Saturday, May 12, 2012

Hope Island

 It's a short paddle from Ala Spit across to Hope Island, although there can be a lot of water moving through this passage, leading to some tricky rips and swirls.


The island is about a mile long and less than half a mile wide and is entirely managed as a Washington State Park (there's another Hope Island State Park in South Sound, just to keep things confusing).  There's a small primitive camping area on a protected cove (Langs Bay) on the north side - the camp sites are on a low bench that looks like it is several feet of shell midden sitting on several feet of clay.

The highlight of the island is the small 40' high promontory at the southeastern corner, which is connected to the main island by an isthmus that is part bedrock ridge and part tombolo.  Most of the rock appears to be serpentinite and some of the exposures are pretty complicated.  There's a wonderful gravel beach extending west along the southern shore - backed by serpentinite cliffs and a dense band of very large wood (a south facing beach north of the mouth of the Skagit is a natural trap for large wood).

The metamorphic bedrock on the island is mantled in some places with till or other Pleistocene materials. A small bluff at the northeast corner of the island displays a series of gravelly shell-rich beds - are these old beaches (but why so tilted?) or are they reworked deposits - sort of a shell-conglomerate or coquina?  To the south, there are even more complex deposits that include fossil shells.

Friday, May 11, 2012

Smith Island

Two weeks ago, I had an opportunity to fly up to Friday Harbor.  On the way I saw plenty of familiar beaches and took an awful lot of crummy pictures.  But I thought it might be an opportunity to highlight a shoreline that few people (myself included) have ever visited, but for which I have some interesting historical views.

Smith Island lies west of Whidbey Island and is sometimes called Battleship Island due its appearance from land - five miles away.  It's a lighthouse station and now a portion of the San Juan Island National Wildlife Refuge.  It's the remaining subaerial portion of one of several large shoals in the western Strait of Juan de Fuca.  Waves coming down the Strait from the west erode the bluff on the west side, redistributing the coarse sediment in a long tail to the east, ending in Minor Island.

The first two shots are mine from late April.  The next photo is a nice one taken in 2007 by Jeff Bash - the wave refraction patterns are worth checking out. The map is from Ralph Keuler's 1988 USGS Map (Misc Invest 1198E) - that's a 69cm/yr average erosion rate on the west side. 

The Lighthouse was reportedly 200' from the bluff when it was built in 1858 (Wikipedia).  In the 1960s, a new tower was constructed when folks realized the old lighthouse might not last.  By the end of the 1990s, it was gone.

1948 (National Archives and Wikipedia)
1970s (Wolf Bauer)

1980s (Gerald Thorsen)

Woodway Beach

There's not much beach left below Woodway - the upscale bluff-top community just south of Edmonds.  Once upon a time, this would have been a wonderful beach walk from Edmonds south through Woodway to Point Wells at all but the highest tides, but in the late 1800s the railroad chose the beach at the toe of the bluff as its route between Seattle and Everett and the beach got narrower.

Unfortunately, the bluffs along this stretch continued to fail magnificently long after the waves stopped cutting at their base, and landslides and busy rail corridors don't mix well.  
In the 1950s, Great Northern, faced with the high costs of keeping the Empire Builder out of Puget Sound, relocated the entire line away from the bottom of the cliff.  The result was a long linear lagoon between the old grade at the bluff and the new causeway on the lower beach. The beachface has become a lagoon. Large slides in the 1970s filled portions of this trough, as did the 1997 Woodway landslide near Deer Creek.

Burlington Northern Santa Fe - the inheritor of the Great Northern - plans to eventually complete double tracking of this corridor (all the better to hall Powder River coal to Bellingham? - 2011 Wyoming, 2012 Black Thunder Mine).  Meanwhile, the local police are kept busy enforcing BNSF's No Trespassing signs - shooing away teenagers trying to navigate Woodway Beach at high tide.


Wednesday, May 09, 2012

Cama Beach

There is a small perennial stream at the south end of Cama Beach.  It emerges from a gully and flows across the beach.  Some years it just ponds behind the berm, seeping out through the gravel.  Other years, it opens a channel through the berm and flows openly.  This is what it's been doing this winter.

Few streams arrive at the beach unimpacted by human activities and this one is no exception.  The historic condition is unknown - perhaps it actually flowed into the old lagoon where the resort is now and exited through the barrier farther north.  Regardless, it's outlet is now fixed with the stream pushed against the adjacent concrete bulkhead.  In addition, at some point, the concrete planks of the old boat ramp were dumped at the outlet (presumably to prevent some historic erosion problem?).  Interestingly, the planks are often buried, but this week they are more exposed than I've seen them in the 16-17 years I've been visiting.

There's always been a small delta on the intertidal beach here, but currently the stream is busy building a fresh gravel fan across it.  People often point to these deltas as evidence of a fluvial source of sediment.  While streams no doubt deliver sediment to the beach, or at least have historically done so, the presence of this kind of feature does not require upstream sediment. Much of the sediment may simply be upper beach sediment, relocated by stream flow to the lower beach.  You could probably form a small delta simply by running a fire hose across the beach for a few weeks.

One consequence of the stream eroding the upper beach is that in areas with significant drift the back beach is often narrower downdrift of the stream mouth.  In this case, the beach widens northward toward the stream mouth, then narrows distinctly on the north side.
 This is not a function of the bulkhead -- although that may complicate the dynamics a little bit.  Basically, the drift is diverted by the stream, starving the downdrift beach.  I like to think of this as a kind of negative groin.

Other examples, although each bears its own complications, include Seahurst in Burien and Narrows Park south of Gig Harbor.


Saturday, May 05, 2012

Cama Beach

I think there will be two posts from this morning's visit to Cama Beach, one on the landslide and one on the stream south of the resort.

The slide hasn't expanded significantly in the last month.  The sandy layer beneath the till on the headwall has continued to erode and there is now a large overhang.  I also think that there has been continued downhill movement of the debris in the gully itself.  From a fairly cursory comparison with earlier photos, it looks like the debris pile has settled somewhat, perhaps as the material at the toe has been eroded by waves.

Previous posts on the slide:
 March 17, March 7

There's been plenty of rain the last few days, including last night, and plenty of water was cascading over the rim and flowing down to the beach.  At least when it's flowing, this may be as important, or more important, than waves in eroding the landslide material.  The stream location hasn't changed - it's still flowing out on the north side of the debris-choked gully.  The beach to the north still shows fresh sand deposition, although it's not like there's a huge thickness of new material once you get away from the slide itself.  There is a lot of very soft sand on the lower beach (the tide during these pictures was around -2' MLLW) and it seems to extend in both directions from the slide area.