Earthquakes, Volcanoes, and Tsunamis

Earthquakes Fault: a break in the Earth’s crust. Blocks of the crust slide past each other along fault lines. When rocks that are under stress suddenly break, a series of ground vibrations is set off. These vibrations are known as earthquakes. Earthquakes occur everyday.

Focus & Epicenter The point beneath the surface where the rocks break and move is called the focus. The focus is the underground origin of an earthquake. Directly above the focus, on the Earth’s surface is the epicenter. Earthquake waves reach the epicenter first. During an earthquake, the most violent shaking is found at the epicenter.

Seismologists Seismologists study earthquakes. They can determine the strength of an earthquake by the height of the wavy line recorded on the paper. The seismograph record of waves is called a seismogram. The Richter scale is used to calculate the strength of an earthquake.

The Seismograph A weight attached to a spring remains nearly still even when the Earth moves. A pen attached to the weight records any movement on a roll of paper on a constantly rotating drum. The drum moves with the Earth and affects the line.

The Richter Scale Used by scientists to quantify the amount of energy released by an earthquake. Magnitude: The measure of the energy released by an earthquake. The scale goes from 1.0 to 10.0. Each increase of magnitude by one whole number is ten times greater in energy than the whole number below it. http://www.geo.mtu.edu/UPSeis/magnitude.html

Types of Earthquakes Convergent boundary:  Here, one plate is forced over another plate during movement creating a thrust fault. This is also called Thrust Earthquake. Divergent boundary: Here, plates are forced apart. This kind is common in ocean floors where new floors are created. Transform fault:  Unlike divergent and convergent, the plates here slip by each other. This is also called Strike-Slip Earthquake.

Types of Seismic Waves Primary waves are a type of elastic wave, and are one of the two main types of seismic waves in seismology. They are the first waves from an earthquake to arrive at a seismograph. Secondary waves cause the rocks they pass through to change in shape. These waves are slower than primary waves and can travel through solids but not through liquids or gases. 

Tsunamis Earthquakes which occur on the ocean floor produce giant sea waves called tsunamis. Tsunamis can travel at speeds of 700 to 800 km per hour. As they approach the coast, they can reach heights of greater than 30 meters.

How a Tsunami Forms

Volcanoes A volcano is a mountain built from magma. Magma: melted rock that found beneath the surface of the earth (called lava when above earth’s surface) Located near tectonic plate boundaries where plates are sliding or separating from one another.

Volcano Diagram

Volcanic Eruptions A volcano erupts when the pressure of the magma inside becomes so great that it erupts. Some volcanoes have magma flowing out of them all the time so the pressure never builds up.

Local Effects of Volcano Eruptions Volcanic eruptions can be devastating to local economies and can cause great human loss. Clouds of hot ash, dust, and gases can flow down the slope of a volcano up to 200 km/hour. Volcanic ash can mix with water and produce a mudflow. Ash that falls to the ground can cause buildings to collapse, bury crops, damage engines, and cause breathing problems.

Global Effects of Volcano Eruptions Clouds of volcanic ash and sulfur-rich gases can reach the upper atmosphere. **Iceland Ash and gas spread across the planet and reduce the amount of sunlight that reaches the Earth’s surface.

Types of Volcanoes Different types of volcanic eruptions form different types of volcanoes. Cinder cones Shield volcanoes Composite volcanoes

Three Types

Cinder Cones Volcanoes made mostly of cinders and other rock particles that have been blown into the air are called cinder cones. Cinder cones form from explosive eruptions. Because the material is loosely arranged, the cones are not high. They have a narrow base and steep sides such as Paricutin in Mexico.

Cinder Cone Volcano

Shield Volcanoes Volcanoes composed of quiet flows are called shield volcanoes. Because it is runny, the lava flows over a large area. After several eruptions, a dome-shaped mountain is formed such as Mauna Loa in the Hawaiian Islands.

Shield Volcanoes

Composite Volcanoes Volcanoes built up of alternating layers of rock particles and lava. They are formed by a violent eruption first, hurling volcanic bombs, cinder and ash out of the vent. Then a quiet eruption, produces lava flow that covers the rock particles. After alternating eruptions, a cone-shaped mountain forms such as Mount Vesuvius.

Composite Volcano

Earthquake Belts