WHAT CAUSES EARTHQUAKES AND VOLCANOES

Chapter 8 Section 4

Earthquakes

Plate movement occurs slowly so you can’t see or feel it.

The rocks jagged edges catch and pressure builds up

If the pressure is too strong then an earthquake happens

Earthquakes

The point underground of an earthquake is the FOCUS

The point directly above the focus on Earth’s surface is the EPICENTER

The energy of an earthquake is carried in waves The waves can move up or down The waves can move back and forth The waves can roll or move in a circular

fashion

Earthquake magnitude

The greatest damage occurs near the focus and epicenter

As the waves move out- they lose energy

Almost all the largest earthquakes have occurred in California and Alaska

The boundary between the Pacific Plate and the North American plate

Richter Scale

The magnitude of an earthquake is measured on the Richter scale

Each increase of 1 on the Richter scale means a 31 times more energy is released

Volcanoes

A volcano- an opening in the surface of one of Earth’s plates through which magma rises.

Ash cloud- tiny bits of rock spew out the opening

Crater- steep-sided depression at the top of a volcano

Caldera-crater that is at least 1.6 km wide

Volcanoes

Most often occur when one plate sinks beneath another

Most volcanoes occur on the ocean floor

Detecting an Earthquake or volcano

Seismometers- detect shaking or tremors in Earth’s crust

Magma rising or Earth’s plates moving Tiltmeter- detects changes in the slope

of the land Seismograph- records the movement or

tremors at faults