Ch. 6 VolcanoesCh. 6 Volcanoes

VolcanoesVolcanoes

A volcano is a weak spot in the crust where magma comes to the surface

Magma is molten rock, gases, and water from the mantle

Magma becomes lava when it comes to the surface

Lava cools to become igneous rock

A volcano is a weak spot in the crust where magma comes to the surface

Magma is molten rock, gases, and water from the mantle

Magma becomes lava when it comes to the surface

Lava cools to become igneous rock

Types of RockTypes of Rock

Igneous- molten material, such as lava or magma, cools and hardensSlow cooling- large crystals (granite)Fast cooling- small crystals (basalt)

Metamorphic- great heat and pressure changes minerals or other rockHeat and pressure increases inside

the Earth

Igneous- molten material, such as lava or magma, cools and hardensSlow cooling- large crystals (granite)Fast cooling- small crystals (basalt)

Metamorphic- great heat and pressure changes minerals or other rockHeat and pressure increases inside

the Earth

Types of RockTypes of Rock

Sedimentary- sediment squeezed and glued togetherSediment- small pieces of rock or

fossils that have been broken down by erosion or weathering

Sedimentary- sediment squeezed and glued togetherSediment- small pieces of rock or

fossils that have been broken down by erosion or weathering

The Rock CycleThe Rock Cycle

The rock cycle slowly builds, destroys, and changes rock

Continuous and many pathways

The rock cycle slowly builds, destroys, and changes rock

Continuous and many pathways

The Rock CycleThe Rock Cycle

Volcanoes and Plate Tectonics

Volcanoes and Plate Tectonics

Volcanic belts are found at plate boundaries, such as the Ring of Fire around the Pacific Plate

Volcanic belts are found at plate boundaries, such as the Ring of Fire around the Pacific Plate

Volcanoes and Plate Tectonics

Volcanoes and Plate Tectonics

Divergent boundaries- magma comes out of rift valleys to build mountains

Convergent boundaries Oceanic plate sinksRock on top melts and becomes magmaMagma erupts and becomes lava

Divergent boundaries- magma comes out of rift valleys to build mountains

Convergent boundaries Oceanic plate sinksRock on top melts and becomes magmaMagma erupts and becomes lava

Volcanoes at Plate Boundaries

Volcanoes at Plate Boundaries

Hot SpotsHot Spots

Hot spots- volcanoes that form when magma erupts through crust to get to the surfaceHawaiiYellowstone National Park

Hot spots- volcanoes that form when magma erupts through crust to get to the surfaceHawaiiYellowstone National Park

Parts of a VolcanoParts of a Volcano

Magma chamber-collects magma

Pipe- tube that connects magma chamber to surface

Vent- opening on the Earth’s crust

Magma chamber-collects magma

Pipe- tube that connects magma chamber to surface

Vent- opening on the Earth’s crust

Parts of a VolcanoParts of a Volcano

Lava flow- area covered by lava

Crater- bowl-shaped area around a volcano’s central vent

Caldera- large circular depression formed when magma chamber empties and the roof collapses

Lava flow- area covered by lava

Crater- bowl-shaped area around a volcano’s central vent

Caldera- large circular depression formed when magma chamber empties and the roof collapses

EruptionsEruptions

Pressure and gases force magma out of a volcano

Silica makes magma thick and stickyTypes of eruptions

Quiet eruptions- lava oozes to surfaceThin, runny lava that is low in silicaHawaiian IslandsExamples are pahoehoe and aa

Pressure and gases force magma out of a volcano

Silica makes magma thick and stickyTypes of eruptions

Quiet eruptions- lava oozes to surfaceThin, runny lava that is low in silicaHawaiian IslandsExamples are pahoehoe and aa

EruptionsEruptions

Types of eruptionsExplosive eruptions- thick and sticky

lava which traps waterWater makes eruptions more explosive

Produces pyroclastic materialMagma that erupts as fragments of molten

material and solidifies in the airPieces of volcano that breaks off

Mt. St. Helens in 1980

Types of eruptionsExplosive eruptions- thick and sticky

lava which traps waterWater makes eruptions more explosive

Produces pyroclastic materialMagma that erupts as fragments of molten

material and solidifies in the airPieces of volcano that breaks off

Mt. St. Helens in 1980

Life CycleLife CycleGeologists determine how likely a

volcano will erupt againStages

Active- erupting or will erupt in the near futureMt. Shasta and Lassen Peak

Dormant- “sleeping,” but can become active againLong Valley in eastern Sierras

Extinct- unlikely to erupt againDiamond Head in Honolulu

Geologists determine how likely a volcano will erupt again

StagesActive- erupting or will erupt in the near

futureMt. Shasta and Lassen Peak

Dormant- “sleeping,” but can become active againLong Valley in eastern Sierras

Extinct- unlikely to erupt againDiamond Head in Honolulu

Volcanic LandformsVolcanic Landforms

Made of lava, ash, and other materials

Types of VolcanoesShield Volcano- made from

nonexplosive eruptionsLow in silicaWide with gentle slopes

Cinder Cone- made from explosive eruptionsHigh in silicaSteep, cone-shaped, found in clusters

Made of lava, ash, and other materials

Types of VolcanoesShield Volcano- made from

nonexplosive eruptionsLow in silicaWide with gentle slopes

Cinder Cone- made from explosive eruptionsHigh in silicaSteep, cone-shaped, found in clusters

Volcanic LandformsVolcanic Landforms

Types of VolcanoesComposite- alternating layers of

pyroclastic material and lava flowAlso known as stratovolcanoMost common

Types of VolcanoesComposite- alternating layers of

pyroclastic material and lava flowAlso known as stratovolcanoMost common

Volcanic LandformsVolcanic Landforms

Lava Plateaus- lava flows out of long cracks called fissuresThin, runny lava flows far before cooling

Lava Plateaus- lava flows out of long cracks called fissuresThin, runny lava flows far before cooling

Shield Volcano- Medicine Lake, CAShield Volcano-

Medicine Lake, CA

Cinder Cone Volcano- Mt. Bromo, IndonesiaCinder Cone Volcano- Mt. Bromo, Indonesia

Composite Volcano- Mt. Shasta, CA

Composite Volcano- Mt. Shasta, CA

Lava Plateau- Modoc Plateau, CA

Lava Plateau- Modoc Plateau, CA

Magma LandformsMagma Landforms

Formed when magma goes into cracks, but does not come to surface

Magma cools undergroundErosion exposes harden magma

Formed when magma goes into cracks, but does not come to surface

Magma cools undergroundErosion exposes harden magma

Magma LandformsMagma Landforms

TypesVolcanic Necks- magma hardens in pipeDikes and sills- magma cools between

rock layersIgneous intrusionsSill are horizontalDikes cross rock layers

Batholiths- massive rock forms when large body of magma cools

TypesVolcanic Necks- magma hardens in pipeDikes and sills- magma cools between

rock layersIgneous intrusionsSill are horizontalDikes cross rock layers

Batholiths- massive rock forms when large body of magma cools

Magma LandformsMagma Landforms