Wall collapse sent a small mountain of boulders and debris across northbound lanes of parkway. Cracks in sections still standing kept clean up crews working with caution. (Photos by Susan Pearsall for ENR)

A massive stone retaining wall adjacent to the Henry Hudson Parkway in New York City, just north of the George Washington Bridge, failed spectacularly on the afternoon of May 12. No injuries were reported, although an unknown number of parked cars were buried and nearby buildings evacuated as a precaution. Witnesses said the failure of a 150-ft-long, 75-ft-high section of the 1,000-ft-long, privately owned wall occurred in two stages, resulting in landslides about 10 minutes apart. The first slide covered an access road and the parked cars with boulders and soil, and the second sent an avalanche cascading across the three northbound lanes of the parkway itself. The collapse happened during clear, dry weather.

In a May 13 press conference, Mayor Michael Bloomberg (R) said emergency crews plan to stabilize the site by reducing the angle on slope and covering it with plastic sheeting to control erosion. He said the northbound lanes should reopen to traffic by early in the week of May 15.

The wall is the property of Castle Village, a five-building residential co-operative on a 7- acre site overlooking the Hudson River on Manhattan's upper west side. The wall was constructed between 1907 and 1909, Mayor Bloomberg said.

Concerned by signs of instability, the owner had engaged Langan Engineering and Environmental Services, Elmwood Park, N.J., to make repairs. Langan was seeking a permit from the State Dept. of Transportation to close the access road to enable the work when the wall failed.

At his press conference, Mayor Bloomberg said the city's responses to concerns about the wall1s stability before the failure were appropriate. "Given they had a licensed engineer who was working on it, we didn't feel there was any reason to be doing anything else," Bloomberg said. "The engineer knew there was a problem. That's why he went to the DOT for a road closing permit."

Officials from Langan and the owner were not available for comment.