Posted by: magmatist | June 7, 2013

Update: Nooksack debris flow initiated by landslide, not outburst flood

By Dave Tucker, with new material provided by John Scurlock and Steph Abegg.

Aerial view looking east up Middle Fork Nooksack. Deming Glacier terminus in the middle ground, around 3950' elevation. photo by J. Scurlock. Click to enlarge any image.

Aerial view looking east up Middle Fork Nooksack. Deming Glacier terminus in the middle ground, around 3950′ elevation. The pale muddy trace of the debris flow is evident down the valley floor, well above the river. J. Scurlock photo. Click to enlarge any image.

Here is an update on the May 31, 2013 debris flow in the Middle Fork Nooksack valley.

Video of the deposit in the river channel is on YouTube.

Thursday afternoon an aerial reconnaissance of the Deming Glacier and upper Middle Fork Nooksack valley was made by photographers John Scurlock and Steph Abegg. Their photos show a large landslide scar on the side of the Little Ice Age lateral moraine above the toe of the Deming Glacier.

The May 31 landslide in little ice age glacial moraine on south facing slope above the Deming terminus. J. Scurlock photo.

The May 31 landslide in little ice age glacial moraine on south facing slope above the Deming terminus. J. Scurlock photo.

The Deming Glacier appears intact and does not show evidence that it contributed water in any substantial way to the debris flow. The moraine consists of inherently unstable,  unconsolidated glacial sediment, ranging from sub-millimeter clay to huge boulders. At this time of year, it is likely that the sediment was saturated. Additional water may have come from melting snow banks above- see the first photo. Photos show that the landslide began around 4600′ ASL at the top of the moraine  where it is inset against volcanic rocks erupted from the Black Buttes volcano. It slid about 400 feet down onto the very terminus of the

The Little Ice Age moraine 1 km down valley from the glacier terminus consists of unconsolidated material. Dave Tucker photo.

The Little Ice Age moraine 1 km down valley from the glacier terminus consists of unconsolidated material. Dave Tucker photo.

glacier, and ran up the opposite valley side a short distance.  The water-saturated sediment then gained additional water from the river, and roared down the valley. The high-mud mark is plainly visible well above the valley bottom in John’ s photos.

Close up of the moraine. People are circled for scale. Dave Tucker photo.

Close up of the moraine. People are circled for scale. Dave Tucker photo.

Link to Steph Abegg’s photos from the flight. Link to a debris flow in Indonesia that is probably a smaller scale version of this newest one in the Middle Fork Nooksack.


Responses

  1. […] This post was updated on June 7 with new information. Please visit https://mbvrc.wordpress.com/2013/06/07/update-nooksack-debris-flow-initiated-by-landslide-not-outburs… […]

  2. Tuck,

    You, John, and Steph have done an excellent and first class job of scoping out both the extent and the cause of this astounding topographical event. That it was a harmless one to we earthlings was only a sweet bonus.

    Bob Mooers

  3. […] The source of the debris flow in the Middle Fork Nooksack River is now believed to be a large landslide rather than a glacial outburst flood. This is based on new aerial photos provided by John Scurlock and Steph Abegg. The updated post is on the MBVRC blog. […]

  4. […] the hazard of repeated debris flows. The Ridley Creek and Elbow Lake trails access the hazard area. Learn more about this significant flow elsewhere on this website. Here is the press release as it appeared in […]


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