If you look at the east coast of the United States from even a bird's eye view, you can notice the most interesting geological features. And if we are all somehow used to rivers and mountains, then, of course, you cannot say the same about tens of thousands of oval-shaped swamps. Scientists have long puzzled over where they came from in more than a dozen of the states located here, and recently received a convincing answer.
These depressions are known as “Carolina bays”, which can be translated as “Caroline depressions”. They spread over a vast territory from New Jersey to the northern part of Florida. The depth of these “holes” does not exceed three meters, and the diameter varies from 100 meters to 12 kilometers. To date, a significant part of them have been asphalted, plowed over or otherwise destroyed as a result of human activities, but it is assumed that there were about half a million of them originally.
The hollows have characteristic distinguishing features, These, in particular, mounds of sand along the southern or eastern edge and an elliptical shape oriented northwest to southeast.
The Caroline depressions are also remarkable in terms of the formation of their own ecosystems. They have no connection with rivers, so they most often turn into isolated swamps, fed by rains and groundwater. Much of it is subject to seasonal periods of dryness and filling, which attract turtles, deer, raccoons and opossums. They were also chosen by representatives of endangered species: American beaks, some salamanders and frogs.
The question of the origin of these ovals has long remained an unsolvable mystery. One of the first hypotheses suggested that they were formed as a result of the fall of a meteorite that exploded in the air and showered the surface with its fragments. Which, it seems, is quite logical, since the depressions are really somewhat reminiscent of craters.
The problem, however, is that the depressions are only deployed on sandy soil, and the fragments of the celestial alien should have hit North America indiscriminately. There have also been opinions that these are the remains of sinkholes or traces left by large schools of fish when the entire area was at the bottom of the ocean.
However, the most convincing looks like a hypothesis that these are the remains of ancient lakes. It was confirmed thanks to the method of optical dating. It is often used to determine the age of certain geological events.
Scientists study quartz crystals and try to figure out when they last saw light. This is possible due to the fact that electrons inside this material accumulate in the defects of the atomic lattice, and then, under the influence of photons, are released. Thus, quartz crystals are something like a geological chronometer.
On the sandy The bottom of the Caroline depressions was rich in quartz crystals. They showed that all the ovals were formed between 95,000 and 92,000 years ago, during the last ice age. It is believed that then this part of North America looked completely different. The air was colder, the winds were stronger, the vegetation was much less.
Something similar can be seen today in the northern parts of the planet. Where, what a surprise, so surprise, there are also plenty of oval depressions on the ground. These are the so-called thermokarst lakes. They form in places where the soil regularly freezes and thaws, as a result of which it falls down, forming characteristic holes.
Then the wind is taken over, which blows mainly in one direction. It gives the “blank” an elongated shape, and the sand carried by it accumulates at the edge on the leeward side. As you can see, all this explains both the oval outlines of the Caroline depressions and the sandy mounds along their edges.