Boulder Mystery

[Acme]

Nice to see folks cooperatively working through the possibilities with open minds. +1Acme and Mman

Thanks Studiot!

 

Let's see if I can continue that work in regards to Arc and his thoughts on the boulder being a glacier deposit.

 

In post #18 Arc offered a link to a study. Find it here: > Quaternary alpine glaciation in Alaska, the Pacific Northwest, Sierra Nevada, and Hawaii

 

In post #19 I commented on it saying:

..Your source gives a map (Fig.2 Continued) wherein the closest 3 alpine glaciers are labeled Lewis, Adams, and Toutle (Toutle corresponding to Mt. St. Helens). By the map scale, Lewis is ~ 50km, Toutle ~60km, and Adams ~100km distant from the boulder's location. Unfortunately I can find no discussion of these 3 alpine glaciers in the text of the paper. Perhaps I overlooked it? ...

The map I referenced is on pg. 6 of the document. While I still don't see any discussion of the 3 marked sites in the body of the paper, the location marked 'Lewis' looked strangely familiar. So here's the scoop, which I think is in line with my contention that no alpine glaciers came near to the area of the boulder which is +- 5 miles from the Columbia R.

 

Anyway, some 30 years ago I was studying geology at a local college and the instructor took us on a field trip to see some glacial deposits. The deposits were not moraines, rather they were glacial lake deposits called varves. They lie between 25 and 30 miles from the Lower Columbia as it sweeps past Vancouver and turns N. I suspect that were there closer glacial deposits, the instructor would have taken us there. My mind being sieve-like notwithstanding, I'm inclined to think I would remember mention of glacial deposits near the Columbia R. I'm certainly open to any evidence contrary to my recollections.

 

Fast forward to a few years ago when I took some young people up to see the varves and help me take some measurements, locate them with GPS, and take samples. If you all will indulge me, here are the results.

 

So I took the coordinates of 3 exposures and they appear to correspond with the Lewis site marked on the map in the study. They are:

#1 45°56'41.39"N 122°16'28.24"W

#2 45°56'44.00"N 122°16'0.06"W

#3 45°55'34.65"N 122°13'32.07"W

 

Here's a shot of us measuring the height of an exposure and the measure was 30 ft.

 

This is a wider view of the measured exposure. (The bright area is water seeping out.)

 

Here is a shot showing erratics in the varve. These occur when a larger rock falls out onto the frozen surface of the lake, and then falls to the bottom during the seasonal thaw.

 

Finally, this is a shot of a sample with a scale. I didn't count the layers again, but my notes say 15 layers. So 15 layers in 2.5" and with a measured exposure of 30 ft. we get a rough estimate of 1,800 years for the lakes age. Not only is this rough because the layers differ widely in thickness, but I don't know how much of the top of the deposit was eroded or how much lay below the level of the roadbed it adjoins. (Neither do I know the period of the deposits.)

 

Well, a bit of a digression perhaps, but fun all the same.

Edited January 29, 2017 by Acme

[arc]

Perhaps something like the Missoula Floods.

https://en.wikipedia.org/wiki/Missoula_Floods

 

http://columbiariverimages.com/Regions/Places/missoula_floods.html

 

An interesting feature of these flood events (maybe around 40 of them) was the icebergs. From your link;

https://en.wikipedia.org/wiki/Missoula_Floods

 

"As the water emerged from the Columbia River gorge, it backed up again at the 1 mile (1.6 km) wide narrows near Kalama, Washington. Some temporary lakes rose to an elevation of more than 400 ft (120 m), flooding the Willamette Valley to Eugene, Oregon and beyond. Iceberg rafted glacial erratics and erosion features are evidence of these events."

 

This map at the site below allows you to zoom in to amazingly close resolution.

http://www.oregongeology.org/pubs/ims/IMS-036_print.pdf

 

This is a screen shot of that map I made as an example of the range that the flood water could carry these icebergs that in turn were carrying the erratics. That is the Columbia River with the entire Vancouver metropolitan area within the flood zone that extends to Kalama 47 km to the north.

 

 

This site below chronicles the location of erratics around this region within the range of the flood carried Icebergs.

http://www.waymarking.com/cat/details.aspx?f=1&guid=a4f0434e-37f7-4bf9-b13e-d3d0824b86ea&lat=45.13745&lon=-123.290867&t=6&wo=True&p=2&gid=3&sg=c17d366f-f627-497e-b248-6a40cee476ff&st=2

 

http://www.waymarking.com/waymarks/WMCT67_Erratic_Ridgefield_National_Wildlife_Refuge_Ridgefield_Washington

 

It is located at the Ridgefield National Wildlife Refuge just north of Vancouver. It looks very similar to Acme's example.

 

Here's another erratic located farther to the east;

 

http://www.waymarking.com/waymarks/WM36CY_Round_Lake_Erratic_Camas_Washington

 

And here's a nice video about the Lower Columbia Floods Chapter; http://iafi.org/local-chapters/lower-columbia-chapter/

They chronicle and educate about the floods around this region.

 

http://iafi.org/grants-getaways-oregons-erratic-rocks/

 

 

/

Edited January 30, 2017 by arc

[Acme]

An interesting feature of these flood events (maybe around 40 of them) was the icebergs. From your link;

https://en.wikipedia.org/wiki/Missoula_Floods

 

 

"As the water emerged from the Columbia River gorge, it backed up again at the 1 mile (1.6 km) wide narrows near Kalama, Washington. Some temporary lakes rose to an elevation of more than 400 ft (120 m), flooding the Willamette Valley to Eugene, Oregon and beyond. Iceberg rafted glacial erratics and erosion features are evidence of these events."

 

This map at the site below allows you to zoom in to amazingly close resolution.

http://www.oregongeology.org/pubs/ims/IMS-036_print.pdf

 

This is a screen shot of that map I made as an example of the range that the flood water could carry these icebergs that in turn were carrying the erratics. That is the Columbia River with the entire Vancouver metropolitan area within the flood zone that extends to Kalama 47 km to the north.

 

Missoula Flood PDX.png

 

 

This site below chronicles the location of erratics around this region within the range of the flood carried Icebergs.

http://www.waymarking.com/cat/details.aspx?f=1&guid=a4f0434e-37f7-4bf9-b13e-d3d0824b86ea&lat=45.13745&lon=-123.290867&t=6&wo=True&p=2&gid=3&sg=c17d366f-f627-497e-b248-6a40cee476ff&st=2

 

http://www.waymarking.com/waymarks/WMCT67_Erratic_Ridgefield_National_Wildlife_Refuge_Ridgefield_Washington

Erratic Ridgefield National Wildlife Refuge Ridgefield Washington Image 3.png

It is located at the Ridgefield National Wildlife Refuge just north of Vancouver. It looks very similar to Acme's example.

Here's another erratic located farther to the east;

http://www.waymarking.com/waymarks/WM36CY_Round_Lake_Erratic_Camas_Washington

Round Lake Erratic .png

And here's a nice video about the Lower Columbia Floods Chapter; http://iafi.org/local-chapters/lower-columbia-chapter/

They chronicle and educate about the floods around this region.

http://iafi.org/grants-getaways-oregons-erratic-rocks/

Nice research Arc. A flood delivered iceberg-with-erratic I might buy. Add the quake induced granular convection uplift, and voila, my boulder on top of the plain! A key bit of evidence still missing is a proper rock identification which might fix the boulder's origin. It may well be fairly local from just up the gorge. I'll be working on that, but it won't be quick. Stay tuned.

 

I have hiked and done botanical photographic work at both Ridgefield and Round Lake. The partially buried erratic at Ridgefield is most like what is at the boulder area as it is a predominately flat terrain with sedimentary soils. That the Round Lake erratic is sitting free and clear is not surprising as the terrain there is hilly and rocky.

 

I don't seem to have any photos of Round Lake itself or the terrain, but here is a shot from Oct. 2015 of the sign-board mentioned at your link. Alas it appears I did not get the part mentioned, i.e. " According to the signboard at Round Lake, the massive boulder's rounded surface and huge shape suggests it was rolled along by the enormous, extremely fast moving flows of the Missoula Floods."

 

This image at the Ridgefield Preserve was taken on the Autumnal Equinox of 2015. There is one relatively short hiking trail which is only open Spring to Fall, and otherwise you have to drive through. I did hike that day, but along the drive route are a few lookout stops and this photo is from one of those wildlife viewing areas.

Post Script: Looking at the flood deposits map, figure Map B shows the locations of glacier erratics and all appear to be on the Oregon side of the river, with none marked in Clark County Washington.

[Acme]

I sent a short report on my findings to my immediate managers; it was well received and forwarded to state geologists for review. Thanks to all who have contributed here and I'll update you on any new findings.

[arc]

Acme, I look forward to their opinion.

 

I have been thinking a bit about this and have concluded; For your specimen to have gravitated to the surface through granular convection it would have require the sub-straight to be as thoroughly mixed as a container of nuts would be when raising a Brazil nut to the surface.

 

In other words, for that scenario to be true; a former stratified or time layered sub-straight could not exist currently beneath that boulder due to the requirement that the same materials would have to be, according to granular convection, vigorously shaken, resulting in their rotational mixing of lower and upper layer materials together as the specimen was simultaneously moved upwards.

 

Frost heave would have also left a tell tale trail to follow. Since the process of frost heaving stones is a group activity engaging any number of other stones in the same area to some degree, at the very least some other stones that reside there would no doubt have been lifted during the process. A freeze cycle regimen capable of lifting that immense specimen would have little difficulty with smaller varieties. There should be many other rocks of more common dimensions laying about the surface in that area. Field stones that are commonly seen made into the walls that line so many Old World and N.E American rural roads and farm fields attest to these "crops" being elevated continuously to the surface over seasonal periods of time.

 

The lack of any sign of appreciable field stone quantity at the subject site would suggest frost heave is not the agent at work here. This rather temperate region does not attain the lower temperature that those seasonally colder field stone regions do. New England winters we do not have. Interestingly though, the loss of top soil is almost universally observed in modern farming practices, this lends to the probability that many of these smaller drop stones around this area that were excavated by farming equipment in the last century are possibly not only due to frost heave but the fact that the surface is being lowered from soil loss while farming equipment has gradually increased in size and strength, thus they have over the last century gradually increased there till depth. These factors alone have assured for the continuous removal of these stones whether or not the stones themselves were rising from frost heave.

 

Although, as you mentioned, graph B indicates most iceberg erratics reside to the south across the Columbia, the two examples I did furnish shows that the one to the east is completely above ground while the other being to the northwest is just breaking the ground's surface. These appear to reside where they initially landed, carried within their parental iceberg to where it had grounded and melted away. The example to the northwest was no doubt buried by the tremendous amount of silt of the Missoula Floods and the Columbia's changing river coarse as it silted up and overran its older channels. These erratics are most easily and most likely explained as erratics that lie where they dropped out of the melting iceberg and either stayed above grade or were covered over based on the local geologic conditions.

 

Occam's Razor would place your example with all the others, all from the same circumstances that were then mediated by various local geologic conditions. But none very far beyond the ordinary circumstances of the others. In other words: If your example was shaken to the surface than many others should have also done the same.

[studiot]

Yes please tell us the results when available. +1

 

Edited February 2, 2017 by studiot

[Acme]

Acme, I look forward to their opinion.

Me too.

Yes please tell us the results when available. +1

Definitely.

 

The lack of any sign of appreciable field stone quantity at the subject site would suggest frost heave is not the agent at work here. This rather temperate region does not attain the lower temperature that those seasonally colder field stone regions do. New England winters we do not have. Interestingly though, the loss of top soil is almost universally observed in modern farming practices, this lends to the probability that many of these smaller drop stones around this area that were excavated by farming equipment in the last century are possibly not only due to frost heave but the fact that the surface is being lowered from soil loss while farming equipment has gradually increased in size and strength, thus they have over the last century gradually increased there till depth. These factors alone have assured for the continuous removal of these stones whether or not the stones themselves were rising from frost heave.

I have not reported on the field stone quantity in the immediate area of the boulder so there is no basis to judge that quantity. The ground is heavily covered by grasses, sedges, rushes, and forbs, with occasional patches of Rosa sp. as seen surrounding the boulder.

 

The recent [last ~200 years] history of the farming at the site has consisted of grazing stock and mowing hay. While ditches were cut in the 20's & 30's in attempts to drain the area, there has been no tillage noted in any of the reports and records that I have read. The only boulders that would have to be moved would be those sitting proud enough to interfere with haying.

 

Prior to the arrival of Europeans, Native Americans regularly burned the prairies to kill off shrubs & young trees and maintain the open prairies. These prairies were a major source of food where Natives dug Camas bulbs, Chocolate Lily bulbs, and Yampah roots. I have read an archaeological report for the area that mentions fire-cracked rock evidencing this burning, but exact locations were redacted by the request of the county officials. Whether these were embedded rocks or remains of Native American roasting pits for the Camas was not made clear in the report either. The burning stopped in the late 1700s after European explorers introduced smallpox; by the time Lewis & Clark visited, nearly 80% of the native population was dead.

 

Although, as you mentioned, graph B indicates most iceberg erratics reside to the south across the Columbia, the two examples I did furnish shows that the one to the east is completely above ground while the other being to the northwest is just breaking the ground's surface. These appear to reside where they initially landed, carried within their parental iceberg to where it had grounded and melted away. The example to the northwest was no doubt buried by the tremendous amount of silt of the Missoula Floods and the Columbia's changing river coarse as it silted up and overran its older channels. These erratics are most easily and most likely explained as erratics that lie where they dropped out of the melting iceberg and either stayed above grade or were covered over based on the local geologic conditions.

Maybe those two are ice floated erratics and maybe not. Your conjecture is duly noted.

 

Occam's Razor would place your example with all the others, all from the same circumstances that were then mediated by various local geologic conditions. But none very far beyond the ordinary circumstances of the others. In other words: If your example was shaken to the surface than many others should have also done the same.

As I mentioned, I don't know whether there are, or were, any other such large boulders in/on prairies in the county. The area is heavily developed and ecologists estimate there is only about 1% of these wet prairies remaining in the whole state. This is why the area is protected.

[studiot]

I would still not rule out river flood transport.

 

Near where I live, there is an ancient clapper bridge across the river Barle on Exmoor.

 

Winter floods have shifted/transported large stones weighing several tonnes, downstream from the structure again.

 

The river Barle is an inconsequential trickle compared to your american rivers in question.

 

http://www.bbc.co.uk/news/uk-england-somerset-38844162

[Acme]

I would still not rule out river flood transport.

 

Near where I live, there is an ancient clapper bridge across the river Barle on Exmoor.

 

Winter floods have shifted/transported large stones weighing several tonnes, downstream from the structure again.

 

The river Barle is an inconsequential trickle compared to your american rivers in question.

 

http://www.bbc.co.uk/news/uk-england-somerset-38844162

Nice! We've got nothing on you when it comes to 500 year old stone bridges, even over trickles.

 

I'm ruling nothing out at this stage. Well, nothing reasonable. I'm not entertaining alien intervention or propositions of that ilk.

[Acme]

The e-mail string following my report has grown a fair amount. My manager has the same ideas as Arc, i.e. that the boulder is an ice-rafted erratic. The regional geologist said he is unaware of any ice-rafted erratics in Washington, but that they likely exist. He also said my photo of the sample chip does look like basaltic andesite as I suggested. It will take a more detailed analysis of the rock to determine if its exotic to the region and depending on the origin, the ice-rafting might be affirmed or rejected.

 

The geologist also gave my manager a few other geology folks to contact who have worked and mapped in the area, so the string will continue stringing out. I'm feeling more hopeful that one or more experts will come out and have a look in the field. As an amateur and volunteer, it's very gratifying to have spawned so much interest among professionals.

[Acme]

I'm told that the fella who dug the nearby pond (in the early '80s I think) says the boulder was where it is now at the time and was not excavated from the pond.

 

No word yet on a geologist visit, however I hope to get out in the next couple weeks to give the rock a better look-over and start cataloging the lichens growing on it. I'll also poke around the immediate area and see what's to be sawn.