An earthquake is an intense shaking of Earth's surface. Scientists use an instrument called a seismometer to measure the shaking waves. Each whole number up in magnitude means a tenfold increase in measured wave size and about 32 times more energy released. For most earthquakes the moment magnitude scale is a more accurate measure of size than the Richter scale, which is now used mainly for small local earthquakes. Parts of the San Andreas Fault creep steadily in many tiny shocks, but where creep is not constant, strain can build up for hundreds of years and produce great earthquakes. 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.

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. The tsunami hazard is greatest near subduction zones, where large earthquakes and landslides can produce damaging waves. DART systems were developed by NOAA for early detection, measurement and real-time reporting of tsunamis in the open ocean. Once a tsunami is detected, warning centers use forecast models to forecast wave height and arrival times, the location and amount of flooding, and how long it will last. 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 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. A supercell is a long-lived, highly organized storm with a tilted, rotating updraft. A mesocyclone, the large rotating updraft in a supercell, is usually 2-6 miles in diameter, much larger than the tornado that may develop within it. Most tornadoes form in supercell thunderstorms, but not all supercells produce tornadoes. Scientists do not fully understand how tornadoes form. NSSL researchers discovered the Tornado Vortex Signature, a Doppler radar velocity pattern that shows a region of intense concentrated rotation.

Experts rate a tornado by studying the damage it caused. The Enhanced Fujita Scale has six ratings, EF0 to EF5, and over two-thirds of all tornadoes are weak, rated EF0 or EF1. Official tornado records only go back to 1950, so the true average number of tornadoes each year is not known. The widest tornado path on record, near El Reno, Oklahoma on 31 May 2013, was officially 2.6 miles wide. 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, and a tornado warning means a tornado is near and it is time to move to a safe place.

A safe room built to FEMA criteria or a storm shelter built to ICC 500 standards is the best tornado protection. The next best is a small interior windowless room on the lowest level. Highway overpasses offer no extra protection in a tornado. Opening windows to equalize pressure does not help, because the tornado will blast open the windows anyway. The "safe southwest corner" of a basement is a myth, because walls and furniture can fall into any corner. Families can practice going to a safe place before a tornado comes.

A hurricane is a big storm that forms over warm ocean water. Scientists call hurricanes and their relatives tropical cyclones, and a tropical cyclone is a hurricane when its winds reach 74 miles per hour. Hurricane conditions occur in the tropics, typically between five and 20 degrees of latitude north and south of the equator. Because of the Coriolis effect, hurricanes rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The Saffir-Simpson scale rates hurricanes from 1 to 5 by their wind speed, and those rated Category 3 and higher are called major hurricanes.

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. Storm surge height depends on a storm's intensity, forward speed, size, angle of approach, and the shape of the coastline. A wide, gently sloping continental shelf allows a higher storm surge than a narrow, steeply sloping one. The National Weather Service SLOSH model lets forecasters customize storm surge predictions for particular storms and coasts. When high tide happens at the same time as a storm surge, the combination is called a storm tide, and the water can be 20 feet or more above normal.

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. In 2005, flooding hit New Orleans days after Hurricane Katrina came onshore because the levees designed to protect the city failed. As of November 2026, homeowner's insurance policies do not cover flooding, and a flood insurance policy typically takes up to 30 days to go into effect.

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. If the ground shakes, drop down, cover your head and neck, and hold on until the shaking stops. A family can make a plan together for what to do in a disaster, and they can pick a place to meet if they are ever apart.

Words to know

• magnitude: earthquake size
• subduction: plate sinking
• mesocyclone: rotating updraft
• supercell: rotating thunderstorm
• latitude: distance from equator
• levees: flood walls