As for a picture or diagram of this, I suggest https://earth.google.com/web
The web page is trying to blackmail you to use Chrome. Tried in Maxthon MX5, and tried in Edge, no hit.
People who think the earth or sea is a sphere tell me this:Sea lines are arcs with very small radians.
but,If what they say is true,
I should like to know, from the point of view of a man in the middle of the sea, how, in the case of radians, the sea lines in all directions close on the spherical surface of the sea?
If this "arc" could be closed, the left and right ends of the sea line should have a pronounced twist at any observer's Angle, because the closed sea line looks like a lying circle that is an ellipse, and the two ends of the ellipse look like this.Isn't it?
I can only imagine this happening when the sea is flat, the sea is straight, and the distant object looks smaller.I really can't imagine how this could have happened if the sea was a sphere and the sea was curved.
If anyone knows, please draw a picture to explain it, although I don't think anyone knows.
By the way,I have read in Buddhist texts that the volcano is because there are six other SUNS at the bottom of the sea.
I'm sure not many people have even heard of it.So I'm just paraphrasing it.
If you are in the middle of the sea, standing in small boat, your eye is 6 feet (1.8 m) above the water and your horizon is 5 km away in all directions.
From that altitude the Apparent Horizon Dip is 0.0449 degrees.
(If you saw a protractor you know how small is one degree, now imagine how much smaller is 0.0449 degrees. Invisible.)
Looking at your horizon circle from that position is like looking at hula-hoop horizontally around your head at the eye level.
It will look straight wherever you look.
As you go higher, the Apparent Horizon Dip will be bigger. Horizon will be lower, but until you reach some high altitude you still can't see the dip with naked eye.
You need sextant, quadrant, theodolite, astrolabe, ... to measure it.
For example at the height of 1000 feet (330 m) you will have Apparent Horizon Dip of just 0.5 degrees (and your horizon is 67 km away in all directions).
Now your hula-hoop around your head is a bit lower, at the level of your nose.
It still looks pretty straight whichever direction you look at it.
If you go much higher, let's say 40 000 feet (12 000 m), your Apparent Horizon Dip is 3.28 degrees (and your horizon is 426 km away all around you).
Now your hula-hoop is down to the level of your mouth, and you begin to see some slight curviness from that angle, if you look carefuly.
If you go even higher you will begin to see the curviness even better.
From ISS (400 km high) your horizon will be 2470 km away and your Apparent Horizon Dip 18.4 degrees.
Your hula-hoop will now be somewhere around your shoulders and you will clearly see it curved.