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Brushbuffalo
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Joined: 17 Sep 2015
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Location: there earlier, here now, somewhere later... Bellingham in between |
| moonspots wrote: | | I also wondered if all the sand surrounding these rocks were removed, would the rock pillars be observed to be just "sitting" on top of a base of rock |
In the vast majority of cases sea stacks are bedrock remnants, meaning they are still 'attached'. It is the rock. above and between stacks that has been removed, not beneath.
Of course there are exceptions (the rule in geology) in which a boulder has been plopped (not an official geologic term, more of a doug-ism) on top of sediment. These are generally not behemoths in size and are often different rock than the immediate local bedrock. Also sea stacks are often taller than wide, which for an unattached structure is physically unstable. The main reason stacks will topple is due to weathering at their near- sea level base.
Passing rocks and trees like they were standing still
Passing rocks and trees like they were standing still
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Songs2
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Joined: 21 Mar 2016
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Songs2
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 Sat Feb 15, 2020 5:55 pm |
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It looks as though there are vertical cleavages in the "before" photos of the seastack, and the splitting occurred along these cleavages, with additional pushing by the ocean.
I am also wondering whether there were caves or other hollows at water level that might have contributed to weakening of the whole structure
Flowerpot Island in Georgian Bay, off Bruce Peninsula, Ontario, has structures highly eroded at the base (hence, lending a flowerpot shape). Gorgeous to look at, and some have trees growing on the tops and sides, but I wouldn't want to be close by in the critical 30 seconds when one collapses.
puzzlr, very nice photo!
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D. Inscho
Not bored yet...
Joined: 28 Feb 2010
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Location: Bellingham,WA |
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D. Inscho
Not bored yet...
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Sun Feb 16, 2020 11:09 am |
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I am reminded of the Oscar nominated short (2001) Das Rad (Rocks) illustrating geologic time as compared to our own sense of it: Das Rad
http://david-inscho.smugmug.com/
The key to a successful trip is to do the planning during work hours. -- John Muir
“My most memorable hikes can be classified as 'Shortcuts that Backfired'.” --Ed Abbey
http://david-inscho.smugmug.com/
The key to a successful trip is to do the planning during work hours. -- John Muir
“My most memorable hikes can be classified as 'Shortcuts that Backfired'.” --Ed Abbey
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puzzlr
Mid Fork Rocks
Joined: 13 Feb 2007
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Location: Stuck in the middle |
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puzzlr
Mid Fork Rocks
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Mon Feb 17, 2020 12:56 am |
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Great movie. Thanks for the link.
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moonspots
Happy Curmudgeon
Joined: 03 Feb 2007
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Location: North Dakota |
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moonspots
Happy Curmudgeon
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Mon Feb 17, 2020 5:48 am |
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| puzzlr wrote: | | Great movie. Thanks for the link. |
Yeah, quite right, and a very good imagination! "I hate moss"! 
"Out, OUT you demons of Stupidity"! - St Dogbert, patron Saint of Technology
"Out, OUT you demons of Stupidity"! - St Dogbert, patron Saint of Technology
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ale_capone
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Joined: 22 Sep 2009
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Interesting.
We did some sea stack seeing in the Orkney archipelago. The old man of hoy is over 400' tall, and only a few hundred years old. Used to have 2 legs. Now It's only standing on one, and not expected to last a lot longer. People still climb it!
Not surprising. It gets pretty rough and windy up there.
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Songs2
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Joined: 21 Mar 2016
Posts: 200 | TRs | Pics
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Songs2
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Mon Feb 17, 2020 8:53 am |
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I found this on the USDA-Oregon site:
| Quote: | | In the cliffs that form the headlands there
are areas that are more fractured or have inclusions
of softer rocks. Breaking waves exploit the fractures
by pounding them with loose pebbles and forcing air
into them. Wave action will erode weak areas more
quickly, isolating outcrops of more resistant rocks to
make sea stacks. The south Oregon coast consists of
mixed sedimentary and volcanic rocks that have
some shear fractures. The heterogeneity of these
rocks makes them prone to developing sea stacks. |
Sea stacks
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Brushbuffalo
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Joined: 17 Sep 2015
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Location: there earlier, here now, somewhere later... Bellingham in between |
| Doppelganger wrote: | | This might help explain (not fully, but partly) how we start to see different weathering patterns over time in the same rock formations in the same environment. |
Yes, along with slight variations in lithology and structure there will be slight variations in external factors. For example, on a seascape once irregularities in shape of the coastline develop, possibly due in part to the preceding, a positive geomorphic feature (such as a point) will have wave energy more focused upon it compared to a negative geomorphic feature( an indentation or embayment). This uneven focus of energy is due to wave refraction ( bending), resulting in erosion of points and deposition in embayments. The long term result, assuming constant sea level (unlikely), is straightening of the coast.
The question still remains: under the exact same conditions, would we find the exact same result?
My question is purely hypothetical actually, because in the real world the conditions would never be exactly repeated. There would be one more or one less violent storm, earthquake, prolonged warm or cold period, feedback loops, etc.
Edit: the material Songs2 quoted is a nice summary.
Passing rocks and trees like they were standing still
Passing rocks and trees like they were standing still
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moonspots
Happy Curmudgeon
Joined: 03 Feb 2007
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Location: North Dakota |
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moonspots
Happy Curmudgeon
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Mon Feb 17, 2020 10:42 am |
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| Doppelganger wrote: | | ...maybe some sea stacks may have had varying degrees of more dense and tough material to bear the brunt of erosion? This might help explain (not fully, but partly) how we start to see different weathering patterns over time in the same rock formations in the same environment. |
Hmmm, good point, and this may (?) help explain to me why the buttes of southwest ND are there while some are...not - erroded away. I've always wondered why this rock (and I'm not certain it can be classified as rock, not even sandstone, maybe "mudstone"? Anyway, I've wondered for ~50 years now why there are buttes standing and it isn't all washed away. It's all so friable it seems to me.
Before I retired, this is one of the first things i was going to do - go back to school and study geology when I retired...now I'd better get to it if ever I'm going to!
"Out, OUT you demons of Stupidity"! - St Dogbert, patron Saint of Technology
"Out, OUT you demons of Stupidity"! - St Dogbert, patron Saint of Technology
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Brushbuffalo
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Joined: 17 Sep 2015
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Location: there earlier, here now, somewhere later... Bellingham in between |
| moonspots wrote: | | go back to school and study geology |
It's never too late....and you don't need to go to formal school. Just read a lot from many sources, ask lots of questions, and get out to the geologic world* as much as possible.
* geologic world = everywhere 
Passing rocks and trees like they were standing still
Passing rocks and trees like they were standing still
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Songs2
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Joined: 21 Mar 2016
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Songs2
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Mon Feb 17, 2020 11:24 am |
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A little book-larnin' doesn't hurt, just so that one can check the box "syncline" or "Proterozoic Miette Group" (I took a year in undergrad, unbidden, and liked it), but there are many assists in the form of popular and increasingly scientific publications. The Roadside Geology series has helped many understand the land they are traversing. It makes the experience richer, like knowing a bit about the flora and fauna.
Hiking the Grand Canyon's Geology is fabulous and makes me want to go back and see everything again.
There are similar publications for the southern Canadian Rockies and Icefields Parkway.
Going to lectures is also useful, especially if the geology talk is combined with some anthropology talk -- how people earlier on the land used it, perhaps weaving it into their cosmology.
I appreciate the earlier insight by Doppelganger that what happens around the feature of interest is important.
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Brushbuffalo
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Joined: 17 Sep 2015
Posts: 1887 | TRs | Pics
Location: there earlier, here now, somewhere later... Bellingham in between |
| Songs2 wrote: | | A little book-larnin' doesn't hurt |
'A little' can be a dangerous thing, but we are talking geology, not surgery, so any knowledge is preferable to none. I devoted my career as a geology professor helping people discover some of the wonders of our planet.
Here is a fellow who does a superb job of just that...Nick Zentner of Central Washington University. His lively instruction is both informative and entertaining. Check it out!
https://www.kcts9.org/show/nick-rocks
Also this:
http://www.nickzentner.com/#/downtown-geology-lectures/
Passing rocks and trees like they were standing still
Passing rocks and trees like they were standing still
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Songs2
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Songs2
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Mon Feb 17, 2020 4:02 pm |
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Oh, that's fun! Nick's quick videos. I viewed the Yakima River Canyon from season 1.
Thanks for the links.
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moonspots
Happy Curmudgeon
Joined: 03 Feb 2007
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moonspots
Happy Curmudgeon
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Mon Feb 17, 2020 4:29 pm |
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| Brushbuffalo wrote: | | ...and get out to the geologic world* as much as possible.
* geologic world = everywhere |
 And that's the part I like. It's good to explore, and wonder.
"Out, OUT you demons of Stupidity"! - St Dogbert, patron Saint of Technology
"Out, OUT you demons of Stupidity"! - St Dogbert, patron Saint of Technology
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Slugman
It’s a Slugfest!
Joined: 27 Mar 2003
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Slugman
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Mon Feb 17, 2020 10:58 pm |
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In Search of Ancient Oregon is a good book to own for those interested in geology. I like visiting places such as the John Day fossil beds, or the volcano-dotted landscape near Bend and having a handy reference to help interpret what I am seeing.
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