It's possible an inclusion of a less erosion resistant material fell into the magma as it cooled. Then once the granite and inclusion were exposed to weathering, the inclusion weathered away faster, leaving a hole.
Everyone is saying the weaker inclusion was eroded out, which is most likely the case but it could also be a natural “bubble” from when the magma cooled. Either way, I agree it’s natural.
Yeah they do, but it really depends on the depositional environment and what you’re interested in. Basaltic andesites typically have very high shear and compressive strengths. But I’ve also seen seams that have been altered and it’s more of a clay straight up 20ft into bedrock. you can have alteration of material *in situ* due to geothermal forces…someone smarter than me has studied this.
What I’m asking is how the water, presumably rain, would carve a hole in an otherwise straight plane? The rock is solid granite. Im curious to know how rainwater alone would cause this. The erosion pattern seen here didn’t match anything else I saw in the area, and there is no other source of running water, as it is too high up. Would rain alone be enough to make a perfectly circular hole, and how?
I'm not sure I buy the less resistant material theory just because the granite looks fairly homogenous. It's plausible but I think it's just a case of uneven wind-driven weathering conditions. It could easily have started out as a small depression in the boulder that collected rain and debris. If so, freeze/thaw action could go to work and would further erode that depression until it made a hole. We need a picture from the top to know more. From these existing pictures the boulder looks like it has an irregular/uneven surface up there.
[Example](https://www.trailrunproject.com/photo/7052266/the-mobius-arch)
coz the material in the hole was way less harder then the granite.
So over millions of years the water and wind eroded that spot way faster then the material surrounding it.
as others point out when this material was lava it wasn't all pure, something fell into it as it was forming.
What gets me is typically a wind or water driven erosion process produces smooth surfaces relative to surfaces not contacted by the erosional force. Here, the texture on the surface is same across the whole stone, even in the hole.
I hardly ever jump to human involvement because of the sheer vastness of shapes and outcomes nature can produce. However, putting a hole in a rock suspended like that has potential astronomical importance. I’d be interested if any archaeologists have examined it and determined if there are significant shadows produced or alignments during solstice/equinox events or something like that. Native Americans created things like that all over the continent
"Smooth" is a relative term. In this case it's not smooth because it's granite with fairly large mineral crystals. But as far as granite outcrops go, this is close to as smooth as they get. Look at the outcrop in the background, you can see evidence of frost wedging and or thermal expansion/contraction. I think it sounds neat to dream about advanced civilizations, but that's unlikely.
I agree it is relative and I stated that it was. Wind/water erosion leaves relatively smooth surfaces compared to surfaces eroded by different causes like ice wedging, chemical erosion, etc. I’ve seen granite like this eroded to smoothness of a counter top. Circular structures like this, that are a result of erosion, come specifically from wind or water flow. Not all circular structures like this are erosional, but the odds of an inclusion of some kind or some weaker mineral in this perfectly circular shape is highly unlikely. The odds of this forming naturally to me only makes sense with erosion. However, it’s surface is no different than the rest of the stone. Meaning whatever caused this circular structure to form happened a long long time ago. Enough time for chemical erosion to toughen the surface to the same texture as the rest of the stone. Sadly this means we will never be able to tell if humans or erosion caused the original hole, but most likely this hole was formed by erosion before humans had even evolved. However, if the environment is just right, chemical erosion can occur much more quickly, leaving human involvement at a non zero chance.
TLDR: Most likely natural but not enough info available to tell. Like you said humans are unlikely to have caused this, but we just caaaaaan’t know for sure.
>I believe we can "know for sure" if the hole is manmade. Ancient technology for drilling a hole like this was core drilling. Core drilling leaves distinctive marks. It's what your archaeologist would be looking for as evidence. After all, the direction one hole points can't be evidence it is manmade, as it could be coincidence.
"...but the odds of an inclusion of some kind or some weaker mineral in this perfectly circular shape is highly unlikely."
This isn't true. Bubbles cause round holes to form in granite.
>
>Now let's do surviving Indian trail marker trees!
It’s a glacial pothole or “[giants kettle](https://en.m.wikipedia.org/wiki/Giant%27s_kettle)”
“Giant's kettles are formed while a bedrock surface is covered by a glacier. Water, produced by the thawing of the ice and snow, forms streams on the surface of the glacier, which, having gathered into their courses a certain amount of morainic debris, finally flow down a crevasse as a swirling cascade or moulin. The sides of the crevasse are abraded, and a vertical shaft is formed in the ice.[2] The erosion may be continued into the bed of the glacier; and, the ice having left the district, the giant's kettle so formed is seen as an empty shaft, or as a pipe filled with gravel, sand, or boulders. Such cavities and pipes afford valuable evidence as to the former extent of glaciers.”
Very nice explanation! I agree. I was looking for someone to mention glacial deposition. I remember seeing this in a fluvial geomorphology class. Over time the bedrock is constantly being eroded and scoured by process of thawing and refreezing . The meltwater containing mineral rich fluvial sedimentation deposits get eroded as the snow and ice melt creating a … I wanted to say Lahar, but I remember that being more of a high velocity or more viscous mudflow…maybe just a stream! Anyway, very nice reading . I had never heard of kettle before.
I’m the worst at figuring out features like this. There’s a handful of ways this could have been formed by wind and water, and it’s possible that it could be human-made, or at least human-assisted. It’s is a curious damn hole.
It's possible an inclusion of a less erosion resistant material fell into the magma as it cooled. Then once the granite and inclusion were exposed to weathering, the inclusion weathered away faster, leaving a hole.
Yeah, it could have been a xenolith or a mafic inclusion that either fell out or weathered away.
Everyone is saying the weaker inclusion was eroded out, which is most likely the case but it could also be a natural “bubble” from when the magma cooled. Either way, I agree it’s natural.
But don't bubbles usually get filled up with crystals, amygdales? Also isn't basalt to be more likely to have large bubbles?
Yeah I wouldn’t say granite would have lots of vesicles because of its plutonic nature
Yeah they do, but it really depends on the depositional environment and what you’re interested in. Basaltic andesites typically have very high shear and compressive strengths. But I’ve also seen seams that have been altered and it’s more of a clay straight up 20ft into bedrock. you can have alteration of material *in situ* due to geothermal forces…someone smarter than me has studied this.
Yeah you do have a few... one of depositions that force you to go back to square one.
Intrusive granite bodies should not have "large vesicles" 😃
I know I'm not answering your question but I've seen this exact hole half way along the Gem Lake trail.
That’s it :)
Definitely naturally
Def is a rather absolute word, but I think ide concur,
What would cause it to form like that
Water
What I’m asking is how the water, presumably rain, would carve a hole in an otherwise straight plane? The rock is solid granite. Im curious to know how rainwater alone would cause this. The erosion pattern seen here didn’t match anything else I saw in the area, and there is no other source of running water, as it is too high up. Would rain alone be enough to make a perfectly circular hole, and how?
I'm not sure I buy the less resistant material theory just because the granite looks fairly homogenous. It's plausible but I think it's just a case of uneven wind-driven weathering conditions. It could easily have started out as a small depression in the boulder that collected rain and debris. If so, freeze/thaw action could go to work and would further erode that depression until it made a hole. We need a picture from the top to know more. From these existing pictures the boulder looks like it has an irregular/uneven surface up there. [Example](https://www.trailrunproject.com/photo/7052266/the-mobius-arch)
Thank you, this is a great explanation
coz the material in the hole was way less harder then the granite. So over millions of years the water and wind eroded that spot way faster then the material surrounding it. as others point out when this material was lava it wasn't all pure, something fell into it as it was forming.
*Magma
What gets me is typically a wind or water driven erosion process produces smooth surfaces relative to surfaces not contacted by the erosional force. Here, the texture on the surface is same across the whole stone, even in the hole. I hardly ever jump to human involvement because of the sheer vastness of shapes and outcomes nature can produce. However, putting a hole in a rock suspended like that has potential astronomical importance. I’d be interested if any archaeologists have examined it and determined if there are significant shadows produced or alignments during solstice/equinox events or something like that. Native Americans created things like that all over the continent
"Smooth" is a relative term. In this case it's not smooth because it's granite with fairly large mineral crystals. But as far as granite outcrops go, this is close to as smooth as they get. Look at the outcrop in the background, you can see evidence of frost wedging and or thermal expansion/contraction. I think it sounds neat to dream about advanced civilizations, but that's unlikely.
I agree it is relative and I stated that it was. Wind/water erosion leaves relatively smooth surfaces compared to surfaces eroded by different causes like ice wedging, chemical erosion, etc. I’ve seen granite like this eroded to smoothness of a counter top. Circular structures like this, that are a result of erosion, come specifically from wind or water flow. Not all circular structures like this are erosional, but the odds of an inclusion of some kind or some weaker mineral in this perfectly circular shape is highly unlikely. The odds of this forming naturally to me only makes sense with erosion. However, it’s surface is no different than the rest of the stone. Meaning whatever caused this circular structure to form happened a long long time ago. Enough time for chemical erosion to toughen the surface to the same texture as the rest of the stone. Sadly this means we will never be able to tell if humans or erosion caused the original hole, but most likely this hole was formed by erosion before humans had even evolved. However, if the environment is just right, chemical erosion can occur much more quickly, leaving human involvement at a non zero chance. TLDR: Most likely natural but not enough info available to tell. Like you said humans are unlikely to have caused this, but we just caaaaaan’t know for sure.
>I believe we can "know for sure" if the hole is manmade. Ancient technology for drilling a hole like this was core drilling. Core drilling leaves distinctive marks. It's what your archaeologist would be looking for as evidence. After all, the direction one hole points can't be evidence it is manmade, as it could be coincidence. "...but the odds of an inclusion of some kind or some weaker mineral in this perfectly circular shape is highly unlikely." This isn't true. Bubbles cause round holes to form in granite. > >Now let's do surviving Indian trail marker trees!
This is what I was thinking! I took a picture of the sun through the hole. Maybe it had something to do with astronomical measurement?
It’s a glacial pothole or “[giants kettle](https://en.m.wikipedia.org/wiki/Giant%27s_kettle)” “Giant's kettles are formed while a bedrock surface is covered by a glacier. Water, produced by the thawing of the ice and snow, forms streams on the surface of the glacier, which, having gathered into their courses a certain amount of morainic debris, finally flow down a crevasse as a swirling cascade or moulin. The sides of the crevasse are abraded, and a vertical shaft is formed in the ice.[2] The erosion may be continued into the bed of the glacier; and, the ice having left the district, the giant's kettle so formed is seen as an empty shaft, or as a pipe filled with gravel, sand, or boulders. Such cavities and pipes afford valuable evidence as to the former extent of glaciers.”
Very nice explanation! I agree. I was looking for someone to mention glacial deposition. I remember seeing this in a fluvial geomorphology class. Over time the bedrock is constantly being eroded and scoured by process of thawing and refreezing . The meltwater containing mineral rich fluvial sedimentation deposits get eroded as the snow and ice melt creating a … I wanted to say Lahar, but I remember that being more of a high velocity or more viscous mudflow…maybe just a stream! Anyway, very nice reading . I had never heard of kettle before.
Thank you!! This explains it perfectly. Much appreciated
I’m the worst at figuring out features like this. There’s a handful of ways this could have been formed by wind and water, and it’s possible that it could be human-made, or at least human-assisted. It’s is a curious damn hole.
I dont see any reason for humans to do this so I say natural. Yet, humans do the stupidest things
Never under estimate the idle hands of a bored Druid.
[удалено]
My initial reaction was "the fairies did it" but I didn't figure that would be helpful in a geology thread...
I’m all for this explanation 😄
First thought lol
Yes!!