earthquakes volcanoes - monadnock … volcanoes effects of plate tectonics. earthquakes earthquake:...
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When plates move, they bump into each other
Depending on the type of plate boundary, different
deformations result
Two special events/formations happen as well:
Earthquakes
Volcanoes
EFFECTS OF PLATE TECTONICS
EARTHQUAKES Earthquake: shaking of the ground that results from
the movement of rock beneath Earth’s surface
Stress on rocks from pushing/pulling changes its
shape/volume of the rock
Types of Stress:
Shearing – causes rocks to slip
Tension – stretches rock
Compression – pushes rocks together
Fault: a break in Earth’s crust where slabs of crust
slip past each other.
Rocks on both sides of a fault can move up or down
or sideways
Usually occur along plate boundaries, where the
forces of plate motion compress, pull or shear the
crust so much that it breaks.
FAULTS
Strike-Slip Faults: where rocks on either side of the fault slip past each other sideways with little up or down motion
Occurs at transform plate boundaries
Ex: San Andreas Fault, California
Normal Faults: a fault at an angle so one block of rock lies above the fault and the other block of rock lies below the fault, caused by tension
Occurs where plates diverge
Hanging wall – half that lies above
Footwall – half that lies below
TYPES OF FAULTS
Reverse Faults: have the same structure as a normal
fault, but the blocks move in the opposite direction
(toward each other)
Produced by compression forces
Ex: produced part of the Appalachian Mountains in the
eastern US
TYPES OF FAULTS
Friction is the force that opposes motion between surfaces
When friction along a fault is low, the rocks pass easily without sticking
When friction along a fault is high, the rocks lock together and do not move.
Energy continues to build until it’s strong enough to overcome friction.
When they jerk free, you get an earthquake
The strength of the quake depends on the amount of energy built up (how much friction there was)
FRICTION ALONG FAULTS
Two things we need to know
when earthquakes happen:
Where they’re located
How “big” they were
MEASURING EARTHQUAKES
Focus – the point beneath the Earth’s surface where
stressed rock breaks
Epicenter – the point on the surface directly above
the focus
Found by measuring the difference between arrival times
of P and S waves.
EARTHQUAKE LOCATION
Earthquakes produce vibrations called waves, which
carry energy as they travel through solid material
Seismic Waves– vibrations that carry the energy of
an earthquake away from the focus, through Earths’
interior, and across the surface
EARTHQUAKE STRENGTH
Primary Waves (P Waves) – first waves to arrive;
compress and expand the ground like an accordion
Move through solids & liquids
Secondary Waves (S Waves) – come after P waves;
vibrate from side to side, as well as up and down,
shaking the ground violently
Cannot move through liquids
Surface Waves – P and S waves that reach the
surface; move more slowly but produce the most
severe ground movements
TYPES OF SEISMIC WAVES
Magnitude: measuring earthquake strength based on
the seismic waves and movement along faults
Three ways to measure:
Mercalli Scale
Richter Scale
Moment Magnitude Scale
MEASURING EARTHQUAKE
MAGNITUDE
Measures intensity (strength of ground motion in a
given place)
Not precise
12 steps describe how quakes affect people,
buildings and land surface
Same quake can have different ratings because it
has different amounts of damage at different
locations
MERCALLI SCALE
Rates the size of seismic waves measured by a
seismograph
Developed in 1930’s and used for about 50 years
Provides accurate measurements for small, nearby
quakes
Does not work well
for large or distant
earthquakes
RICHTER SCALE
More commonly used
today
Rating system that
estimates the total
energy released by an
earthquake
MOMENT MAGNITUDE SCALE
Can be used to rate earthquakes near or far
Does not work well for large or distant earthquakes
Building damage
Liquefaction : earthquake’s shaking causes loose soil
to turn to liquid mud; often causes landslides
Tsunamis: when earthquake jolts ocean floor, this
causes the floor to rise and push water; can form
large waves called tsunamis
DAMAGE DONE BY
EARTHQUAKES
Volcano: a weak spot in the crust where molten
material (magma) comes to the surface
Constructive force (builds land)
Magma: molten mixture of
rock-forming substances,
gases, and water from the
mantle
Lava: magma that reaches
the surface; when cooled,
it forms solid rock
WHAT IS A VOLCANO?
600 active on land, with many more beneath the sea
Form along the boundaries of Earth’s plates
Weak, fractured crust allows magma to reach the surface
Most volcanoes occur along diverging plate
boundaries (mid-ocean ridges) or subduction zones
at the edges of oceans
Some volcanoes form at “hot spots,” far from plate
boundaries
LOCATION OF VOLCANOES
Divergent boundary: plates divide; magma rises
Volcanoes form along the mid-ocean ridge
Rarely, these volcanoes rise above the ocean surface
Iceland
Azores Islands
VOLCANOES @ DIVERGENT
PLATE BOUNDARIES
Convergent boundary: plates collide; oceanic crust melts/returns to mantle; magma rises
Volcanoes form where magma erupts through the surface as lava
Many occur on islands where two oceanic plates collide
Island arc: a string of volcanoes that form islands at converging oceanic crusts Japan
New Zealand
Caribbean
Philippines
Indonesia
VOLCANOES @ CONVERGENT
PLATE BOUNDARIES
Hot Spot: an area where magma from deep in the mantle melts through the crust like a blow torch
Often lie in the middle of plates, far from edges
Not a result of subduction (crust sinking/melting/rising)
Hot spots can produce a series of volcanic mountains as the plate drifts over the hot spot
Hawaii
Yellowstone National Park
HOT SPOT VOLCANOES
Magma is formed in the asthenosphere, where the
rock becomes liquid
Magma rises because it is less dense than the
surrounding solid rock
During a volcanic eruption, the gases dissolved in the
magma rush out, carrying magma with them
VOLCANIC ACTIVITY
Magma Chamber: the pocket of magma beneath a volcano
Pipe: a long tube in the ground that connects the magma chamber to Earth’s surface
Vent: an opening in the volcano through which gases leave
Lava Flow: the area covered by lava as it pours out of a vent
Crater: a bowl-shaped area that may form at the top of a volcano around the central vent
INSIDE A VOLCANO
TYPES OF VOLCANIC
ERUPTIONS The silica content of magma determines whether the
volcanic eruption is quiet or explosive
Quiet Eruptions: magma flows easily and relatively
constantly
Explosive Eruptions: trapped gases build up pressure
and explode
QUIET ERUPTIONS
The most common type of volcanic activity on Earth
Runny lava oozes from vent quietly and builds land
over thousands of years
Ex: Mount Kilauea, Hawaii
Produce two different types of lava:
Pahoehoe – fast moving, hot lava; looks like wrinkles
Aa – slow moving; forms a rough surface with jagged
chunks
EXPLOSIVE ERUPTIONS
Thick sticky magma clogs up the volcano pipe like a
cork in a bottle
Trapped gases build pressure until they explode into
fragments of lava
Volcanic ash – fine rocky particles
Cinders – pebble-sized particles
Bombs – larger particles of lava from
baseball to car-sized
Pyroclastic Flow: occurs when an explosive eruption
hurls out ash, cinders, bombs, and gases
LANDFORMS FROM LAVA &
ASH Shield Volcanoes – wide, gently sloping mountain
made up of thin layers of lava that pour out and
harden on top of previous layers
Cinder Cone Volcanoes – a steep, cone-shaped
mountain made up of ash, cinders, and bombs piled
up from explosions of thick magma
LANDFORMS FROM LAVA &
ASH Composite Volcanoes – tall, cone-shaped mountains
with alternating layers of lava and ash from
alternating quiet and explosive eruptions
Lava Plateaus – high, level areas of lava that floods
and area and cools