after all, steam sizzling from a rocky dome thrust up from the molten magna below and earthquakes still rattling this mountain. the volcano is very much align deep low. >> we have evidence that sometimes it erupts at least intermittently for a series of centuries. so there's all the evidence that it's going to erupt again. >> reporter: but when? next week or next century, scientists don't know. this dam is designed to stop the landslide. the debris is much than buried across the path. >> change is going to occur. it's just a matter of how we as man deal with that change. >> reporter: perhaps several human lifetimes from now, nature will have repopulated this volcano sculpted valley bringing in dense stance of native fir. >> the plan did not work. it didn't work for man's advantage but we've learned after 20 years that there has been some advantages of it. >> reporter: youngsters too kwroupg -- young to remember the eruption play soccer on the ash. and you can still hear folks measure time from the volcano. >> it was awesome then the devastation was awesome too. you cannot believe what i