which form a relatively steep slope.
• Stratavolcanoes are characterized by violent/explosive eruption styles.

Volcanic Examples

• Crater Lake was produced when the summit of a volcano collapsed.
• Mount St. Helens and Mount Rainier are examples of stratavolcanoes.
• Vesuvius is an example of a stratavolcano that erupted in 79 A.D., resulting in ash and pumice completely covering the town of Pompeii.

Volcanic Features

• A crater is a steep-walled depression located at the summit of a volcano.
• A batholith is a massive and discordant body of intrusive, igneous rock.

Volcanic Gases

• Water vapor and carbon dioxide are the most abundant gases emitted during basaltic volcanism.
• Water vapor is the most abundant gas associated with volcanic activity.

Magma Types

• Basaltic magma is the most abundant type erupted at oceanic spreading centers.
• High viscosity and dissolved gas content increase the explosive potential of a magma body beneath a volcano.

Volcano Types

• Shield volcanoes are large, gently sloping mounds composed mainly of basaltic lava flows.
• Composite cones are known for their violent eruptions of gaseous-rich, intermediate magma.
• Cinder cones are small, steep-sided volcanoes built from ejected lava fragments.
• Stratavolcanoes are characterized by both explosive and quiet eruption styles.

Eruptive Activity

• Fissure eruptions feeding lava to flood basalt accumulations are not highly explosive.
• Eruptions of big, continental margin, composite cones or stratovolcanoes are highly explosive.
• Lahars are volcanic mudflows that develop when volcanic debris becomes saturated with water and move rapidly downslope.

Volcanic Landforms

• A caldera is a large depression (> 1 km in diameter) at the summit of a volcano, formed by collapse following a large eruption.
• A crater is a smaller depression (< 1 km in diameter) at the summit of a volcano.
• A dike is a tabular, discordant intrusive structure.

Volcanic Hazards

• Pyroclastic flows are highly destructive and composed of hot gases infused with incandescent ash and larger rock fragments.
• Nuee ardentes are hot, fast-moving clouds of ash, gas, and rock that flow down the sides of a volcano.
• Lahars are dangerous due to their rapid movement and ability to cause widespread destruction.

Volcanic Regions

• The Ring of Fire is a region of high volcanic activity around the margins of the Pacific Ocean, characterized by composite cone volcanoes.
• Hot spot volcanoes are located at oceanic hotspots, where mantle plumes rise to the surface.

Magma Viscosity

• Magma viscosity is affected by composition, temperature, and amount of dissolved gases.
• Low viscosity magma flows more readily and easily, resulting in a fluid and passive eruption.
• High viscosity magma is more likely to produce an explosive eruption.

Volcanic Eruptions and Features

• The volcano that erupted in 79 A.D. and covered the town of Pompeii with ash and pumice is Vesuvius.
• Magma injection into fractures produces tabular discordant bodies known as dikes.
• Mauna Loa and Kilauea are classified as shield volcanoes.

Volcanic Gases and Activity

• Water vapor is the most abundant gas associated with volcanic activity.
• Water and carbon dioxide are the most abundant gases emitted during basaltic volcanism.
• A low viscosity magma will flow more readily and easily, resulting in a fluid and passive eruption.

Volcanic Structures and Landforms

• The steep-walled depression at the summit of a volcano is called a crater.
• Spreading center volcanism produces rocks that are basaltic in composition.
• A sill is a tabular and concordant intrusive structure.
• Stratavolcanoes are very steep-sided, very tall mountainous accumulations found on the overriding continental plate.
• Parasitic cones are features that form on the flanks of the main volcanic structure.

Volcanic Terms and Concepts

• Viscosity refers to the relative "thickness" of magma.
• A caldera is a large depression (> 1km in diameter) at the summit of a volcano.
• Fumaroles are eruptive vents that emit only gases.
• Volatility is a term that describes the relative "thickness" of magma.
• A batholith is a massive and discordant body of intrusive, igneous rock.

Types of Volcanoes

• Paricutin is an example of a cinder cone.
• The big Hawaiian volcanoes are situated above a hot spot deep in the mantle.
• Cinder cones are built from ejected lava fragments and form a relatively steep slope.

Other Volcanic Concepts

• Nuee ardent is a term for the dangerous, fast-moving, hot, turbulent cloud of volcanic gases and fine-sized pyroclastic particles that precede an explosive eruption.
• Pyroclastic material is any material that is ejected into the atmosphere during a volcanic eruption.
• Intraplate volcanism occurs when a mantle plume rises from below, as seen in the Yellowstone region.
• The confining pressure, composition of the material, and water content all affect the melting point of rock.

Plate Boundaries

• Diverging plate boundaries are associated with rift valleys, shallow earthquakes, and volcanic activity.
• Convergent plate boundaries are associated with subduction zones.
• New oceanic crust forms at divergent plate boundaries.
• Convergent plate boundaries produce the most and greatest magnitude earthquakes.
• Oceanic crust is neither created nor destroyed along transform fault boundaries.

Plate Tectonics

• The movement of heat from deep in the mantle to the top of the asthenosphere drives the lateral motions of Earth's lithospheric plates.
• New seafloor is generated at divergent plate boundaries.
• Deep ocean trenches are surficial evidence for sinking of oceanic lithosphere into the mantle at a subduction zone.
• Alfred Wegener argued forcefully for continental drift in the early 20th century.

Continental Drift

• Evidence for continental drift includes fossils, fit of the continents, polar wandering, and rock type similarities on different continents.

Volcanoes

• Volcanic island arcs are developed in oceanic-continental convergences.
• Continental volcanic arcs are developed in continental-continental convergences.

Earth's Interior

• The whole-mantle convection model accounts for oceanic material at depths greater than 660 km and illustrates mantle plumes originating from the core-mantle boundary.
• The Earth's core is thought to consist predominantly of iron.

Earthquakes

• The circum-Pacific belt is a region of high earthquake activity.
• The mechanism of elastic rebound is responsible for storing and releasing energy in the form of an earthquake.
• A seismograph records earthquake events.
• Tsunamis are ocean waves generated by earthquakes.
• The Richter scale measures the magnitude of an earthquake.
• An increase of one unit of magnitude on the Richter scale equates to about a 10-fold increase in energy.
• P waves are the most rapid type of seismic wave.
• Surface waves are the most destructive type of seismic wave.

Folds and Faults

• Folding occurs in mountain building processes where two oceanic plates converge and one is subducted beneath the other.
• Faulting occurs in response to compressional stress.
• The mechanism of elastic rebound is responsible for storing and releasing energy in the form of an earthquake.

Earth's Surface

• The apparent movement of Earth's magnetic poles over time is referred to as polar wandering.
• The breakup of Pangaea occurred about 200 million years ago.
• The best approximation of the true outer boundary of the continents is the seaward edge of the continental shelf.