A very simple explanation of a volcano is a vent in the Earth’s surface where magma (molten rock), ash and gases erupt. The basic structure of a composite volcano is the main vent, which is the pipe up the middle. The molten rock flowing down the side is called the lava flow. The layers that form the volcano are the ash and lava strata.
Sometimes on the side of the volcano is a secondary cone. The magma chamber is at the very bottom of the volcano and is the source of the molten rock. Gas escaping to the surface is called fumerole. A crater forms at the top of a vent. The material that is in the air during and after an eruption is ash and gas clouds.
Shield volcanoes are huge. An example of one is the Mauna Loa volcano in Hawaii. They are built from many layers of lava flows leaving a broad shaped cone. The slopes are gentle because the very fluid lava cannot pile up into a steep mound.
Pressure builds in a magma chamber and forces magma up through the pipe and out of the vents. That is called an eruption. Once magma has been ejected out onto the surface it is commonly referred to as lava. The type of eruption varies based on the viscosity and the types of gases in the molten rock.
Viscosity means how sticky the magma or lava is. The stickiness is largely determined by how much silica is in the molten rock. Flows that have low viscosity, low levels of silica, are very runny and flow fast downhill. A higher viscosity, which is lots of silica, will make the magma ooze down the surface and forms a thick dome.
The gases that are contained within the magma determine how violent an eruption will be. Some of the gases are toxic and can suffocate people and animals. Examples of a few gases are steam, sulphur dioxide and carbon dioxide. If the magma contains large amounts of dissolved gases, the volcano will erupt like a soda that has been shaken, very explosive. Small amounts of gases will erupt quietly and overflow down the side.
Most volcanic eruptions cause widespread devastation. People and animals killed, loss of land and home, sometimes permanently, and even the climate can be changed for a period. There are many hazards associated with eruptions. One of the most hazardous is a pyroclastic flow, which is a mixture of hot gas, ash and volcanic rocks moving quickly down slope. Pyroclastic flows cannot be outrun. A pyroclastic surge is a low-density flow of material. They are less concentrated and controlled and contain many toxic gases that kill.
Despite all the bad effects immediately during and after an eruption, there are some positives. The ash thrown out is turned into very fertile soil. The minerals in the ash create a rich growing area, which is why many people return after an eruption.
The heat from the earth’s crust in the area can be used for geothermal resources like energy. Beautiful scenery occurs afterward when plants and animals return and the lay of the land as been changed. Spectacular sunsets can last for weeks after an eruption from the ash and dust in the atmosphere.