Scientists have known a lot about the earth. They understand how mountains are made and what a volcano is. The following example is about volcanic eruptions. Mt. Vesuvius in Italy and Mt. St. Helens in the USA are both famous mountains. They are both volcanoes. A volcano is a mountain that is open at the top. Smoke and hot air come out of the hole. Sometimes, very hot rock also comes out of the mountain. That can make trouble for people nearby. This is what happened with Mt. Vesuvius and Mt. St. Helens. Hot rock poured out of Mt. Vesuvius and covered the town of Pompeii in 79 AD. Everyone in the town was killed. The Mt. St. Helens volcano didn’t kill many people.