Friday, June 29, 2007

Samish Beach

This stretch of spit on Samish Bay has a complicated history, as does the shoreline to the west from which this spit is fed (see May 2006 post). Beach erosion was rapid in the 1980s and early 1990s, leading to bulkhead failures in 1996-1997. A gravel beach was reconstructed in 1998 as an alternative to building more massive walls or placing riprap. The beach continues to look good. Sediment has continued to be lost to the east, as was expected, although at relatively low rates. This past winter's storms (maybe December 14-15th, in particular) reportedly caused significant erosion at the west end and has prompted residents to begin thinking about whether some minor renourishment may be in order.

Thursday, June 28, 2007


Different sizes and shapes of particles behave in different ways on beaches and there are folks (mainly British, I suspect) who have spent their careers looking at ridges of disc-shaped cobbles and bands of spherical pebbles found on shingle (gravel) beaches.

Based on this limited sample of an unusual sediment type, I have found that cast-iron bathtubs on southwest facing gravel-sand beaches in central Puget Sound tend to wind up upside down and are left projecting a few inches above the beach surface. I am not sure if this is generalizable to other types of bathtubs or other types of beaches, but I am absolutely sure this is pretty much irrelevant to just about anything.

Perkins Lane

A dynamic coastal city like Seattle deserves to have a big landslide within site of downtown. Perkins Lane is draped along the southern face of Magnolia Bluff, and has been for some time, although it has drooped with age. By the 1930s, the WPA was installing drain systems to stabilize the slope. It may have helped a little, although Perkins Lane remains possibly the best example of a large deep-seated landslide complex on the Sound - certainly the one most accessible to UW geology classes. Others include Ledgewood on Whidbey, Termination Point on Hood Canal, Sunrise Beach near Olympia, and some wonderful landslides north of Kingston (there are many more).

In 1996, six homes at the eastern end of Perkins Lane began their migration to the sea. It was slow, and even in 2000, the forms of houses were still fairly evident. Last Sunday, the homes were little more than piles of cement and rusty metal. And enough remnants of daily life to remind me that archaeology often begins as a sad story. The plastic high chair tray, for example. I was impressed by large sections of plumbing strewn across the beach and framing compressed between the hillslope and the concrete foundations slabs as if they were in a trash compactor.

Magnolia Bluff

I dropped the family off at SeaTac at 6AM last Sunday morning and then looked for ways to delay the inevitable return to a working weekend. Had coffee on Alki Beach, watched a cruise ship unload at Bell Street, wandered through the Sculpture Park, and then headed out to Magnolia.

There used to be more houses perched along this beach - evidenced by old piles and plumbing and photos. Only a few are left, though those seemed to be suffering from one storm too many. This large boulder still had dirt plastered on top, suggesting it came down fairly recently - probably this winter. Thump. I half expected to find a wicked witch pinned underneath. And I wondered what would have happened if it had come down the slope above one of those houses. I guess that's one reason people aren't allowed to build in places like this anymore.

Thursday, June 14, 2007

Bywater Bay

The Wolfe Property is one of Washington State Parks' best kept secrets. And a wonderful little study in barrier beaches and lagoons. The aerial photo (click on the title of the post) provides some context. A spit, a tombolo, a lagoon, and a forest.

The spit has multiple beach ridges, recent berms curving out from the old one, and an undulating shape. My instinct tells me this is a sign of instability, or at least of highly variable sediment supply. Even the beach south of the spit - at Seven Sisters Road - shows signs of both significant accretion and erosion. There may be both natural variability and a human history to this. Plus, like Shine Tidelands, this site is north of the bridge - so its sediment source has been impacted and the southerly fetch significantly reduced.

Today the beach had thousands of little crabs (maybe more) and dozens of herons (maybe less) - but it was the first day in the field in a long time that I don't recall seeing a bald eagle.

(Turn right at the west end of the bridge, go a mile to Seven Sisters Road, drive down to the parking area, and walk the beach north to the spit. But remember, it's a secret.)

Shine Tidelands

In an earlier post, I mentioned how the Hood Canal Bridge may have modified sediment transport at Salsbury Point at its eastern end. There's no question that the bridge mucked up the beaches at it's western end. The bridge is constructed on a fill that blocks northward drift and buried the southern end of a spit and its associated lagoon. Shine Tidelands is a beach with no sediment source and far less southerly wave action than prior to 1961. The southern end of the spit is riprapped and the beach is a cobble lag - starved of sand and gravel. The marsh is largely intact and remains a bit brackish near the northern end, where you can still see salicornia and the remains of the old drift logs.
We can't make the beach whole - at least not without the bridge sinking again - but we could make it a lot better. Pull the riprap out and get some small gravel and sand back onto the beach at the southern end, remove as much of the old fill as possible and plant native backshore vegetation, and maybe even restore tidal circulation with an inlet nearer the north end.
Today's meeting was exciting - maybe some of this stuff can really happen.

Thursday, June 07, 2007

Butterball Cove

I hadn't walked the beach east from Tolmie State Park in over a decade, so I was a bit apprehensive about doing it with a class. As it turned out, it not only went well, but provided me an opportunity to revisit a site that I had wondered about for years.

In the mid-1990s, a brand new bulkhead was built at the base of the near-vertical bluff just west of Butterball Cove. Shortly afterwards, the bluff collapsed on top of the new wall. I've used a picture of that partially buried seawall for years to show the limitations of a narrow-minded focus on the bluff toe. It turns out that more failures have occurred since then and folks had to take my word that there was indeed a concrete seawall buried deep beneath the dirt and broken trees.
The bluff itself has now been sprayed with gunnite (or shotcrete - are they the same?) and flowers neatly planted across the top. Someday, I suppose the bulkhead will be exhumed by waves - probably much to the surprise of the future owners of the property!

On very rare occasions on Puget Sound, we find Pleistocene sediments so resistant to erosion that they persist as headlands while the adjacent bluff recedes. This prow on the beach at Butterball Cove is one such example - the older iron-stained conglomerate is a natural bulkhead, extending out to a mid-tide. Interesting that on the beach to the west we saw what appeared to be this unit and possibly an underlying one outcropping in shore parallel bands on the beach. Again, not something we observe very often, since it probably requires resistant rock units, limited wave energy, and a minimal veneer of beach sediment.

Point Wilson

Lighthouses should have wheels. This one was built on the northern edge of a spit at the mouth of Admiralty Inlet, the better to be seen by ships returning to Puget Sound. But like so many spits, this one is moving, and the lighthouse is in danger of being left behind. A fortress of rock, rebuilt as recently as last year, protects the building, but doesn't stop the spit's inexorable southern march. The rock now buries the beach - 100 years ago we could have walked the beach around the point on sand at high tide, but now we can barely do it at a low tide. What a mess it will be in 50 more!

Montauk, Cape Hatteras, Morris Island. Point Wilson isn't the only lighthouse that has suffered from an injudicious geologic location. Afterall, lighthouses are built in such locations for very good reasons. Some have eventually thrown themselves into the sea; some have abandoned the land and now stand offshore, marking a point that was once dry; some have surrounded themselves with rock until the lighthouse is less a landmark than the rockpile. And some lighthouses (some much bigger and more fragile than this one) have simply picked up their stuff and moved back from the edge.

Point Wilson isn't going away. It isn't even moving very fast. If the lighthouse and the other structures were 100 feet or so farther south (which the shape of the point allows), the rock could be removed, the beach restored, and the lighthouse's life extended hundreds of years. Its position near the tip of the spit would be maintained and the view of the lighthouse from Fort Worden changed only slightly. Its relocation would be relegated to a historic footnote and a credit to our foresight. Or we can pile on more rock.

Saturday, June 02, 2007

Shipwreck Point

We cut a wide circle around Shipwreck Point, which is surrounded by No Trespassing signs and watched over by its owners, who are probably tired of the curious tramping across their little piece of paradise.

I first saw this place from the train many years ago, and have been fascinated by it ever since. The shipwrecks are actually the remains of a salvage operation reportedly begun in the 1920s. I would like to know how much their skeletons have influenced the morphology of this small point of land. The largest hulk acts as a groin to northward transport, stabilizing the beach on the south and creating a small marshy cove on the north.

If ships being dismantled on beaches catches your fancy, visit Alang Beach, north of Mumbai on the western coast of India. Search the web or locate the article in the Atlantic Monthly (Langewiesche, The Shipbreakers, August, 2000). You might also visit it with Google Earth: (search 21°24'9.02"N, 72°11'17.67"E).

Ripple Marks

Moving water forms ripples in sand, their size and spacing dictated by the flow and depth of the water. The ripples in these two photos are similar in scale and taken within a few hundred yards of one another, but the red ones are a trillion times older than the gray ones.

The red ripples are in sedimentary rocks of the Belt Series, deposited over a billion years ago in a shallow sea in what is now western Montana. They were brought here by the railroad from the Rockies to repair damaged portions of the revetment. The ripples in the wet sand on the beach were also formed under shallow water, but probably less than a couple hours ago.

Possession Lagoon

I'm not sure if Possession Lagoon is what anyone else calls it, but this is the lake formed by the railroad cutting off the bend in the shoreline just north of Picnic Point. The homes along Possession Lane are perched on this strange little feature, although the hillslope threatens to push them into it very decade or so. The winter of 1997 was pretty scary for these folks. I would love to know more about the history of the railroad causeway here -- was it originally built across the embayment or was it relocated after some big landslide took out the original line? A narrow beach has developed along the seaward side of the tracks, but as elsewhere along the railroad it is lucky to extend to mid-tide - the upper beach is still missing.

Picnic Point

Enough of these white sand beaches, thousands of miles from Puget Sound. Time to bring this blog back home. This morning D&I headed north 15-20 miles and spent a couple hours tossing the frisbee on the beach and getting our shoes wet. Picnic Point is one of a few stream deltas between Seattle and Everett that extend seaward of the railroad grade. The stream mouth bounces around from season to season or year to year, but currently makes a sharp northerly bend (as it is supposed to do, given the southern exposure and the northerly drift) before fanning out down the beach.

The persistence of features like Picnic Point is intriguing. The supply of sediment to the beaches from bluff erosion has been largely, but not enitrely, eliminated by the railroad grade. The streams may provide some sediment. But I suspect that these points may attract what little coarse sediment remains in the system (I think this is a function of the oblique wave environment, which might shunt sediment to these places rather than away from them), keeping them from disappearing. This is an idea, one that might be tested, but by no means something I expect anyone else to actually believe!