Flash flood

Water can rise very fast.

This is a flash flood. It happens in less than six hours. Heavy rain can cause it. Melting snow or ice can also do it.

The water moves very quickly. It can sweep away cars. It can even move large rocks and logs. These floods can happen in dry areas too. Do not try to cross the water. It is safer to turn around and stay away.

A flash flood is a very fast flood. It happens in less than six hours.

Heavy rain from storms can cause it. Melting ice or snow can also start one. Even a broken dam can let out too much water.

Flash floods are very dangerous. The water moves fast. It can sweep away cars. A large SUV can be carried away by just a little water.

In dry deserts, these floods are even trickier. The soil there often cannot soak up the rain. This creates runoff, which is water that flows over the ground.

In deserts, the water can carry rocks and logs. Deep slot canyons are also risky. A storm far away can send water into a canyon. This can trap people inside.

In the U.S., more people die from floods each year than from lightning or tornadoes. The weather service says, "Turn Around, Don't Drown." This means you should stay away from the water. Do not try to drive through it. It is much safer to turn around.

A flash flood is a very fast type of flooding. It happens in low areas like rivers, dry lakes, or deep valleys. These floods are different from regular floods because they happen quickly. The time between the rain and the flood is less than six hours.

Heavy rain from a thunderstorm or a hurricane can start them. Melting ice and snow can also cause a sudden rush of water. Sometimes, a dam built by people or a natural dam of ice can break. When this happens, a huge amount of water is released all at once.

Flash floods work by moving water very fast across the land. In dry desert areas, this can be very tricky. The soil in deserts is often like clay. This type of soil does not soak up water well. Instead, the rain becomes runoff, which is water that flows over the ground.

This water rushes into channels and rivers very quickly. In some places, the water also carries heavy debris. This includes things like large rocks, branches, and logs. This moving mess can make the flood even more powerful.

History shows us how dangerous these events can be. In 1889, a flood happened after a dam failed in Johnstown. More recently, a big storm hit southern Utah on September 14, 2015. That storm caused a cloudburst that led to 20 deaths. Seven of those people were hikers in Zion National Park. They were trapped in a deep slot canyon by the water.

These canyons are dangerous because they are hard to climb out of quickly. A storm can happen on a mesa many miles away and still send water into the canyon.

There are many important facts about these floods in the United States. The National Weather Service says floods are a major hazard. On average, 127 people die in floods every year in the U.S. This is more than the 73 people who die from lightning. It is also more than the 65 people lost to tornadoes.

Even small amounts of water are dangerous for cars. As little as a little bit of water can carry away an SUV. Most people who die in floods are swept away while in vehicles.

We can see how these floods change the world around us. They can wash away soil, which is called erosion. This can even move sand into places like the Nile delta. Floods can also hurt plants that like dry ground. However, some plants like certain types of rice can handle the water.

To stay safe, experts say, "Turn Around, Don't Drown." This means you should never try to cross a flooded road. It is always better to find a different path and stay away from the moving water.

A flash flood is a sudden and rapid flooding of low-lying areas. These areas include riverbeds, washes, dry lakes, and depressions. Flash floods are distinct from regular floods because of their speed. The timescale between the initial rainfall and the onset of flooding is fewer than six hours. This rapid onset makes them a significant hazard to humans and the environment. They can occur almost anywhere downstream from a source of precipitation.

Several different mechanisms can trigger a flash flood. Most often, they are caused by heavy rain from severe thunderstorms, hurricanes, or tropical storms. They can also be caused by meltwater from melting ice and snow. In volcanic regions, the intense heat of an eruption can melt glaciers. This sudden release of water creates a flash flood. Another cause is the collapse of a dam. This could be a natural dam made of ice or debris. It could also be a man-made structure, such as a human-built dam. When a dam fails, a massive quantity of water is released. This water can destroy everything in its path.

Flash floods behave differently depending on the local landscape. In arid or desert regions, they can be especially deadly. These areas often have clay-like soil that is poorly absorbent. Because the ground cannot soak up the water, the rain becomes runoff. Runoff is water that flows over the land surface instead of sinking in. This increases the volume of water that rivers and channels must handle. In these regions, storms are infrequent but can deliver enormous amounts of water quickly. Furthermore, desert roads may cross dry creek beds without bridges. A driver might see clear weather, but a river can form in seconds.

Geography also plays a major role in how dangerous these floods are. In the United States, they are common in the high mountain ranges. They are also frequent in the arid plains of the Southwest. Deep slot canyons present a unique danger to hikers. A storm might occur on a mesa many miles away from the canyon. That rain can still send a flood sweeping through the canyon. Because the walls are steep, it is very difficult to climb out of the way. For example, a cloudburst in southern Utah on September 14, 2015, caused 20 fatalities. Seven of those deaths occurred at Zion National Park when hikers were trapped in a slot canyon.

Flash floods are a leading cause of death from natural hazards. In the United States, they cause more fatalities on average than lightning, tornadoes, or hurricanes. According to 2005 data from the National Weather Service, an average of 127 people die yearly in floods. This is higher than the 73 deaths from lightning, 65 from tornadoes, or 16 from hurricanes. Vehicles are a major factor in these statistics. More than half of the fatalities involve people being swept away in vehicles. Even a small amount of water is enough to carry away an SUV-sized vehicle. The National Weather Service advises people to "Turn Around, Don't Drown" to avoid these risks.

These events have a wide range of impacts on the environment. They can cause rapid soil erosion, which is the wearing away of the earth. Some flash floods contribute to sedimentation in places like the Nile delta. While they cause little bedrock erosion, they deposit large amounts of sediment on floodplains. Flash floods also affect vegetation. Plants that are not adapted to frequent flooding may be destroyed. However, some plants, like certain varieties of rice, are adapted to endure these events. Other plants that thrive in dry areas may experience stress from the large amount of water.

Scientists use various tools to study and predict these hazards. Researchers use datasets like the Severe Hazards Analysis and Verification Experiment (SHAVE). They also use U.S. National Weather Service Storm Data datasets. These help connect physical processes to flood impacts. In 2020, an impact severity scale was proposed to classify flood effects. This scale groups effects into four categories. These include impacts on the built environment, man-made mobile objects, the natural environment, and the human population. This research helps improve forecasting models and helps with prevention planning.