Short term: The effect of volcanic eruptions on life in a shorter period is destructive, as it destroys vegetation, civilizations (as seen in Pompeii) as well as other things. The air around the volcano will also be temporarily heavily clouded with dusts and other debris, making the area hard to live in (unless with breathing assistance). Because of this, volcanic eruptions are a "natural disaster" because it changes the area around the volcano in a negative way, at least for short term.
Long term: The long term affect is actually much more positive, as the Volcanic ashes are high in nutrients, and the nutrients are returned into the ground. This usually would generate a high-amount of vegetation growth, and the area would usually be deemed best for farming.
Even though in a shorter term, volcanic eruptions are negative, because of loss of life and destruction of the land life around it, in a long run, volcanoes are good for the land, for it helps continue the cycle of allowing farmers to plant food and feed the planet
hope this helps
