Flash Crash Rumble and roll

Flash Crash Rumble and roll

The day is quiet. The air is still and hot. Leaves do not move. Flowers droop. Even the birds are still and quiet. There are big white clouds in the sky. a

They grow bigger and taller. And they get darker and darker. “ Look at those black thunderclouds, " people say. “ We're going to have a thunderstorm. "

Warm air near the earth is rising into the clouds. The air goes up fast. Inside the clouds it keeps moving upward. It may go all the way to the top and spill over. The clouds keep growing. After a while the clouds may be ten miles high. The rising air carries water. But it's not liquid. It is a gas called water vapor. When water vapor cools, it becomes liquid water. That's what happens in the clouds to make them grow. Water vapor cools and changes into small drops of water, and also into small crystals of ice.

Air inside the cloud carries the water and ice up and up. The air gets colder. When it gets very cold, the air falls. So the air inside some parts of a cloud is moving up very fast, and in other parts it is moving down. Planes stay out of these dark thunderclouds. The rushing air could turn a plane upside down. It could even rip off the wings.

Also, there's electricity in the clouds. Each water droplet and ice crystal carries a tiny bit of electricity. There are billions and billions of droplets and crystals. So the amount of electricity gets greater and greater. When the amount is very great, the electricity jumps from the top of the cloud to the very bottom. It makes a giant spark-a flash of lightning.