Transcript Earthquakes, Volcanoes & The Ring of Fire

Earthquakes, Volcanoes
& The Ring of Fire
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1. Convection in Earth’s Mantle—heat from
Earth’s core and the mantle itself cause
convection currents in the mantle.
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2.Continental Drift: Wegener’s idea that the
continents slowly moved over Earth’s surface.
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3. Wegener’s hypothesis was that all the
continents had once been joined together
(Pangaea) and has since drifted apart.
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His hypothesis was originally rejected by scientists,
and now it is believed he was correct.
Continental Drift Animation
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He believed this based on
3 types of evidence:
a. Evidence from Landforms
b. Evidence from Fossils
c. Evidence from Climate
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4. Mid-Ocean Ridge—the longest chain of
mountains in the world; curves like the seam of a
baseball along the sea floor, extending into all of
Earth’s oceans.
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Q: How did scientists map the mid-ocean ridge?
sonar
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5. At the mid-ocean ridge, molten material
rises from the mantle and erupts. The
molten material then spreads out, pushing
older rock to both sides of the ridge.
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6. Sea-floor Spreading: the process that
continually adds new material to the ocean
floor
Sea-Floor Spreading Animation
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7. There are 3 types of
evidence of sea-floor
spreading:
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a. molten material near the
mid-ocean ridge had a
strange shape, like pillows,
which can only form when
molten material cools
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b. magnetic stripes
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c. drilling samples from the
ocean floor found that
samples of rocks nearest
the mid-ocean ridge were
younger than the samples
of rock that were farther
away
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8. At deep-ocean trenches, subduction allows part of the
ocean floor to sink back into the mantle.
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9. The Theory of Plate Tectonics —explains the
formation, movement, and subduction of Earth’s plates.
The plates move only one to ten cm per year.
10. Plate Boundaries
(illustrate each of the following)
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a. Transform Boundaries
• c. Convergent Boundaries
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b. Divergent Boundaries
• d. Collisional Boundaries
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11. Plate movement
can alter Earth
systems and
produce changes in
Earth’s surface such
as faulting,
earthquakes,
volcanoes, rift
valleys, mountain
building, trenches
and volcanoes- just
to name a few!
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12. Faults usually
occur along plate
boundaries.
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13. EarthquakesMovement along a
fault releases strain
energy. When this
potential energy is
released, it moves
outward from the
fault in the form of
seismic waves.
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14. The focus of an earthquake is the point
inside Earth where it starts. The epicenter is
the point on Earth’s surface located directly
above the focus. Seismic Waves emanate from
this point.
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15. Most earthquakes occur in well-known
belts. About 80% of them occur in the Pacific
Ring of Fire- the same belt in which many of
Earth’s volcanoes form.
Focus, Epicenter Animation
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16. When plates collide, rather than being
subducted, the plates pile into each other, causing
one or both plates to fold up like an accordion. This
process elevates the crust, folds and deforms it
heavily, and produces a mountain range.
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17. Folding and
faulting that is
driven by plate
movement results
in mountain
building.
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18. Rift Valleys
occur along
divergent
boundaries where
the plates separate
or are moving away
from one another.
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19. Land Subsidence
occurs when the land
surface sinks as a result
of geologic processes or
human activities.
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20. Trenches are deep,
linear, relatively narrow
depressions in the sea
floor, formed by the
subduction of oceanic
plates (where one plate
slides beneath the
other).
 21.
Most volcanoes occur along
diverging plate boundaries; most are
along the edge of the continents.
Plate Boundaries
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22. Volcanoes form
2 ways:
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a. One way is when
two oceanic plates
collide. This can
produce a string of
volcanic islands like
the Caribbean
Islands.
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b. The second way volcanoes can form is when an
oceanic plate collides with a continental plate.
The older and denser oceanic plate subducts, or
sinks below the less dense plate. Rock in and
above the sinking plate melts, forming chambers
of magma that erupt.