Looking down on the Earth from space, we can easily find that less than one-third of the Earth's total area is covered by oceans. Surrounding the continents are long coastlines, which not only outline the contours of the continents, but also create beautiful landscapes. On the coastlines, there are not only beaches that we love very much, but also many rugged cliffs. Why do the same coastlines create different landscapes? This is actually due to the combined effects of topography and the sea.
17,000 years ago, the Earth's surface ended the cold of the last ice age, and the climate began to warm up. The ice and snow that had once gathered on the land gradually melted and flowed into the ocean. This caused the sea level to rise gradually, and the new coastlines gradually moved towards the continents. The parts of the land that had been directly exposed to the air were submerged by the sea, and the places that had only been subject to wind and rain now had to withstand the erosion of the waves.
Raging waves. On the sea surface, there are usually strong winds because there are no tall windbreaks. The waves they raise are also surprisingly powerful. When they reach the shore, the huge waves will first directly transform the coastal landscape. Some rocks on the coast are crushed and battered by the waves, and some rocks with weaker texture are carried away by the retreating waves, forming concave landforms. The harder rocks nearby can form convex landforms. Over time, the soft rocks will continue to be eroded and retreated, creating arc-shaped bays on the inside, while the harder rocks on the outside will protrude outward to form headlands. When the bays become deep enough, the waves, hindered and resisted by the headlands on both sides, will become slow and gentle inside the bays, with little destructive power. The previously broken rocks will be repeatedly washed and rubbed by the gentle waves, gradually turning into extremely fine sand and piling up in the bays. This deposition continues with the repeated action of the waves. When there are enough sand particles, we often see beaches. Karon Beach on Phuket Island in Thailand is formed in this way. Karon Beach is surrounded by headlands on both sides, with a length of about 3,000 meters. The blue sea, blue sky, and golden sand beach shine brightly in the sun.
We turn our attention to the headlands around the beach. The front of the headlands is often a bare rock wall, which directly contacts the sea. Its steep appearance and angular foundation stones give people a sense of awe, which comes from its resilience in weathering and its majesty in the raging waves. Due to the direct contact with the surprisingly destructive waves, the lower part of the rock wall is often broken and eroded after years of collision and erosion. Over a long period of erosion, narrow cavities will gradually be carved out at the lower part of the rock wall, which are often called sea caves or sea erosion caves. Such sea erosion caves gradually grow larger and deeper, and the upper rock wall, having lost its foundation, will collapse. The rocks on the cliff will fall down in a clatter, and a new steep cliff will form on the cliff. Such cliffs are called sea erosion cliffs. As the name suggests, they are cliffs formed by the erosion of the sea.
The sea erosion cliffs formed in this way are not very large, but there are also magnificent sea erosion cliffs stretching for thousands of kilometers on Earth, such as the Cliffs of Moher in Ireland and most of the sea erosion cliffs on the west coast of the United States. The famous Qing Shui Cliffs on the east coast of Taiwan, China, also have large differences in height and length. How can this be explained? Their formation methods are different from those of the headlands mentioned above. Plate tectonics determines the general location of land and sea distribution and also affects the basic characteristics of the coastline. While these large patterns are determined, there is also a controlling factor in geological processes that may affect the coastline.The landscape of the coast is decisively influenced by faults. If a major fault develops precisely where the mainland meets the sea, the waves will no longer encounter layers of rock with varying degrees of softness and hardness. Instead, they will face a large exposed bedrock cut by the fault, with steep slopes winding to either side. The length of the cliff will depend on how far these steep slopes extend. However, the cliffs we see today may not be the original fault surfaces. Over time, as waves erode and the cliffs themselves collapse, the original fault surfaces gradually retreat, forming new cliffs. These new cliffs often inherit the steepness and ruggedness of the previous fault surfaces, creating the familiar cliff coastlines we see on many coastlines.