The English Channel and Eastern Washington

A few news outlets have had fun with a new geology paper and Brexit. Gupta and others (2017) used high resolution sonar imagery as well as seismic line investigations to support a theory about the formation of the Dover Strait and the formation of Great Britain as an island. Hence, the term Brexit being applied by news stories about the paper. The resemblance to eastern Washington landscapes of the sonar imagery is striking.

From Gupta and others (2017)

Smith (1985) proposed that the Strait of Dover was carved by a large glacial age flood event. That idea has gained strong support (see for example Gibbard (2007) and Gupta and others (2007)).

Gupta and others (2017) further support the idea of a huge ice-age flood using far higher resolution data than what was available to Smith (1985), and their recent work helps refine the idea. They noted similarities between the topography in the Dover Strait and the landscape of eastern Washington's Channeled Scabland, "We interpret the amphitheater-shaped channel heads as abandoned cataracts formed by focussed knickpoint popagation similar to those formed by high-magnitude floods in the Channeled Scabland, Snake River Plains and Iceland".

Channel Shifting on an Alluvial Fan

Four hazards are typically present on alluvial fans: 1) debris flows, 2) debris floods, 3) flooding, and 4) erosion. The debris flows and floods are the most worrisome because of their suddenness and violence. In many cases they are rare events which makes them more dangerous particularly in areas that have no previous recorded history of debris flow or debris flood events.

Another hazard on alluvial fans is the tendency for the stream channel to become filled with sediment and the stream then moving to another location on the fan. The new flow path causes flooding but also can cause significant erosion as the stream erodes into its new channel. This hazard can be mitigated, but in some cases it is a too costly a fight. 

Last week I got some experience on an alluvial fan stream that has left its old channel of many decades and has begun the process of establishing a new channel on the fan surface.     

Uncertainty and Public Officials

I am giving a short talk to some public (elected) officials on a particular geology hazard in Whatcom County. I included the following picture that I lifted from a talk given by the someone else on a similar subject. Alas this science/public policy problem can be applied to more than just my subject. 

More on the talk itself at some later date.

Breckenridge Creek Flooding, Whatcom County

After a visit to the Sumas Valley in north Whatcom County, I headed south via Telegraph Road, Sorenson Road and Goodwin Road. Lots swampy ground is present along the Sorenson and the north end of Goodwin. Water was pouring over Goodwin Road.

Road erosion at the head of the spill over is thus far minor

The water is from Breckenridge Creek. The creek is having a hard time passing all of its water under Goodwin Road and my general sense looking into the brush is that the stream may be going through a bit of a channel change upstream. The problem for the creek, and the Public Works folks, is that the gradients in this area are very low and the creek is flowing onto a landform area not of its own making.

Breckenridge Creek is flowing into an area of large glacial river outwash channels and late ice age moraines associated with what has been termed the Sumas Stade. That is the ice front lingered in the Sumas area leaving behind a landscape that has very little to do with the current streams.

DEM of part of the west edge of the Sumas Valley

Moraine features are evident north of the Kinney Creek label

Note also that the glacial outwash contains several gravel mines

In the DEM image above Kinney Creek and Breckenridge Creek flow off the north slopes of Sumas Mountain and encounter an old glacial outwash channel that flowed out of the ice front, the moraine of that ice front can be seen just north of the Kinney Creek label. Kinney Creek has somehow managed to flow north opposite the former outwash flow path. Brekenridge Creek flows west across the old channel then flows southwest along the base of an elevated area of outwash before turning west and joining the Sumas River. The west path of Brekenridge is intriguing in that it makes a narrow cut through a ridge of elevated glacial sediment. Just how that happened would be a rather difficult exercise that requires pulling back further and thinking through a lot of factors. And for that matter, Why is there such a narrow ridge of glacial sediment at that location?

The main take-a-way is that this is an area where the existing streams are flowing across a landscape that was formed by other processes. It does not take much for these creeks to fill their channels and spill over and find new courses. Brenkenridge Creek is actively eroding its incised valley upstream of the low lands. That sediment load will readily fill its channel on the low lands. Breckenridge is not the only creek posing flooding problems in this area. Most of the streams entering the Sumas Valley pose flooding problems and many have long histories of sediment management issues. Any large change in sediment flux in these streams poses a big challenge (hint: look at the DEM at Swift Creek). 

Waterfall on Vedder Ridge and the Sumas Valley

I previously posted on Vedder Wall noting its glacial origin. There is a seasonal waterfall on steep cliff face that was visible during a recent trip to the Sumas Valley.

Based on the elevation of the top of the wall at this location and the valley floor, I estimate the falls to be about 400 feet.

Prior to checking out the waterfall view, I had had a very wet day. I was fairly pickled by the rain as well as the need to do a bit of stream wading. So it was nice to have a bit of late afternoon spring sun, and despite the wet weather spring has arrived in the Sumas Valley below Vedder Mountain.

Spring hay and the view across the Sumas Valley floor to the northeast to the Chiilwack and Fraser Valleys

Blueberry field just south of the border

The richness of the Sumas Valley farmland is the result of the area being a former lake that occupied the low area left by the Sumas ice lobe. Keeping the area drained on the Canadian side requires a lot ditches, a pumping station and a levee to hold back the Chilliwack River. With the wet weather and low gradients of the ditches there was still a fair bit of water on the valley floor when I had a view from above the Vedder wall.

Working Through Theories at an Accretion Shoreform

I had a recent venture to Marrowstone Island in Jefferson County. Just south of the beach access at Fort Flagler (http://www.fortflagler.net/) I noted a well built up shore with driftwood and vegetation on the backside of the driftwood/beach berm. This section of shore is termed by the shoreline wonks as an accretion shore form, that is it shows evidence of beach build up with the accumulation of sediment - in short the beach at this location shows evidence of growth. Enough so that vegetation has become well established on the upper beach. I am not a big fan of the term "accretion shore" because it implies a process stability that may not be very stable. That is accretion can be a temporary phenomena.

I also noted that the trees on the backside of the berm between the berm and the base of the shoreline bluff were mostly dead. Why?

I ventured into the thicket of dead trees with the theory that perhaps the soil had become saturated as the berm had grown and blocked water flow from the slope above and thus killing the trees. However, that theory was killed off when I found no wet ground. In fact the ground was dry despite all the recent rain and the area of the dead trees was covered with thickets of salal, a plant that prefers dry conditions. 

The accretion shore feature continued to the north. Its presence jutting out from the base of the bluff seemed a bit out of place, but along shore spits like this are not uncommon. 

There was a hint as to what might have been the cause of the accretion shoreform near the shore access at the Fort Flagler State Park. Old pilings in the beach suggested a former structure which would have blocked sediment transport or driftwood causing the shore up drift to build out.

Old pilings for a former pier

 The history of the shore was well presented at the shoreline trail access in the park. I was walking this shore reach from a different direction so my seeing the sign was after walking the shore.

Note the large build up of driftwood south of the pier in this photograph

1951 aerial (USGS)

So the likely origin of the accretion shoreform was the past presence of the pier. The wood pilings would block driftwood on the south side but allowed sand to pass through as the south wind generated waves moved sediment generally from south to north.  The pier though not used since the 1950s was still present up through 2006.

Oblique aerial view (Ecology, 2006)

My theory on the dead trees was that the accretion shore form is beginning to erode now that the pier has been removed and thus the trees were being inundated with saltwater on a more frequent basis and the beach had narrowed. Nice theory; however, a closer look at the 2006 oblique aerial shows that the trees were already dead before the pier was removed.

Dead trees can be seen all along the base of the bluff (Ecology, 2006)

A view of the 2002 oblique shore aerial shows that the trees alive in 2002.

Same location in 2002 with live trees (Ecology, 2002)

My theories up to this point have not done well! So a new theory is proposed. A large storm surge in 2006 may have been responsible.

This particular storm along the east shore of Marrowstone Island caused significant shoreline erosion that stripped away the toe of the slopes at many locations along the east shore of the island. That erosion set up ongoing bluff failures that took place in the years that followed once the toe of the slope had been eroded. So my theory is that surge of salt water over the berm may have killed the stand of Douglas firs growing between the berm and the toe of the slope.    

Samish Island Heron Rookery Take Flight

Lisa captured a short clip of dozens of heron circling over the Samish Island heron rookery. The great blue herons nest in trees in the forest as a big group. Bald eagles do prey on heron and an eagle caused the heron to take flight in mass.

https://www.instagram.com/p/BSJb0ubFfuX/

The heron began the early stages of breeding and nesting within the past few days.