RIVERDALE — It’s been said that change is the only constant in life. The Riverdale landslide is proving to be the perfect illustration of that idea.
Since the initial Nov. 19 slide forced the evacuation of three homes on 600 West in Riverdale, land atop the bluff has been steadily — if unpredictably — disappearing over the side of the 200-foot sand cliff. The slide is now beginning to eat into the backyard lawns of homes closest to the slide.
After more movement along the slide in the last week-and-a-half, geologists say the area is as dangerous as ever. And they don’t expect things to get better anytime soon.
Ben Erickson, project geologist with the Utah Geological Survey, says another piece of the Riverdale hillside gave way on Jan. 9 or 10, and a second slide occurred sometime this past weekend, on Jan. 14 or 15. Between the two incidents, Erickson says they probably lost another 10 to 20 feet of the land atop the bluff.
Add that to prior movement over the past two months and Erickson estimates between 30 and 40 feet of the cliffside has given way since the initial landslide just four days before Thanksgiving. That first slide dropped a 650-foot section of the bluff in mere seconds, sending between 4 and 7 feet of mud and debris onto a pasture below.
“It’s alarming,” Erickson said. “The land just caves into the slide. You could be standing there and it just lets go, without warning.”
The without-warning part is the most troubling aspect, according to Erickson. With many landslides, there are often signs that something is about to happen — cracks appearing in the ground, or movement detected by various scientific instruments. But the so-called Spring Creek Road landslide gives no such heads-ups.
On Thursday, Jan. 18, Erickson and fellow UGS project geologist Greg McDonald were back atop the slide, taking measurements and installing a new survey stake to replace one that was once located at least a dozen feet from the edge but is now only inches from it.
What’s more, the slide’s movement has begun shifting toward the north and is undercutting a section of lawn in one backyard, according to McDonald.
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Geologists have to be careful where they step. “We’re not going to sacrifice ourselves for one data point,” McDonald joked.
Two months in, the experts still have a lot more questions than answers about the landslide.
But one thing’s for sure: “The more water, the more activity at the slide,” Erickson said. “Water’s always the culprit.”
Erickson suspects rain caused this latest slide activity. He said an active spring is coming from the bottom of the bluff that is carrying a lot of sand out with it, which allows the hillside to collapse more.
Erickson and McDonald believe that when the spring snowmelt comes, and area residents begin watering their lawns again, the increase in groundwater in the area will result in more slide activity.
This week, wells were scheduled to be drilled atop the bluff in an attempt to further study and monitor the groundwater level that is exacerbating this natural disaster, according to Erickson.
Riverdale city administrator Rodger Worthen said the slide face still remains quite vertical — and therefore unstable.
“It’s doing what the geologists have indicated it will do until it finds this angle of repose,” Worthen said. “Until then, it’s going to continue to move. I don’t want to act like it’s not important or significant, but it’s something we knew would be ongoing.”
As the slide continues to enlarge, Worthen stresses that the areas immediately above and below are extremely dangerous. And he says the city has had a problem with some people ignoring the warnings and venturing into the slide area.
“You can tell people to stay out until you’re blue in the face, but some people just won’t listen,” he said.
Although no one saw the Riverdale slide coming, Erickson says that, in hindsight, a few signs were there. Historically, landslides have occurred along both sides of the sandy bluff flanking the Weber River.
“And back in the 1950s, there was a similar slide just a couple of houses down in this neighborhood,” Erickson said.
What’s more, aerial photographs taken last June indicate there may have been some early movement of the slide area, even back then.
Whatever its past, the Riverdale landslide will likely continue to be active for the foreseeable future as scientists work to better understand what’s causing it, according to Erickson.
“It’s an interesting slide now, to say the least,” he said.