Why do volcanic soils often become very fertile after eruptions?

Volcanic materials contain minerals such as potassium, phosphorus, and iron that become available as the rock weathers. Over time, ash turns into fertile soils that can be excellent for farming, especially in warm climates with enough rainfall. That is why regions around volcanoes, including parts of Indonesia and Italy, have supported dense agriculture for centuries. However, fertility usually develops only after the immediate danger from eruptions has passed.