Major disaster types.

Earthquakes

An earthquake is the sudden release of strain in the Earth's crust, producing seismic waves that shake the ground. Magnitude is measured on the moment-magnitude scale (Mw), which has effectively replaced the older Richter scale for events larger than about M5. The intensity of shaking at a specific location is measured on the Modified Mercalli Intensity (MMI) scale from I (not felt) to X (extreme), and depends on magnitude, distance, soil conditions, and structural design.

Extreme Heat

Extreme heat is the most lethal weather hazard in the United States in most years. The CDC's National Vital Statistics System and the CDC's heat-related illness surveillance both consistently rank heat above hurricanes, tornadoes, floods, and winter storms in average annual fatalities. Unlike storms, heat kills without dramatic imagery: most fatalities occur indoors, often alone, in homes without air conditioning or with failed AC, in older adults and people with chronic illness.

Floods

Flooding is the temporary inundation of normally dry land by water, and it is the most common and most costly natural disaster in the United States. The National Weather Service distinguishes among several flood types: river (riverine) flooding driven by sustained rainfall or snowmelt, flash flooding driven by intense short-duration rainfall, coastal flooding driven by storm surge or tides, urban flooding driven by overwhelmed stormwater systems, and dam or levee failures.

Hurricanes

A hurricane is a rotating, organized system of clouds and thunderstorms that forms over warm tropical or subtropical waters and produces sustained surface winds of at least 74 miles per hour. The same storm is called a typhoon in the western North Pacific and a cyclone in the South Pacific and Indian Ocean basins. In the Atlantic and eastern Pacific basins, the National Hurricane Center (NHC) classifies hurricanes on the Saffir–Simpson scale from Category 1 (74–95 mph) through Category 5 (157 mph or higher).

Tornadoes

A tornado is a violently rotating column of air extending from the base of a thunderstorm to the ground. Tornadoes can produce the strongest winds on Earth — the highest measured wind in a tornado, captured by mobile Doppler radar near El Reno, Oklahoma in 2013, exceeded 300 mph — and the most concentrated structural damage of any natural hazard.

Wildfires

A wildfire is any unplanned, unwanted, uncontrolled fire in wildland vegetation. In the United States the term encompasses forest fires, brush fires, grass fires, and the increasingly common wildland-urban interface (WUI) fires that destroy structures along the boundary where development meets undeveloped vegetation. The National Interagency Fire Center (NIFC) coordinates the federal wildfire response and publishes daily situation reports during fire season.

Winter Storms

A winter storm is a weather event that produces hazardous winter precipitation — snow, sleet, freezing rain, or some combination — often accompanied by strong winds and cold temperatures. The National Weather Service uses a family of products to describe winter storms: Winter Storm Watch (conditions favorable in 12–48 hours), Winter Storm Warning (conditions occurring or imminent), Blizzard Warning (sustained winds 35 mph+ with falling or blowing snow reducing visibility below ¼ mile for at least 3 hours), and Ice Storm Warning (significant accumulations of freezing rain).