A volcano is an opening on the Earth's surface, which allows hot lava, volcanic ash, and other gases to escape through the Earth's crust. Volcanoes cause a lot of damage in many different places, for example in Pompeii, where Vesuvius erupted. Vesuvius is considered one of the most dangerous volcanoes in the world because in 79 AD it destroyed the entire city of Pompeii and killed around two thousand people. Pompeii was a city of the Roman Empire, located on the western coast of Italy. Many wealthy Romans had large homes there. At its peak Pompeii had a population of around twenty thousand people. Pompeii is a highly active volcanic area and on 24 August 79 AD the city was reduced to ruins by the eruption of Vesuvius. Most people fled when the eruption began, but about two thousand people decided to stay and were buried in the eruption along with the city. Most of the material covering Pompeii consisted of small, light pebbles and some ash. Most of the people died due to the toxic poisonous gas explosion. The eruption lasted about a day, due to the eruption Pompeii was buried under about 25 feet of volcanic ash and lava. Throughout the world there are many different types of volcanoes, but there are only three main types, Composite, Shield and Dome volcanoes. A composite volcano is also known as a Stratovolcano, this volcano is built from numerous eruptions that have occurred throughout history. Composite volcanoes are tall cone-shaped mountains. These volcanoes erupt in different ways at different times. Shield volcanoes are the largest volcanoes on earth. These volcanoes are built almost entirely of lava. Shield volcanoes are produced by the gas and heat of the earth... middle of paper... different types of gases start coming out of the mouth of a volcano, some of these gases can be harmful because they are extremely toxic. Therefore, you can easily find out when a volcanic eruption is about to occur due to the signs or sudden changes that the volcano emits about weeks or months before the eruption. Many major volcanic eruptions have occurred throughout history. Those volcanic eruptions caused starvation, tsunamis, ash flows, mudslides and many diseases. For example, Mount Tombora erupted in Sumbawa Island, Indonesia, in 1815, and is one of the highest volcanic eruptions in human knowledge. The eruption produced tsunamis with waves approximately 10 meters high. The eruption was so loud that it was heard more than twelve hundred miles away and killed approximately seventy thousand people. Mount Tambora is still active today.