By Naomi Klouda
Photo courtesy of Homer Tribune. Geologist Ed Berg leans over to pick up a tool used when he measured the length of land separating the Sterling Highway at MP 153 from a gaping hole that drops straight down 100 feet.
Homer Tribune
The bluff north of Anchor Point took another hit this winter, crumbling off four feet of topography and sending the Sterling Highway at Mile Post 153 ever closer to caving in.
A strip of land separating the highway from a gapping, 3.5-acre hole is now the size of a small garage. When geologist Ed Berg took measurements Sept. 27, 2011, he found the road poised 53.5 feet from the cliff. To measure, he hammers a nail into the edge of the pavement and pays out tape from there to the edge of the cliff.
At Thursday’s measurement, he used the same methodology. The tape stretched 49.4 feet, showing a loss of more than four feet.
“I am amazed it was that much. In the Google Earth view of 1996 and 2006, the distance from the hole to the highway edge showed a loss of 25 feet in a 10-year period, which is 2.5 feet per year,” Berg said. “Here, we are seeing a greatly accelerated loss of 4.1 feet in eight months, which would be about 6.1 feet per year.”
The point of reference Berg used in September — an old stump on the cliff edge — fell off during the winter.
A look over the edge proves daunting. Dropping straight down 100 feet is a barren valley stripped of topsoil by an ever-present northeastern wind. Draped around the rim, grasses form an overhanging lip, dangerous for viewers stepping too close to the edge for a better look.
Using LiDAR imagery, elevation at the top of the bluff measures 231 feet. LiDAR, Light Detection and Ranging, is a new form of topographic mapping based on aerial surveying with a laser beam.
“The drop more or less straight down is about 100 feet, as shown on the profile. The slide hole is 475 feet wide, measured parallel to the Sterling Highway,” Berg said.
These numbers spell concern for the stability of the Sterling Highway at that point. What happens if an earthquake rolls through? What about the continuous pressure of freight trucks and fuel tankers shaking the substrata?
The Alaska Department of Transportation and Public Facilities has monitored the highway with an eye toward fixing or preventing a potential road collapse. One option was to reroute that portion away from the bluff, based on the fear that in a worst-case scenario, people may one day wake up and find a piece of the highway fallen over the edge.
“The ever-decreasing buffer between the highway and the eroding bluff is a concern for the long-term stability of the highway itself,” said DOT spokesman Rick Feller. But for now, the department feels the erosion isn’t “aggressive.”
When first measured in 2006, the bluff was 63 feet from the edge of pavement. The most current DOT measurement, taken in January, sets the buffer at about 55 feet, Feller said.
“Though the rate of erosion has been somewhat steady, it has not yet been aggressive. And while the threat of a sudden, aggressive sloughing event is possible, based on the known rates of erosion, the department does not anticipate an immediate threat to the highway,” he wrote in an email.
For a long-term solution, DOT sought funding and completed a reconnaissance study of a potential fix.
“It was determined that the best course of action would be to shore up the bluff from below, as opposed to relocating the highway alignment inland,” Feller said. “The department is seeking authorization to proceed with further design and permitting work, all leading to eventual permanent repairs. The timing of these repairs is still dependent upon funding.”
After Thursday’s examination of the situation, Berg expressed disbelief that the bluff could be shored up in an effective manner. The rate of erosion, at four feet in eight month’s time, is starting to feel aggressive, indeed, he said. The substrata itself is weaker than along the road closer to Homer, which is underlain by bedrock of shale, coal and sandstone.
As Berg put it, “Sand isn’t glued together. It’s not cemented.”
Mary Landrus, a homeowner living across the street from the bluff at MP 153, also doubted that the weakened area could be rebuilt.
How would you build anything that far down?” she said.
Erosion on this section appears to take a different process — and therefore is a poor candidate for stopping nature in its tracks.
“The wind’s blowing so hard I am constantly cleaning sand off my windows. It’s on the roof,” Landrus said.
When her family first built their home in 1996, the wedge of land across the highway was more substantial.
“This was all trees,” she said, indicating the length of about 200 feet. The land stretched further out by more than 15 feet, she figured. Once, she hugged a small spruce tree while leaning over the edge to check on erosion.
“That same day, the tree broke off and fell in,” she said. “I haven’t been that close to the cliff since.”
To either side are large copse of cottonwood and spruce trees. But the trouble spot is treeless, leaving it to grasses, wild plants and heavy wind.
Berg found it interesting that heavy winds appear to be responsible for most of the erosion. That, and a weak infrastructure that lacks bedrock. Further down the beach at Bluff Point in Homer, the geological record shows the story of the Bluff Point collapse. That was an event sometime after the last Ice Age when a 2.8 mile-long strip of bluffs collapsed, leaving the large hole with ponds below Bay Crest Overlook. It occurred after ice retreated 17,000 years ago, Berg said. Millions of tons of rock and earth crashed down and ran 500 yards out in the bay. A contrast between MP 153 and this area provides a cautionary tale.
“My concern about MP 153 is that a much larger area could slough off than what has failed so far,” Berg said. “Perhaps the hole can be patched, but what if a much larger slice of the bluff collapses, like at Bluff Point? The safest solution is to relocate this section of the road away from the bluff.”
Changes in erosional and depositional zones can be viewed on a nearly daily basis. The height of the tides, the force of the waves and the shoreline surfaces dictate the extent to which the shoreline is reshaped.
Scientists know that the foundation of the sandstone and coal bluffs is eaten away by the high-energy waves that crash against the bluff base. This weakening combined with large amounts of groundwater moving through results in severe bluff erosion.
At MP 153, the groundwater also could be contributing to weakening the bluffs, Berg said. But wave activity is not at issue.
Feller said that DOT shares the public’s concerns regarding the bluff erosion threat. An initial response, in the event of a sudden catastrophic threat or failure of the highway, would mean scooting the road over.
“We have determined that there is adequate right of way to re-establish the highway to the inland side of the current alignment in the event of an imminent threat,” Feller said.
Until permanent repairs are made, DOT plans to monitor the erosion and “respond with any short-term improvements, such as markings or physical barriers, when and if that becomes needed.”
There is, as yet, no target date for scheduled repairs or relocation.
- I’ve examined this extensively for my bluff land, I’m a pretty clever engineer and can get things built for a LOT less than the State can. I couldn’t come up with anything as cheap as acreage (i.e. build further back from actively eroding bluff).
- In 5 or 10 years when the ravine is even closer to the highway, (or now if we’re concerned about an earthquake-induced large landslide), what happens if there’s a large slip during the night? I’d suggest that a driver’s ability to perceive the danger and react is often less than their response time at 60 mph (e.g. the driver who went into the hole in the SF Bay Bridge after an earthquake damaged the bridge). So how about a string under the road, tied to a weight buried in seaward soil on one end and to a electrical contact on the landward side? A landslide would pull the string, the string completes the circuit, causing really bright flashing lights to warn traffic coming from each direction.