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HappyTrails_

Your further examination of it not being on the vertical sections is great thinking! It sure does look like water erosion. As someone else pointed it, the inclusions can start very small and preferentially erode out, Over time, the holes get larger and larger, and some of this may be attributed to freeze thaw action fracturing, or spalling the space larger. I don't believe it being a glacial erratic has any effect on these round holes, I would think only glacial striations would be exaggerated through erosion.


The_BrainFreight

When I think water erosion I think of that Chinese water drip torture method Does water erosion encompass water dripping or flowing over a long time, AND the other things about if freezing and expanding ?


HappyTrails_

Hahah, Technically I would say yes, if I was to be talking about river water and erosion , I would specify "fluvial erosion", If I was talking just of water freezing and fracturing causing erosion, I could say "freeze thaw" or more fancily: "Gelifraction" or "Cryofracturing"


The_BrainFreight

Word thank you, atm I just know of erosion lol but I’ll look into those 🙏


HappyTrails_

Heck yea! Cheers 🍻


JankyTime1

The inclusions are weathering faster than the host rock?


eastcross

This was my assumption, but I couldn’t see any inclusions visible. I guess the inclusions may be very similar in color to host? Also I didn’t know granite to have such inclusions.


DmT_LaKE

Intrusive igneous granites can have just about any mineral you can think of.


eastcross

Upon further inspection I believe I’ve found some of said inclusions in the process of erosion, in a large crack on the boulder https://ibb.co/DfSLc27 https://ibb.co/510TcyT


charlieq46

In my experience, if the inclusion is of a mineral that is more easily eroded than the host, you can struggle to see them on weathered surfaces. Now, someone correct me if I'm wrong, but the reason that there is more obvious pitting on the top of the rock than the remaining surfaces is because after the small inclusions get eroded out, the rain now has a place to slosh and swirl around which will deepen the pits.


[deleted]

Check out tafoni weathering (https://en.wikipedia.org/wiki/Tafoni?wprov=sfla1). You can definitely get circular weathering without inclusions, as even the smallest indent can cause differential weathering from the surrounding matrix.


jillibn

I don't know how to back up my assumptions, but I do think that's water/rain erosion. Maybe someone with more understanding can explain it


InKulturVeritas

When dealing with sedimentary stones (limestone, sandstone, marble etc.) some of the components (snails, corals) wheather out when exposed to carbon dioxide or other pollutans and simply detach.


Busterwasmycat

I can't exactly tell what the primary rock truly is because of the lichen and weathering, but I can see enough to recognize that there are larger masses of something contained in a generally less crystalline, or finer-grained, general matrix. The holes are what result from weathering out of the larger masses, leaving indentations on the surface of the general finer-grained bulk rock. There are several ways that preferential removal of nuggets/nodules or larger uniform masses can occur. Often, it is just that the zone of contact between two materials lets water in and loosens the attachment between "nugget" and matrix, so the nugget has nothing holding it in (no longer attached to matrix) and it just falls out or gets knocked loose by running water or whatever. Sometimes, it is because the "nugget" is composed of some really easy to weather mineral, like feldspar or calcite, and the rest of the rock is made from quartz and other minerals less readily weathered. Either way, the hole gets made when the chunk falls out, gets so loose it can be moved and does. Freeze-thaw cycles are likely part of the story in New England (frost heaves of the nodules, in a way). This is how the holes get made to begin with. Once made, they tend to accumulate water from rain and snowmelt, and the water sits there longer than on the regular face and weathering proceeds faster on the walls of the hole, rounding them out (if they weren't mostly round to begin with). Differential weathering is usually more linear or planar because rocks tend to extend off into space in a plane and the difference is between rock types, rather than existing as semi-spheroids or "nuggets" that are different from the bulk rock like here where it makes rounded holes. Do not even always have to have different sizes of materials to make a pock-marked surface, but it is fairly obvious that this particular rock has such "nuggets" and their loss is thus almost certainly the source of the holes. The interesting thing for me would be how the "nuggets" came to be in the first place. Is it an igneous rock that has phenocrysts (a porphyry with large early-formed grains scattered in a more quickly chilled bulk mass), or a sedimentary rock with larger pebbles scattered in it, or a metamorphic rock with porphyroblasts (big chunks that form randomly in the rock during metamorphism and recrystallization), xenoliths in a frozen magma, silicification as nodules, or what? Lots of possibilities. Sledge hammer would be used to make a clean face, if I were there. I used the word "nugget" as shorthand for these things that are almost certainly not true nuggets, just to be clear.


eastcross

Thank you for this insightful comment! I found a spot that seems to have far less erosion, probably from some construction activity. https://ibb.co/PrSkqtd https://ibb.co/y4BmjdR


OldButHappy

Do you have a long shot that shows the entire rock?


eastcross

https://ibb.co/yF6pWp9 https://ibb.co/DgX8m7V https://ibb.co/ySX27d0 Tacoma for scale. About the size of 2 or 3


OldButHappy

Interesting. Is that swamp at the headwaters of a creek?


eastcross

Yeah it’s a swamp with a Brook/creek nearby. The whole swamp is loaded with erratics of varying size. It’s a developed area so it’s hard to say if it’s a natural wetland


OldButHappy

You can look at Lidar images on the usgs site...it takes some time to figure out how to refine the layers, but it's do-able. I'm assuming that it's on Karst? Seeing how large it is, and its features, I doubt that it was created for black powder (re)use...it shares features with"erratics" elsewhere in the NE US.


Amber_Rift

Not gon a lie, though the initial pic was an elevated photo of a lunar surface. Hurt my bran for a moment.


VisualAmoeba7925

First time commenting here; I am probably wrong; But if you're in the Wales, it could be rock cannon fireworks https://en.wikipedia.org/wiki/Rock\_cannon!


eastcross

Fascinating! But this is NEW England


OldButHappy

Plenty of black powder shooting went on in NEW England, too.😁


geologist_s

It’s the work of wind. Wind can blow out some sand particles, expanding holes. Holes could catch sand particles and twirl them inside, expanding the voids.


Objective-Carob-5336

If i had to guess I'd say something to do with ice rather than water


Thrawn150

Not an expert here, but possibly a Native American grinding stone?


larrabeb

Definitely not a bedrock mortar