How do Volcanoes from?
Volcanoes form when magma rises through the cracks and weaknessess of the Earth's crust. Then pressure starts to build up below the crust and eventually the pressure releases causing magma to explode above the surface. This is called a volcanic eruption. Finally the magma cools down above the surface making a new crust from where the eruption happened. This whole process happens several times, with each eruption creating a new crust and over a period time a cone-shaped volcano will form. Below is a diagram of a cone-shaped/coposite volcano.
The Effects of a Volcano
The effects of a volcanoes can be good as well as bad. Volcanoes can have devasting effects such as taking the lives of people but it can also have positive effects e.g. providing geothermal energy using it's intense heat. The lava and ash from a volcano provides valuable nutrients for the soil which is amazing for agriculture but at the same time the ash and mud from a volcano can mix with rain water or melting snow causing fast-moving mud streams called Lahars. Lahars and Lava streams can seriously damage woodlands, farmlands or human landscapes making some damage caused irreversible. The first video is negitive effects and the second video is positive effects.
Types and Differences
The are two types of volcano. One is called a Shield volcano and this particular type is a very low-lying volcano with genty sloping sides. The eruptions caused by a Shield volcano tend to be calm and not very explosive. Shield volcanos are found ontop of two constuctive crustal plates, which means that the two crustal plates are moving away from each other explaing why the Shield volcano is low-lying and have gently sloping sides. The diagram of a Shield volcano is below.
The other type of volcano is called a Composite volcano, the type of volcano we tend to know and see. Composite volcanoes have relatively steep sides and are usually quite high in comparison to the Shield volcano. Eruptions from this volcano are usually destructive and explosive and some eruptions can even create pyroclastic flow. Composite volcanoes are found ontop of two destructive plates (destructive - two plates moving towards each other). The diagram for a Composite volcano is underneath the explanation of how volcanoes form.
Finally there are three more categories for both types of volcano depending on its activity. There is an active volcano, one that erupts often, a dormant volcano which is temporarily inactive but not fully extinct and a extinct volcano, a volcano that is never likely to erupt again.