Instruction 2-4

Water Movement | Rivers and Streams | Beaches | Habitats and Geological Events | Summary

Geological events can have a major effect on the places where people and animals live. Those places are called habitats. Sometimes those effects are good. Mostly, however, they are disastrous -- as we see on television. The geological events we're going to talk about today are floods, volcanic eruptions and earthquakes.

Floods
http://www.pbs.org/newshour/infocus/floods/science.html
 
Floods occur when the water rises above the banks of a stream, lakeshore or ocean coast and submerges land that is not usually under water.
Floods are naturally recurring events in every stream, lake and coastal environment. They are the most frequent and costly of all natural disasters.
 
Floods can be caused by:

• unusually heavy or prolonged rain,
• spring snowmelt or ice and debris jams that cause a river or stream to overflow its banks,
• the failure of a dam or levee, or by
• low or no absorption of rainfall (this sometimes happens in places where roads, parking lots and buildings have replaced the natural terrain).

Most of the world's population lives on or near coasts, rivers and floodplains (areas where floods occur regularly). Therefore floods are a threat to hundreds of millions of people. Floods can cause loss of life, extensive damage to property, contamination of drinking water and destruction of crops and fields.
 
The areas at highest risk are those within what is called "the 100-year floodplain." This means that floods occur once every one hundred years on average. However, it is possible to have several 100-year floods in a single year. With all their dangers, however, floods often help produce rich soils for agriculture. That's why so many people live on floodplains.
 
 
Flooding and Agriculture
 
Many rivers flow through relatively flat land surrounded by broad floodplains. When these rivers overflow, they cover the floodplain with shallow water. This water deposits silt, which greatly improves the fertility of the floodplain. Throughout history, these silt deposits have attracted agriculture and other human development.
 
The annual cycle of flooding and farming was crucial to many early farming societies. This was especially true for the ancient Egyptians of the Nile River Valley. It was also true for the Mesopotamians near the Tigris and Euphrates Rivers. Many historians think that without flooding there would have been no agriculture, and that without agriculture there would have been no civilization.
 
For a more extensive exploration of the early River Valley civilizations, go to: http://etap.org/members/history_files/grade6/lesson2/lesson.htm 
 
 
History & Mythology
http://www.ancientgreece.com/

There have been many great floods throughout history. About 5 million years ago, a flood turned a desert into what is now the Mediterranean Sea. When the last Ice Age ended about 5600 B.C., a flood created the Black Sea.

In addition to historical floods, many cultures have myths about floods. These mythical floods may or may not be supported by scientific evidence. The story of Noah's Ark, in Genesis (the first book in the Bible) is probably the best known. A great flood also occurs in the Hindu Epic of Gilgamesh. To read about NASA's ongoing search to find the real Noah's Ark, click: http://www.space.com/scienceastronomy/ark_hunt_020830.html   
 

Volcanic Eruptions

Like floods, volcanic eruptions can be both destructive and constructive. Over 80 percent of the Earth's surface originally came from volcanoes. Geologists think that gasses erupted by volcanoes formed the Earth's earliest oceans and atmospheres. That's because these gasses are mostly water vapor.
 
Volcanoes can even have cultural consequences. During the Bronze Age, the eruption of Thera in the Mediterranean weakened Crete and allowed the Greeks to take over. This eventually led to The Golden Age of Greece, which had a tremendous effect on Western civilization.
 
 
What are Volcanoes?

Volcanoes are mountains, but they're not like other mountains. The folding and crumpling of the Earth create other mountains, but volcanic mountains are created by debris from their own eruptions.

To see an animation of the different types of volcanic eruptions, click: http://www.cotf.edu/ete/modules/volcanoes/veruptanimation.html 
 
 
Devastation

Volcanic eruptions can have devastating consequences. There are 50 "active" volcanoes in the United States, active volcanoes being those that are currently erupting or showing signs of unrest.
 
In 1980, when Mt. St. Helens in Washington State erupted, the following things happened:

• 57 people were killed (the bodies of 21 of them were never found),
• an estimated 4 billion board-feet of timber were blown down (enough to build 300,000 two-bedroom homes),
• 7,000 deer, elk and bear were killed,
• all the birds and small mammals in the area were killed,
• 12 million Chinook and Coho salmon died,
• air quality was "unacceptable" for months,
• countless homes and businesses were destroyed, and
• a rich green forest was turned into a gray, lifeless wasteland.

People, plants and animals are often buried under the flow of ash, mud or lava from a volcano. Something else happens: the land becomes impossible to farm. This can have serious long-lasting consequences that are even worse than the original destruction.

Earthquakes
http://www.seismo.unr.edu/ftp/pub/louie/class/100/plate-tectonics.html

As we told you in our first Instruction, the surface of the Earth is not solid. It is made up of moving masses of rock called tectonic plates. Earthquakes can happen anywhere, but they mostly occur on the borders where these tectonic plates collide. They can also occur along fault lines (faults are cracks in the middle of plates).
 
To see an animation of how earthquakes happen, click: http://www.pbs.org/wnet/savageearth/animations/earthquakes/main.html 
 
 
Earthquake Damage
http://www.ngdc.noaa.gov/seg/hazard/slideset/earthquakes/
 
Earthquakes are measured in two ways. First by how big they are. And second by the amount of damage they cause, which can be catastrophic.
 
Magnitude (The Richter Scale)
http://www.geo.mtu.edu/UPSeis/intensity.html
The size (magnitude) of an earthquake is rated on the Richter Scale. You will often hear it mentioned on radio or TV when an earthquake occurs. Here are Richter Scale ratings:

• Magnitude 1 - 2.9: Very Minor Earthquake
• Magnitude 3 - 3.9: Minor Earthquake
• Magnitude 4 - 4.9: Light Earthquake
• Magnitude 5 - 5.9: Moderate Earthquake
• Magnitude 6 - 6.9: Strong Earthquake
• Magnitude 7 - 7.9: Major Earthquake
• Magnitude 8+: Great Earthquake

The Richter Scale is logarithmic. In other words, an increase of one number indicates a 10-fold increase in magnitude. For example, a magnitude 7 earthquake is:

• 10 times bigger than a Magnitude 6 earthquake,
• 100 times bigger than a magnitude 5 earthquake, and
• 1,000 times bigger than a magnitude 4 earthquake.

Intensity (Modified Mercalli Scale)
http://www.sizes.com/natural/quakintens.htm
 
The intensity of an earthquake is rated on the Modified Mercalli Scale. This measures two things: the first is how likely an earthquake is to be felt and the second is how much damage it's likely to cause.
 
Here is The Modified Mercalli Scale:

• I - felt by almost no one,
• II - felt mostly by people lying down,
• III - felt by people indoors on upper floors,
• IV - felt indoors by many people; walls crack,
• V - felt by almost everyone; unstable objects fall,
• VI - felt by everyone; heavy furniture moves,
• VII - little damage in well-designed buildings but considerable damage in poorly-built structures,
• VIII - considerable damage even in substantial buildings; partial collapse of chimneys and columns,
• IX - considerable damage in even the best-designed and most substantial structures,
• X - destruction of all wooden structures and most masonry and frame structures; rails bent,
• XI - few (if any) masonry structures left standing; bridges and underground pipelines destroyed, and
• XII - total devastation; lines of sight and levels distorted; objects thrown into the air.

The degree of damage depends on many things, of course. These include the quality of building construction and the stability of the ground underneath. Buildings on unstable ground (like sand or clay) are more likely to be destroyed than structures built on granite. Earthquakes also alter the landscape -- forming mountains, valleys and lava fields that look like the surface of the moon.
 
Liquefaction

In some areas, severe earthquake damage is also caused by liquefaction of the soil. Under certain conditions, the violent shaking of an earthquake can cause loosely packed soil to behave like a liquid. When buildings are constructed on this type of soil, they are apt to collapse. Liquefaction can also cause mudslides, like the ones that took so many lives in El Salvador in 2001.
 
 
Major Earthquakes
http://www.infoplease.com/ce6/sci/A0857867.html
 
The biggest earthquake ever recorded measured 9.5 on the Richter Scale. It took place in Chile on May 22, 1960, and caused damage as far away as Japan.
 
The second biggest earthquake on record measured 9.2 on the Richter Scale. This 9.2 earthquake took place on Good Friday, 1964, in Prince William Sound, Alaska. This earthquake and its resulting tsunami caused death and destruction as far away as Hawaii.
 

Experiments for Home and Classroom

This Instruction explains how geological events like floods, volcanic eruptions and earthquakes have a major effect on the places where people and animals live. In ancient Egypt, the annual flooding of the Nile River made agriculture and civilization possible. For a related "fun quiz" and other activities about the Nile and ancient Egypt, click:
http://www.seaworld.org/fun-zone/fun-guides/egypt/nation-of-irrigation.htm  and http://www.seaworld.org/fun-zone/fun-guides/egypt/secrets-of-the-nile.htm

This web site is called Volcanoes Online and features a "games" section in which students can try to "Save the Village" from the wrath of a volcano or solve a Volcanoes Crossword Puzzle. Click: http://library.thinkquest.org/17457/english.html

Earthquakes can happen anywhere. This Home Hazards Hunt is designed to help students determine how safe their homes would be if an earthquake struck. Click: http://www.fema.gov/kids/eqhunt.htm

For additional earthquake and volcano experiments and activities, refer to the Experiments section in Instruction 1-3 of the previous Lesson.

Now let's do Practice Exercise 2-4 (top). Choose printer friendly or online exercises. Printer friendly version requires the Adobe Acrobat Reader 5. Click HERE to obtain a free copy.

Summary

You have now completed this Lesson and are ready to do the Problem and Test sections.

You may wish to review any or all of the topics before answering the questions that follow. You may also wish to obtain additional material from the Links in any of the Instructions before answering the questions.

Good luck!

Problems