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