Image courtesy of the Arizona Department of Transportation (ADOT) web banner
For those following the closure of US Highway 89 near Page, AZ on February 20, 2013, the Arizona Department of Transportation (ADOT) has just issued an update on the geotechnical work underway at the road failure site on the slope of the Echo Cliffs. You can view the video of what's been found here. I've watched this video twice now and am impressed with the level of professionalism and expertise ADOT has brought to bear on the matter so far.
In the video you will hear some technical jargon but it's possible to break it down into simpler English. First, you'll hear about what has been going on at the site since February 20. Thus far, seventeen holes have been drilled at levels above, at, and below the roadbed, as geologists and engineers attempt to "map" what's in the subsurface beneath the slump. About 500 feet of roadway was affected by the slide but downslope there is a 1,200 foot wide swath of rock that is involved (picture an inverted cone of rock that has failed). Drillers have found that the breaking point, or shear zone is between 105 and 125 feet deep beneath the roadbed. That is still within the confines of the Chinle Formation, the clay-rich deposit that is responsible for so many slumps in both the Echo and Vermilion cliffs. In the video you'll see images of technicians pulling clay cores from the drill holes and how saturated the clay can be at these depths.
The Vermilion Cliffs (background) and its slope-forming Chinle Formation at the base of the upper cliff. The foreground shows a huge slump block on the Echo Cliffs near the present road failure.
Inclinometers have been placed within the drill holes to see if the slumped block of Chinle Formation is still gradually moving downslope. This information is critical in determining what the future might hold for Highway 89. It also explains why it seems to take so long for an answer from ADOT - they are assessing what is going on here and it takes time to see if the earth is still moving beneath the roadbed. Gathering information with the long view in mind will help to frame the central question that everyone in Page is asking, "How long will it take to fix the road?"
If you listen carefully at the end of the video, a deeper question and more important aspect of the problem is expressed, "How should we proceed in the future with this particular road alignment?" The larger meaning of course being, "Is it entirely certain that we should rebuild here." The paraphrasing and emphasis is entirely mine but is gleaned from the ideas alluded to within the interview. You will hear one of the geotechnical engineers state that they are asking the central question, "Can it be fixed here" or even "Should it be fixed here." The rebuilding of the highway here is not yet a done deal and that's refreshing in my view and let me explain why.
First, I think (and hope - along with every citizen in Page) that ADOT will attempt to rebuild the highway here if they possibly can. It's just too damned scenic and loved. And everyone loves the view! However, from a completely geologic standpoint this is not an automatic slam dunk. Especially in light of the fact that Navajo Route 20, now a dirt road of 28 miles, is in the initial phases of being paved, with completion set for sometime in August.
The "Big Cut" through the Kayenta and Navajo formations, immediately uphill from the February 20 slump. A large amount of rock was blasted from here to make the current alignment of Highway 89. Curiously, a much simpler route existed along what is now Navajo Route 20.
I've driven Navajo 20 twice since the February 20 slump and have repeatedly asked myself, "Why wasn't the original alignment of Highway 89 to Glen Canyon Dam placed here instead of the BIg Cut?" This route is very direct and the climb up the Echo Cliffs from Gap is much gentler than at the Big Cut. At most, it may be only two miles longer than the route through the Big Cut and it would not have required such a massive excavation of rock. Simply put, there is a gap in the Echo Cliffs at Gap. In my estimation, the length of Route 20 is nearly exact to the mileage traveled on Highway 89 through the Big Cut and it may even be a tad bit shorter.
Map of the area involved showing US Highway 89 (dark blue dotted line) between Gap and Page. The location of the Big Cut and the nearby slump are labeled in red, Navajo Route 20 shown as the dotted red line. The dotted light blue line represents a possible scenic spur road between the two routes should engineers determine that rebuilding Highway 89 is unfeasible. This road is entirely a creation in my own mind as I ask myself whether rebuilding Highway 89 makes sense or not.
Perhaps the engineers will determine that rebuilding 89 in its present alignment is safe for the time being. Maybe they won't. But geologically, it makes perfect sense to close the current route of Highway 89 and instead use the alignment of Navajo Route 20. That's because as geologists, we are used to thinking long term. In the long run, there will be much lees maintenance needed on the newer alignment. Rebuilding 89 could prove quite costly in the long run and is more dangerous to travel. If a spur road to the Big Cut were made from the newer alignment (about 4.5 miles long), everyone would be happy and the view could still be had! Exciting times ahead as the geotechnical studies continue.
This seminal event marks a curious intersection between humanity and geology. Our knowledge and exploratory techniques allow us, as never before, to visualize many possible futures that could occur here. Preliminarily, one must ask the question, "Why should we rebuild the road here?" Even a cursory examination of the slope aspect, underlying rocks, and the geologic inheritance that is found here, leads one to accept that maybe this is not the best place for a road. When you toss in the viable alternative presented by Navajo Route 20 (less steep, less Chinle Formation, no history of slippage, and perhaps even shorter in length) then you have a real dilemma for highway managers. Stay tuned!