Volcanic activity is commonly perceived as a process that produces a picturesque, shaped structure that periodically erupts in a violent manner, like Mount St. Helens. Although some eruptions may be very explosive, many are not. What determines whether a volcano extrudes magma violently or "gently”? The primary factors include the magma's composition, its temperature, and the amount of dissolved gases it contains. To varying degrees, these factors affect the magma's mobility, or viscosity(viscos=sticky) The more viscous the material, the greater its resistance to flow. For example, compare syrup to water-syrup is more viscous and thus, more resistant to flow, than water. Magma associated with an explosive eruption may be five times more viscous than magma that is extruded in a quiescent manner.