Wednesday, March 27, 2013

Ledgewood Beach

For better and more up-to-date information on the geology of this landslide, see:
DNR's Ear to the Ground:  Whidbey Island Coupeville Landslide

Early this morning (4:15AM, 3-27-2013), a very large landslide occurred up at Ledgewood Beach on Whidbey Island.  This neighborhood is no stranger to slides, but nothing like this has happened in a long time.  The slide was a large rotational failure within the much larger landslide complex that extends along this stretch of shoreline.  It may have been 700-800' long and several hundred feet deep, with the head scarp stepping back several tens of feet into the 200' high upland surface.  The failure surface - based on what we've seen on the beach elsewhere along here, but confirmed by today's observations - is a little below sea level.

KING5: Huge landslides damage, threaten homes on Whidbey Island

Previous Post on Ledgewood Beach (April 2006)

For a beach wonk, the toe was the coolest part. The shoreline along here was relatively straight prior to the slide and is now marked by a bulge that extends more than 100 feet into Admiralty Inlet.  This is not just a big pile of debris from the slope above, but rather it is the uplifted toe of the rotational landslide.  Distorted dark gray clay is pushed up along the base (the tide was too high to see the lowest portions of the toe), but as the clays pushed up, they simply raised the beach into the air.  The toe bulge is mantled by a remarkably intact sand and gravel beach.  Barnacle covered boulders sit on the surface.  The driftwood still marks yesterday's shoreline, which just happens to be 20' higher and 100' seaward of where it was a few hours ago.  I could still follow a discontinuous band of dead eelgrass and beach wrack, marking an earlier high tide. Sections of the raised beach were broken by tension cracks, or arrayed in a series of terraces (drift logs on the top step, sand and gravel on the middle steps, cobbles on the lowermost steps).

I've posted several entries recently about deep-seated landslides:

South Whidbey State Park, February 2013
Camano Island State Park, November, 2012

These geologic landscape are best reserved for open space or parks, not subdivisions.  In this case, we were very lucky that only one or two homes along the lower bench were affected -- in other places along here it could have been much more serious.

Monday, March 25, 2013

Southwest Seattle

This post encompasses a longer stretch of shoreline already addressed in the two previous posts and is mainly just an excuse to show the variety of seawalls I encountered on my Sunday afternoon stroll.  Some of this shoreline has been developed for a long time, so some of these structures are very old.  Some reflect recent tweaks to older walls.  And some are relatively new replacements of bulkheads built decades earlier.

There is one common theme to all of these pictures.  The upper beach - the part that we walk on at higher tides and relax on in nice weather - is gone. No dune grass. No drift logs. No madronas or big leaf maples hanging out over the beach, creating shade or a place to tie a swing. The walls, and the reclaimed land behind them, have created beachfront property while at the same time eliminating the beach!   

Seola Beach

For a shoreline once characterized by eroding coastal bluffs, spilling gravel and sand onto the beach, Seattle has remarkably few of these places left. They exist on the north and south sides of Discovery Park and there is a short stretch on the south edge of Magnolia Bluff. And there is this one elegant bluff left between the developed shorelines of Arroyos Beach and Seola Creek. Elsewhere they've been built on, excavated away, or locked behind seawalls.

Gravel was running in a continuous stream down the bluff while I watched - gradually adding to a talus cone on top of the drift logs.  Next door, the remains of someone's bluff-top backyard perch had landed in a jumble. The views from the homes along Marine View Drive must be spectacular, made more vivid by the excitement of participatory geomorphology.


The beach south of the Arroyos, all the way down to Seahurst Park in Burien, is marked by a broad sandy low tide terrace.  But to the north, the upper beach becomes coarser and the low tide terrace diminishes - it downright disappears in the vicinity of the previous post where the bathymetry drops off precipitously.  Longshore transport here is to the north (southerly waves dominate along this shoreline), but I suspect it's hard for sand to make it past the Arroyos without getting lost into deep water close to shore.  I wonder if that's why the beaches seem so different to the north?

The Arroyos

This may be one of Seattle's least known beaches, in part because it is hard to get to. Most of this shoreline is lined with homes, but this large segment of forested bluff remains intact, albeit rising above an ugly riprap revetment.


The story of this site is linked to that of Stimson Bullitt (1919-2009), who built a home nearby. A section of the bluff was donated by the family to the City of Seattle as green space. And last year, a sculpture was commissioned and placed on the site.

The sculpture is Gerard Tsutakawa's Illusion Dweller (2012).  Illusion Dweller is the name of a rock climbing route (5.10b) in Joshua Tree that Bullitt had climbed (at an age that most of us will be happy to be able climb out of bed).

"The loss of illusions, which goes with self-awareness, saves us from some folly while it takes away security and boldness." Stimson Bullitt  (engraved on the base)

Chambers Bay

I think this beach is where I'll bring the class in May, since it's close to the classroom (which looks down on it from the top of the hill) and because it's a beach that looks like it can tell some interesting stories.  The challenge will be finding geologic stories that are relevant to other Puget Sound shorelines, not just stories unique to this strange anthropogenic coastline.

Just like Richmond Beach in the previous post, this site began as a late glacial delta, become a gravel pit (a very large one), and has ended up a park.

Previous post from here:  Pioneer:  October, 2010
Post from the active mine at Dupont, south of here:  Sequalitchew Delta, October 2011


A high bluff once rose steeply from this beach.  The beach itself probably ran in a fairly straight line, interrupted only by occasional clusters of large logs and downed trees.  The bluffs receded rapidly when the mining began and now they now lie 1000 meters to the east.

Beaches are active and often very young geologic landscapes.  The wave environment at this one probably hasn't changed much in the last 150 years, but much else has, and the beach has responded accordingly.  Resistant headlands have been imposed in the form of concrete structures, pier abutments, and coarse cobble lags leftover from loading operations, and these have altered the configuration of the beach. The original bluff sediment sources have been replaced by the beach itself, as one part erodes to supply another.  Transport patterns have changed to reflect the beach's new shape and the shifting sediment sources.

It's a wonderful beach, but also a very different one than the one that had gradually transgressed into the forested bluffs for thousands of years.  It tells some neat stories, but the most obvious have to do with its human history.

Wednesday, March 13, 2013

Richmond Beach

Saltwater Park in Richmond Beach is perched in a large divot (one of my favorite geomorphic terms) that apparently corresponds quite closely to a post-glacial delta on the shores of Lake Russell (or Lake Bretz?).

Steep glacial deltas are little more than well-organized piles of gravel which means that they often disappeared by the barge load in the 20th century to provide aggregate for a growing city.  The gravel mine explains the amphitheater- shaped divot and the barge-loading explains the beach.  Which might be easy to mistake for a spit of some sort if you didn't know the history - and didn't notice that it looks much more like a pile of gravel than a spit (for one thing, the backshore is much too high).


Richmond Beach is a great place to watch sunsets.  And I was here for a good one.

It's also a good place to watch trains.  While I was on the beach between here and Boeing Creek (previous post), a series of northbound trains passed, including two Sounders, the Empire Builder, and this coal train - which was probably on its way from southeastern Montana to a terminal near Vancouver, where the coal will be transferred to a ship going to Asia.  It will all be kilowatts and carbon dioxide in a couple of weeks. (For anyone interested in coal, a popular topic around here these days, there are more photos on my hshipman blog (selected for the word "coal", but they reflect my fascination with geology, trains, and the Wyoming landscape more than any particular position on the current environmental politics!)

And for geologists not interested in Pleistocene deltas, in Holocene beaches, or in the Anthropocene coal industry, I've included a picture of some real rocks - in this case bright red ones used to repair riprap along the railroad.  Those are Precambrian Belt Series rocks from western Montana and those are very, very old ripple marks from a billion year old shoreline (I included a similar photo from six miles north of here in a post five years ago:  Ripple Marks - June 2007).

Boeing Creek

Boeing Creek flows out under the tracks a mile or south of Richmond Beach, in a ravine that runs between the posh chateaus of the Highlands and the upscale, but somewhat less posh, suburban tracts of Innis Arden.

The creek flows through a concrete box culvert (as does the walkway) dated 1951, but there are old rusty culverts dating, I assume, to it's previous path.

It's an interesting contrast to the Elwha from the week before.  It's obviously a much smaller stream to start with and I also suspect that the delta is composed not only of stream sediment but also a significant fraction of sediment eroded from bluffs farther south, transported north by waves, and trapped in the complex dynamics of the creek delta.  Like the Elwha (particularly recently), there are broad sandy bars extending far offshore on the downdrift side of the stream mouth.


Like many streams in this part of the sound, Boeing Creek reaches beach level upstream of the mouth of the valley, suggesting that it may have originally been graded to a lower sea level and then its valley floor rose in pace with rising sea level over the past few thousand years.  The railroad has altered both the landscape and the movement of sediment, obscuring the historic pattern of alluvial valley, wetlands, estuary, and stream mouth spit - all of which were likely present to some small extent.

Elwha Delta

With the lower dam completely gone and the upper dam nibbled down until only a much shorter version remains, the Elwha is releasing the sediment stored in the reservoirs for many decades.  Gravel from Lake Mills is moving its way down the river between the dams as a large wave, filling pools and braiding channels across the valley bottom.  Sand is moving through the system more quickly and is now appearing as large shoals at the delta – low tide and subtidal bars that are encroaching at the base of the cobble beaches on both sides of the river’s mouth.

A bulk of the material appears to be shifted eastward, a predictable consequence of the westerly swell.  Which is fascinating all by itself.  The waves wrap around the delta from the west, breaking along the shore at incredibly high angles, with big implications for both sediment and surfers.

Wood has also been flushed out of the reservoirs.  Wood of all sizes from small chunks of bark to large branches has been piled into broad debris fields at the river mouth, stacked in ridges by successive high tides, and then more recently eroded or washed away, spreading out in a thin band along the beach to the east.

The new sand has had little noticeable effect on the ongoing erosion of the gravel berms on the east side of the delta, which have been retreating rapidly for decades.  Maybe the new sediment will begin to slow this process, but will it do it by accreting new sand and gravel directly to the beach face, by dissipating wave energy on the broad sandy bars, or will the current beach face simply be abandoned as a new series of spits and lagoons forms farther offshore?

The removal of the dams is unleashing a complex chain of events, much as the construction of the dams did a century earlier. Some things will change rapidly – particularly those things that are moved readily by frequent processes, like sand moving through the lower river.  Some things will take much longer, particularly those that involve difficult to move material moved by infrequent processes – like new cobble berms forming on the delta.

The Elwha isn't just about emptying the reservoir and watching the exposed soils revegetate.  It isn't just about restoring a natural grade to a river that had been ponded behind two large dams.  The removal of the dams restores an incredibly complex system that extends far beyond the reservoirs.  Fish that spend most of their time in the open ocean will now be able to swim up into Olympic National Park, for the first time in a century, to lay their eggs in the upper watershed and give rise to new generations of Elwha River salmon.  Sand and gravel that has been trapped in reservoirs will now move downstream, rebuilding the delta and influencing the beaches all the way to Ediz Hook in Port Angeles.

I’m just an excited spectator out at the Elwha.  There are many folks much more actively involved and much more knowledgeable about the river and its beaches. Here are a few of them.

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