A very tragic scene is playing out in Washington state. Sadly, this even was entirely avoidable. However, as is so often the case, real estate values trump geology.

The NY Times article In Ocean of Mud, a Plea: Leave Me and Find My Wife has a good sidebar explaining in simple terms how landslides happen. Local officials have claimed that this disaster could not have been forseen, but that is B*** Sh**, to put it mildly. Down about the middle of the linked NYT article is an pre slide air photo ("Extent of the Mudslide"). Anyone with the least bit of geologic background would recognize the old scarp from a previous slide, and the active undercutting of the toe of the old slide by the river.

And in fact, the Seattle Times article Risk of slide ‘unforeseen’? Warnings go back decades points out that this slide had been recognized and well documented numerous times in the past. Unfortunately, as the geologist interviewed in the video points out, people are unwilling to listen to mere scientists. And, in many cases, real estate interests have blocked efforts at zoning around recognized hazards. In some cases, geologists, engineeers, and others have been threatened with law suites if by publisizing hazards they impact real estate values.

The Atlantic photo spread At Least 14 Dead in Washington State Mudslide shows a number of good views of the slide and the body recovery efforts. In particular check out photo #10 which shows a before and after view. As in the photo noted in the NYT article, it is trivial for the trained eye to recognize the old slide being undercut by the river.