Mona had gone to visit her friend's boat on the Visakhapatnam jetty. She was surprised to see that the boats seemed to have sunk because the water level in the jetty was low and the gangways to the boats were almost vertical. As a student of geography name and explain the phenomena that caused this.

The phenomenon that Mona observed is called a Low Tide.

Tides are the regular rise and fall of sea levels caused by the gravitational pull of the moon and the sun on the Earth's oceans. During low tide, the water level recedes from the shore, exposing more of the seabed and causing boats at a jetty or dock to appear lower than usual. This can make gangways steep or even vertical, as Mona noticed.

So, what she saw was the effect of low tide, a natural and periodic event that occurs twice a day in most coastal areas.