Can we predict, maybe prevent, the next Rockfish Gap rock slide?
Hindsight being what it is, Chuck Bailey, a structural geology professor at William & Mary, would have predicted the May 3 rock slide on Rockfish Gap, if he’d been asked.
What does that say for the future of rock slides in the area, an important connection point between the Shenandoah Valley and Central Virginia?
“You might argue that if we’re looking forward, we could identify locations on the mountainside there that maybe have the highest probability of slipping and then think about trying to do something proactive as opposed to reactive,” said Bailey, who happened to be driving through the area a day ahead of the slide that has closed U.S. 250 for the foreseeable future, as VDOT engineers are working overtime to try to stabilize the slope.
“I actually had to go over to the Valley that day, so I ended up crossing over on Route 250. I hadn’t done it in months and months and months, so it was it was sort of unusual of late. I was in a hurry and climbing up the hill, really right near the Albemarle-Nelson line, and I noticed some trees that were a little cattywampus, and then rocks that were lying sort of in the gutter by the side of the road. And immediately I was like, hmm, we’ve got some kind of a mass movement happening here,” Bailey said.
“It’s not unusual to see a little bit of rock fall, and as I said, I zoomed on by, and it sort of receded in the rearview mirror. I’m like, I’m wondering if this is going to turn into a bigger deal. And it was the next day when some of my Williamsburg friends who have parents in the Augusta County area were, like, the road is closed, everything is coming down the hill. And that was when I realized it was a big deal.”
It’s also pretty much an inevitability that these kinds of things will happen, given the complicated geology at Rockfish Gap, a low point in the Blue Ridge, with an elevation of 1,903 feet.
Mountains in the Blue Ridge are generally 3,000 feet or higher in elevation, so the Rockfish Gap has long been viewed as a connector between east and west, dating back to the days when Claudius Crozet was tasked with trying to build a railroad tunnel through the gap back in the 19th century.
Problem is, it’s not perfect, from the standpoint of the geology of the area.
“When you look at the landscape on that side of the hill, on the east side of Rockfish Gap, it’s pretty steep to begin with, and to get those roads, and also the railroad below that, to the kind of the grade they wanted, basically, construction engineers had to remove a lot of rock, and they used that rock in places to fill in little valleys and hollows,” Bailey said.
“Effectively, human activity oversteepened some of the slopes there. That is a natural consequence of sort of building these roads,” Bailey said.
This is something that Bailey witnessed firsthand on a recent visit to the site, post-slide.
“What I noticed when I was up actually examining the slide was that, that’s cut into a really steep part of the hill there,” Bailey said. “I don’t think I’d appreciated actually how steep it was until I was there. They’re not the highest road cuts. If you’re on the interstate, some of those are just well, from just a geology point of view, glorious. They’re big, they’re broad. These are smaller and older, but they’re still very, very steep.”
What that translates to: “If you were going to sort of predict where you might expect the landslide to occur, the places that have the steepest cuts would be ones to look at,” Bailey said.
The area of the most recent slide is one of about a dozen that Bailey said appear to be prime for slipping in the near-future, which is why trying to get ahead of future slides is probably a good idea, even as VDOT is consumed in the here and now with trying to correct for the issue at hand.
The last thing any of us want to see happen is a major slide that closes Interstate 64, which crosses roughly 100 yards above the site of the current slide that has U.S. 250 closed between Route 6 and Route 151.
VDOT in 2016 pegged the average annual daily traffic of Interstate 64 over Afton Mountain at 18,000 vehicles a day both eastbound and westbound in 2016, with an additional 6,700-7,000 vehicles using the stretch of U.S. 250 between the Nelson County and Albemarle County lines that is currently closed to traffic.
Losing I-64 would be a state of emergency-type situation considering the economic connections between the Valley and Central Virginia.
Good news there: according to Bailey, it doesn’t look like the current slide should have an impact on the slope that the interstate crosses.
“VDOT has their hands full with the big mess right above 250,” Bailey said. “Part of their remediation is going to be to make sure they can take the slope down so that it’s no longer a significant risk to 250, and at the same time, not allow that landslide to kind of chop away and go uphill. It’s still probably 100 yards or more away from getting close to the interstate. On first glance, it doesn’t appear to be moving up slope, so that’s a good thing.”
Story by Chris Graham