A natural disaster is a powerful event in nature, such as an earthquake, tsunami, volcanic eruption, hurricane, tornado, flood, drought or wildfire, that harms people, homes or the land. Almost all of them come from just four forces: the ground moving, the weather going wild, too much (or too little) water, and fire spreading out of control.
Natural disasters sound scary, but warnings now save far more lives than they did when your grandparents were kids. Learning what causes each one is the first step to staying safe, so let's sort them by what drives them.
When the Ground Moves: Earthquakes, Tsunamis and Volcanoes
Earth's outer shell is cracked into giant pieces called tectonic plates. They move about as fast as your fingernails grow, a few centimetres a year, pressing and scraping against each other so that the rock stores up strain like a bent ruler.
Earthquakes
When the rock finally snaps and slips, it sends out waves of energy that make the ground shake. That is an earthquake. Scientists measure its size on the moment magnitude scale. Each step up is a big jump: a magnitude 7 releases about 32 times more energy than a magnitude 6. The biggest earthquake ever recorded struck Valdivia, Chile, on 22 May 1960, at magnitude 9.5. You can read more about why the ground shakes in our guide to earthquakes for kids.
Tsunamis
When a big earthquake happens under the sea, the seafloor can jump up or down and push the whole column of water above it. That creates a tsunami: a series of waves that race across the deep ocean at about 700 to 800 km/h, as fast as a passenger jet. Out at sea they may be under a metre tall, but in shallow water near the coast they slow down and pile up.
On 26 December 2004, a magnitude 9.1 earthquake off the island of Sumatra in Indonesia set off the Indian Ocean tsunami. Waves up to 30 metres high hit the province of Aceh, and others reached Thailand, Sri Lanka, India and even Somalia. About 230,000 people died in 14 countries. One big reason so many were caught by surprise is that the Indian Ocean had no tsunami warning system at the time. One was built afterwards and has been fully working since 2011.
Volcanoes
Melted rock called magma collects beneath volcanoes, and when pressure builds up it can burst out. On 18 May 1980, an earthquake shook Mount St Helens in Washington State, USA. The swollen north side of the mountain slid away in the biggest landslide ever recorded, and the volcano exploded sideways. An ash cloud shot about 24 kilometres into the sky, around 600 square kilometres of forest were flattened, and 57 people died. The mountain lost about 400 metres of its height in a single morning.
When the Weather Goes Wild: Hurricanes and Tornadoes
The Sun heats the Earth unevenly, and warm, wet air rises. Usually that just makes clouds and rain. Sometimes it builds into a monster storm.
Hurricanes
A hurricane is a huge spinning storm that forms over tropical ocean water warmer than about 26°C. Warm water is its fuel. In the Atlantic and eastern Pacific it is called a hurricane, in the western Pacific a typhoon, and in the Indian Ocean a cyclone. They are all the same kind of storm. In the middle sits the eye, a calm patch where you can sometimes see blue sky, but it is ringed by the eyewall, which has the strongest winds of all. Our page on how hurricanes form explains each step.
Scientists rate hurricanes on the Saffir-Simpson scale, from Category 1 to Category 5, using the speed of the storm's steady winds. Hurricane Katrina reached Category 5 over the Gulf of Mexico, then came ashore in Louisiana on 29 August 2005 as a Category 3. The worst damage came from water, not wind: a wall of seawater called a storm surge broke through the levees that protect New Orleans, and about 80 percent of the city flooded. More than 1,300 people died, and some counts put the total near 1,800.
Tornadoes
A tornado is a spinning column of air that stretches from a thunderstorm cloud down to the ground. The strongest ones grow out of supercells, thunderstorms with a slowly rotating updraft inside. The United States gets more tornadoes than anywhere else, about 1,200 a year, mostly in the central plains nicknamed Tornado Alley. Scientists study the damage a tornado leaves and rate it on the Enhanced Fujita (EF) scale, from EF0 (winds of 105 to 137 km/h, which snap branches and peel roof shingles) up to EF5 (more than 322 km/h, strong enough to sweep a well-built house off its foundation).
Hurricane or Tornado? How the Two Spinning Storms Differ
Both spin and both have powerful winds, but they differ in size, lifetime and birthplace.
| Hurricane | Tornado | |
|---|---|---|
| Where it forms | Over warm tropical ocean | Under a thunderstorm, usually over land |
| Size | Hundreds of kilometres across | Usually less than 1 km wide |
| How long it lasts | Days, sometimes more than a week | Usually a few minutes, rarely over an hour |
| Rating scale | Saffir-Simpson (Category 1–5) | Enhanced Fujita (EF0–EF5) |
| Warning time | Several days | Often only about 10 to 15 minutes |
| Biggest danger | Storm surge and flooding | Extreme wind and flying debris |
Surprisingly, hurricanes can make tornadoes: as one comes ashore, thunderstorms in its outer bands sometimes spin up small twisters.
The fastest winds on Earth belong to tornadoes: in May 1999 a radar truck measured about 480 km/h inside one near Bridge Creek, Oklahoma. But because a hurricane is so enormous and lasts so long, it usually causes far more damage overall.
When There Is Too Much Water, or Too Little
Floods are the most common natural disaster in the world. A flood happens when water covers land that is normally dry. There are a few kinds:
- River floods build up over days, when heavy rain or melting snow fills a river until it spills over its banks.
- Flash floods arrive within minutes or a few hours, often after a sudden downpour in hilly or dry country where the ground can't soak the water up fast enough.
- Coastal floods come from storm surges and tsunamis pushing seawater inland.
Floods along China's Yangtze and Huai rivers in 1931 are thought to be among the deadliest disasters in history. Death toll estimates range from about 400,000 to several million, because records are incomplete.
The opposite problem is a drought: months or even years with much less rain than usual. Droughts creep up slowly, so they don't look dramatic, but they dry up crops and drinking water. In the 1930s Dust Bowl, drought and ploughed-up grassland let the wind blow the soil of the US Great Plains away in huge dust clouds.
When Fire Spreads: Wildfires
A fire needs three things, often called the fire triangle: heat, fuel (dry grass, leaves, trees) and oxygen from the air. In a long dry spell, forests and grasslands turn into a huge pile of fuel. Lightning can light it, but many wildfires are started by people, through campfires, sparks from machines or fallen power lines. Strong winds push the flames on and carry embers ahead to start new fires.
Australia's "Black Summer" of 2019–2020 burned more than 18 million hectares, an area about half the size of Germany, and killed or displaced an estimated three billion animals. In August 2023, wind-driven fires swept through the town of Lahaina on the Hawaiian island of Maui, killing about 100 people.
Fire is not always bad, though. Some pine cones only open after a fire, and small controlled burns clear away fuel so a later wildfire is less dangerous.
How Scientists Send a Warning, and How You Can Be Ready
Nobody can stop a hurricane or an earthquake, but scientists have become very good at spotting danger early:
- Weather satellites spot hurricanes days before they reach land.
- Doppler radar can see rotation inside a thunderstorm, so tornado warnings go out before a funnel touches down.
- Seismometers detect earthquakes within seconds. Japan and the US West Coast (through a system called ShakeAlert) send phone alerts that can give a few precious seconds before the strongest shaking arrives.
- Ocean buoys called DART buoys sense the pressure change of a passing tsunami and report it by satellite.
- Volcano observatories track small earthquakes, gas and swelling ground. Warnings had closed the area around Mount St Helens before it erupted.
Warnings work best when people know what to do. Bangladesh is a great example. A cyclone in 1970 killed around 300,000 people there. Since then it has trained tens of thousands of warning volunteers and built storm shelters. When Cyclone Sidr, an even stronger storm, hit in 2007, far fewer people died, roughly 3,400.
What you can do to be ready
- Make a family plan. Agree on a meeting place and learn a grown-up's phone number by heart.
- Pack a kit. Include water (about 4 litres per person per day for three days), snacks that don't spoil, a torch, batteries and a first aid kit.
- Earthquake: Drop to your hands and knees, Cover your head under a sturdy table, and Hold On until the shaking stops.
- Tornado: Go to a basement or a small room in the middle of the lowest floor, away from windows.
- Tsunami: If you are at the beach and feel a strong earthquake, or see the sea suddenly pull far back, head to high ground right away. Don't wait for an official warning.
- Flood: Never walk or ride through moving water. Just 15 centimetres of fast water can knock an adult off their feet.
Practising these steps means your body will remember them even if you feel frightened. If you want to see where the ground is most likely to move, try reading about how tectonic plates shape the planet and spot the places on the map where earthquakes and volcanoes keep happening.