Complex sentence: Norwegian Thor Heyerdahl also visited this Havitta (in November 1982), but was not allowed to do excavation work; the site had already been ruined by non-professional digging after Bell's visit.
Split into simpler sentences: Norwegian Thor Heyerdahl also visited this Havitta (in November 1982), but was not allowed to do excavation work. Anyways, the site had already been ruined by non-professional digging, after Bell's visit.