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Ski ><((((°>
Joined: 28 May 2005 Posts: 12798 | TRs | Pics Location: tacoma |
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Ski
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Mon Jul 27, 2020 9:15 pm
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the rock is about the size of an orange or a baseball - 3 inches x 4 inches (approx.)
absolutely no clue where it came from - possibly up near Snoqualmie Pass
"I shall wear white flannel trousers, and walk upon the beach.
I have heard the mermaids singing, each to each."
"I shall wear white flannel trousers, and walk upon the beach.
I have heard the mermaids singing, each to each."
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Songs2 Member
Joined: 21 Mar 2016 Posts: 200 | TRs | Pics
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Songs2
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Tue Jul 28, 2020 6:05 pm
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Brushbuffalo,
I came across an interesting photo in a trip report from the Lake Louise - Skoki Lakes (Banff) area. It is the 7th in this TR, captioned "Painted Landscape":
TR to Purple Mound
The author has some close-ups of the purple talus later in the TR.
I'd be interested to know what kind of rock is producing such a variety of color, especially that grand aubergine.
(Apologies; I don't know how to link the photo.)
Thanks!
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Brushbuffalo Member
Joined: 17 Sep 2015 Posts: 1887 | TRs | Pics Location: there earlier, here now, somewhere later... Bellingham in between |
Usually purple is due to high iron content. Not uncommon in siltsone or sometimes sandstone of deep marine origin.
Passing rocks and trees like they were standing still
Passing rocks and trees like they were standing still
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Ski ><((((°>
Joined: 28 May 2005 Posts: 12798 | TRs | Pics Location: tacoma |
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Ski
><((((°>
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Wed Jul 29, 2020 8:59 am
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Brushbuffalo - thank you again very much for your help.
"I shall wear white flannel trousers, and walk upon the beach.
I have heard the mermaids singing, each to each."
"I shall wear white flannel trousers, and walk upon the beach.
I have heard the mermaids singing, each to each."
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Alden Ryno Member
Joined: 04 Jun 2019 Posts: 150 | TRs | Pics Location: Issaquah, WA |
I encountered this rock formation during a traverse between Kimtah and Cosho Peak along Ragged Ridge in NCNP yesterday (location cited for typical rock formations/compositions in the area for context).
Slightly zoomed out
Initially it appears that this column fell in some way, however, it also seems like two differently composed types of rock (based solely off of color).
The large column doesn't rely match the rest of the slope yet the top portions are almost perfectly matched in angle without touch apparent erosion. I know very little of geology and my observations likely reflect that ignorance.
Thoughts?
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ThinAir Member
Joined: 15 Feb 2020 Posts: 36 | TRs | Pics Location: Federal Way |
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ThinAir
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Sat Aug 08, 2020 9:58 pm
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Washington is made up of 3 or 4 different landmasses that have been smushed together over the eons. You have found one of those boundaries. Congrats. Nature is beautiful, isn't it?
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Frango Member
Joined: 21 Nov 2012 Posts: 183 | TRs | Pics
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Frango
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Sun Aug 09, 2020 7:54 am
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This is in an old avalanche field near Ferguson Lk in the Pasayten. Granite boulders as far as the eye can see....except for this chunk of what looks like pahoehoe lava. Is it? And if so, where the heck is the rest of the flow?,
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Mike Collins Member
Joined: 18 Dec 2001 Posts: 3086 | TRs | Pics
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Brushbuffalo Member
Joined: 17 Sep 2015 Posts: 1887 | TRs | Pics Location: there earlier, here now, somewhere later... Bellingham in between |
Frango wrote: |
This is in an old avalanche field near Ferguson Lk in the Pasayten. Granite boulders as far as the eye can see....except for this chunk of what looks like pahoehoe lava. Is it? And if so, where the heck is the rest of the flow?, |
Excellent observation and question!
Mike Collins' explanation is a good start.
The geologic map of the North Cascades shows Ferguson Lake to be in an area mapped as Ktm, which in English translates to 'Tonalite plutons in Methow block (Late Cretaceous)".
That was English, you ask? Maybe this is a little more clear:
"These rocks crystaliized from magma 70 to 90 million years ago. They are part of the same intrusive suite [set of rocks] as the tonalitic [ granitic] plutons in the Wenatchee and Chelan blocks, but most have not been metamorphosed."
Included is the Pasayten Group, which includes some volcanic deposits formed in the now-filled ancient Methow Ocean.
That might account for the seemingly out of place boulder that does indeed look like well-preserved pillow structure.
I would bet there are similar rocks nearby.
Passing rocks and trees like they were standing still
Passing rocks and trees like they were standing still
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Alden Ryno Member
Joined: 04 Jun 2019 Posts: 150 | TRs | Pics Location: Issaquah, WA |
Thanks, y'all!
You've certainly help satisfy my curiosity.
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Brushbuffalo Member
Joined: 17 Sep 2015 Posts: 1887 | TRs | Pics Location: there earlier, here now, somewhere later... Bellingham in between |
Revised Most of Ragged Ridge is rock of the KTto formation, which is granitic orthogneiss.However, on the geologic map there is a small fault- bounded mass of TKns, which is schist, a medium- grade metamorphic rock that is notoriously chossy.
On your epic climb of Cosho you have some excellent pictures of the disintegrated nature of the rock. The different appearances are due to variations in composition but largely the state of alteration and both physical and chemical weathering,
Note that the prominent rib shown in your picture is partly detached such that it has developed a 'cannonhole.' A major fracture extends upslope from the canninhole. This rib will continue to disintegrate, either bit by bit or as a singular sizable mass, in which event I wouldn't want to be below.
Passing rocks and trees like they were standing still
Passing rocks and trees like they were standing still
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texasbb Misplaced Texan
Joined: 30 Mar 2009 Posts: 1153 | TRs | Pics Location: Tri-Cities, WA |
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texasbb
Misplaced Texan
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Sun Aug 16, 2020 5:04 pm
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Okay, got a landform question. What mechanism formed the dozens of tiny little islands here?
Marshy upper end of Swamp Lake, Wallowas
Hi-res
Here's a wider view:
H-res
And a view from about 800 feet up, directly above the inlet marsh:
Hi-res
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HitTheTrail Member
Joined: 30 Oct 2007 Posts: 5452 | TRs | Pics Location: 509 |
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texasbb Misplaced Texan
Joined: 30 Mar 2009 Posts: 1153 | TRs | Pics Location: Tri-Cities, WA |
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texasbb
Misplaced Texan
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Sun Aug 16, 2020 8:37 pm
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HitTheTrail wrote: | OK,where is this basin? |
In the western Wallowas, west of the Lostine River canyon. Some of the headwaters of the North Minam River.
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Brushbuffalo Member
Joined: 17 Sep 2015 Posts: 1887 | TRs | Pics Location: there earlier, here now, somewhere later... Bellingham in between |
Based on your pictures, I think you have an example of a bio- geological runaway feedback loop.
HUH? Zzzzz😴
Let me explain the theory that I have.
Sediment, mostly gravel, accumulates in a braided stream channel during times of lessening flow velocity. If the little bars remain slightly above average water level, plants are able to become established. These plants trap more sediment thereby increasing the size of the mini islands, which facilitates more plant life on them...a runaway process by trapping more sediment and increasing the island size up to a point limited by erosion.
Key to this is in a gravel- rich stream channel we find that braiding is the dominant pattern, which causes bars to form separated by many divergent/ convergent channels (called ' anastomosing channels' by hydrologists).
I have another theory....theory the second.
And it's mine.(how about that, Anne Elk?)
Passing rocks and trees like they were standing still
Passing rocks and trees like they were standing still
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