A is a violent storm with strong winds and heavy rains. They are the largest and most powerful of all storms. A is a small, powerful windstorm over land. It looks like a giant funnel. A is a huge flow of water over land that is usually dry. They can be caused by heavy rains, melting snow or breaking dams. Sudden movement in the rocks that make up Earth's crust is caused by an . A is an opening in Earth's surface.