Wednesday, April 18, 2018

Self Armored River Bluff

We recently traversed along the base of a late-Pleistocene terrace consisting of glacial till and ice proximal meltwater. The terrace formed by incision and erosion by the Nooksack River to create a river bank bluff. The bluff is about 25 feet high. There are numerous large cobbles and boulders at the base of the bluff along the river edge derived from cobbles and boulders that have fallen from the terrace slope forming a lag of very course sediment along the edge of the river. Many of the boulders are much larger that the cobble sediment within the gravel and cobble bars within the river area. 




Cobbles and boulders in the river bluff slope 

The large cobbles and boulders accumulated at the base of the slope along the river appeared to be limiting the erosion along the terrace. The bare slope above shows that some erosion has taken place, but the size of the rock large on the lower slopes was considerably larger than that within the river gravel and cobble bars.

Post our traverse, a review of aerial photographs dating back to the 1930s found no discernible change in the position of the terrace edge over a period of 80 plus years. The historic aerials also showed the river was frequently flowing right at the base of the terrace. Hence, the rocks armoring the lower terrace were effectively reducing erosion for most river flow events.     

Saturday, April 14, 2018

Dungeness Spit Notes

I had a brief venture to the Dungeness River delta. Standing on the saltwater mash flats of the delta I had a view across the marsh and the water of Dungeness Bay.


The Dungeness Lighthouse was a speck on the horizon and only a bit more visible with the telephoto view.


Dungeness Bay looking towards the tip of the spit

Lighthouse viewed via telephoto view

The Dungeness Spit is a remarkable thin stretch of sand and gravel beach extending out into the Strait of Juan de Fuca over 6 miles from the main coast.


A big chunk of sediment comes from the high eroding bluffs to the southwest of the spite. These bluffs are exposed to fairly large waves coming into the open water of the Strait of Juan de Fuca. Ian Miller has put together a scheme for getting a better understanding of this remarkable spit (surveying-dungeness-spit). And it is remarkable - its the longest spit in the United States. Schwatz, Fabbri and Wallace (1987) provide a map of the sediment (drift) movement on this complex spit.

Drift map (Schwartz, Fabbri and Wallace, 1987)

The spit is complicated by the presence of another source of sediment from the southeast from sediment inputs from the Dungeness River as well as periodic waves generated by south winds blowing onto the backside of the spit.

Light House on distal lobe of the spit

Beyond the lighthouse, the spit is a no-entry wild life preserve as critical habitat for many bird species.

Wednesday, April 11, 2018

Cool Oblique Lidar Image of Racehorse Slide by Washington DNR

The Washington State Department of Natural Resources has a set of new images derived from utilizing lidar (new-lidar-screensavers-of-washington). One of the images is the Racehorse Slide in Whatcom County which I very recently coincidentally posted on recently (first-description-of-racehorse-slide).   


The steepness of the upper part of the slide appears a bit exaggerated, but the imagery overlain on the lidar and aerial oblique views does provides a compelling image.

Within the news post associated with some other great images, there is a series of changing images of the Racehorse slide. I screen saved on that has labels added.


The slide is a complex slide associated with large scale dip slope failures and appears to consist of multiple failures. There are a number of these large scale dip slope failures in the Chuckanut Formation in Whatcom County and the scale and potential consequence is a bit disconcerting. The marked up image shows the Racehorse Creek landslide of 2009 that appears to have failed on the same bedding plain.

Images like this are a good wake up call to the potential hazards in our mountain valleys. This slide could use a bit more study and understanding.     

Thursday, April 5, 2018

First Description of Racehorse Slide

I visited the Racehorse Slide in Whhatcom County this week. The Racehorse Slide is a big slide that extended across the valley floor of the Nooksack River.

Lidar of racehorse slide

The first description of the slide may be attributed to the government land survey crews. I took a look through the field notes from the original government land survey that traversed this slide. Galbraith noted the piles of rocks and none of his survey witness tress were large. 

   

Pringle, Schuster, and Logan (1998) took a crack at dating the slide via a log exposed in the Nooksack River bank below the slide. They got a date of 3,780 radiocarbon years ago. Given the location of the log this date can be viewed as a maximum date; the slide may be younger, and based on the appearance of the boulder field I suspect it is substantially younger.


Note lack of weathering rind on this coarse sandstone

Besides the rather unweathered appearance of the sandstone boulders, there are no large old stumps within the boulder field. Perhaps there are some elsewhere on the the slide. The lack of large stumps is by no means definitive regarding the slide age - it may simply mean that fire recurrence may have been frequent enough to prevent large tress from growing in this area. Early accounts of the area summarized by Cashman and Brunengo (2006) suggest that the area had been burned over in the late 1800s.




    


Monday, April 2, 2018

Whatcom-Labounty Wild Land Northwest of Bellingham

Just to the northwest of the Bellingham city limits is a swath of land between Interstate 5 and Northwest Road. From a map perspective, I have long been familiar with this area. The city designated it as an urban growth area back in the early days of the Growth Management Act in the mid 1990s. The land is underlain by Bellingham Glacial Marine Drift consisting mostly of silt and clay. Glaciomarine drift consists of silty clay soils that were deposited by melting glacial ice floating on the sea at a time near the end of the last glacial period when the local relative sea level was higher than the present (the mass of thick glacial ice that had covered the area had depressed the land surface hundreds of feet in the region).

Northwest of Bellingham, the glacial marine drift topography is a relatively hummocky landscape. I suspect the hummocky landscape was the result of underwater currents during the late stages of glacial marine deposition. Soils maps indicate the soils are Whatcom-Labounty soils. The Whatcom soils are well drained at shallow levels and wet at depth and the Labounty soils are poorly drained and tend to be wet. The poor drainage and hummocky nature of the area is such that it was poor farm land and poor forest land. The wetlands as well as very soft soils also have made it rather poor land for urban development; I estimate the area is on the order of 60 percent or more wetlands. 

The result is a swath of land at the city's edge that is wild land. While other wild lands at the city edge attract recreation, the brush, wet ground and lack of trails means a venture into this area is a brief wilderness experience even if one can hear the freeway and air planes at the nearby airport.

Start of my venture was a classic bush wack only on level ground.  


The wetlands rewarded me with an early bloomer - Lysichiton americanus (skunk cabbage).

The biggest challenging was navigating across or in some cases through areas of standing water.

Water coverage of this landscape has been increasing. Beavers in this area can go about their works relatively free of disruption. They do not bother with permits to cut trees down in forested wetlands or get hydraulic permits or dam permits.


A forested hummock raising above the wetlands as an island provided a brief spell of easy walking.

A partially blown over Douglas fir redirected the lead to a limb.

Sometime in the past fire had visited this island in the wetlands.

I did manage to get to my sample site along a particular branch of wetland drainage. Under the black organic layer the soil is stained by iron precipitate.

Saturday, March 31, 2018

Daffodils on the Skagit Delta

The tulips are not quite in bloom yet on the Skagit Flats, but the daffodils are in full display. 


I got a glimpse of the workers - these flower fields are a business and not simply a display for tourists.

Thursday, March 22, 2018

Comparing Lidar of Different Years at Dynamic Landscapes

The Washington State DNR has recently uploaded more lidar coverage (http://lidarportal.dnr.wa.gov/). Some of the recent uploads are of lidar that was flown in the early 2000s such as Jefferson County, but there is also some 2017 high resolution lidar that has been a bit of distraction to geomorphologist.

With multiple year available on the portal, there is also the opportunity to do comparisons at sites that have undergone change. Alluvial fans can be a good place to see significant changes.

Canyon Lakes Creek alluvial fan has been going through significant recent changes. The fan is in part controlled by the meanders of the Middle Fork Nooksack River as well as human infrastructure.       

2006 lidar

The change in flow on the fan has eroded into an old elevated terrace.

2013 lidar

The results have been significant property damage as the creek erodes new channels and flows and floods into areas not previously near the creek.    



Racehorse Creek is another creek that has been going through some big changes. A large landslide in the watershed in 2009 has greatly increased the sediment inputs to the stream. On the creeks lower reaches that has lead to the channel being filled and flooding and new overflow channels forming.

2006 lidar

2013 lidar, note the channel has been entirely filled 

The slide in Racehorse Creek has had some consequences to the few folks on the lower reaches of Racehorse Creek. One home has been abandoned due to the nearly winter long constant flooding.

The lumpy ground west of the lower reach of Racehorse Creek is a very large landslide deposit that dwarfs the event that took place in Racehorse Creek. The slide extended across the Nooksack River Valley. The age of this slide is not currently known.
 
Racehorse Slide

A comparison between 2006 and 2017 lidar shows the 2009 slide before and after. 

2006 lidar

2017 lidar
The slides are on dip slope of a sandstone unit within the Chuckanut Formation.

The 2009 slide is readily visible from the Nooksack Valley south of Kendal and appears as a sharp edged block missing from the the slope. The lidar suggests that the slip was off the same bed of the formation.