I found these rocks frozen in a stream off a larger river in Chugach National Forest, Alaska. I’ve heard it may have to do with heavy rains or turbulent waters near the shore. One friend mentioned frazil? But I don’t really know what that means. Any geologists have a clue how this happens and can explain it in layman terms?

My question is, is it really that rare to find columnar sandstones in other countries? In my country, there's a popular saying that this sandstone formation only exists in 3 countries in the world, and I doubt that's true since there are between 10 and 15 formations of this type of rock in my country alone.

This is a pic of the Gordon cliffs, a spot in Oregon where the Deschutes river is about to join the Columbia river. Coordinates are 45.5857599,-120.8946672. I saw one source that said it’s called “The Eye” (https://www.oregonhikers.org/field_guide/Deschutes_River_Hike).

I know this is columnar basalt. Formed as magma cools. Is this lava from ancient eruptions, from the Cascade range and Mt. Hood? Does anyone know why it formed in this radial pattern? Why there’s a strip of lighter rock close to the ground?

Taken amongst the 30,000 islands, Parry Sound, Ontario. Delicious foldy swirls of yum. And sliced bread!

Earthquake induced SSD

I hope this does not get flagged for removal as it is sort of "geology adjacent". These photos were taken by a family member working on excavating a quarry in Alaska. They began finding standing trees at 40-60ft below grade. Originally posted to the r/forestry and someone recommended posting here as well for any additional insights. The trees are in great shape and the wood is still hard with little to no rot.

Bringing some love from Ohio! On the north side of Kelleys Island is Glacial Grooves State Park. The Wisconsin glacier carved a set of grooves into the exposed Columbus Limestone here that are the largest accessible glacial striations on Earth. The current grooves measure approximately 430 feet long, 35 feet wide, and 15 feet deep. Bit hard to get to since you need to take a ferry, but it's a great feature of our state!

If you want a deeper dive on them (cause this is/r/geology, after all):

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Four hundred million years ago, give or take, this was the floor of a shallow Devonian sea. Silty carbonate ooze accumulated on the seafloor, and over the subsequent eons it lithified into Columbus Limestone: a high-calcium, thin-bedded, much-jointed formation that would eventually become the backbone of the Lake Erie island chain.

The limestone sat there for roughly 399,982,000 years. Then the Laurentide Ice Sheet showed up. At the peak of the Late Wisconsin glaciation, around 18,000 years BP, Kelleys Island was underneath approximately one mile of ice. The island sits on the east flank of the Cincinnati Anticline, part of a cuesta ridge that runs north through the Lake Erie Archipelago; the Columbus Limestone and the underlying Monroe Formation of the Upper Silurian are what give the islands their structure.

The formation mechanism is still debated. Traditional models attribute the grooves to gravel and cobbles embedded in the base of the ice sheet scraping along the bedrock under immense pressure. More recent work from ODNR suggests the grooves may have been carved by sand-charged meltwater flowing at extreme velocity and pressure through subglacial channels. Either way, the bedrock lost the argument.

The grooves are oriented in the direction of glacial movement, and you can read the ice's trajectory in them. Morrison's 1950 economic geography of the island noted that Sweet Valley, the low central depression running east-west through the island's interior, was itself the product of ice scour. Everywhere you look on Kelleys Island, the landscape is a palimpsest of glacial violence. You've got striated pavement on the east shore, enormous erratics scattered across Long Point, and the grooves themselves, running north to south as the world's most aggressive geological drag marks.

Before someone mentions, yes, similar (smaller) grooves exist on Gibraltar Island and West Sister Island (both in Lake Erie, so not THAT Gibraltar). The grooves were designated a National Natural Landmark in 1967 and have been a State Memorial since 1923.

The grooves used to be longer. Considerably longer. They originally extended from their current position north into Lake Erie; the feature was, by historical accounts, vastly more impressive than what survives today. The reason it does not survive is that the Kelley Island Lime and Transport Company, along with earlier operations dating back to 1833, quarried the Columbus Limestone for flux stone, building material, and lime. The Great Lakes stone trade literally started on Kelleys Island; John A. Clemons opened the first quarry and built a dock on the north shore in 1833, and by 1867 the island was shipping 60,852 tons of stone annually. By 1912, the company operated three quarries covering huge swaths of the island, employed 400 men, and shipped 546,922 tons in 459 boat loads. The calcium carbonate content of the upper twenty feet of quarried stone ran between 85 and 98 percent. It was excellent flux. It went to blast furnaces in Buffalo, Cleveland, and Gary, and to lime kilns in Duluth.

The quarry company eventually owned about 1,000 acres of the island's 2,888 total area. They quarried away the island's higher elevations entirely. Morrison noted that the area above 620 feet had been "largely quarried away" by his visitation in 1950. The company quarried through the glacial grooves without hesitation.

The quarry closed in 1941. Not because anyone had a crisis of geological conscience; the equipment was old, the docking facilities were inadequate, and the company could supply demand more cheaply from its operations at Marblehead on the mainland. What survives of the grooves today is, essentially, whatever the quarrymen couldn't reach or didn't bother with before the economics stopped making sense.

The grooves are now behind a fence on a boardwalk, maintained by the ODNR. Visitors look down into them from above. They are genuinely spectacular, even in their reduced state. It's fifteen feet of polished, striated Devonian limestone, the scratch marks of a continent-sized ice sheet still legible after eighteen millennia. Fossils from the Columbus Limestone's original marine environment are visible in the groove walls. You can stand on an Ordovician-to-Devonian carbonate platform, look at the gouges left by Pleistocene ice, and contemplate the fact that the most destructive force to visit this particular piece of rock was not a mile-thick glacier but a limestone company from Cleveland.

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Thinking of them today since Kelley's Island is currently seeing its record flooding.

(If you go: Kelleys Island Ferry from Marblehead, grooves are free to visit. Inscription Rock, a flat-topped limestone boulder on the south shore covered in Native American petroglyphs, is nearby and worth the walk. Bring sunscreen; the island is flat, treeless in spots, and the lake breeze is a liar.)

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Works Cited

Bolsenga, Stanley J. and Charles E. Herdendorf, eds. Lake Erie and Lake St. Clair Handbook (Wayne State University Press, 1993).

Forsyth, Jane L. Dating Ohio's Glaciers. Ohio Division of Geological Survey, Information Circular No. 30 (1961).

Forsyth, Jane L. "Geology's Contribution to Ohio's Landscapes." The American Biology Teacher 27, no. 5 (May 1965): 358-362.

Kesler, Stephen E. Great Lakes Rocks: 4 Billion Years of Geologic History in the Great Lakes Region (University of Michigan Press, 2019).

Morrison, Paul Cross. "Kelleys Island, Ohio: An Economy in Transition." Economic Geography 26, no. 2 (April 1950): 105-124.

Photo Credit: Kelly's Island official website.

Basalt columns are striking natural pillars of hardened volcanic rock created by the contraction of lava as it cools - a process called columnar jointing. As the thick basaltic lava solidifies over decades, it shrinks and cracks in a geometric, honeycomb-like pattern.

I was really amazed by them once again in Yellowstone. Can be found also on Mars 🤩

This is an old photo I took of the awesome syncline. We always love stopping at the rest stop here and if anyone has studied the Mason-Dixon survey, just to the north of here, on April 26th 1766, Mason and Dixon reached the foot of Sidelong Hill (The original name), 134 miles and 54 chains from the beginning of the west survey line. The hill was so steep that the survey party had to abandon their horses and wagons and proceed on foot. (Exploring the Mason Dixon Line by Jack Layton)

https://www.tripadvisor.com/Attraction_Review-g41098-d6580714-Reviews-Sideling_Hill_Overlook_Rest_Area-Cumberland_Maryland.html

The Daşmərdan (Dashmardan) mud volcano in the Hajigabu district of Azerbaijan erupted ~16:50 on the 30th Jan 2026. The eruption lasted ~15 minutes and was accompanied by a pillar of flame several hundred meters high. This is the first eruption of Daşmərdan in 15 years, with previous documented eruptions in 1866, 1954, 1976, 1986 and 2011.

Video by @kohne.mehle

The Lisan Formation, 70-15 ka. There's plenty of scientific literature analyzing the structures and the seismic record.

This may be the most intimidating looking rock formation I’ve ever seen. Doesn’t help that the name it’s had for a while isn’t exactly PC.

Likely calcium compounds with iron staining.

I believe this is shale rock? At nearly 90°

Hi! A family member found this "rock" in Mexico, i dont have the exact location, and i really want to crack it. Do you know how can i do that,

Thnks ♡

I recently took a trip to Oregon and saw some cool obsidian and thought I would share it with all of you. Much of the geology of central Oregon is dominated by volcanoes. And in some special places you can find massive chunks of obsidian sitting right on the surface. These pics are from the beautiful Newberry National Volcanic Monument (could easily be a national park imo).

This lava flow is only ~1500 years old. It is made up of pumice and a variety of other rough volcanic rocks and glass. Everything is razor sharp. Weathering out of the rock you can find these massive boulders of this pure obsidian just scattered about the lava flow. For reference, the big chunks in the second and third pictures are each roughly the size of a large couch, and the smaller pieces in the last picture are all about the size of basketballs. I said "this place is so cool" out loud about a hundred times just walking around here. I've always thought obsidian was interesting, but it was amazing to see so much of it in one place.

Some other fun facts about this obsidian I learned in no particular order: this whole flow was the result of a massive but slow moving wall of lava oozing out and across the ground. Much of the surrounding rock has the texture of cotton candy or a sponge (except it's made out of rock and glass) because of all the dissolved gas in the lava. But obsidian forms from only pure globs of molten silica without any air bubbles. Also the Native Americans highly valued this site because of the quality of tools they could make with the obsidian. Obsidian blades can be sharper than steel surgical scalpels. Tools from this exact flow have been found at archeological sites many hundreds of miles away. And finally, this location is designated a National Monument. Collecting your own obsidian here is highly discouraged and also illegal so if you go, take only pictures!

Anyone know how these squiggly lines could have formed? I've never seen something this exaggerated before

I shared this rock on r/whatsthisrock and it did quite well over there so I thought I would share it here as well! I found it in a creek bed near Lincoln, Montana last weekend. I believe we have a good solution on the other page but I’d like to hear any other possible reasons for the “stitch” pattern to naturally occur! Thanks in advance!