This is a survey of Old Salts Atoll based on what geological knowledge that I possess. I did this when @Pasha-Entreri mentioned in this here thread that there may be at least long extinct volcanoes in Sea of Thieves while specifically mentioning Old Salts Atoll. So I took it upon myself to take a look and see what was there.
Full disclosure, I am not a professional Geologist in any capacity. While I am currently studying Geoscience if some of my conclusions are incorrect, please let me know.
Here goes.
Old Salts Atoll is located in the south-western corner of the map. Beyond that lies the Devil's Shroud. It is just west of Shark Bait Cove and is in the Ancient Isles. The most notable feature of the atoll is a wreck that is of undetermined age. There are signs of previous habitation on the island as parts of the wreck appear to be repurposed for crude living arrangements. There is no indicator on the wreck as to the who the previous crew was. The wreck could not be identified in any way. Other signs of habitation is a carved stone head and what appears to be a carved stone brazier or bowl of some kind.
The only wildlife present on the surface was a handful of chickens. There was also the ever present skeletons that came on occasion from the ground. Moderate marine life was present in the shallows in the form of fish schools and a pair of sharks. I did not take the opportunity ot take pictures of the sharks since they seemed to be keen of making a meal out of me. And of course I had to choose to conduct a survey when the sharks appear to be quite agitated for currently unknown reasons. I did not see any coral while looking around in the shallows.
Here is the center of Old Salt Atoll. There are some rocks and some sea water. The opening that is visible in the top left of the image indicates a partially closed lagoon. That means that the water in the interior of the atoll is not isolated from the rest of the ocean and is allowed to mix. This is not the only opening in the atoll rim. Lots of sand was present inside the lagoon which may indicate the atoll is reaching the final stages of its formation into a mature atoll.
The rocks that I found interesting are the two partially submerged rocks that I have highlighted in the image. These rocks appear to be also buried in the sand. My opinion is that these would be the remnants of the volcano that allowed the atoll to form though it is hard to tell without being able to drill a bore hole or take samples with hammers. I didn't want to ruin my cutlass trying to get rock fragments. It is better suited for the skeletons that cropped up every now and then. Dealing with skeletons and sharks made me too busy to extract any samples from rock fragments that were visible nearby.
Another interesting feature is the evidence of subsidence. The above picture was taken off of the north-eastern shore facing south I think. That was also one of the times where I had to quickly fend off a pair of sharks that decided to say hi. I did get confused as to where I was working. Thankfully, these features are visible in more than one place in the shallows around the atoll.
Subsidence is when the land decreases in elevation. Adding mass to the land causes it to subside. Conversely, removing mass from land causes it to increase in elevation or rebound. Near the beginning of the life cycle of an atoll, coral reefs start to form. As reefs grow, they increase in mass which causes them to sink. In order to stay alive, the reefs have to keep building themselves up. Along with erosion, this effectively pushes the extinct volcano downwards and it eventually gets covered by the reef itself and sand.
As the reef builds itself up, the adjacent slopes may become unstable which causes them to fail. The above picture shows terraces in the slope leading to the island surface where the slope has failed in a series of slumping events. The highlighted portions indicate two portions of what could have been a single slump event. The portion on the right is where the portion closer to center used to be. There is also another piece that may have come from the same event partially hidden behind my compass. I indicated a potential path for the Slumps are basically almost landslides that move in slow motion. My opinion then is that these slumps formed because of the atoll being built up to the point of slope instability and portions of the slope have collapsed.
The only problem is that there are no reefs present at Old Salts Atoll. At least, none that I could see. So perhaps the reefs have long since died and has been buried in sand? That could be plausible since the slumps don't appear to be particularly 'fresh'.
That about sums up what I noticed when I surveyed the atoll. Did I miss anything?
