geography chapter 2.3

Tectonic plates are massive, moving pieces of Earth’s lithosphere

Plates ride above circulating, heated rock Geographers study plate movements to

understand: - how the earth is reshaped - how earthquakes and volcanoes are formed

The largest plates are named after continents: page 37

Plates move in one of four ways: page 38-39

Divergent- by spreading, or moving apart

Subduction - diving under another plate

Convergent- collision, or crashing together

Transform- sliding past each other in a shearing motion

Movement of plates effects surface of the earth

Saudi Arabia–Egypt’s plates are spreading apart, widening Red Sea

India’s plate is crashing into Asian continent, building up Himalayas

Peru-Chile Trench

Two plates meeting can cause folding, cracking of rock -Plates move very slowly - Causes rocks to become more flexible and

fold under pressure

Faults occur when pressure causes rock to fracture, or crack. - Sometimes the rock is not flexible and will

crack due to plate movement

The crack is called a fault

Fault line is place where plates move past each other

As the plates move past each other at a fault, the earth shakes or trembles

This movement may become violent, called an earthquake

Seismograph -Special device used to detect earthquakes -Measures the size of the waves created by

an earthquake

Earthquakes release energy in the form of motion, causing: - landslides - land displacement - fires (broken gas lines) - collapsed buildings

Richter Scale — numeric scale showing relative strength of earthquake -Uses info from seismographs to determine the

strength of an earthquake -Has no absolute upper limit -Major quake measures a 7 or more

Location in the earth where an earthquake begins is called the focus

Epicenter — the point directly above focus on the earth’s surface - In most cases, the epicenter is the area

that receives the greatest damage Nearly 95% of earthquakes occur at

tectonic plate boundaries

Tsunami, a giant ocean wave, begins at epicenter of an earthquake: - travels at up to 450 mph - waves of 50–100 ft. or higher

May travel across wide stretches of the ocean and do damage on distant shores

On March 11, 2011 an 8.9 magnitude earthquake struck Japan.

The earthquake and subsequent tsunami has caused vast amounts of damage and the death toll continues to rise.

Nearly 16,000 people died as a result.

On December 26th, 2004, an earthquake caused by subduction caused a series of tsunamis along the coasts of the Indian Ocean.

Some waves were said to be upwards of 98ft. high.

Killing over 230,000 people, the 2004 tsunami is the worst natural disaster in history.

Volcanoes occur where there are cracks in the earth’s surface. Material, such as magma, pours out of the vent.

Most volcanoes occur at tectonic plate boundaries

There are several types of eruptions—violent explosions where lava, gases, ash or dust are expelled from the vent in Earth’s crust

Lava — magma that has reached the earth’s surface; may create landform

Ring of Fire — zone around rim of Pacific Ocean: - meeting point of

eight tectonic plates

- vast majority of the earth’s active volcanoes located here

“Hot spots” are where magma rises to surface from mantle

Hot springs, geysers indicate high temperatures in earth’s crust

Some volcanic action is useful: - volcanic ash produces

fertile soil - hot springs are tapped

for heat, energy