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. Each whole number up in magnitude means a tenfold increase in measured wave size and about 32 times more energy released. An earthquake has a single magnitude, but the shaking it causes varies from place to place with distance, type of surface material and other factors.
If the ground shakes, drop down, cover your head and neck, and hold on until the shaking stops. Aftershocks are smaller earthquakes that follow a larger earthquake in the same area. As of November 2026, the USGS developed the ShakeAlert Earthquake Early Warning system together with many partner organizations, including universities and state agencies. An earthquake under the ocean can push the water above it and start a tsunami. In deep water a tsunami moves as fast as a jet plane. A tsunami wave grows taller as it moves into shallow water near the shore.
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. Most tornadoes form in supercell thunderstorms, but not all supercells produce tornadoes. Experts rate a tornado by studying the damage it caused. The Enhanced Fujita Scale has six ratings, EF0 to EF5. Over two-thirds of all tornadoes are weak, rated EF0 or EF1.
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. Opening windows to equalize pressure does not help in a tornado; the tornado will blast open the windows anyway. After the Tri-State tornado of 18 March 1925, checks and papers fell from the sky in Missouri, Illinois, Indiana and even Ohio, which the tornado did not reach.
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. Because of the Coriolis effect, hurricanes rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Hurricane names come from six lists that rotate, so each list is used again every six years.
Storm surge is sea water pushed onto land by the winds of a storm. It is primarily caused by the strong onshore winds of a hurricane or tropical storm. Hurricanes are called typhoons in the western North Pacific and cyclones in some other places. In 2011 Cyclone Yasi made a direct hit on the Queensland, Australia coast and produced seven meters (23 feet) of storm surge. Hurricanes usually get weaker when they move over land.
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. Melting snow or warm rain can break up river ice, and chunks of ice can jam against bridges and make the water rise quickly behind the jam. Flash floods can happen within minutes of heavy rain. Where it rains it can flood, even if a place is not near a river or on a flood map. Never walk, swim or drive through flood water.
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.
Words to know
- magnitude: earthquake size
- supercell: rotating thunderstorm
- Coriolis: spin effect
- surge: pushed water
- aftershocks: later small quakes
- evacuate: leave for safety
