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Tacoma, the City of Destiny, was destined to be built on the hills that rise above the western edge of the Puyallup Delta. The Foss probably began as a tidal slough along this edge, fed by the creeks that emerged from the hills to the south and west. In some ways, this is still what it is, albeit straightened, deepened, and devegetated. The streams enter through storm drains - two very large ones at the head end, in particular -- cascading across rocks at low tide and into the Sound.
It's hard to define what a natural shoreline is along such an artificial body of water, but the current banks are probably higher and steeper than they were before the waterway was dredged and the adjacent land was filled. In recent years, there have been some efforts to soften the edges a little bit - for habitat, for recreation, for aesthetic variety.
Beaches have been built near the mouth of the Foss where wave action is higher -- without waves, beaches become something else. These include the tightly constrained gravel pocket beach at Thea's Park and the north-facing beach along the Olympic View shoreline to the east.
On the west side of the Foss, where most of the recent redevelopment has occurred, there have been attempts to build narrow benches into the steep bank, often just below the seawall at the edge of the promenade. These benches become narrow strips of marsh, perched atop walls made from rows of logs and large boulders. I can't speak to how much biological value these features add, but they certainly appear more diverse and more interesting than the uniformly rocked banks typically found in such situations.
Figuring out how to do this offers some interesting possibilities for enhancing the inside edges of marinas (which for all practical purposes, the southern part of the Foss Waterway is), but some design issues need be worked on. For example, perching boulders atop the steep slopes looks like a challenge, since in several places they have toppled, leaving a ragged sheet of geotextile.
More pictures at hshipman: Tacoma
There are hundreds of spits and barrier beaches on Puget Sound, but the longest and the best known is Dungeness Spit on the Strait of Juan de Fuca, north of Sequim. It is also the most elegant, composed of a long slender bar, a rapidly growing tip, and a complex series of secondary and tertiary spits along its inner shores.
AERIAL VIEW
It's a 4 1/2 mile walk from the base of the spit to the lighthouse and another 1/2 mile out to the end (much of which has formed in the last 150 years). You can't actually walk to to the tip -- the spit is a National Wildlife Refuge and much is off limits to casual exploration.
Saturday's weather was magnificent, which meant that I returned with hundreds of photos and dozens of possible stories. In the interests of time, I'm simply going to post some of my favorite pictures and provide a few chapter headings: The eastward transport of bluff-derived sediment. The influence of long-period, but low amplitude ocean waves. Overwash and spit migration. The growth of the spit since the 1800s. The configuration of the spits on the bay side. The distribution and role of large wood. The partitioning of sand and coarser gravel and cobble on the beach face, the berm, and the backside. The development of beach cusps.
There's even a story about riprap, but fortunately it looks like perhaps it was a mistake that nature is already trying to erase.
George Vancouver called the spit New Dungeness, after the original Dungeness, a cuspate foreland located on the English Channel. Ness is a British term for a low-lying coastal area typically associated with a spit or barrier - so the term "Dungeness Spit" may be a bit redundant.
There are some more pictures of Saturday's hike to the lighthouse at hshipman.
This is a beautiful stretch of steep, wonderfully layered bluffs north and west of the entrance to Sequim Bay. I'll have to go back and check the maps, but I believe the geology is late glacial -- till on the bottom, overlain by river gravels, and capped with glacial marine drift (?). The stratigraphy changes slightly along these bluffs, painting an interesting picture of complex goings on right as the glacier retreated from this area and both sea level and perhaps the Dungeness River were doing something very different than they are today!
(NOTE: Well, I was right about till on the bottom and glacial marine drift on top, but better geologists than me report that the till at the bottom is Possession, suggesting this sequence covers two glaciations, not just the end of the last one. And there is a lot of interesting sedimentary detail in here, too, from rip-ups to cross-bedding.)
The bluffs are steep, consistent with higher erosion rates and fairly coherent units. The fluvial gravels are strongly cemented at the south end, resulting in a near vertical bluff. Farther north, the gravels are less consolidated and are a distinct slope-forming unit mid-bluff, above the steep till and below the steep upper drift unit. They were so unconsolidated that they were raveling as I walked the beach, cascading over the till and forming beautiful cones on the beach.
AERIAL VIEW
The wet conditions that led into the winter of 1998-99 must have exceeded some region-wide threshold. Deep-seated slides reactivated all over Puget Sound, from Olympia to Point Roberts, as well as here on the west side of Fox Island. At first blush, and perhaps at high tide, this might have looked like a large shallow failure, but low tide revealed that the clay below the tide beach had been raised 10-20 feet in a big arc, marking the toe of a deeper rotational slide.
The initial report that I heard was that a spit-like feature had appeared. When I first saw it - at low tide - the impermable clay ridge had turned the upper beach into large tidepool.
The uplifted clays, although much eroded and/or subsided, still crop out on the beach 13 years later. The house (try typing "askew" into Google) remains as it was left.
AERIAL VIEW
Way back in 2005, I picked as a subtitle for this blog:
PUGET SOUND BEACHES ... NOT REALLY JUST GRAVEL, BUT SAND, BROKEN SHELL, AND OCCASIONALLY A BOULDER THE SIZE OF A LARGE TRUCK.
This beach on the southwestern side of Fox Island fits that nicely. The beach face is gravel - or at least the surface layer is fairly uniform looking gravel - but beneath the natural armor is a much more diverse mixture of sand, gravel, and broken shell. There is a distinct break at low tide to a flatter, sandier terrace, although the transition is far from uniform along this beach. There's a lot of uneveness to this beach - a rolling topography and an irregularity to the low tide terrace. There are gravel bedforms that contribute to this, but I suspect it is related mainly to the underlying geology. The gravel-rich bluffs leave little doubt of the source of the beach sediments.
The largest pebble on this beach is 10' high and is called "The Big Rock." It has the remnants of a survey marker on top, along with small divots that may once have supported a tripod.
The development along the beach is limited to a few homes and cabins tucked into low spots along the otherwise high bluffs. Most of the new development is upland - big homes typical of the high end suburban sprawl that characterizes the Gig Harbor Peninsula.
Madronas (Arbutus menzeii) are a signature tree of many of our bluffs, particularly on dry south facing slopes. They can hang tenuously on the edges of cliffs for decades. I've seen some that from their size and growth habit have probably been in a perpetual state of falling over the edge for more than a century. Apparently, the owners of this bluff didn't like them, but I thought we'd moved beyond this kind of thing.
AERIAL VIEW
Camano Head lies at the southeastern tip of Camano Island and rises more than 300' from the beach. Not unlike Possession Head at the south end of Whidbey Island, Camano Head is marked by a large, deep landslide complex. The bench is heavily forested and looked broad enough for a small, but very scenic, subdivision (The Homes on Undercliffe?). Finer grained silts and clays ledge out on the beach near low tide. Some dip landward, suggesting they lie within the toe of the deep-seated slide.
On a sunny Saturday afternoon, the place seemed pretty benign, but it has not always been so. Tulalip accounts describe a major landslide in the early 1800s, one that generated a tsunami that reached Hat (Gedney) Island more than two miles to the south, with devastating consequences (History Link, or check a short piece I wrote a number of years ago, The Fall of Camano Head, pp 13-14).
There were no shortage of neat geologic and geomorphic features to check out -- but the tide was starting to come back up and I head to head back. The beaches heading north on both sides of the island are wonderfully sinuous, likely reflecting the shape of the steep submarine topography. The bluffs northwest of Camano Head are not quite as dramatic, but contained many more slides, some beautiful exposures of a gravel-rich till (pre-Vashon, I believe), and a few beach cabins precariously perched atop seawalls at the bottom of the bluffs.
AERIAL VIEW
Rosario Beach lies just north of Bowman Bay. It's a smaller pocket beach, the southern portion of which lies in the State Park. I've posted from here before (September 2009), but the purpose of this entry is mainly to provide a counterpoint to the previous post from Bowman Bay.
The Walla Walla University marine research station lies immediately north of the park. As at Bowman, they have had recent erosion problems, but the setting and the history are a little different. At the far end there is an eroding bank and there are also facilities vulnerable to storm damage. The closer end is a low lawn, perhaps fill across the historical backshore. High tide storms likely throw both water and logs up and over the berm and back toward the buildings -- erosion in itself may not have been a problem, but overtopping certainly was.
The solution that emerged is an interesting example of the kind of hybrid structure we are increasingly seeing on the Sound. There's some large rock, a row of logs, and an artificial berm or dune. I suspect the latter is actually the most useful element of this project, since it adds elevation and will likely reduce overtopping. I'm a little more skeptical about the purpose or the utility of the rock and the logs (they provide a sense of security, if nothing else), but regardless, the result is a naturalistic approach that provides benefits during storms while maintaining the basic character of the beach. It will look great when the dune grass grows in and the natural logs begin to obscure boulders.
AERIAL VIEW
The landslide at Cama Beach, combined with the realities of work and home, meant that that this post and the next have been stuck in my drafts folder for over two weeks. These two posts are from two pocket beaches on Fidalgo Island, just northwest of Deception Pass. Although both beaches tell many stories, these entries focus on recent efforts to deal with erosion control.
At the north end of Bowman Bay, the beach lies at the base of a gradual slope, but at the south end, it forms a barrier with a wetland behind it. The wetland used to be larger, but historic development led to filling of the central portion of this area. It appears that this fill was placed out across the backshore, which maximized upland real estate (for the state fish hatchery that used to occupy the site), but created a shoreline subject to erosion where a stable beach may have existed before.
For decades, the resulting bank had eroded, despite efforts to armor it with riprap and old concrete. This erosion was a very real problem, but one likely attributable to the placement of the historic fill. If there were homes or a railroad or a nuclear power plant built on edge, perhaps the only viable option would be to further armor the bank. But here, what is threatened is a narrow strip of a large poorly drained lawn. Not to trivialize the task, but pulling back the waterward edge of the fill might simply eliminate the erosion problem while creating a natural and much more enjoyable beach.
This recent effort to address the erosion focused on improving the ragged armor that was previously on the site. It's an engineering fix focused on the integrity of the rock structure, not the underlying cause of the erosion nor, unfortunately, the recreational potential of the beach. Technically, the solution may be fine. It was probably less expensive and bureaucratically simpler than other options. But it's also a missed opportunity (but not a lost one).
The north end of the beach, up near the old CCC shelters and the campground, offers a wonderful template for the eventual future of this central segment.
AERIAL VIEW
Just to show that blogging naturalists can visit the same site, yet find completely different things to marvel at, you might check out Wild Fidalgo: The Robins of Bowman Bay (also posted today). Check out Dave's other blog, Fidalgo Island Crossings, too.
I went back to Cama Beach Saturday morning to see how the landslide was evolving. It's hard to tell how much new material is being added from the headwall, although small chunks kept falling during my visit. The debris in the gully has continued moving on down to the beach, with new trees and large blocks of till perched on top.
AERIAL VIEW
The landslide itself is interesting enough - but I think I am most curious about how the beach responds to the slide. The debris cone at the base projects out onto the beach, acting like a groin, and has resulted in the accumulation of a small wedge of beach up against the southern side of the landslide debris. Some of this new material may be beach sediment from the south, while some is derived directly from the eroding toe of the slide. Most wave action here comes from the south. While I was on site today, a gentle northerly breeze gradually gave rise to stronger southerly waves over a period of several hours.
Fine grained sediment is being winnowed from the toe of the slide during high tides and moved way in suspension - there is turbid water along the water's edge and extending in a plume offshore. What is less clear is how the coarser fraction - sand and gravel - is moving. We'll watch this, qualitatively at least, over the next weeks and months to see if it leads any noticeable change in beach profiles or sediment texture in the vicinity.
The headwall of the slide remains scary, with the loud thump of falling blocks of till reminding me to stay back from the edge. Too much is still moving and there are some significant overhangs.
I've posted more photos of the landslide at:
Photos: March 7th
Photos: March 17th
It was raining when I left Seattle shortly after 7:00. It was slushing in Marysville. But it stopped by the time I got to Cama. And then the sun gradually worked its way out from behind the clouds. I posted some less geologic pictures at hshipman, for those less interested in landslides and dirt and more interested in new places to enjoy coffee and scones while overlooking the beach.
Along the high bluffs north of Cama Beach, there is a deep box canyon cut back into the till. The upper end was pretty spooky when I first visited it in the 1990s, with vertical till cliffs on three sides, but a small window in the till at the base of the head wall offered a glimpse of the underlying fluvial sands. At the beach at the base of the ravine, there was a block of hardened debris that suggested some sort of big slide in the past.
There was a slide in the canyon last year - you can actually see the toe on the beach in the 2011 Google image linked at the bottom of this post. And then during the past couple of weeks, more material began sliding out of the canyon and onto the beach.
I estimated close to 1000 cubic yards of debris on the beach and an awful lot still in the ravine. Water flowing across the edges of the debris cone were depositing soft fans of sand, but the bulk of the slide was remarkably firm and dry and appeared to have arrived in an avalanche of fairly dry material. Most of the surface of the slide consisted of sandy material, but there were also large angular blocks (some 1-2 meters across) of till.
The source of the slide was massive failures in the high cliffs at the head of the canyon. Water was cascading from the forested surface (perhaps 140-150' above the beach?) down the face of the till - as I recall, the canyon coincides with a low point in the upland topography and may be drainage related. I couldn't get close enough to see if there was seepage from within the fluvial sediments themselves. Given the most recent failure last night, despite the lack of rain, and the current character of the steep cliffs at the head of the slope, I suspect additional large failures are likely.
The geology along these bluffs consists of till draped down over the seaward edge of the older flat-lying fluvial beds. In places the till comes all the way to to the beach, yet at the head of the slide, the till appears to be just 10-15' thick on top of the very thick sandy unit. You can sort of see this if you blow up the photo looking up the slope.
This is a fairly quick account - I'm sure I'll check back on this one -- and maybe the story will become a little clearer.
ADDENDUM: Here's a link to a cool video taken last week (not by me) - before the big stuff came down.
Landslide @ Cama
AERIAL VIEW
Beaches have been built near the mouth of the Foss where wave action is higher -- without waves, beaches become something else. These include the tightly constrained gravel pocket beach at Thea's Park and the north-facing beach along the Olympic View shoreline to the east.
Figuring out how to do this offers some interesting possibilities for enhancing the inside edges of marinas (which for all practical purposes, the southern part of the Foss Waterway is), but some design issues need be worked on. For example, perching boulders atop the steep slopes looks like a challenge, since in several places they have toppled, leaving a ragged sheet of geotextile.
