A volcano is a surface landform resulting from the extrusion of magma from underground as lava, ash, rocks, and gasses are erupted in various proportions. Each year, around 60 major volcanoes erupt globally. How hazardous each one is, depends on a variety of human and physical factors that interrelate to determine the level of impact on human activity that each event exerts. I will be looking at how the physical properties of a volcano, interact with human variables to make certain volcanoes more hazardous than others. This essay will incorporate exemplification from countries at different stages of development to discuss human factors and how this links with their physical geography. The scale will be primarily global; both development spread and tectonic activity are best presented in this manner.
The strength of an earthquake, measured on the Richter scale, often determines the level of damage caused by an earthquake. Therefore, it is reasonable to assume that the power of a volcanic event is illustrative of how potentially hazardous an eruption is going to be. The explosiveness can be measured by the Volcanic Explosivity Index (VEI); the higher the VEI, the greater the potential hazard. The type of magma, and ultimately the classification of volcano that is created, is a huge physical factor in determining a volcano`s explosivity. Magma comes in many forms and each chamber is unique. Therefore, a wide spectrum of lava types can occur. The viscosity of the magma is primarily determined by three factors: temperature, dissolved gasses, and the chemical make up. The hotter the magma is and the lower the silica content, the more fluid it will be and therefore the less explosive; if magma has a high level of dissolved gasses, then it is also likely to be less viscous. Thick lava, for example acid lava, has the potential to cause much larger and more explosive eruptions, therefore presenting a larger threat and increased potential for hazardous activity.