Do volcanos really create fertile soil?

Question

I'm developing an ecology for a portion of my world that's geologically active and I remembered hearing that volcanic ash in soil makes it more fertile to agriculture. \n\nAfter extensive googling I've found surprisingly little information about the subject, and nothing convincing. Is this just a science "fact" that gets spread around without actually being completely true? If it is true, or partly true, what is the chemical process at work, and under what conditions is it the most effective?

Answer 1