A volcano is defined as an opening in the earth's surface crust through which molten lava, ash, and gases are ejected.
All volcanoes follow this basic volcanic structure.
Mount Etna is a Stratovolcano. Stratovolcanoes are tall, cone shaped volcanoes made up of many layers of hardened lava, tephra, and volcanic ash. These kinds of volcanoes are characterized by a steep shape and regular, explosive eruptions.