I've taken this shot in 2002. This volcano erupt usually 1-2 minutes every 45-60 minutes, these eruptions aren't usually dangerous, so you can climb the mountain (with hundreds of tourists from all the world) and stay on the summit, only 300 meters far from the mouth, to take a lot of pictures with a long exposure. The permanence on the summit during the night is not permitted, but nobody keep to this rule.
Sometimes it become dangerous due to the increase of activity (i.e. 2 months ago).