Friday, April 12, 2013

The Highway 89 Slump Near Page - A Re-Evaluation

A colleague in Page, AZ walked up the lower slope of the Chinle Formation beneath the base of the slump along Highway 89. He did this only three days after it happened and got some really good shots, which he shared with me. It is clear from his pictures that the slump is truly a geologic event as ore than just road metal is involved. See my previous posting here where I postulated that maybe just the backfill in road construction was what failed. However, you will clearly see here that Chinle Formation bedrock also broke away from beneath the road.

This is a sequence of four pictures that progressively approach the lower scar of the break. You can see it here beginning in the upper right and traversing across the center towards the large white boulder in the lower left.

It is more clearly visible here. It looks like the material has collapsed vertically downward.

The break is likely about four to five feet in height. This is located well beneath the roadbed.

This material may have risen upwards as the mass of the slide exerted pressure from above

Another view from above of other parts of the failure. Now we'll look at the road damage itself.

The small crack running from the bottom center of the photograph up towards the top shows that a long stretch of highway was affected by movement

It was this unusual (?) straight break in the roadbed that initially caused me to think that perhaps only road metal hade been involved in the movement. A purely geologic event didn't seem to make sense with such an ordered break.

Note the oil streak likely caused when a very surprised driver "discovered" that something was horribly wrong with Highway 89 below the Big Cut at approximately 5 AM on February 20, 2013. As this person was driving north (uphill) in the slow lane (and this is purely a guess), their left wheels must have dropped into the slumped portion of the highway, causing the entire vehicle to lurch to the left. It looks like their oil pan or some other vehicle reservoir ruptured, leaving the oil streak. Looks like they gained control (?) and steered back to the right as shown by the streak going toward the upper right.

Close-up of the oil streak

Look at these tension cracks beneath the break. They look cavernous in this close-up view and they likely go down into bedrock on the slope of the Echo Cliffs. Remember that larger, older slumps are located on this slope.

Damaged road

It's hard for me to tell if this oil streak is part of the previous one shown or if it is another one that pre-dates the slump. But it shows a few inches of offset here and on the white line.

Yikes! That's a pretty good gape.

It looks like some surface rocks were also involved in the gravity affair

Note how the tension ripped apart the metal guardrail

View in the downhill direction (south) showing the extent of the damage in a telephoto shot. The prominent oil streak shown earlier is barely visible in the center of the photograph crossing the double yellow line back to the left. It looks like someone was clearly surprised by this early morning collapse. It is fortunate that no one was seriously hurt and that the geologic event was rather small.

An earlier human mishap on the slope below - the car obviously is well rusted

1 comment:

Mare said...

wow, thank's for posting these. they give a great overview of what happened here.