These different pyroclasts will fall on the volcano and, over time build up the volcano. The lava also rises and oozes down the mountain, spreading out as it goes down. This will continue for some time. After that the volcano starts cooling down, releasing hazardous gases. And after all of this, the volcano is dormant again.
Volcanoes also have a damaging effect on the weather.
In 1982, El Chichon, in Mexico, erupted. El Chichon was just a small volcano. However, there are still small clouds of ash hanging in the sky because of it. It was a very unlucky year that year because it happened to be an El Nino year. The volcanic eruption just exasperated the bad situation.