Plate 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 one Another. Tectonics are the forces that cause the Earth’s crust to continually move and create new landforms such as mountains, mid-ocean ridges, trenches, or faults.

Plate tectonics incorporates the idea of “Continental Drift”----this was first proposed by a scientist, Alfred Wegener in He noticed that the continents appeared to fit together 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,

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 were different than today --Glacial deposits in tropical regions --Coal deposits in the Arctic

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

1. Igneous Ocean Rocks Igneous 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 Polarity Over thousands of years, the magnetic poles of Earth reverse their polarities. This is recorded in the rocks of the ocean floor.

N S

1. Convergent Ocean-Continental Collision

2. Divergent

3. Transform Find 1 example of each plate boundary type on 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 arrows indicating 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 Volcano Non-explosive eruptions, gentle slopes, basaltic lava flows (low in silica)

Example: Hawaiian volcanoes

2. Composite volcano Repeated pattern of explosive & non-explosive eruptions. Moderate slope; built from alternating layers of lava & tephra

Example: Mt. St. Helens

3. Cinder Cone volcano Explosive 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 instruments called seismographs.

TYPES OF ENERGY WAVES RELEASED BY EARTHQUAKES 1)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-waves Are BODY waves

Both P & S-waves create “shadow Zones”… Where no waves are recorded

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 earthquake Is measured on 2 different scales: 1. Richter scale 2. Mercalli scale

The Richter scale measures the amount Of 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 earthquake Increases 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 measures earthquake intensity The Mercalli scale is a measure of the effect on people & buildings……measures damage