Sea Floor Spreading & Plate Tectonics Ch. 2 part 2

Objectives 1.The basics of plate tectonics 2.Convergent vs. divergent boundaries 3.Diagram the geological provinces 4.Active vs. passive continental margins

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

Plate Tectonics What is the general idea behind plate tectonics? – Earth’s lithoshpere broken into plates – Plates all moving in different directions

Plate Tectonics What is the lithosphere? – The crust and top part of mantle – Lithospheric plates float on asthenosphere 100km or 60 mi thick

Plate Tectonic Boundaries Three types Draw them

Movement Plates moving in different directions This is continental drift What happens when plates separate (we looked at this already) or collide?

Sea Floor Spreading: Divergent Boundaries I’ll 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

Subduction: Convergent Boundaries Subduction: – Downward movement of lithospheric plate into mantle – Causes earthquakes, volcanoes, and trenches Three types – Oceanic --> <-- Oceanic – Oceanic --> <-- Continental – Continental --> <-- Continental Animations

Subduction Oceanic-Continental Which plate always descends into the other? Oceanic --> denser. What does this cause?

Oceanic --> <--Continental I’ll draw on board---you copy Trenches volcanoes Mountain ranges

Oceanic--> <--Oceanic Trenches Volcanoes Forms island arcs: – Curved chain of volcanic islands along a trench – Examples: Aleutian and Mariana Islands Older, colder plate becomes denser than underlying hot, weak asthenopshere. Upper sediments become melted --> magma forms --> heads towards surface I draw on board--you copy

The Curve Why are trenches and island arcs curved? – Due to the earth’s spherical shape – Notice Aleutian islands and Mariana trench What do they call this “ring” in the Pacific?

Aleutian Islands

Cleveland Volcano, Aleutians

Mt. Saint Helens Erupts: 1980 Play Mt. Saint Helens video clip

Ring of Fire (Play Ring of Fire clip)

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?

Continental--> <-- Continental I draw on board---you copy No subduction Continental plates light, resist downward motion Rocks buckle and fold and are “welded” together Mountain range formed What example is in this picture? The Himalayas

Himalayas from space

Himalayan Collision

Transform or Shear Boundary Draw diagram below Plates slide past each other What is a classic, local example of this?

Quiz a partner What are the three types of plate tectonic boundaries? Give examples of each and the result of each – Convergent Oceanic-oceanic (trenches, volcanoes, earthquakes & island arcs) Oceanic-continental (trenches, volcanoes, mt. ranges) continent-continent (earthquakes, mountain ranges) – Divergent Sea floor spreading  forms mid ocean ridges – transform earthquakes

Plate Overview Vid Clip

Fault lines in the Bay Area Yes, there is more than just one...

San Andreas Fault Map and Pic of 1906 quake

1906 Quake

Quake of 1989

Hayward Fault Let’s look at this fault through Google Earth (in demo section—stop at UCB football stadium) Covers some of the densest urban terrain in CA Article on Hayward Fault

Formation of a New Ocean in Africa? 3 plates pulling apart from each other at the Afar Triangle (shaded part) – Arabian plate and two parts of the African plate (splitting along East African Rift Zone) – Rift: 36 mi long, 26 ft wide Red triangles are volcanoes More on Ethiopia's Afar region More on Ethiopia's Afar region

Afar Triangle video clip

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

Satellite View Let's zoom in

Continental Drift

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?

750 mya to present BBC Interactive Timeline

Plate Tectonics

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.

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...

If the sea level rises...

Geological Provinces Two main regions in the sea floor: 1.Continental Margin 2.Abyssal plain

Continental Margin 1.Continental Shelf: Submerged; almost flat ( 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

Deep Sea Fan Sediment accumulating at canyon’s base

CA Continental Margin (Monterey Bay)

Active vs. Passive Margins Active Margin: – Shelf colliding with another plate – Little or no shelf; steep – earthquakes, volcanoes Passive Margin: – Trailing edge – Little activity

Width of margin: East vs. West coast of South America

Hydrothermal vents What are plates doing at center of ridges? – Pulling apart Water seeps down cracks, heats up, and emerges How hot? – Up to 650º F!! Does anything live down there?

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)

Question #1 p. 39 How can you tell which way the plates are moving? Trenches indicate plates colliding Mid-ocean ridge indicates plates separating