Final answer:
An explosive volcanic eruption is caused by high-viscosity magma and the buildup of gases. The decrease in pressure as magma ascends allows gases to expand, leading to a violent eruption. Such eruptions can lead to global climate cooling due to the release of sulfur dioxide and particulates.
Step-by-step explanation:
An explosive volcanic eruption is primarily caused by high-viscosity magma and the buildup of gases within the magma. When such magma ascends towards the Earth's surface, the pressure decreases, allowing the dissolved gases to exsolve and expand rapidly.
This rapid expansion of gases increases the pressure within the magma until it exceeds the strength of the surrounding rock, leading to a violent and explosive release of magma and gases into the atmosphere. This can result in the cooling of the global climate, as with the 1783 eruption in Iceland, which released large volumes of sulfur dioxide, contributing to haze-effect cooling.
Moreover, the composition and characteristics of magma play a significant role in the explosiveness of a volcanic eruption. High-viscosity magma impedes the escape of volcanic gases, leading to higher pressure buildup and more explosive eruptions.