This is the sort of thing that can put a kink in the regional economic recovery...
massive rockfall on Interstate 40 - could take months to clear
It's not the first time that stretch of road, which runs through the steep Pigeon River gorge, has had trouble. In 1997, a large rockslide in the same area closed I-40 from July through September.
Sunday's huge slide was reported about 2 a.m. at mile marker 2.6, about 50 miles west of Asheville near the Tennessee border.
One woman driving on I-40 struck some rocks before the road was shut down, according to N.C. Highway Patrol Trooper Gene Williamson. She was taken to a local hospital with non-life-threatening injuries.
UPDATE: Reclisted. Thanks! Perhaps there is a market for non-HCR diaries after all. :)
There are alternative routes, but they add significantly to travel time. They're not especially tall mountains, certainly not by Western state standards but when it comes down to it this is the most imposing portion of the Appalachian mountain chain.
I-40 and The Interstate Highway System
I-40 is one of the ost important east-west travel routes across the continental United States.
The North Carolina end of the highway has experienced a disproportionate share of challenges. especially in the area of interest this morning:
One of the most dangerous portions of I-40 throughout its entirety is the section that travels through the Pigeon River Gorge in Haywood County. Known locally as simply "the gorge", this part of I-40 cuts a path west from Waynesville to the Tennessee state line. This section of the interstate is fairly curvy and tends to become a bit narrow in some places when compared to other portions of the highway. Because much of the road was cut through mountainside, concrete retaining walls have been built on both sides of the road and in the median, cutting down on the width of the breakdown lanes. Coupled with speeding vehicles, the extremely thick fog that tends to plague the area, and little room to maneuver in case of accident, this area has become notorious for its severe and many times fatal accidents. It is reported that a person is 20 times as likely to die on I-40 in Haywood County than they would be to win the Powerball lottery, which equals to be twice the average of any other Interstate Highway in North Carolina.[7]
...
This portion of the highway is, also, notorious for rockslides and rocks falling onto the highway. The main cause is an engineering flaw, in that sections of the highway have been built on the north side of the Pigeon River, where the rock strata foliate towards the highway. In July 1997 a rockslide near the Tennessee state line closed the road for nearly six months.[8] In 1985, a severe rockslide buried the westbound entrance to one of two tunnels that carry the highway through the gorge. Repair of the slide area and the tunnel required shifting westbound traffic to the eastbound tunnel, while eastbound traffic was diverted onto a temporary viaduct around the tunnels.
Local Geography and Geology
So why's it so tough to build a safe road in these here parts? Well let's take a looky here for one reason: These are the highest mountains east of the Rockies (h/t to Bill White for the catch). Not just some of them - almost all of them.
The Blue Ridge contains the highest mountains in eastern North America. About 125 peaks exceed 5,000 feet (1,500 m) in elevation.[5] The highest peak in the Blue Ridge (and in the entire Appalachian chain) is Mt. Mitchell in North Carolina at 6,684 feet (2,037 m). There are 39 peaks in North Carolina and Tennessee higher than 6,000 feet (1,830 m); by comparison, only New Hampshire's Mt. Washington rises above 6,000 feet (1,800 m) in the northern portion of the Appalachian chain.
The composition of the rocks doesn't help, either: you get a mix of rock types - granites and gneisses that are hard to blast through and softer sedimentary layers such as limestone, and crumbly rocks such as shale.
Landslide risk and risk mitigation
Landslides of various kinds are worldwide concern, not just for keeping transportation routes open but for keeping people alive. Deadly slides can occur anywhere, including underwater. One 1998 slide in New Guinea killed 2,200 people. The next year, the Vargas mudslides in Venezuela killed tens of thousands:
The disaster caused estimated damages of USD $1.79 to $3.5 billion [1][2]. More that 8,000 homes were destroyed, displacing up to 75,000 people[2]. The mudslides significantly altered more than 60 kilometers of the coastline in Vargas. Over 70% of the population of the state of Vargas was affected by the disaster. All public services, like water, electricity, phone lines, and land transportation (roads and bridges) disappeared. There were no supplies of food and water for months, so most of the population had to be evacuated. Looting and sacking sprouted up everywhere, forcing the military to implement Martial law for more than one year.
The death toll was considered to be between 10,000[5] and 30,000[1] — the exact number of casualties is difficult to estimate as there were no reliable census data, especially about shanty towns and small communities that were completely wiped out; moreover, only some 1,000 bodies were recovered, with the rest swept to sea by the mud or buried in the landslides[1].
By 2006, the state was back to its pre-disaster population level, and infrastructure projects were slowly being carried out to reconstruct the damage caused by the widespread disasters[5]. Nine years after the event, thousands still remain homeless. Real estate loss of worth in zones untouched by the floods was as high as 70%, due to the destruction of infrastructure.
What's unsettling is just how huge an impact slides can have. Take Heart Mountain, Wyoming for instance. It's a nice mountain in Park County, rising over 2,160 feet over the surrounding landscape. There's just one thing - It shouldn't be where it is.
The mountain is composed of limestone and dolomite of Ordovician through Mississippian age (about 500 to 350 million years old), but it rests on the Willwood Formation, rocks that are only about 55 million years old—rock on the summit of Heart Mountain is thus almost 300 million years older than the rocks at the base. For over one hundred years geologists have tried to understand how these older rocks came to rest on much younger strata.
Geologists eventually figured out what happened.
Between 50 and 48 million years ago a giant sheet of rock about 500 square miles (1,300 square kilometers) in area detached from the plateau south of the Beartooths and slid tens of kilometers to the southeast and south into the Bighorn and Absaroka Basins. This sheet, consisting of Ordovican through Mississippian carbonate rocks and overlying Absaroka volcanic rocks, was probably originally about 4-5 kilometers thick. Despite the slope being less than 2 degrees, the front of the landslide traveled at least 25 miles (40 km) and the slide mass ended up covering over 1,300 square miles (>3,400 km²). This is by far the largest rockslide known on land on the surface of the earth and is comparable in scale to some of the largest known submarine landslides.
Basically, 48 million years ago the front face of an entire mountain range broke off and, riding on a low-friction cushion of air and superfine rock, accelerated to about 100 miles an hour and wound up 25 miles away.
Ask yourself how many major cities on the planet Earth are within 25 miles of a mountain. Downhill, that is.
Now, perhaps you are thinking - well, that was 50 million years ago. How common are these super-slides, anyway?
Well, that's just it...They happen quite a bit, geologically speaking:
The three Storegga Slides are considered to be amongst the largest known landslides. They occurred under water, at the edge of Norway's continental shelf (Storegga is Old Norse for the "Great Edge"), in the Norwegian Sea, 100 km north-west of the Møre coast. An area the size of Iceland slumped, causing a very large tsunami in the North Atlantic Ocean. This collapse involved an estimated 290 km length of coastal shelf, with a total volume of 3,500 km3 of debris. Based on carbon dating of plant material recovered from sediment deposited by the tsunami, the latest incident occurred around 6100 BC. In Scotland, traces of the subsequent tsunami have been recorded, with deposited sediment being discovered in Montrose Basin, the Firth of Forth, up to 80 km inland and 4 metres above current normal tide levels.
We are assured by the same article that offshore drilling will in no way raise the risk of a new North Sea slide, which is nice because the last time it happened was about the time that the island of Great Britain was separated from the European mainland.
More on the interaction of natural structural weaknesses and human disturbance of same in just a moment.
Ack! What's to be done!
The good news is people are on this:
Landslide hazard analysis and mapping can provide useful information for catastrophic loss reduction, and assist in the development of guidelines for sustainable land use planning. The analysis is used to identify the factors that are related to landslides, estimate the relative contribution of factors causing slope failures, establish a relation between the factors and landslides, and to predict the landslide hazard in the future based on such a relationship.
...
Using satellite imagery in combination with Geographic Information Systems and on-the-ground studies, it is possible to generate maps of likely occurrences of future landslides [11]. Such maps should show the locations of previous events as well as clearly indicate the probable locations of future events.
and here's some of what's being done with this information
slope stabilisation methods in rock or in earth, can be collocated into three types of measure:
• Geometric methods, in which the geometry of the hillside is changed (in general the slope);
• Hydrogeological methods, in which an attempt is made to lower the groundwater level or to reduce the water content of the material;
• Chemical and mechanical methods, in which attempts are made to increase the shear strength of the unstable mass or to introduce active external forces (e.g. anchors, rock or ground nailing) or passive (e.g. structural wells, piles or reinforced ground) to contrast the destabilising forces.
Some of the approaches are very industrial in thinking, such as injecting concrete (also known as shotcrete or gunite) under high pressure into the rock to help stabilize the slope. Other tactics include protection of human settlements and infrastructure with metal frames or catch nets, or planting drainage infrastructure, both surface and subsurface varieties to mitigate water erosion.
Other approaches are more green in concept, such as geogrids or bionets, made of various woody and grassy fibers, serve to hold soil and surface rock to mitigate the impact of rainfall and runoff.
The ultimate solution from an ecological vantage is to plan the location of structures and connecting infrastructure with an eye toward impact on the natural habitat, impact of the natural habitat on human development, and and the interplay of artificial and natural structure over time.
Alas this is not always done, with sadly predictable results for both the interests of nature and of human endeavor.
Wrap
Today's Interstate 40 rockslide will impair traffic through the southern Appalachians for several months. However, this risk of slides is part of living on a geologically active planet where all of the safe places to live, work and travel are pretty much taken up. We see in the slums, favelas and barrios of both hemispheres the first sign of this increasing risk - more of us are living in marginal locations.
This pattern holds true even in developed countries such as the United States. The means to link real time seismic readings, satellite observations with geographic data give us the means to not only respond quickly to slides but the potential to warn people and save lives - if not of specific slides, which would be daunting, but to warn of areas of risk based on ever-improving understanding of the factors that predispose a region toward slide activity, and to evaluate the engineering practices and development choices that can keep our citizens safe and, among other considerations, our highways open and our economy thriving.
Thank you for taking the time to read this.