Measuring Earthquakes

Earthquakes are measured by an instrument called a seismograph. The seismograph records the motion of the ground underneath it. By studying data from the seismograph, scientists can figure out exactly where and when the earthquake took place. They can also tell how big it was.

The magnitude (size) of an earthquake is measured with something called the Richter scale. The Richter scale goes from Magnitude 1, which means Very Minor, to Magnitude 8 and above, which means a Great Earthquake.

The biggest earthquake ever recorded took place in Chile on May 11,1960. It measured 9.5 on the Richter scale and caused damage as far away as Japan. The world's second biggest earthquake, measuring 9.2 on the Richter scale, took place on Good Friday 1964 in Prince William Sound, Alaska.


Volcanoes

Volcanoes are mountains, but they are not formed like other mountains.

The folding and crumpling of the Earth where continental plates collide create most mountains.

Volcanoes, on the other hand, are created by debris from their own eruptions.

Most volcanoes erupt where oceanic plates collide. However, some volcanoes erupt simply from "hot spots" where the Earth's Crust is thin.

A volcano begins with a crack (or vent) in the Earth's Crust. When pressure inside the Earth builds up, magma (hot molten rock from inside the Earth) and gasses shoot up through this vent. Geologists call magma "lava" once it comes out of the volcano.

Over time, material builds up around the vent and a volcano is born. About 80 percent of the Earth's surface (both above and below sea level) originally came from volcanoes.

There are three main types of volcanoes:

Mountain Building
http://www.physicalgeography.net/fundamentals/10k.html

Like earthquakes and volcanoes, mountains are created because of the movement of Earth's Tectonic Plates.
 
When plates collide, the Earth's Crust folds up into mountains or mountain ranges. Many of the rocks inside these mountains or mountain ranges were once buried deep beneath the Earth. Some of these rocks are over 3.5 billion years old. 
 
There are five ways in which mountains are formed:

1.      Volcanic activity (already discussed)

2.      Folding: takes place when the Earth's continental plates are pushed together. Folding bends many layers of rocks without breaking them. The Appalachian Mountains and The Rocky Mountains of the United States were formed in this way.

3.      Faulting: occurs when mountains form after pressure along fault lines causes layers of the Earth's Crust to move upward. The Sierra Nevada range in California is an example of Fault-Block mountain building.

4.      Dome building: happens when the Earth's crust is heaved upward without folding or faulting. Typically, this results in low, rounded mountains. The Black Hills of South Dakota and Wyoming and the Adirondack Mountains of New York are good examples of dome mountains.

5.      Erosion: changes the contours of many mountains and creates others. Erosion is the wearing away of the Earth's surface, primarily by water (rain, oceans, lakes and rivers) and wind.

Experiments for Home and Classroom

For a simple way to construct a model of a slip-strike earthquake, click: http://www.madsci.org/posts/archives/jun2001/991869199.Es.r.html

For an experiment that illustrates how earthquakes happen, go to this web site (Styrofoam can be substituted for the "thermocol" packing material suggested).

For another "real working volcano" experiment, click the following web site (if you don't mind getting a little messy!):
http://www.spartechsoftware.com/reeko/Experiments/volcano.htm

Reading List:
From the California Dept. of Education http://www.cde.ca.gov/ci/sc/ll