Tornadoes are violently rotating columns of air that are in contact with the Earth and either a cumulonimbus or a cumulus cloud. Tornadoes are often referred to as twisters, whirlwinds, or cyclones. While most tornadoes attain winds of less than 110 miles per hour (180 km/h), are about 250 feet (80 m) across, and travel a few miles (several kilometers), the wind speeds in the most intense tornadoes can reach 300 miles per hour (480 km/h), are more than two miles (3 km) in diameter, and stay on the ground for dozens of miles (more than 100 km). Various types of tornadoes include the multiple vortex tornado, landspout, and waterspout. Other tornado-like phenomena that exist in nature include the gustnado, dust devil, fire whirl, and steam devil. Most tornadoes occur in North America (in the United States and Canada), concentrated in a region nicknamed the Tornado Alley. Tornadoes also occur in South America, South Africa, Europe, Asia, and Oceania.