Plate Tectonics, Earthquakes, VolcanoesPlate Tectonics, Earthquakes, Volcanoes

--A theory that says the Earth’s lithosphere (Remember what that is?...hint: think crust)is divided into solid sections of rock called“plates.” These plates move in relation to oneAnother. Tectonics are the forces that cause the Earth’s crust to continually move and createnew landforms such as mountains, mid-oceanridges, trenches, or faults.

Plate tectonics incorporates the idea of “Continental Drift”----this was first proposed by a scientist, Alfred Wegener in 1915.

He noticed that the continents appeared to fittogether like pieces of a giant jig saw puzzle, which led him to propose that the continents were once connected together as a giant land mass (Pangaea).

Wegener, 1880-1930

Evidence for Plate Motion:Similar rock types & fossils found along the

eastern coast of South America match those along the western coast of Africa

Mountain chains appear to be continuous (Appalachians)—once connected.

Rock & Fossil Evidence:Similar rocks and fossils found on opposite continents

Ancient climates weredifferent than today

--Glacial deposits in tropical regions--Coal deposits in the Arctic

Rocks of the ocean basins are MUCH younger than continental rocks—youngestrocks are located at mid-ocean ridges

1. Igneous Ocean RocksIgneous rock of the mid-ocean ridges are younger than the igneous rock farther from the ridges

Evidence for Sea Floor Spreading:

2. Reversal of Magnetic PolarityOver thousands of years, the magneticpoles of Earth reverse their polarities.This is recorded in the rocks of the ocean floor.

N

S

1. ConvergentOcean-Continental

Collision

2. Divergent

3. Transform

Find 1 example of each plate boundary typeon page 5 of your ESRT!

Mantle Convection Cells:A stream of heated material moving due to

differences in density.Evidence suggests convection cells exist within

the asthenosphere. (See ESRT page 10 for arrowsindicating convection movement under crust)

Heat left over from the formation of Earth PLUS heat generated by radioactive decay

Hot spots are places on Earth’s surface with high heat flow rising upward--Usually occur along active plate margins--Caused by plumes of magma rising up from the mantle---produce active volcanism

Hawaiian islands Produced as the Pacific plate passes over a hot spot..the only active volcano is the one directly over the hot spot.

The Hawaiian islands have moved Northwest over time.

1. Shield VolcanoNon-explosive eruptions, gentle slopes, basaltic

lava flows (low in silica)

Example: Hawaiian volcanoes

2. Composite volcanoRepeated pattern of explosive & non-explosive

eruptions. Moderate slope; built from alternating layersof lava & tephra

Example: Mt. St. Helens

3. Cinder Cone volcanoExplosive eruptions. Built from tephra (lava

blasted into the air then solidifies as it falls)Steep slope

Example:Mt. Paricutin, Mexico

EARTHQUAKE:- Any vibrating, shaking or rapid motion of the earth’s crust.- Most occur when stress builds along a zone of weakness or break in the rock known as a FAULT.FOCUS: The earthquake’s point of

origin

EPICENTER:- The location at the earth’s surface, directly above the focus.

When an earthquake occurs, seismic waves are generated & move out in all directions from the focus. The waves are detected and registered on instrumentscalled seismographs.

TYPES OF ENERGY WAVES RELEASED BY

EARTHQUAKES1)PRIMARY WAVES: “P-WAVES” -The fastest & first to arrive at a seismographic station

- Also known as “push-pull waves”

-Like the motion of a spring pulled tight, then released

P-waves travel through solid, liquid & gas

2. SECONDARY WAVES: S-WAVES-Travel more slowly than P-waves

-Vibrate in all directions perpendicular to the direction of travel. -Travel only through solids

**P & S-wavesAre BODY

waves

Both P &S-wavescreate “shadowZones”…Where no waves arerecorded

SURFACE WAVES: L-waves or (Long period waves)

Are Rayleigh & Love waves that ripple the surface of Earth

-Surface waves are the waves that cause the damage associated with earthquakes

We can determine the origin time of an earthquake if we know the distance from the epicenter (remember what that is?) & the travel time of the S-waves & P-waves.

The epicenter location is determined by calculating the difference in arrival time of the P & S-waves, & by using a minimum of 3 seismograms

The epicenter is located where the 3 circles intersect:

The intensity of & energy of an earthquakeIs measured on 2 different scales:

1. Richter scale

2. Mercalli scale

The Richter scale measures the amountOf energy released during an earthquake

**A measure of magnitude

Each step increase in magnitude on the Richter scale represents an increase in wave amplitude of 10 times.

But, the energy released by the earthquakeIncreases about 32 times!

Example:An earthquake of Richter magnitude 8.0 is 3

magnitude units higher than a 5.0 earthquake.So, its wave amplitude is 1000 times greater (10x10x10) But, the energy released is about 30,000 times greater (32x32x32)!

The modified Mercalli scale measuresearthquake intensity

The Mercalli scale is a measure of the effecton people & buildings……measures damage