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    Northwest Geology Field Trips, by Dave Tucker, is licensed under a Creative Commons Attribution-Noncommercial- Share Alike 3.0 United States License. You can use what you find here, repost it with attribution to the author, "remix" it for your own purposes, but may not use it with the intent of making money off of it.

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Stillaguamish Landslide- Geologic Perspectives

Interpretation of landslide scarp on LiDAR image, by Dan McShane.

Interpretation of landslide scarp on LiDAR image, by Dan McShane. Click to enlarge.

Dan McShane has written some geologic perspectives about Saturday’s landslide into the Stillaguamish River. Dan is a consulting geologist based in Bellingham and author of ‘Washington Landscapes’ blog, and has some great insights into the geology and history of the slide area. Rather than trying to rewrite his excellent reports, I’ll just provide the links. It is not the first landslide in this location. In my view, it  is a tragedy that people are permitted to live in this location.

 

Dan’s Initial report:

http://washingtonlandscape.blogspot.com/2014/03/arm-waving-notes-on-stilliguamish.html

Geologic background:

http://washingtonlandscape.blogspot.com/2014/03/geology-of-silliguamish-blocking-slide.html

LiDAR images and slide history.

http://washingtonlandscape.blogspot.com/2014/03/aerial-history-and-lidar-of.html

Stay tuned for more posts from Dan. Consider subscribing to his blog.

 

Clay Banks landslide video is uploaded

View a 2 minute video on YouTube I made at the Clay Banks landslide toe Thursday. The vid is annotated and narrated.

The video is here: http://youtu.be/Hxwu-cf3bFo

Dave

Nooksack River landslide near Deming- Update #2

Red line marks scarp of Feb 21 landslide. A later, undated slide is outlined in green. The second slide send brown soil over the top of the earlier clayey slide.

Red line marks scarp of Feb 21 landslide. A later, undated slide is outlined in green. The second slide sent brown soil over the top of the earlier clayey slide. Click to enlarge any image.

Thursday I visited the toe of the February 21 Clay Banks landslide on the Nooksack River, in company with Scott Linneman (landslide geomorphologist at WWU Geology) and John Thompson, a geologist with Whatcom County Natural Resources. If you haven’t been following this story, please visit Dan McShane’s blog post for the background to the story including some fine maps and photos, and my original post from February 22, the day after the landslide. Dan has also posted a great set of old maps and LiDAR showing changes at the Clay Banks as the river changes position. The landslide occurred just at midnight Friday February 21; you can see the sudden radical, short-lived drop in the river discharge graph below (recorded at the river gage a mile downstream at Cedarville). Click link to annotated You Tube video.

The Nooksack River gage at Cedarville (Nugents Corner) recorded a brief but sharp drop in discharge while the landslide dammed the river.

The Nooksack River gage at Cedarville (Nugents Corner) recorded a very brief but sharp drop in discharge (from ~2500 to 400 cfs) while the landslide dammed the river. Click to enlarge.

Annotated Google Earth image, with corrected location of 2-21 landslide and new river channel at the toe. Click o enlarge any image.

Annotated Google Earth image, with corrected location of 2-21 landslide and new river channel at the toe. Click to enlarge any image.

The Clay Banks are a steep bluff of Pleistocene glacial clay around 100 feet high on the south side of the river about 1.8 river miles upstream of the Nugents Corner bridge. The landslide bit deeply into only the upper half of the bluff, leaving a prominent bench hanging above the river. There is landslide debris on the bench, but most of it appears to have flowed over the bench, down the bottom of the bluff and into the river.

Shaky split log spans a side channel.

Shaky split log spans a side channel.

We crossed a shaky foot log across a narrow side channel to get to the big gravel bar on the north side of the river, and then walked 350 yards to the river side directly opposite the landslide toe. The landslide began in a layer of glacial clay a few meters above a prominent alluvial bed called the Deming Sand. If there is a stratigraphic layer at this level in the Clay Banks that contributed to this landslide it was not apparent using a high power spotting scope.

The toe of the landslide consists of large blocks of clay.

The toe of the landslide consists of large blocks of clay.

The river is still ponded against the landslide toe which protrudes into the river for 200 feet or so from the south bank. The river has cut through the outermost edge of the landslide toe. The river drains the partial impoundment by racing through a 60-foot-wide (19 m, measured with a laser range finder) gap. We couldn’t measure the river depth, but know it was 5 feet right up against the bank we were standing on, and 10 feet or more may be a reasonable guess. The landslide toe consists of car-sized, or maybe even garage-sized, clay blocks, and rests on the surface of a gravel bar; the bar gravel is exposed beneath the debris. At the time of the landslide, the river was closely beneath the high bluff, and the gravel bar we now see beneath the toe was part of the one we were on. The river then cut a new channel around the outer edge of the deposit, isolating the bar gravel beneath the toe from the gravel bar on the north side of the new channel. We found a single, angular clay block lying on the north side side of the channel, and a number of rounded ones. We figure the angular one (see photo below) was tossed laterally out of the landslide toe. It hadn’t been rounded by river flow, so is almost certainly right where it landed at around 12AM Friday 2-21-2014. You can see the same block in Dan McShane’s post, though when he visited the river bank was a few feet furthe away. This block is direct evidence that the river is continuing to cut outward and remove the bar on the north shore. This block will probably tumble into the river in the next few days.

Angular clay block marks extreme outer margin of the landslide toe. River has cut a new channel between this block and the rest of the landslide.

Angular clay block marks extreme outer margin of the landslide toe. River has cut a new channel between this block and the rest of the landslide.

The surface of the landslide toe is covered with large clay blocks. These sit on topo of a pre-landslide gravel bar.

The surface of the landslide toe is covered with large clay blocks. These sit on topo of a pre-landslide gravel bar.

The river makes an end run around the toe, and then cuts sharply south and runs directly into  the base of the bluff below the landslide. This is certainly undercutting the base of the Clay Bank, setting the stage for another collapse, perhaps involving the entire bluff height rather than the upper half.

Among our observations is that there has been a second, much smaller landslide in the same place. We don’t know when this occurred, but it sent darker material over the bank and down onto the southern margin of the Feb 21 toe. Compare the photo taken by Dan McShane on the morning of Feb 22 with the one I took today (Feb 27). The center of the 12-hour old scarp in his photos is now deeper where the 2-?? landslide collapsed. Also in the photos, note the toppled trees that rode the slide over bank.

The Clay Banks extend another 1/4 mile or so upriver and 1/2 mile downriver from the 2-21 landslide. Earth movements have been happening here at various scales for decades, and are likely to continue long into the future.

ACCESS NOTE: All access is over private land, so you are dependent on reports from authorized visitors. Sorry. Don’t even try to get there yourself. It is difficult to see the Clay Banks scarp from anywhere on the north side of the river. You may get a glimpse from the Deming Road somewhere in the first half mile after it branches off Mount Baker Highway a bit east of Nugents Corner. However, you will be 7/10 of a mile away, and for sure can’t see the river or the landslide toe.

Nooksack River landslide near Deming: An update

My friend Dan McShane visited the Nooksack shore immediately across from the Clay Banks landslide toe Saturday and posted a great set of photos on his Washington Landscapes blog, as well as further analysis of the changes to the river channel at the Clay Banks in the past years. Click this to read his report. Dan visited a different area than I did, and his report is well worth reading. His newest photos of the landslide deposit are toward the bottom of the post. Among his observations are blocks of clay across the river from the failing hillside of the Clay Banks. One of his photos is below, showing the landslide toe where the river has cut through it.

Landslide diverts Nooksack River near Deming, Washington

View up river from top of Clay Banks in a snowstorm. Landslide toe in river is at right center. Photo by D. Tucker. Click to enlarge photos.

View up river from top of Clay Banks in a snowstorm. Landslide toe in river is at right center. Photo by D. Tucker. Click to enlarge photos.

A landslide about 1 AM February 21 diverted the Nooksack River. The slide occurred at the infamous ‘Clay Banks’ about 1.8 miles upstream of the Baker Highway bridge at Nugents Corner, near Deming. I’m passing along the essentials from Dan McShane’s Washington Landscapes blog. I visited the site this morning with geologists Scott Linneman (WWU) and Eric Grossman (USGS), and have posted a few photos and a new Google Earth map. The river has cut through the low-relief landslide toe, and there is now no impoundment of the river. According to residents we spoke with there was another large landslide a couple (?) of weeks ago. They said they could hear a deep rumbling when the February 21 slide released.

T'photo of slide toe in river. The river has cut around the toe, and also through its body. Photo by D. Tucker

T’photo of slide toe in river. The river has cut around the toe, and also through its body. Photo by D. Tucker

Annotated Google Earth screen capture. D. Tucker

Annotated Google Earth screen capture. Blue lines indicate river channel as of AM, Feb. 22, 2014. D. Tucker

Access to all viewpoints is on various private properties, which are amply posted ‘No Trespassing’, etc, etc. You can’t see anything from anywhere without trespassing. Watch for possible updates. We’ll make and effort to get more information and better photos soon.

The Clay Banks consist of Pleistocene glacial till sitting on top of a very permeable sand layer, which in turn sits on top of older glacial till. It is very prone to sliding and has destroyed two houses that were built in the forest several hundred yards back of the top of the bluff in the late 1980s or early 1990s.

John Thompson's photo from the gravel bar, Feb. 21, 2014.

John Thompson’s photo from the gravel bar, Feb. 21, 2014.

This house was gradually undercut and has slid off the brink of the Clay Banks. Photo by Dave Tucker, Feb. 2013.

This house was gradually undercut and has slid off the brink of the Clay Banks. Photo by Dave Tucker, Feb. 2013.

Dan’s post:

Nooksack River Temporarily Blocked by Landslide

Via a network of folks that pay attention to the Nooksack River:. The flow on the river at the Cedarville gage took a brief plunge last night from 2,300 cfs to 400 cfs.
 

At Lynden 11 miles downstream a less substantive, but still sharp drop and recovery took place. Lynden Public works reported a sharp increase in river turbidity.

USGS staff noted the dip in the discharge and Whatcom Flood Division confirmed a large landslide at the Clay Banks had blocked the current main channel and deflected the river back to an older channel.

Clay Banks landslide can be seen at bottom center
Topo of Nooksack River and Clay Bank

…As can be seen the river has been up against the steep bluff in the past. However, the frequency and duration of the river being against the steep bluff has been enhanced by the construction of a high rip rap levee on the opposite bank preventing the natural meander of the river.

1998
Note the slide on lower left and rock levee on the opposite upstream bank

Posted by at 9:35 PM

Updated trip to Nodule Point & Liplip on Marrowstone Island

Concretions in Scow Bay sandstone at Nodule Point. B. Mooers photo.

For whatever reason, the webpage describing the geology at Nodule Point on Marrowstone Island (south of Port Townsend) has received a lot of visits lately. I decided to see what I’d written back in the fall of 2010. I found that somehow I had deleted the photographs. I have replaced those with the originals from Dan McShane, or new ones provided by Bob and Adena Mooers, who field-checked the original trip. The trip describes latest glacial deposits, cannonball-like concretions, and best of all for this volcanophile, a basalt dike intruding the sandstone bedrock.

Visit the webpage here.

A dike cuts sandstone at Nodule Point. B. Mooers photo.

Ice-rafted erratics in eastern Washington

Dan McShane has posted photos of some really huge basalt blocks stranded on ice-age lake terraces in eastern Washington. Read Dan’s story here: http://washingtonlandscape.blogspot.com/2011/08/glacial-erratics-near-grand-coulee-dam.html

The basalt blocks sit on or in lake deposits. They were carried by very large icebergs that had calved off the nearby terminus of the glacier covering the northern part of the region in the Pleistocene, and which plugged Columbia river drainage in the area of Grand Coulee Dam.The underlying bedrock is Columbia River basalt or, in places at least, much older gneiss. The basalt blocks did not travel very far, either within the glacier or in the ‘bergs, since CRB doesn’t extend very far north of the southern limit of ice flow and consequently not much available to the glacier to erode.

Field trip to Beach 4, Olympic coast

Dear friends,

At long last, I’ve added a new field trip. This one investigates an angular unconformity, a disconformity, and turbidite layers at Beach 4, just north of Kalaloch in Olympic National Park. You’ll find the full story here.

This field trip is an excerpt from the book I’m writing, Geology Underfoot in Western Washington, to be published by Mountain Press.

And not one single mention of ‘erratics’ in this field trip!

Many new people have subscribed to this blog; my apologies tp you that it has taken me so long to get some new material written. I’ve been focusing writing and remodeling my home office.

Now, back to the grindstone!

Cheers, Dave

Take me to the field trip!

The Duvall erratic (aka ‘Big Rock’)

Duvall's Big Rock. John Scurlock photo. Click to enlarge.

A new field trip is posted, directions to visit to ‘Big Rock’ just south of Duvall, Washington. The field trip is posted here in the ‘Glacial erratic field trip section of the Northwest Geology Field Trips website.

If you visit, see if you can tell what type of rock it is. I haven’t been there.

DT

Appeal to citizen scientists: Do you know of any Jackass conglomerate erratics ?

Adena Mooers and a Jackass conglomerate erratic, Pt. Wilson. Photo courtesy A. Mooers. Click to enlarge

Dear readers,

Have you seen erratic boulders of Jackass conglomerate? I’m specifically interested in learning of any sightings south of Whatcom County, on either side of Puget Sound, or on the shores of the Strait of Juan de Fuca. The easiest place to spot them is on beaches.There’s an idea out there that all these rocks came down to the lowlands only during the last phase of the Pleistocene continental glaciation, the Sumas stade of around 11,000 14C years BP (before present). That glacial advance apparently didn’t get any further south than Bellingham, so if Jackass boulders are found to the south, then that hypothesis must be rethought. I am aware of a Jackass erratic on the beach at Port Townsend, which in itself casts doubt on this hypothesis. Examples of Jackass conglomerate erratics have previously been discussed, with photos on this website: Donovan Avenue erratic, Bellingham; Aldergrove erratic, BC; Malloy Village erratics, Ferndale; H Street erratic, Blaine.

In any case, these are really distinctive conglomeratic boulders that originated up the Fraser River valley, either east of Hope near Manning Park, or in another area considerably further north, around Lillooet. If they are present in deposits predating the Sumas, for instance in Everson glaciomarine drift or Vashon till, then we can say with certainty that the ice that formed the glaciers of the last glacial maximum, terminating south of Olympia, came out of the interior of BC via the Fraser valley as well as the west flank of the BC Coast Mountains. This is the most widely accepted idea, and will be well-demonstrated if the distinctive Jackass boulders are found beyond the Sumas stade deposits in Whatcom County .

If you spot one of these cool boulders outside of Whatcom County, please send a photo, directions, and GPS coordinates (be sure to specify what coordinate system you are using) to me:

email contributions to this address.