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The Interlaken sinkhole is growing — and nobody knows why — UPDATE

Thanks to @GordonOfSeattle for the picture

A hole appeared recently in the pavement at the intersection of E Galer and 19th Ave E above Interlaken Park — and nobody is 100% sure why. Meanwhile, a ring of orange safety cones hasn’t contained the modest but gaping maw which continues to grow and crumble the pavement, ever so slightly.

The Seattle Department of Transportation said Thursday city crews were “continuing to work to assess this damage and determine the best repair plan.” Seattle Public Utilities is assisting in the repair effort “by testing the water to verify that it is not connected to their underground pipes,” SDOT said.

The hole is growing in an area known for some slipping and sliding. In March 2011, rainwater flowing under the roadway washed out the foundational soil below Interlaken Drive running through the park, causing the road to crack. Several large cracks formed nearly overnight as the road shifted as much as an inch in one day, prompting the city to close the road indefinitely pending a geotechnical study. It was finally repaired and reopened that August. Smaller slips and slides have occurred over the years.

CHS’s nature column Pikes/Pines has documented the landslide risk of the area including the Hill’s geologic past of glacial till and water-pooling clay:

Then we come in. The grade is altered, creating new faults. Hills are denuded of trees, which hold slopes and mitigate flooding. Barriers to natural water flow diverts it toward unforeseen consequences. People understandably want views and build on cliffs, changing the loads on hills. Generally things more even more unstable. West Capitol Hill, Interlaken, North Capitol Hill. Slides every decade going back in our modern record.

A city study of the problem also showed shifting along western Capitol Hill with major slides occuring in 1916. “Four landslides occurred in the 1930s, one in 1961, one in 1974, two in 1986, and seven in 1997,” the study (PDF) reports.

Meanwhile, Seattle’s roadways suffer major weather challenges and the city’s maintenance backlog has been notoriously huge for more than a decade. Crumbling infrastructure adds to the costs.

Back to the modest new Interlaken hole, a department spokesperson didn’t seem overly concerned about the appearance of the “void.”

“We often work with other utility agencies to repair certain kinds of road damage. Sinkholes (technically referred to as “voids”) are often caused by underground water sources and can sometimes be a symptom of a problem that runs deeper than the visible hole in the road,” the spokesperson writes. “Seattle Public Utilities is assisting in this repair effort by testing the water to verify that it is not connected to their underground pipes.”

The spokesperson said the first objective is to figure out if the issue may be related to any “other kinds of utility work.”

UPDATE: SDOT has installed a barrier over the hole. We’ll check in to see if a cause and long term fix has been identified.

UPDATE x2: SDOT says the problem first identified in mid-April has been determined to have been caused by a busted pipe:

On April 17, City crews were called to 19th and Galer where a void, commonly referred to as a sinkhole, had developed. They performed a dye test, which can indicate if a pipe is leaking, and that test came back negative. On Thursday, May 4, SPU crews inspected the pipe via CCTV and discovered that a section of the 18-inch clay pipe is broken, causing the void.

Seattle Public Utilities is working on a plan to repair the broken pipe and SDOT says the street will be more fully repaired when that work is complete.


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Gordon Padelford
Gordon Padelford
4 months ago

Thanks for the reminder that Interlaken was closed to cars in 2011 thanks to erosion. The NE part of Interlaken Park that is car free all the time thanks to a landslide back in the 1970s is such a relaxing and beautiful place. A real gem of Seattle’s park system. Maybe someday all of Interlaken will be car free (except for access to the houses and school)

Yelahneb Unicornucopiax

That was an amazing summer for bicyclists like myself. They blocked traffic from just past the houses on both ends, so no one who lives in the park was stranded – having it be permanent would have been a boon to everyone (except folks who use the park as a shortcut and drive too fast).

Nelson M.
Nelson M.
4 months ago

Happy Sinkhole de Mayo!

Jeff fisher
Jeff fisher
4 months ago

Seattle has a generalized hole problem this week.

West Seattle bridge.
Transit tunnel clock removal.
Now Interlaken.