Volcanic eruptions are one of Earth’s most dramatic geomorphological processes. Not only can powerful explosive eruptions drastically alter land and water for tens of kilometers around a volcano, but tiny liquid droplets of sulfuric acid erupted into the stratosphere can change our planet’s climate temporarily.
Eruptions will often force people living near volcanoes to abandon their land and homes, sometimes forever. Those living farther away are likely to avoid complete destruction, but their cities and towns, crops, industrial plants, transportation systems, and electrical grids can still be damaged by tephra, ash, lahars, and flooding.
There are a couple of very good websites where you can learn more. The first is the USGS (United States Geological Survey) volcano hazard section. The second is the BBC Science Natural Disasters section with plenty of useful video clips.
Monitoring volcanic activity is very important in order to prepare for the possibility of a hazard occurring, this section of the USGS website explains how monitoring takes place. There is a limit to the extent of what can be done and a certain amount of responsibility is put upon individuals to have robust evacuation and contingency plans in place. The impacts and consequences of an eruption will be linked very closely to the level of development and access to resources.