Plate Tectonics, Volcanoes & Earthquakes!

What is Plate Tectonics?

Plate Tectonic Theory= constant slow motion of Earth’s plates b/c of convection currents in the mantle

Plate= pieces of the lithosphere/Earth’s surface-crust

Plates move & change Earth’s surface

PT creates volcanoes, mtn ranges, deep-ocean trenches, mid-ocean ridges, rift valleys & earthquakes

What evidence proves PT Theory?

Proves the

Alfred Wegener (1910) was the 1st to say that Earth’s surface moves

Pangaea= Wegener’s supercontinent; all the continents together as one landmass

He based his idea on 3 facts:1) continents look like they fit

together like puzzle pieces

continents HAD moved, but not HOW

Explains HOW the continents moved and proves Wegener’s Theory

2) fossils of the same organism are found on many different continents that are now far apart

3) evidence of tropical climates in the polar region & vice versa

Wegener’s idea was rejected b/c he only proved that the continents HAD moved, not HOW they moved

He died before his idea was proved (1930)

1960 technological advances led to:

4) Sea-Floor Spreading= magma spreads through cracks in the ocean floor and turns into new rock Creates a mid-ocean ridge=

under H2O mtn range Makes the oceans bigger

and pushes continents apart5) Subduction Zones= oceanic

crust slides UNDER continental crust or another

piece of oceanic crust b/c it is denser

Creates a deep ocean trench= deep under H2O canyon

The plate that sinks melts into magma in the mantle

*plates move slowly! 1-24 cm/yr How do plates interact w/e@ other? (boundaries)

(glued in diagram)Notes UNDER diagram:

Tectonic Plate boundary= the place where tectonic plates touch e@ other

1a: runs down the middle of the Atlantic Ocean-lrgst one!

1b: The Great Rift Valley in E. Africa

2a: Indonesia Islands in the W. Pacific

2b: Cascade Range along the northwest coast of N. America (Mt. St. Helens, Mt. Ranier, Mt. Olympia) & the Andes Mtns on the west of S. America

2c: Himalaya mtn range btwn India & Asia

3: San Andreas Fault in CA!What is a volcano?

Volcano= a weak spot in the crust where magma flows out of a mountain, AKA “Nature’s Fireworks”

Magma= molten/liquid rock INSIDE a volcano

Lava= molten/liquid rock that has been spit OUTSIDE a volcano

How does PT cause volcanoes?

Plates moving makes cracks in the crust where magma can come up

Form @ colliding subduction boundaries & spreading boundaries

What is a Hot Spot volcano?

Hot spot volcano= a volcano in the middle of a plate, NOT on a plate boundary

Hawaii, in the center of the Pacific Plate & Yellowstone National Park, in the center of the NA plate

What is the structure of a

1) Magma chamber= pool of magma @ the bottom of a

volcano? volcano2) Pipe= long tube up the center

of a volcano that connects the chamber to the outside

3) Vent= opening at the top of a volcano where lava comes out

4) Side vent= opening NOT at the top of a volcano; (optional! Can have 0 or several)

5) Crater= bowl shaped area around the top vent

What causes a volcano to erupt?

Gases trapped in the magma expand, creating great pressure which forces magma up & out of the vent

Amt of silica in magma determines the type of eruption:

1) Quiet Eruption= LOW silica magma that is thin & runny & flows like a river

2) Explosive Eruption= HIGH silica magma that is thick & sticky so it plugs up the vent & causes ++++pressure

Pyroclastic flow= thick, heavy, giant clouds of ash, poison gases, cinders & bombs rushing down the volcano killing everything in its path

What landforms are created by volcanoes?

1) shield volcano= quiet erupting volcanoes that create a gently sloping mtn with layer upon layer of runny lava; Hawaii

2) composite volcano= TALL, layers of lava and ash; Mt. Fuji in Japan, Mt.St. Helens in US

3) cinder cone volcano= formed by ash, cinders & bomb piles making steep sided mtns; Mt. Paricutin

4) caldera= huge hole created by the collapse of a volcano; Crater Lake in Oregon

5) volcanic neck= made when magma hardens in the pipe; Ship Rock in New Mexico

6) dike= magma hardens across rock layers; around Ship

Rock7) sill= magma hardens btwn

rock layers; around Ship Rock

8) batholith= formed when magma hardens in the magma chamber to make a HUGE body of rock; Sierra Nevada Mtns in CA

9) lava plateau= FLAT areas of layer upon layer of runny lava; Columbia Plateau USA

10) volcanic soil= very rich & fertile! Excellent for growing plants/crops

11) hot springs= magma heated H2O that collects in a natural pool;

12) geysers= “H2O volcano”! super, magma heated H2O shooting out of the ground; Yellowstone National Park

Video notes:Earth Science: Volcanoes

word “volcano” came from Vulcan, the Roman God of the Forge (blacksmith!)

when magma stops coming into

the magma chamber, the volcano starts to die

Greeks believed when Vulcan was making weapons, the volcano was erupting

Subduction zones volcanoes are the strongest

1511 volcanoes, 500 active, approx 60 eruptions/yr

When rain falls on volcanic ash, it turns to “concrete” (Mt. Vesuvius & Pompeii)

DVD Notes:How Earth Was Made: Ring of Fire!

**Why are Ring of Fire volcanoes and earthquakes so destructive?**

¾ of all volcanoes & 90% of all earthquakes occur on the R of F

Extensive zone of destruction on Earth

25,000 miles around the P. Ocean

75% of all US volcanoes are in Alaska

R of F volcanoes are Strato volcanos

High silica lava is thick, like pnut butter & sticky

High silica lava traps gas and causes massive eruptions & Pyroclastic flows

Hornblende in the magma forms in the presence of H2O which causes rock to melt into magma and rise

megathrust earthquake @ subduction zones due to one plate sliding under the other

Megathrust quakes create tsunamis which are highly destructive!

R of F shape is determined by deep-ocean trenches, not the volcanoes

14 plates on the planet The Earth is NEVER at rest!

What is an earthquake & what causes them?

Earthquake= when the ground shakes so hard, things sometimes fall

Caused by built up rock stress that is released by plate mvmts

Compression, tension &

(diagram)

shearing build up stress in rocks

Rock stress=stored energy! Seismic waves= energy released

during an EQ Fault line= crack/break in the

crust where rocks slip by e@ other creating an EQ

Focus= the point in the lithosphere where an EQ happens—where the rock breaks!

Epicenter= the point on the surface directly above the focus

What type of seismic waves are there?

1) P wave= primary/first waves; moves in & out like an accordion

2) S waves= secondary waves (comes next!); move up,down,side to side; CAN’T move through liquids

3) Surface waves= S & P waves together @ the crust; slower than other waves BUT are the most destructive; move in a combo. of all mvmts

What is a fault & what kinds are there?

Fault= where an EQ happens

1) Normal Fault= tension stress faults (pulling); hanging wall slips down

(diagram)

2) Reverse Fault= “backwards normal fault!” compression stress faults (pushing); hanging wall pushes over the foot wall; can form mtns

(diagram)

3) Strike-slip fault= shearing stress faults (rubbing); both sides of the fault move against e@ other

(diagram)San Andreas Fault!

Video notes Longest recorded EQ was 4 minutes!

1 mil+ EQ daily! EQ’s can NOT be predicted b/c

there are no warning signs

1965 Alaska EQ lrgst in US history

Can’t see most faults b/c they’re underground

What tools & scales do seismologists use to measure & monitor EQ’s?

TOOLS: to MONITOR1) tilt meter 2) creep meter3) laser-ranging devices4) GPS (global positioning

system)

SCALES TO MEASURE:1) Mercalli Scale : from 1 to 12,

ranks the intensity of an EQ & level of damage

2) Richter Scale : measures the magnitude of a seismic wave w/ a seismograph; not good for far away EQ’s, only close ones

3) Moment Magnitude Scale : scale of 1 to 10; measures all aspects of an EQ!

There has never been a 10 EQ in recorded history

Each ranking is 10x bigger than

the ranking b4 it The bigger the #, the bigger the

EQ! Big #’s=more destruction! Most destruction/shaking

occurs close to the epicenterHow do EQ’s cause damage?

Shaking knocks down buildings & schtuff!

Amt of damage depends on: magnitude of the seismic wave, distance from the epicenter & quality of buildings (good quality survives; bad quality collapses)

Aftershocks= weaker/smaller EQ that happens in the SAME spot after a major EQ; the fault settling in to its new spot