The following is a transcript of a report by Team 4 investigator Paul van Osdol that first aired Sept. 28, 2006, on WTAE Channel 4 Action News at 6 p.m.

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The rain is slowing the cleanup of the landslide along Route 65, and Thursday night, we have new insight as to what may have caused the massive slide that's jammed traffic and frayed nerves for the past week.

Jim Hamel got his Ph.D. in the late 1960s studying a major landslide that occurred along Interstate 79 just a mile away from the current landslide location.

He said you combine unstable slopes with heavy development and you have a good possibility that the earth will move.

This might look familiar, a landslide closing Route 65 in Kilbuck Township, but this landslide happened 16 years ago -- just two miles from where Route 65 is now closed.

Last year, there was this landslide -- also in Kilbuck -- that shut down Toms Run Road.

Hamel, of Monroeville, said the area around Kilbuck is particularly landslide prone. It's full of a weak rock known as the Pittsburgh redbed.

"Because you've got more weak, thick material high up on the slopes, you have more potential for natural landsliding in a setting like that," said Hamel.

Intensive development like a Wal-Mart only make the hillsides more likely to slip away.

"We have an Appalachian heritage of throwing things on hillsides, dumping things on hillsides, which exacerbates the situation by loading some of the hillsides," said Hamel.

Hamel investigates landslides for a living, and while he does not know what caused the one in Kilbuck, he does know where he'd look.

"You always look at the land modifications, man-made land modifications. That's almost the first thing you look at in an investigation like this -- who did what to the ground when?" said Hamel.

Hamel said blasting could be a factor -- as it was in the last landslide at the development site in April.

Another possible factor -- the steepness of the slopes. Wal-Mart opponents said Kilbuck Township never should have allowed variances to its grading rules that permitted steeper slopes at the site.

"It's sort of like gravity in action," said Hamel. "Put things up on a steeper slope, they tend to fall down more than if you put them on a flatter slope."

Hamel said hillside developments can be made landslide-proof, but it takes a lot more money. He said western Pennsylvania ranks right up with southern California in the number of landslides.