1. Changing Earth’s Surface
Chapter 4 Lesson 4
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2. How can environments change?
Environmental changes can be caused by natural events or by human actions
Natural events include natural disasters and changes caused by organisms other than humans
Earthquakes, floods, storms, volcanoes, droughts, and other natural disasters can drastically alter environments
Another type of natural change is caused by organisms.
Beavers build dams by using mud, stones, and trees. They create an artificial pond but their dams can cause flooding.
Dams can be beneficial by creating new habitats and food supplies

3. How can environments changes?
Large animals such as elephants can cause changes by trampling trees and seedlings
Aquatic environments are also changed by organisms
Algae can rapidly reproduce, using all the nutrients and oxygen in the water
Coral change their environment by building reefs and this creates new habitats for many other organisms
People can cause changes to the environment by shaping the land to meet their needs
These changes can alter or destroy habitats and the organisms that live there
Forests get cut down to build homes and roads
People use pesticides that can harm organisms for which they were not intended
Humans cause pollution that can damage water, soil, and air quality

4. How do tsunamis affect habitats?
One of the most damaging but infrequent natural disasters is a tsunami: a series of huge waves caused by an earthquake or volcanic eruption underneath the ocean
The waves can cause flooding that can sweep people, houses, boats, and even trees into its wake
December 26, 2004, an earthquake measuring 9.3 on the Richter scale occurred in the Indian Ocean that caused a massive tsunami.
It killed hundreds of thousands of people and destroyed whole villages

5. How do floods affect habitat?
Floods are usually caused by a large amount of rain that falls in a short period of time
Floods may also develop when snow melts in the spring
Sometimes floods occur where people have interfered with the natural flow of water- when a dam breaks it can flood the area
Floods are dangerous to nearby inhabitants for several reasons: water is heavy, so it moves quickly.
The force of flowin floodwater can be enough to uproot a tree or knock down a person or an animal

6. Changing landscapes
Floodwater picks up and carries away tons of mud and debris.
This mud and debris can bury crops and other plants, damaging or killing them, but the nutrient rich mud remaining after the flood renews the soil and makes it more fertile
People can control the water’s flow by building dams or levees
A levee is a wall or a large mound of earth built along a river to prevent it from flooding
Building levees can be a good solution to areas that flood often
If a levee breaks, it can cause some of the most dangerous floods such as the flooding in New Orleans from Hurricane Katrina in 2005

7. How do earthquakes and landslides affect habitats?
Earthquakes can change landforms.
Some earthquakes open large cracks in the ground, the ground shifts vertically, producing a cliff in a few seconds
If the land shifts enough in a particular place, it can change a river’s course, drain a lake, or change the appearance of the natural and human-made features of the region
A landslide can cause more damage than an earthquake
A landslide can carry buildings down a hillside or bury highways under debris
It may rip trees and plants from the ground and change a gentle slope to a steep cliff
If debris falls into a river or a stream, it may create a natural dam, change the course of the waterway, or cause a flood

8. What are long term affects of natural disasters?
Some natural disasters, such as volcanoes, can affect the climate for both short and long periods of time
A volcanic eruption sends gases and particles of ash into the air and this debris spreads into the atmosphere around the globe
Natural disasters can also be positive
Volcanoes build more land
Floods and landslides can add to the soil by leaving behind nutrient-rich mud
Volcanic ash can block sunlight from small plants so that surrounding trees grow more quickly
These can create new habitats or bring fresh minerals to Earth’s surface