What is 'Alaska Triangle', where 20,000 people mysteriously disappeared?

Over 20,000 people have mysteriously disappeared in "Alaska Triangle", located around three points of Anchorage and Juneau in the south, and northern coastal city Utqiagvik, since early 1970s. It first came to attention in 1972, when a small plane carrying two US politicians suddenly disappeared en route from Anchorage to Juneau. Some believe there's unusual magnetic activity in the area.