Flowing water pushes small rocks and dirt down the river. The dirt and stones settle in different places over time, changing the shape of the river and the land around it. Large ice sheets flow down the hill, grinding and smoothing the rock under it over thousands of years. Many of Earth's changes happen so slowly that you cannot even see them. But sometimes the Earth goes crazy and the shape of everything in sight changes in an instant.
Heavy rains fill a river and it flows over its banks, destroying farms and houses. Swirling winds smack into a town, knocking down buildings as if they were made of toothpicks. Lightning hits a dry forest, starting a fire that burns across the land, threatening nearby homes. Floods and fires can change the face of the Earth overnight. We call this a catastrophe
, which is a sudden event that causes a lot of damage.
Things are getting a little hot around here.
A loud rumble and strong shaking make buildings sway and cars tumble. A large hole seems to open up in the Earth. The ground is not as solid as you think. The surface you stand on floats on melted rock, like a boat floats on the ocean. Different pieces of land and water sit on different plates. Sometimes these plates crash into each other or slip past each other, releasing a lot of energy that makes the Earth move and shake. An earthquake
is when the Earth's solid top layer moves because the plates under it shift, letting out waves that we feel as shaking.
The San Francisco earthquake caused a fire that destroyed the city.
Many earthquakes happen deep in the ocean floor, far away from buildings, homes, and people. Even though the shaking itself may not hurt people, the moving earth can make powerful waves that wash to shore. The energy from the moving earth makes waves that may be 100 miles apart or more. These waves can move faster than an airplane. When they reach shallow water, the waves slow down and grow much higher. These waves, now taller than a 15-story building, can smack into the land, destroying buildings along the coast. A tsunami
is a huge wave that is made when Earth moves suddenly under the ocean floor, on an island, or on a beach.
Looks like it's time to go.
A few months ago, a fire moved through a hilly place, burning away trees, grass, and other plants. Now a heavy rain soaks the bare land for many hours or days in a row. At some point, the ground becomes too wet to soak up any more water. Without trees or grass to hold the ground in place, the Earth's gravity pulls the rain-soaked dirt down the hill. It becomes a river of mud and rock, which flows down the hill, washing away cars and buildings below. A mudslide
is a wall of mud, water, and rocks that moves down the hill.
I'm going to need more than a shovel for this.
Catastrophes have the power to change the shape of the land overnight. After a fire, a mudslide might wash away buildings, roads and cars, as parts of the hill fall away. Two of the Earth's floating plates crash or slip, sending strong waves and shaking through the land. That earthquake might even set off a giant wall of water that hits the coast. These changes happen far faster than those made by the slow wearing away of the Earth that we see.
"Be Prepared, Build a Kit." Ready.gov. FEMA,
"Call a Family Meeting and Make a Plan!" Ready.gov.
FEMA, 2013. <http://www.ready.gov/kids/make-a-plan>
"Debris Flow." World of Earth Science.
"Early Warning System Forecasts Deadly Mudslides." NOAA.
"Earthquake." World of Earth Science.
"Earthquakes." Ready.gov. FEMA, 2014. <http://www.ready.gov/earthquakes>
"Landslides & Debris Flow." Ready.gov. FEMA,
"Tsunami" NOAA, 2014. <http://www.tsunami.noaa.gov/>
FEMA, 2014. <http://www.ready.gov/tsunamis>