When I first visited the bluff shore below Morgan Hill in Port Townsend approximately 10 years ago, the base of the bluff was for the most part lined with past landslide debris that was well vegetated. The landslide material was acting as a wedge of material protecting the toe of the slope from erosion. But high tides combined with an approximately 2-foot storm surge and winds with waves removed a significant amount of the toe of the slope in 2006. The same storm eroded the base of the bluffs on the east side of Marrowstone Island and numerous other location in the Salish Sea. Following that erosion event shallow soil slope failures began to progress up the bluff slopes and at one location culminated in the high glacial till bluff breaking off a slab of till that collapsed onto the beach this winter.
The storm surge from this event can be seen from this plot of the February 4, 2006 tide at Port Townsend.
I was curious how the 2006 event stacked up with the December 17, 2012 high tide/storm surge.
The December 17, 2012 tide measured at the Seattle gage was the highest ever recorded in Seattle breaking the previous record from January 1983.
A couple of things to note. The storm surge from in Seattle was at its peak during the low tide or otherwise the record would have been broken by a larger margin. Another note is that the storm surge in Port Townsend was larger than in Seattle. The storm surge in Port Townsend tends to be on the order of 2 feet. And again, wind driven waves are an important factor in driving erosion.
I went through this exercise as I had been to another beach that appeared to have had no erosion at all from this winter's high storm surge. In this case the beach has a significant sediment source to remain built up from eroding bluffs to the south as well as lots of large drift wood which acts as a natural bulkhead. Indeed, despite the lack of landslide debris at the base of the slope, landslides along this shore reach have been very infrequent over the past 50 years.