Chapter 7
Volcano: a weak spot in the crust where molten material or magma comes to the surface
Magma: a molten mixture of rock forming substances, gases and H 2 O from the mantle
Volcanic Belts: Form along the Earth s plate boundaries The boundaries Converge or Diverge
Divergent Boundary: Plates move apart Ex: Sea Floor Spreading Rift Valley Lava pours out and volcano formed
Convergent Boundary: plates collide Subduction at trenches
The Crust breaks and magma can reach the surface The denser plate is subducting and melts to form magma The magma rises and breaks through the crust to form volcanoes
Ring of Fire: major volcanic belt Formed by many volcanoes that rim the Pacific Ocean
Island Arc: string of islands created by volcanoes Follow the curve of the Trench Examples Japan New Zealand Aleutian Islands Caribbean Islands
Hot Spots: An area where deep inside the mantle material rises and melts to form magma Volcanoes form above a hotspot when magma erupts through the crust and reaches the surface.
Hot spots are Found Near plate boundaries In the middle of plates Under the continents Ex: old faithful in Yellowstone national park
General Properties Element: substance that cannot be broken down into another substance
Compound: substance made of 2 or more elements
Physical Property: any characteristic of a substance that can be observed or measured without changing the composition of the substance Examples: Hardness and melting point
Chemical Property: any property that produces a change in the chemical composition of the matter. Examples: Ability to burn
Viscosity: the resistance of a liquid to flow
Depends on the silica content More silica: Higher viscosity When lava cools it form rock rhyolite which is like granite Less Silica: Lower viscosity Flows fast, lava cools to form Basalt
Depends on temperature Hot magma flows quickly Cool magma flows slowly
Temperature difference produces 2 kinds of lava
Pahoehoe- fast, hot lava Low viscosity Looks like: wrinkles or coils of rope
Aa: slow, cooler lava High viscosity Looks: rough: jagged chunks
Pele s Hair: type of rock formed by hardened lava sprays
Magma collects in the magma chamber Magma then rises upward to the vent
Pipe: a long tube in the ground that connects the magma chamber to the surface of the Earth. Lava Flow: an area covered by lava as it flows out of a side vent Crater: a bowl shaped area that may form at the top of the volcano around the central vent
How it erupts: Gases that are dissolved in the magma expand as the magma goes up the pipe pushing it upwards until it reaches the top
Two kinds of volcanic Eruptions Quiet Eruptions Low viscosity magma Bubbles out of vents Can produce both kinds of lava Ex: Kilauea
Explosive Eruptions High Viscosity magma
Lava breaks into fragments and cools quickly Lava hardens into different sizes Small: Volcanic Ash Fine rocky
Medium: Cinders Pebble Large: Bombs Larger (baseball)
Pyroclastic Flow: occurs during an eruption when hot gases, ash, cinders and bombs are expelled
Obsidian: rock from lava that has cooled rapidly Glossy Texture Pumice: forms when gas bubbles get trapped in fast cooling lava
Burning: quiet eruption can cover a large area Clouds of deadly gas Cinders Bombs
Ash: can burn entire towns Roofs collapse Jet planes stall Avalanche, landslides and mud flows
Active Volcano: a volcano that is erupting or shows signs of erupting soon
Dormant Volcano: a sleeping volcano It can awaken in the future
Extinct Volcano: a volcano that is unlikely to erupt again
Different instruments are used to measure The temperature of ground H 2 O Earthquakes around the volcano Gases escaping
Shield Volcano Quiet Eruptions Gentle, sloping mountain Ex: Hawaiian islands are shield volcanoes that arise from hot spots
Cinder Cone Volcano Cinder, Ash & Bombs erupt Explosively forms cone shaped hill
Composite Volcano Alternate quiet and explosive eruptions Tall cone shaped mountains
Lava Plateau Lava flows out of cracks Thin, runny lava Ex: Columbian Plateau in Washington, Oregon, & Idaho
Calderas Not the same as crater This is a huge hole left by the collapse of a volcanic mountain
Soil is Very Fertile Contains potassium, phosphorus, and other substances
Sometimes magma breaks through cracks in the upper crust but does not reach the surface
Five different kinds Volcanic Necks: magma hardens in the pipe
Dikes: magma hardens across rock layers
Sills: magma hardens between horizontal layers of rock
Batholith: large amount of magma cools in the crust
Domed Mountain: magma forces the layers of rock to bend upward
Magma that is only a few kilometers beneath the surface heats the ground water
Occurs in an area of present or past volcanic activity Hot springs Geysers