Vertical Talus "Ripples/Waves" near Wetterhorn?

[geojed]

While climbing Wetterhorn last weekend with my two older sons we saw these very interesting "ripple marks" formed in talus on the slopes of a PT12421 which is on the south side of Matterhorn Creek. It's easy to understand how ripple marks can form in talus if the talus "creeps" down a slope as a rock glacier or a soil flow. Those kinds of ripples will form crests that are aligned "across" the slope. The ripples on this slope are strange because the ripple crests are aligned "vertically" on the slope with the parallel ripple crests going up & down the slope and not across. If you look closely, you can also see that the ripples form larger wavelengths lower on the slope while towards the top of the slope they are much shorter wavelengths and are more densely packed together.

Talus Ripple Marks

IMG_6428.jpg (246.51 KiB) Viewed 939 times

Here is a satellite view of them in CalTopo with a contour overlay.

CalTopo Satellite View of ripples w/ contours

vertical ripple marks.png (834.13 KiB) Viewed 939 times

It seems like it would have to have been caused by glacial action but I would think that the glacier retreated so long ago any fabrics they created in something as movable as talus would have been destroyed by other erosional processes by now. I googled "talus ripples" and the only thing I found was from a 1923 USGS publication on geomorphology in Alaska. The ripples there were going across the slope horizontally due to "soil flow".

USGS Soil Flow

USGS1923 paper.png (473.17 KiB) Viewed 939 times

I'm a Geologist, hence the username "Geojed", and the formation of these ripples is quite perplexing! Anyone have ideas/theories of how these formed or have seen similar "vertical" talus ripples elsewhere?

[Peak200]

Cool pics and interesting post : curious to find out what caused them

[Peak200]

The only thing I could think of is large amounts of water
On a very steep slope; snow melt/water pushing down the talus consistently over time

Or there is a lot of more unstable volcanic tuft or similar in
The San Juan's. It looks to me like the dirt has piled up at the
Bottom thus causing the bigger ripples( more stable dirt below
The talus above thus smaller ripples) looks like some type of sluff
Has happened or small landslides

A combination of both above is my guess

[Boggy B]

Google imagery back to 1998 shows the same features, even the streaks of lighter and darker rock. That image is b/w with poor definition, but the clearer color image from '05 shows very little change in the location/orientation of the runnels in the last 17 years except for plant growth.

[mindfolded]

Is this related to rock circles? Over time, ice and snow and rockfall cause the talus to form patterns. On a low grade they form circles, but those circles stretch out into lines as the terrain gets steeper.

I'm having a hard time finding something quickly on the internet about this, but I just read about it in "Rocks Above the Clouds" and RMNP has a sign about it at the Forest Canyon Overlook. From that point, you can see really neat shapes on the side of Sundance mountain. I'll find my copy of that book and post what it says about them.

[mindfolded]

Here we go: https://en.wikipedia.org/wiki/Patterned_ground

[geojed]

Is this related to rock circles? Over time, ice and snow and rockfall cause the talus to form patterns. On a low grade they form circles, but those circles stretch out into lines as the terrain gets steeper.

I'm having a hard time finding something quickly on the internet about this, but I just read about it in "Rocks Above the Clouds" and RMNP has a sign about it at the Forest Canyon Overlook. From that point, you can see really neat shapes on the side of Sundance mountain. I'll find my copy of that book and post what it says about them.

That's what I've been wondering as well. I remember that sign in RMNP and even found it on Google Maps Street view of the Forest Canyon Overlook! There is another small sign about them along the Toll Memorial Trail near Mushroom Rocks. I also found a research article about Block/Rock Streams (https://www.researchgate.net/publicatio ... ck_Streams) and think it might be related to them. I even emailed the author of that article about it. We'll see what he says.

Most of those rock streams you see on Sundance Mtn have tundra between the rock streams, with the stream being a "negative" feature, the tundra being a positive feature, and the streams not really paralleling each other like these talus waves/ripples do.

That Wikipedia article you linked to has a section on rock stripes and says they form at angles of 2-7deg. But when I overlay the slope angle shading layer in CalTopo over this slope the angles are in the 20-40deg range.

[Scott P]

It's probably an extinct rock glacier.

Inactive rock glaciers still look like rock glaciers, but movement has ceased. Once the ice core melts, the rock glacier becomes extinct (and looks a little less like a rock glacier) and becomes rippley to to the ice no longer supporting the talus and formerly embedded rocks.

I say "probably" because while extinct rock glaciers do often display lateral "ripples", there are usually transverse ones as well. I don't see any in the photo.

[justiner]

Looks very much like this photo that's in the article mindfolded posted,

Periglacial stone stripes in Antarctica

https://en.wikipedia.org/wiki/Patterned ... tripes.jpg

[HikerGuy]

Looks very much like this photo that's in the article mindfolded posted,

Periglacial stone stripes in Antarctica

https://en.wikipedia.org/wiki/Patterned ... tripes.jpg

Yep. Almost certain that there is some sort of mechanical weathering process involving freeze/thaw cycles. The stripes have a north/south orientation vs. fall line orientation, which does seem odd. Could be something particular about that basin/slope and sun angles. I am NOT a geologist, but I am surrounded by Arctic researchers at work, I'll chime back in if I corner one and get any useful info from them.

EDIT: also note that the stripes do continue on higher up on the slope, but they are less defined.

[geojed]

Looks very much like this photo that's in the article mindfolded posted,

Periglacial stone stripes in Antarctica

https://en.wikipedia.org/wiki/Patterned ... tripes.jpg

Yep. Almost certain that there is some sort of mechanical weathering process involving freeze/thaw cycles. The stripes have a north/south orientation vs. fall line orientation, which does seem odd. Could be something particular about that basin/slope and sun angles. I am NOT a geologist, but I am surrounded by Arctic researchers at work, I'll chime back in if I corner one and get any useful info from them.

EDIT: also note that the stripes do continue on higher up on the slope, but they are less defined.

Yeah it has to be some type of frost action causing it. Not much soil or tundra has formed between the ripples/waves/stripes on most of the slope except for the extreme western edge and in the center. The slope shading shows those areas to be 28-40deg angle.

• The smaller ripples seem to have a fall line orientation of around N10E or 10deg.
• The larger ripples switch to a non-fall line NNW orientation of N25W or 335deg.

• Larger Ripples average wavelength = 18ft (I measured a 3 wave set at 3 different locations on the slope)
• Smaller Ripples average wavelength = ~8ft (I measured a 6 wave set at 4 different locations on the slope)

[Monster5]

Solifluction meets general erosion.