According to NationalGeographic.com, bays are formed through various ways, such as plate tectonics, overflowing of the ocean to a coastline and the slicing of a glacier through a bedrock. Bays are bodies of water partially surrounded by land, and they are typically less enclosed and smaller than a gulf.
Plate tectonics involves continents drifting together and rifting apart, which leads to the formation of large bays, explains NationalGeographic.com. One of the most notable bays formed through this process is the Bay of Bengal, which is the biggest bay in the world. Another way that bays are created is when the ocean overflows a coastline. For example, Kowloon Bay in Hong Kong was formed when the South China Sea overflowed the Kowloon Peninsula’s coastline. Bays are also formed when the coastline erodes into the ocean. An example is Guanabara Bay, which formed when the Atlantic Ocean eroded an inlet in South America.
When a glacier slices through an area’s bedrock, it leaves a long, steep canyon as it recedes. The sea penetrates the inlet, creating a fjord, which is the term for narrow bays formed by glaciers.
The BBC explains that bays form next to headlands, which are created when the sea hits a coastal area with alternating bands of soft and hard rock. The bands of soft rock, like clay and sand, erode faster than resistant rocks like chalk. This results in the formation of a headland and subsequently a bay.