Snoqualmie Pass Rockfall

May 14, 2009

Interstate 90 through the Snoqualmie Pass/Hyak area is a very unstable area and has resulted in numerous rockfalls each year. WSDOT has conducted a Report to the Governor on Snoqualmie Pass (and other highways) and can be accessed here. According to the report, at least 5 fatalities have been caused by rockfalls on Interstate 90:

7/25/1970: 1
2/5/1998: 1
9/11/2005: 3
Source: WSDOT, Transportation Data Office, Collision Data and Analysis Branch

So, there shouldn’t have been much of a surprise when Interstate 90 was closed due to a rockfall. Here is an excerpt from WSDOT:

“Falling boulder closes eastbound I-90 at North Bend for five hours

Date: Tuesday, May 12, 2009

HYAK – Eastbound Interstate 90 closed to all traffic at North Bend earlier today. The road is now open. WSDOT crews closed the road at 2 a.m. after a large boulder fell off the hillside, bounced over the concrete jersey barrier and came to rest in the eastbound lanes. The boulder did not hit any vehicles, but a commercial truck struck the boulder.

WSDOT’s geotechnical experts climbed to the top of the hill to assess the situation and determined the road was safe to reopen at 7:15 a.m., Tuesday, May 12.

“We only opened the road when our experts told us it was safe for drivers,” said Paula Hammond, Washington State Secretary of Transportation. “Safety is our number one concern.”

An initial review of the site shows it is not on WSDOT’s list of unstable slopes. A more likely cause is the freeze thaw cycle in the area. …

“This can happen,” said Don Whitehouse, WSDOT Regional Administrator. “When you build a road through a mountain pass, rocks will fall. Our job is to make the area as safe as possible for drivers.”

Between 6 a.m. and 7 a.m. geotechnical experts hiked up the rocky slope, found two loose boulders, and pushed those onto the roadway below. Crews cleared the debris and reopened the road to all traffic.”

The boulder involved in the rockfall is quite small:

WSDOT Rockfall Highway 90

WSDOT Rockfall Highway 90

WSDOT Scarp of Rockfall Area

WSDOT Scarp of Rockfall Area

WSDOT Damage from Boulder

WSDOT Damage from Boulder

Luckily, no one was killed in this event, unlike the rockfall in 2005.

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