A volcano is an opening in the Earth's surface where molten rock, ash, and gases can escape from below. When pressure builds up inside the Earth, it can cause an eruption, sending lava flowing down the sides of the volcano. Some famous volcanoes include Mount St. Helens in the United States and Mount Fuji in Japan. Volcanoes can be found all over the world, often in areas where tectonic plates meet. They can create beautiful landscapes, but they can also be dangerous. When a volcano erupts, it can affect nearby communities and the environment, making it important to monitor their activity.