Cama Beach

 Cama Beach appeared on these pages frequently last year and probably will again this year.  These are from a brief foray in mid-January following some more landsliding.  Not only has the big gully been active, but a couple of new slides have occurred as well.

The big slide we posted about last year (search on the label 'camano') was quiet all summer and early fall, but has gotten more active this winter.  Water was flowing over the top during this visit and was eroding the sandy unit below the till.  This appears to undercut the till which then fails in larger blocks, although nothing too dramatic has happened yet this year.  Most of the colluvium in the gully still looked like the trodden and rained-on remains of last year's debris.  I would expect more failures as long as the water is flowing, but I wouldn't pretend to guess how large.

One reason for my visit was reports of a new slide south of the one I just described.  Sure enough, there had been a fairly large debris avalanche on the lower half of the slope, in line with a substantial gully that probably corresponds to an earlier slide.  Water was flowing from somewhere mid-slope. This new slide is immediately north of one that occurred in the late 1990s. There is plenty of tree debris on the beach, and a fair amount of dirt, but nothing like the other slide.  There's a steep bare headwall at the very top of the slope, but the upper slope doesn't appear to have failed in this event.  I suppose the recent slide could make that more likely, at least if conditions stay wet.

There was also a small slide - a small earthflow more precisely - on the slope nearer the resort, above where the old bungalows were.  When the park was redeveloped, a decision was made to remove several of the old bungalows at the north end, at least in part due to their vulnerability to slides. Probably a very good idea.

AERIAL VIEW

Thornton Beach

San Francisco's Ocean Beach transitions southward into progressively higher bluffs in the vicinity of Fort Funston, which then continue to rise on into Daly City towards Mussel Rock.  About a mile of the bluffs between Fort Funston and the northern portion of Daly City are marked by a spectacular deep-seated landslide complex - characterized by rolling topography and shore-parallel ridges and swales.


AERIAL VIEW
My brief research suggests a range of ages for this slide - which is often the case with these features - since some people are referring to the age of the overall feature, whereas others refer to specific events or even to more recent reactivation.  From what I can tell, the landslide dates back hundreds of years, but experienced significant movement in the 1906 earthquake and continued to experience some additional sliding during the past century.  Regardless, the railroad, and later the highway, that was built on the face of the bluffs from San Francisco to Pacifica (and beyond), in the early 1900s, has not survived - except in small pieces and on interpretive signs.

Pacifica - Sharp Park

This part of Pacifica is built at beach level -- perhaps on old backshore dunes.  But just as with the bluffs shown in the previous post, this beach has been subject to significant erosion.  For this and many parts of the California coast - the El Nino of the 1982-83 winter was a tough one.  The community has gone through a few iterations of fortifications and is now perched behind a high seawall with a big rock apron.

AERIAL VIEW

It was a blustery day (the photos were taken on December 21st), waves were building, but the tide was not particularly high.  I suspect these were pretty tame conditions and certainly not enough to discourage the fishermen.

Pacifica - Esplanade Avenue

The northern portion of Pacifica is built on the 80' vertical edge of a rapidly eroding marine terrace.  Apartment buildings - some older; some recently remodeled - are lined up along the edge, protected by a discontinuous line of riprap.

AERIAL VIEW

I assume there is some controversy about the riprap.  But I suppose that riprap is all there will be in another decade or two.  There certainly won't be any more beach at high tide by then. Temporary protection of private structures or long-term protection of public resources?  It looks like the trade off for more riprap is better access to the little bit that's left?

Mussel Rock

Daly City is where the San Andreas fault heads out to sea.  It arrives from the south by way of a series of fault valleys and elongated lakes and reaches the coast just north of Mussel Rock.  It continues northward offshore past the entrance of the Golden Gate before reconnecting briefly with California at Point Reyes.

There's a large divot where the fault intersects the high bluffs, at least in part due to past landslides.  In the 1960's tidy rows of homes were built along the top edge of the bluffs.  Remarkably, most of them are still there.

AERIAL VIEW

Mussel Rock Park is the site of a historic landfill, now closed, but heavily fortified with riprap.  Mussel Rock itself is a large block of Franciscan rocks squeezed out along the fault, and described in the opening passage of McPhee's Assembling California.  As McPhee notes, this is a good (but often foggy) spot to "sit and watch the plates move."  Which I suppose is the attraction of those homes perched at the edge of the precipice, witness to storm waves, landslides, and plate tectonics.

Ocean Beach

The west side of San Francisco slopes down to the ocean in rolling sand dunes, now stabilized by the endless residential blocks of the Richmond and Sunset neighborhoods.  The sandy beach is all that remains of the original system, cut off from the city by the Great Highway and the impressive recurved seawall built to keep the Great Highway where it was built.

AERIAL VIEW

This is a complicated beach that has experienced long cycles of erosion at one end or the other for the past century.  Climate and wind patterns shift sediment back and forth as they do on most beaches, but there are also interesting dynamics related to the availability of sand from offshore deposits at the mouth of the bay (USGS Field Trip Report, ASBPA 2005).  The beach is doing well at the north end but there have been serious erosion problems at the south end down near Sloat Avenue for many years and there have been recent efforts to nourish the beach at that area.

The O'Shaugnessy Seawall at the north end is often held up as an example of a successful seawall - although I suspect what it really shows is that seawalls work best, and have the least impact, where the beach in front of them is stable or building.  It is a substantially built structure which means it may continue to protect the Great Highway even if the beach were to go away or sea level were to rise.  For the time being, it provides a nice promenade with easy access to the wonderful beach.

Drakes Beach

The southerly hook of Point Reyes forms Drakes Bay (after Sir Francis).  Drakes Beach lies along its northern shore and is an elegant curve of high bluffs, broken by a few small barriers and a couple of larger spits.

AERIAL VIEW

I believe the bluffs are Miocene siltstones and sandstones of the Purisma Formation.  There is a wonderful planed-off platform at the base of the cliffs.  Wave-cut platforms - shore platforms, more generally - have generated plenty of research and speculation.  I suspect this one reflects some combination of modern waves, historic uplift?, and lithologic variation - but that's mainly a guess.  The sun was setting and we had to get back to the city for dinner - so much for more exploration.

Point Reyes

Point Reyes is separated geographically from the rest of the Northern California coast by Bolinas Lagoon, the Olema Valley, and Tomales Bay.  It is separated geologically by the San Andreas Fault, which bisects all three of these features.  That means Point Reyes is on the Pacific Plate and heading north relative to most of northern California, which is still attached to North America.  It's geolgoic affiliation is really with the coast much farther south - and ultimately with rocks that belong in Southern California.  The headland of Point Reyes is Cretaceous granite, much of the peninsula is Miocene sediments, and much of the west side is mantled in both ancient and modern sand dunes.

The beach on the ocean side consists of a long strand of coarse sand extending north from the headland. It's backed by dunes and low bluffs cut into much older dunes.  The aerial shows the dunes climbing southeastward up the long western slope, which says something about the prevailing winds.

AERIAL VIEW

The dunes are largely stabilized by non-native European beach grass and Ice Plant.  Dunes are like meandering rivers and receding coastal bluffs - they are supposed to erode.  And if they can't - due to levees or seawalls or invasive vegetation, the landscape and the ecology begins to change.  The ice plant was beautiful in its winter colors -- even if there was far too much of it! 

West Beach

In November 2011, I came up here during a windstorm and wondered what it would look like if the tide were two feet higher. This morning it was three feet higher, although I missed the peak by 30 minutes or so.



The road signs pretty much tell the story. I've included a picture from a nicer day (several years ago) for comparison!

And here's a video clip -- excuse the poor quality, but it was hard to stand up in the wind.

AERIAL VIEW

Whidbey Island

This morning was already going to be a very high tide, but an incoming storm turned it into something special.  Below are the barometric pressure and tides in Seattle for the last two days.  As pressure dropped yesterday, the water levels rose above their predicted levels (green curve is difference).  This added "surge" increased to about 2' last night, then fell off a little by morning as the system arrived.  The predicted 12.9' tide arrived at about 14.5' (relative to MLLW in Seattle), roughly matching the previous record set in January, 1983 (during an El Nino).

I spent the morning on the west side of Whidbey Island. I missed the peak of the tide, but got some great shots of storm waves at West Beach (see subsequent post) and numerous other shots on the way down the island.  The winds were out of the southwest on the northern end of the island but from the northwest as I moved down the island.  Ultimately, it was if the wind was barreling eastward down the Strait of Juan de Fuca, then splitting when it reached the west shore of Whidbey near Point Partridge.  In an earlier post (Keystone: October 2012) I mentioned that while winds are often out of the south in the Admiralty Inlet area, the most significant waves in terms of sediment movement might still be out of the northwest.  I think today was a good example.

Bowman Bay, Deception Pass State Park
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Gravel Beach:  March 2012

Failing bulkhead south of Libbey Road
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Gravel Beach:  February 2009

Removing logs off road at Ebey's Landing
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Gravel Beach:  February 2008

Another failing bulkhead, this one at Ledgewood Beach
(for another perspective, see cover image of 2010 USGS Report)
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Gravel Beach:  April 2006

Lagoon at intersection of Shoreview and South Woodard in Freeland
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Lagoon at Freeland Park (you may note that Freeland has several
historic back-barrier lagoons that periodically reassert themselves)
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Gravel Beach:  October 2006