Transcript 4 Tectonics and Geologic Processes.ppt

In this unit, you will:
• Understand Earth’s major geological
processes and hazards, and how they
shape biological evolution
• Know the forces at work driving the
tectonic plates, causing earthquakes,
and volcanoes
5000°-7000° C
In order to
understand
plate
tectonics, you
must first be
reminded of
the dynamics
of Earth’s
interior.
The Kola Superdeep Borehole drilled in the Kola
Peninsula in Russia is the second deepest hole in the
world, nearly 12,262 meters (7.6 miles) It was drilled
with the intent of reaching the Moho, but as drilling
cost increases with depth, it is unlikely to happen any
time soon!
• Generally, thinner under oceans, thicker under
continents
• Both brittle, and bendable
• Vents form along volcanic hot spots, to allow
interior materials to spill out onto the surface.
• The boundary between the crust and the mantle
is known as the “Moho”. Earthquake waves here
change direction, and move faster.
Rodinia
Evolution slows down…
The mantle can be broken down
Evolution speeds up…
into an upper region which greatly
influences the crust above (the
asthenosphere), and the lower
mantle.
Convection currents within the
mantle are responsible for driving
the tectonic plates.
The Earth’s mantle is important, because it causes the
movement apart, and together of the continents. This has
influenced environments and therefore evolutionary patterns
and processes over the millennia.
The mantle is composed of a non-newtonian fluid, becoming
more and more viscous the closer it gets to the crustal
boundary. It behaves like a fluid when pressure is released,
and a solid when compressed.
https://youtu.be/ryrXAGY1dmE
1. What influence does Earth’s hot interior have on the Planet?
2. Because Earth’s crust can bend and break, what structures
form?
3. Why are volcanoes important in their influence on the
biosphere?
4. What is the Moho, and how do we know where it is?
5. What causes the tectonic plates to move?
6. What are the evolutionary consequences of tectonic
movement?
The important thing to
remember about the Earth’s
core is that it is composed of
two separate parts.
• Fluid outer core
• Solid inner core
The inner core is under such
extreme pressure, that even
though temperatures would
permit the fluidity of iron, it
remains a solid.
The outer core is important for two reasons:
• its temperature and convection influence convective currents within
the mantle, and…
• the inner and outer cores’ differential spinning speeds, and direction
creates the magnetic field protecting the Earth.
7. What area is ultimately responsible for the
convection currents within the mantle?
8. What is the significance of the different spin
velocities (speed and directions) within the
Earth’s core?
9. What is created that helps protect Earth from
solar debris?
About a dozen large plates exist within the crust of the Earth,
and as mentioned earlier, are in constant motion. They ride
upon the convective currents within the upper mantle, known
as the asthenosphere.
They move at about
the same rate as
your fingernails and
hair grow.
Nearly all of the
geologic activity
takesand
place
near or
Volcanoes
Earthquakes
at the boundaries of
This geologically significant area is knownthese
as thetectonic
“Ring of
plates…at
areas
Fire”, and it circumnavigates the Pacific Ocean.
Along
its
called
“hot
spots”
borders are some of the most active areas
on the
planet.
Plates that move together (Destructive boundaries)
Earth’s
tectonic
plate boundaries have three
 Convergent
plates
possible
outcomes…
 Oceanic-Continental
Continental-Continental
• 
They
can move together
 Oceanic-Oceanic
•
• They can spread apart
• They can slide against each other
10. What is a geologic hot spot (not to be confused with an
ecological hot spot)?
11. Where is the “Ring of Fire”, and why is it geologically
significant?
12. A tectonic boundary that moves together, or is destructive, is
known as what?
13. What forms when convergent boundaries exist between
• Oceans and Continents?
• Two continents?
• Two oceanic plates?
• Plates that move apart…Constructive boundaries
 Divergent Plate Boundaries
 When they occur in the ocean…
 When they occur on the continents…
Iceland…where the MidAtlantic Ridge emerges from
the Ocean
East African Rift Valley…will
someday be a sea floor.
Most earthquakes occur at plate boundaries, where two plates
are colliding or grinding up against one another.
• Transform
faults occur when
one plate “slips”
past another
Deep Ocean Assessment and
Reporting of Tsunamis
The
greatestuse
risks
in
We
currently
warning
buoys
The
greatest
risk
of
the
When earthquakes happen on earthquakes is death, due to
to detect seismic ocean waves.
tsunami
is
the
coastal
the ocean floor, huge waves
building
failure
(collapse)
Many
areas
of
the
ocean have
devastation
caused.
called tsunamis may occur.
when they’re not up to code.
none.
14. A tectonic boundary that moves apart, or is constructive is
known as…?
15. What forms along divergent plate boundaries…
• When they occur in the ocean?
• When they occur on continents?
16. While earthquakes can occur along any type of tectonic
boundary, they are most common along…
17. What forms many times when earthquakes occur near to or
beneath the ocean?
18. What is the greatest risk in an earthquake?
19. How do we detect tsunamis?
Similar to earthquakes, volcanoes occur in areas known as
geologic hot spots, typically, where oceanic crust is converging
with continental crust…in areas of subduction.
The most dangerous
result of a volcanic
occurrence is not the
viscous lava, but the
ensuing flood of mud
mixed with ash, and
debris known as a “lahar”.
Very few volcanoes
actually produce lava!!!
Pyroclastic flows are also dangerous.
Again, the “Ring of Fire”, a highly seismically active area that
circumnavigates the Pacific Basin, is beautifully illustrated in
this map.
Some volcanoes do not appear to be located by tectonic
boundaries at all. These special volcanoes are known as “hot
spot volcanoes”. Examples would include oceanic hot spots,
such as the Hawaiian Island chain, and continental hot
spots…such as Yellowstone.
The study of volcanoes by
volcanologists is both interesting, and
important. Volcanoes are thought to
be responsible for Earth’s second
atmosphere, through outgassing.
Where’d all the oxygen come from?
Earth’s modern atmosphere was
thought to have originated through
the process of photosynthesis by
early microbes known as
cyanobacteria.
20. Why are converging subduction zones most often
associated with volcanoes?
21. What two features of most volcanic eruptions put
people most at risk?
22. How are hot spot volcanoes different from simple
convergent/subduction-caused volcanoes?
23. Give two examples of hot-spot volcanoes.
24. Describe how volcanoes contributed to Earth’s early
atmosphere, and where our modern atmosphere came
from.