These emerged rocks are situated at a sailing distance of around two hours and they are usually not visible from my vantage point on the beach because they lie beyond the horizon. However, they became visible before sunset on a particular night two weeks ago. I made a few pictures and took some time to do some research.
I found out that this is very likely an optical phenomenon called a “superior mirage” which was well known by ancient sailors. As the sea is still quite cold at this time of the year and since we had had two hot days, the air layer in contact with the sea was still probably much colder than the air layers above. The difference of refraction index between the cold air below and the warmer air above was then curving the path of the optical rays in such a way that they followed the Earth curvature instead of going straight. The rocks were thus appearing higher on the horizon than they really were. This phenomenon is believed to explain why sailors sometimes observe a coastline or a ship that lies actually far away beyond the horizon. For further details see https://en.wikipedia.org/wiki/Mirage and go directly to the paragraph on superior mirages. I had some confirmation of that explanation because when the setting sun came down through the horizon line, it was completely distorted, probably because different parts of its image were travelling through different air layers at different temperatures.
I have cropped the picture in order to remove some extra sky and some extra sea, but I have made no other processing, so the colors are natural SooC.
