The Basics of Geography Part 5 Earthquakes and Volcanoes

Earthquakes As tectonic plates grind or slip past each other at a FAULT or crack in the earth, the earth may shake or tremble.

Thousands of earthquakes occur every year, but most are not felt by humans. A device called a SEISMOGRAPH detects them by measuring the waves from quakes.

The point directly above the surface where an earthquake begins, is called an EPICENTER.

A man named C.F. Richter developed the RICHTER SCALE, which measures the energy released by a quake. A 2.0 quake would not be noticed, while a 4.5 would probably be reported in the news. Major quakes are those over a 7.0. In 1906, the quake that destroyed San Francisco was likely at least an 8.0.

Earthquake Damage Earthquakes can trigger landslides, create fires from broken gas lines, and collapse buildings on people. AFTERSHOCKS may occur for days after a large quake. Earthquakes can also produce deadly TSUNAMIS, such as the one that struck the Indian Ocean in December, 2004.

On April 18, 1906, a massive earthquake struck San Francisco, California early in the morning as most people still slept.

Fire killed far more people than the quake.

Some refugees lived in tents.

On December 26, 2004, a massive earthquake over 9.0 struck in the Indian Ocean. It lasted several minutes, created an enormous tsunami, and killed hundreds of thousands.

Earthquake Clips Earthquake Destruction Earthquakes Seattle Earthquake 2004 Indian Ocean Earthquake and Tsunami

Volcanoes MAGMA (liquid earth), gases, and water from the lower crust or mantle collect in underground chambers. When pressure becomes too great, these materials pour out onto the earth’s surface. Magma that reaches the surface is called LAVA.

Until May 18, 1980, Mount St. Helens in Washington had been dormant.

In spring 1980, the mountain began to show activity, and it bulged.

The largest recorded landslide in human history takes place, helping to trigger the eruption of the volcano.

An ash cloud darkened the Pacific Northwest, and eventually circled the planet.

Mount St. Helens – June 2007

Just 5 miles from the volcano.