An earthquake is an intense shaking of Earth's surface. Scientists use an instrument called a seismometer to measure the shaking waves. In 1935, Charles F. Richter of the California Institute of Technology introduced the idea of earthquake magnitude. On the magnitude scale, each whole number up means a tenfold increase in the measured size of the earthquake's waves. Earthquakes are equally likely in the morning or the evening. 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 deep water a tsunami moves as fast as a jet plane, but near land it slows to about the speed of a car, 20 to 30 miles per hour. A tsunami wave grows taller as it moves into shallow water near the shore. You may have heard the name tidal wave. A tsunami is not a tidal wave: tides come from the pull of the Sun and Moon, and tsunamis are not related to them.

A tornado is a spinning column of air that reaches from a storm cloud down to the ground. Winds moving in different speeds and directions at different heights make the rising air in a storm start to spin. Experts rate a tornado by studying the damage it caused. The Enhanced Fujita Scale has six ratings, EF0 to EF5. Tornadoes can happen at any time of day or night and at any time of the year. "Tornado Alley" is a nickname invented by the media for a broad area of the central United States where tornadoes are fairly common. Tornadoes happen all over the United States, and violent tornadoes happen outside "Tornado Alley" every year.

A tornado watch means tornadoes are possible in and near the area. A tornado warning means a tornado is near and 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. Highway overpasses offer no extra protection in a tornado.

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. The Saffir-Simpson scale rates hurricanes from 1 to 5 by their wind speed. Hurricanes rated Category 3 and higher are called major hurricanes. Hurricane names come from six lists that rotate, so each list is used again every six years. Hurricanes usually get weaker when they move over land.

As of November 2026, the two GOES weather satellites keep watch on hurricanes from 22,300 miles above Earth. Weather forecasters send out warnings so people have time to get to a safe place. If officials say to evacuate before a hurricane, go right away 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.

A flood is water that covers land that is usually dry. Floods can come from heavy rain, from fast-melting snow, or when ocean waves come on shore. Where it rains it can flood, even if a place is not near a river or on a flood map. In the mountains, a creek only 6 inches deep can swell into a 10-foot-deep river in less than an hour if a thunderstorm lingers. Flash floods can happen within minutes of heavy rain. Just 6 inches of fast-moving flood water can knock a person over. Never walk, swim or drive through flood water.

Words to know

• magnitude: earthquake size
• tsunami: big ocean wave
• seismometer: shake measurer
• evacuate: leave for safety
• overpasses: road bridges