Why did the colonist of Roanoke disappear?

The WikiAnswers community has many different thoughts on the subject:

• Some of the tribe members bore the same last names as some of the missing colonists. In addition, many members of the tribe had Anglo features - fair eyes, light hair, and Anglo bone structure.
• There are several theories as to what might have happened. Some of them may have moved south to merge with the friendly natives. Some may have tried to sail back to England. Some may have moved north to the Chesapeake Bay. Some may have moved inland to the mainland. There are no definitive answers, just theories - some sensible, some not so sensible.
• They don't know why they left or disappeared.
• No one knows but vikings might have something to do with it.