An earthquake is an intense shaking of Earth's surface. Earth's outer layer is made of giant puzzle pieces called tectonic plates that slowly move. Scientists use an instrument called a seismometer. It measures the shaking waves from an earthquake. Aftershocks are smaller earthquakes that follow a larger earthquake in the same area. If the ground shakes, drop down, cover your head and neck, and hold on until the shaking stops.

An earthquake under the ocean can push the water above it and start a tsunami. A tsunami can also be started by a volcano in the ocean. Tsunamis travel very fast. In the deep ocean they can move as fast as a jet plane. A tsunami wave grows taller as it moves into shallow water near the shore. If the water pulls far back from the shore after an earthquake, a big tsunami may be on its way.

A tornado is a spinning column of air. It reaches from a storm cloud down to the ground. Experts rate a tornado by studying the damage it caused. The Enhanced Fujita Scale has six ratings, EF0 to EF5. A tornado watch means tornadoes are possible in and near the area. A tornado warning means a tornado is near. It is time to move to a safe place. Go to a small room with no windows on the lowest floor of a sturdy building.

A hurricane is a big storm that forms over warm ocean water. When a storm's winds reach 74 miles per hour, it is called a hurricane. A hurricane has a calm, clear center called the eye. Storm surge is sea water pushed onto land by the winds of a storm. Hurricanes are called typhoons in the western North Pacific. They are called cyclones in some other places.

A flood is water that covers land that is usually dry. Flash floods can happen within minutes of heavy rain. They can come without warning. Just 6 inches of fast-moving flood water can knock a person over. Twelve inches can carry a car away. Never walk, swim or drive through flood water. If officials say to evacuate before a hurricane, go right away to a safe place.

Weather forecasters send out warnings so people have time to get to a safe place. A family can make a plan together for what to do in a disaster. They can pick a place to meet if they are ever apart. A disaster kit holds basic things a family may need, like water, food, a radio, a flashlight and a first aid kit. It should have one gallon of water for each person for each day.

Words to know

• seismometer: shake measurer
• aftershocks: later small quakes
• tsunamis: big ocean waves
• evacuate: leave for safety
• surge: pushed water