Sea Floor Spreading & Plate Tectonics Ch. 2 part 2 Slide 2
Objectives 1.The basics of plate tectonics 2.Convergent vs.
divergent boundaries 3.Diagram the geological provinces 4.Active
vs. passive continental margins Slide 3 Sea Floor Spreading Huge
pieces of oceanic crust are separating at the mid ocean ridge Rifts
are created: Cracks in the crust Releases pressure from mantle
Magma pushes up Animation Paper/desk demo with numbers Slide 4
Plate Tectonics What is the general idea behind plate tectonics?
Earths lithoshpere broken into plates Plates all moving in
different directions Slide 5 Plate Tectonics What is the
lithosphere? The crust and top part of mantle Lithospheric plates
float on asthenosphere 100km or 60 mi thick Slide 6 Plate Tectonic
Boundaries Three types Draw them Slide 7 Movement Plates moving in
different directions This is continental drift What happens when
plates separate (we looked at this already) or collide? Slide 8 Sea
Floor Spreading: Divergent Boundaries Ill draw this on board--you
copy Forms mid-ocean ridges Move 2 cm -18 cm per year Fingernails
grow 6 cm year New lithosphere is created What happens to old
lithosphere? Destroyed in trenches Otherwise......earth would be
continually expanding Slide 9 Subduction: Convergent Boundaries
Subduction: Downward movement of lithospheric plate into mantle
Causes earthquakes, volcanoes, and trenches Three types Oceanic
--> Subduction Oceanic-Continental Which plate always descends
into the other? Oceanic --> denser. What does this cause? Slide
11 Oceanic --> Oceanic-->magma forms --> heads towards
surface I draw on board--you copy Slide 13 The Curve Why are
trenches and island arcs curved? Due to the earths spherical shape
Notice Aleutian islands and Mariana trench What do they call this
ring in the Pacific? Slide 14 Aleutian Islands Slide 15 Cleveland
Volcano, Aleutians Slide 16 Mt. Saint Helens Erupts: 1980 Play Mt.
Saint Helens video clip Slide 17 Ring of Fire (Play Ring of Fire
clip) Slide 18 Hot Spots and the HI islands What are hot spots?
(play Hot Spot video clip and Typical Hawaii Eruption clip) When
will Lo'ihi break the surface? Slide 19 Continental--> What
Causes the Motion of Plates? Slab Pull: Lithosphere cools -->
denser Sinks into mantle --> pulls rest of plate with it
Convection (heat from core causing mantle to swirl) was original
hypothesis Slide 33 Satellite View Let's zoom in Slide 34
Continental Drift Slide 35 The continents once united in a
supercontinent called Pangaea about 180 mya. They have since been
moving into their present locations What about before 180 mya?
Slide 36 750 mya to present BBC Interactive Timeline Slide 37 Plate
Tectonics Slide 38 500 million years in the future? If the plates
continue to move in the directions they move today for another 500
million years, propose a configuration of oceans and continents at
the end of that time. Slide 39 Constantly Changing Earth Constantly
changing SST and Sea Level More ice --> lower sea level Last ice
age about 18,000 years ago There will be more on this later in the
year, but here is a quick clip... Slide 40 If the sea level
rises... Slide 41 Geological Provinces Two main regions in the sea
floor: 1.Continental Margin 2.Abyssal plain Slide 42 Continental
Margin 1.Continental Shelf: Submerged; almost flat (400-600 ft)
2.Continental Slope Steep; edge of continent (10,000-16,500 ft)
3.Continental Rise: Formed by sediments building up at base of
slope Slide 43 Deep Sea Fan Sediment accumulating at canyons base
Slide 44 CA Continental Margin (Monterey Bay) Slide 45 Active vs.
Passive Margins Active Margin: Shelf colliding with another plate
Little or no shelf; steep earthquakes, volcanoes Passive Margin:
Trailing edge Little activity Slide 46 Width of margin: East vs.
West coast of South America Slide 47 Hydrothermal vents What are
plates doing at center of ridges? Pulling apart Water seeps down
cracks, heats up, and emerges How hot? Up to 650 F!! Does anything
live down there? Slide 48 Black Smokers Water dissolves many
minerals as it seeps into crust Emerges hot--> rapidly cools and
solidifies Forms a chimney-like structure Show Hydro Vents movie
clip (5 minutes) Slide 49 Question #1 p. 39 How can you tell which
way the plates are moving? Trenches indicate plates colliding
Mid-ocean ridge indicates plates separating Slide 50
