Download Chapter 17 Notes Know the definition of each of these vocabulary

Chapter 17 Notes
Know the definition of each of these vocabulary words and be able to differentiate the boundaries:
Pangaea:
Magnetometer:
Paleomagnetism:
Magnetic Reversal:
Isochron:
Rift Valley:
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Seafloor Spreading:
Theory of Plate Tectonics:
Divergent Boundary:
Convergent Boundary:
Transform Boundary:
Subduction
Early mapmakers noticed the apparent fit of continents on either side of the Atlantic Ocean.
In late 1800’s Eduard Suess hypothesized that the present southern continents had once been joined as a single
landmass that he called Gondwanaland.
In early 1900’s Alfred Wegener came up with the idea of continental drift which proposed the Earth’s
continents had once been joined as a single landmass. He called this supercontinent Pangaea which means “all
the earth.” He collected rock, fossil, and climatic data to support his hypothesis. Evidence included coal
deposits in Antarctica which would indicate that Antarctica was once closer to the Equator as coal is formed in
warm swampy areas. Additional support is the discovery of glacial deposits in Africa, India, South America, and
Australia which would indicate that they were once located near the South Pole. Most scientists during this time
rejected Wegener’s hypothesis since he could not explain what was causing the continents to move and what
force could move such large masses of rocks such distances.
During World War II sonar was used to uncover submarines. Vast underwater mountain chains called ocean
ridges were also discovered. They also discovered deep sea trenches which are narrow elongated depressions in
the seafloor with very steep sides. The deepest trench is in the Pacific Ocean which is called the Mariana Trench
which is about 7 miles deep.
The ages of the rocks on the seafloor vary in ages in different places. The age increases with distance from the
oceanic ridge. The oldest rocks on the seafloor were found to be only 180 million years old which is younger
than the continental rocks. The thickness of the seafloor sediment increases with distance from the oceanic
ridge.
Rocks containing iron-bearing minerals provide a record of Earth’s magnetic field. Basalt is rich in iron. As
magma cools, the iron minerals become parallel to the Earth’s magnetic field. When the lava hardens it is a
permanent record of the earth’s magnetic field direction. This has changed numerous times over geological
time. This is called magnetic reversal. When a magnetometer records a higher than normal reading, this would
indicate normal polarity (+). When it shows a lower than normal reading it would indicate reverse polarity (-).
Harry Hess proposed the theory of seafloor spreading which states that new ocean crust in formed at ocean
ridges and destroyed at deep sea trenches. This was the missing link needed by Wegener to complete his model
for continental drift.
There are a dozen or so major plates and several smaller plates. Tectonic plates move in different directions and
different rates over the Earth’s surface. Tectonic plates interact at places called plate boundaries. There are
three types of boundaries, convergent, divergent, and transform boundaries. Most divergent boundaries are
found on the seafloor where they form ocean ridges. The formation of new ocean crust at most divergent
boundaries accounts for the high heat flow, volcanism, and earthquakes associated with these boundaries.
Some divergent boundaries form on continents. When continental crusts separate the stretched crust forms a
long narrow depression called a rift valley.
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When an oceanic crust and another oceanic crust form a convergent boundary, one of the two plates subducts
below the other plate which creates a deep sea trench. The subducted plate descends into the mantle and
melts back into magma. Some of this is forced back up and creates a volcano. Subduction also occurs when a
continental crust converges with an oceanic crust. The denser oceanic plate subducts and produces a trench
and volcanic arc. The last type is a continental to continental convergence which uplifts to form a mountain
range.
Convection currents in the mantle are the driving force of plate tectonics along with the aid of ridge push and
slab pull which assist in moving the plates.
At transform boundaries the crust is deformed or fractured along faults to form earthquakes.
Chapter 18 Notes
Know the definition of each of these vocabulary words and be able to label them on a drawing.
Viscosity:
Pluton
Caldera
Tephra
Hot Spot
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Crater
Pyroclastic Flow
Shield Volcano
Composite Volcano
Vent
All volcanoes are fueled by magma deep beneath the Earth’s surface which is a mixture of molten rock, mineral
grains, and dissolved gases. Magma forms when temperatures are high enough to melt the rocks involved.
Temperature increases with depth beneath the surface. The factors that affect the formation of magma are
temperature, source material, water, and pressure. Water lowers the melting temperature of a rock.
There are three types of magma: basaltic which rises rapidly to the surface and has low viscosity and higher
temperatures. It creates a mild eruption. Andesitic magma is found along the continental margins where
oceanic crust is subducted. It has 60% silica which is a medium viscosity and medium eruptions. Rhyolitic
magma has high viscosity which slows the flow. Along with the large trapped volume of gases, it is a very
explosive magma.
The hotter the magma, the lower the viscosity, and the faster the lava flow. The amount of silica increases the
viscosity.
Magma because it is molten is less dense than the surrounding rocks enabling it to move upward and intrude
the overlying crust. These intrusive igneous rock bodies are called plutons. When crystals cool fast they become
fine grained and when they cool slowly they become course grained.
Shield volcanoes have gently slopes with basaltic magma which has the hottest temperature. Shield volcanoes
are the largest. They are not extremely explosive. Hawaiian Islands
Cinder-Cone Volcanoes form when material that is ejected high into the air falls back to Earth and piles up
around the vent. They have steep sides and are generally small.
Composite/stratovolcanoes are much larger than cinder-cone volcanoes with steep sides and very explosive. Mt.
St. Helens is an example of a composite/stratovolcanoes
Rock fragments thrown into the air during a volcanic eruption are call tephra. They are classified by size. The
smallest tephra is dust. Some of the larger tephra which are angular are called volcanic blocks and when they
are rounded they are called volcanic bombs. Lapilli are small stones thrown out as tephra
The Hawaiian Islands are samples of volcanoes created from a hot spot.
Chapter 19 Notes
Know the definition of these words:
Epicenter
Focus
Fault
Primary Wave
Secondary Wave
Surface Wave
Tsunami
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Seismometer
Seismogram
magnitude
Richter Scale
Seismic gap
Modified Mercalli Scale
There are three types of stress, compression, tension, and shear.
Compression is when an item is pushed together making the volume decrease. A compression earthquake
would be a reverse fault. Tension is when an item is pulled apart making the volume increase. A tension
earthquake would be a normal fault. Shear causes a material to twist or deform which results in a strike – slip
fault similar to San Andreas Fault
When stress exceeds a certain value, a material undergoes ductile deformation. Unlike elastic strain, this type
produces permanent deformation which means that the material stays deformed even if the stress is reduced to
zero. When stress exceeds the strength of a material, the material breaks or fails.
Be able to identify, reverse, normal, and strike-slip faults and the stresses that cause them.
P-Waves and S-waves pass through the earth’s interior and surface waves only travel along the earth’s surface.
P-waves reach the seismic center first and can travel through solid, liquid, and move in the direction of the
energy. S-waves can only travel through solids so the disappearance of the S-waves has allowed seismologists to
reason that Earth’s outer core must be liquid. S-waves move perpendicular to the energy creating an S-wave.
Surface waves do the greatest damage and can move in any direction. To find the epicenter, you need at least 3
seismic centers data calculating the time between the P and S waves.
Most earthquakes are caused by movements along the faults. Some are generated with volcanoes and also
some can activate a volcano.
The Richter scale is based on the size of the largest seismic wave generated by the quake. Each successive
number in the scale represents an increase in seismic wave size or amplitude of a factor of 10. The difference in
the amount of energy released by earthquakes is even greater than the differences between the amplitudes of
their waves. Each increase in magnitude corresponds to about a 32 fold increase in seismic energy.
The Mercalli scale rates the type of damage/intensity using roman numerals from 1 to 12.
Earthquake intensity/damage depends primarily on the amplitude of the surface waves generated. Surface
waves like body waves gradually decrease in size with increasing distance from the focus.
The depth of the focus also has to do with the intensity of an earthquake. A deep focus produces weaker
vibrations than a shallow focus.
Soil liquidification can cause landslides which can cause buildings to sink or fall over.
Tsunamis are generated by the vertical displacement of the seafloor that results from an earthquake.
Earthquake recurrence rates, seismic gaps, and strain-accumulation rates are some of the factors considered in
earthquake probability studies.
You should get away from exterior walls, get under a desk, protect your head in the case of an earthquake.
Earthquake proof buildings use cross-bracing, reinforced walls, wider base structures, & shock absorbers.