Saturday, March 02, 2013

Update on US Highway 89 Slump and Road Closure

The Arizona Department of Transportation (ADOT) has established a web site to keep the public up to date on the progress in repairing the rupture to US Highway 89 south of Page, AZ. You can access and bookmark the web site here. It really is a great way to keep abreast of the progress as engineers assess what to do to repair  the scenic road.

Also, my colleague Chuck Larue forwarded some photographs taken a few days after the rupture. I'm not quite sure how he obtained these photo's so I cannot give any more credit than that. But whomever took them, thank you.

You can see the south side of the slump scarp at bottom center. It angles down beneath the road bed and is a wiggly dark line. Then look to the far left of the photograph and you can see automobiles on the road. Between these two is the length of the slump. The cliff above the failed section of road (creating a shadow in the center of the picture) is the massive prehistoric slump block that was shown in my previous posting here (fifth and sixth photographs there). This is the block that slipped down from the whitish cliff near the top of this photograph. That surely was one massive slump but just one of many that have occurred on this section of the Echo and Vermilion Cliffs. Slumps do not have to happen catastrophically - they can form by gradual creep. Of course, gradual to the geologist is relative. This massive block could have slipped in one event within a few minutes or it might have taken a few years to decades to get here. In fact, it could still be moving slightly as evidenced by this event. Or.......

Here is a closer view of the south side of the rupture. I am wondering if the break didn't occur on back fill material placed here when the road was under construction? I find it interesting that the road failed no further back into the cliffside (east) than the double yellow line on the road. In road construction, engineers will often cut into the bedrock on the cliff side, and use the "spoil" or removed material as fill on the outside of the road. I'm wondering if only human-made fill is what failed or slipped here? Certainly that is a possibility and I am sure the engineers on site are considering this as well.

This is likely just a digital zoom from the photo above showing a close-up of the rupture area. Look in the scarp created by this recent break. I do not see any evidence for blueish-grey Chinle Formation here, rather just sandy rubble typical of slope wash, talus, or road fill. Of course, the failure occurred well below this view of the rupture, and could have slipped within beds of the Chinle. But don't rule out failure within road construction backfill for this event. In that case, this would make it kind of a non-geologic event.

Helen and I are headed to Lake Powell today and of course, we will not be able to drive this section  of the highway. We will be taking the Coppermine Road and will report back on its condition. Watch the ADOT web site for updates and check back here for pictures of the Coppermine Road..

1 comment:

Denise Traver said...

Thank you so much for the update. Brad was thinking that there is a high possibility of it being a failure of the road bed fill (he is an engineer and it was his first thought, of course). We'll see what comes of further examination from the engineers.