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theory that pieces of Earth's lithosphere, called plates, move about slowly on top of the asthenosphere.
plate tectonics
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3 ideas that support continental drift.
- -N. and S. America outline fits into Western Europe and Africa
- -fossils of same species seperated by oceans
- -distinctive rocks found on Appalachian Mountain chain.
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Who is Alfred Wegener?
he hypothesized that the continents were once joined in a single supercontinent, which then broke into pieces that moved apart.
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What was pangaea?
supercontinent
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the continents move slowly across Earth's surface.
continental drift
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What is the mid-ocean ridge?
chain of underwater mountains that was discovered in the 50's
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What is the Atlantic mid-ocean ridge?
deep valley running the length of its crest
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more dense, oceanic plate
basalt 3.0 g/cm3
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less dense continental plate
granite (2.7 g/cm3)
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where is new oceanic crust created at?
mid-ocean ridges (AKA spreading center, divergent, rift zone)
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Where is old ocean crust destroyed at?
subduction zones
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process in which new oceanic crust is created at mid-ocean ridges as older crust moves away
sea-floor spreading
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oceanic plates sink into the mantle
subduction
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edges of oceanic plates where subduction occurs
subduction zones
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as plates sink through subduction zones, it bends, forming a depression in the ocean floor.
trench
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What two things did the rock samples from each side of the mid-ocean ridges show identical patterns of?
- -magnetic field reversal in rock crystals
- -aging of rock away from ridge
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how often is ocean floor renewed?
about every 200 million years
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how old is the oldest continental rock?
4.3 billion years old
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Why do plates move?
- 1. rock of the asthenosphere is partially melted
- 2. extreme heat from the mantle causes rock in the lower asthenosphere to expand->less dense-> rises
- 3. rising hotter magma pushes older-cooler, more dense magma to sink (convection)
- 4. friction between moving magma and lithosphere causes plates to move slowly.
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if both plates are continental, what happens?
the crust buckles, thickens, and creates a mountain chain.
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what are two convergent boundaries?
- cont. vs cont. (Ex. india vs. Eurasia)
- oceanic vs. cont. (Nazca vs. S. Amer.)
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What is one type of divergent boudary?
Mid-ocean ridge (ex. N. Amer. and S. Amer. vs. Eurasia and African)
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What are two sources of heat causing convection currents?
- -heat from Earth's formation
- -decay of radioactive isotopes inside earth
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What is a divergent boundary?
plates move away from eachother (ex. mid-ocean ridge)
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What is a convergent boundary?
plates come together; collide
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What two plates form the Andes mountains?
Nazca and S. Amer
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What two plates form the Himalayas?
Tibet and India
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What is a transform boundary?
plates slide past each other, moving in opposite directions.
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A movement of Earth's lithosphere that occurs when rocks in the lithosphere suddenly shift, releasing sroted energy
earthquake
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energy released during an earthquake is carred by these vibrations
seismic waves
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force that squeezes rock together, stretches or pulls them apart, or puches them in diff. direction
stress
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break in a mass of rock along which movement occurs
fault (ex. san andreas)
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bend in layers of rock
fold
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why do earthquakes occur?
because stress forces have exceeded the strength of rock
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location beneath Earth's surface where an earthquake begins
focus
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location on Earth's surface directly above the focus
epicenter
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What are P waves?
- (primary waves) longitudinal waves similar to sound waves.
- -compress and expand ground
- -fastest seismic waves
- -travel through solids and liquids
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What are compression waves?
expansion waves (like a "slinky")
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What are S waves?
- (secondary waves) transverse waves, like light and other eletromagnetic radiation
- -cannot travel through liquids.
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What are surface waves?
- waves that develop when seismic waves reach earths surface
- -move more slowly that P waves and S waves
- -produce larger ground movements and greater damage
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What are siesmographs?
detect and record seismic waves
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what are seismograms?
record of an earthquake on a seismograph
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What scale rates earthquakes based on measurements of the times and amplitudes of seismic waves by certain seismographs?
richter scale
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What scale gives a measurement of the amount of energy released by an earthquake?
moment magnitude scale
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What is the largest earthquake?
Mw 9.5, occured in southern chile in 1960
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What scale ranges from 1-12, based on observations of intensity of ground shaking and damage in the areas affected by an earthquake?
Mercalli scale
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What happens when seismic waves interact with boundaries?
either reflected,refracted, or defracted
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How do we know that Earth's core is mostly iron?
P waves travel through it at a speed that matches labratory exper. on iron
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mountain that forms when magma reaches the surface
volcano
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pocket in which magma collects before a volcanic eruption
magma chamber
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Where do mafic eruptions occur at?
divergent rift zones and hot spots(hawaii)
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narrow, vertical channel
pipe
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opening in the ground where magma escapes to the surface
vent
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top of central vent in most volcanoes is a bowl-shaped pit
crater
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The hollow shel that collapses inward, creating a huge depression
caldera
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what are the 3 main factors that determine the viscosity of magma?
temperature, water content, silica content
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What is the magma with high viscosity like? low viscosity?
thick and resists flowing; thin and flows easily
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What is a quiet eruption?
low-silica and hot magma
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four characteristics about mafic magma.
- -lower silica
- -lower gas
- -lava forms darker rocks
- -hotter than felsic magma
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lava that erupts in a stream of low-viscosity lava is called a
lava flow
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Ash, cinders, etc. ejected from a volcano (esp. subduction boundary)
tephra
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three characteristics about felsic magma
- -lava forms lighter rock
- -higher gas
- -erupts at subduction zones
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What is a explosive eruption?
- -high-silica magma
- -lava solidifies into particles that range in size from fine dust and ash, to pebble-sized cinders, to bombs
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region where hot rocks extends deep within the mantle to the surface
hot spot
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quiet eruption of low-viscosity laca produces wide, flat volcano
shield volcano
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eruption that is entirely ash and cinders, result will be a small, steep-sided volcano.
cinder cone volcano
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forms from an explosive eruption that produces a combination of lava and ash
composite volcano
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What are the 3 major locations volcanos occur at?
mid-ocean ridges, subduction zones, and hot spots
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when the outer rock of volcano erodes what does it leave through?
volcanic neck
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largest of all igneous intrusions; form cores of many of Earth's mountain ranges
batholith
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formed when magma sqeezes in cracks parallel to rock layers
sill
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formed when magma enters a crack cutting across layers
dike
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area on opposite side where an earthquake takes place
shadow zone
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