In this video, we're diving into the incredible ways coastal waters shape our planet's shorelines. We will explore how rivers carry sediment to the sea, how waves and tides wear down coastlines, and how extreme weather can dramatically alter entire landscapes. Let's start with looking at how coastal waters play a crucial role in shaping the beaches we see today. Many of the beautiful sandy beaches in places like Thailand or California are examples of so-called barrier coast formed after the last ice age, when sea levels were much lower.

There are two major forces that help form beaches. The obvious one is, of course, waves that constantly erode cliffs and transport material from the shore into deeper waters. Then we have currents. Even though they're less visible, currents move water and huge amounts of sediment along the shoreline. They transport materials such as stone, sand and clay from the cliffs and deposit them on flatter sandy beaches or in deeper waters. Over time, this process results in net erosion of cliffs and beaches, causing the coastline to gradually move inland. This erosion can range from a few centimeters to several meters per year, depending on the specific conditions of the coast.

Tidal flats are another key coastal feature. These are shaped by the daily tidal cycle, which occurs every 12 hours and 25 minutes. This typically results in two high tides and two low tides every day. Tides occur because of the moon's gravitational pull. As the Earth rotates, the moon draws the ocean's water towards it, resulting in high tides on the side facing the moon. The oceans on the opposite side also experience high tides, while the two diagonal sides will have no tides. This constant movement of water significantly influences many coastlines, contributing to both the formation of tidal flats and erosion of cliffs.

Then we have deltas. As rivers flow into the sea, they carry a mixture of gravel, sand, silt and clay. When the sediment-rich water meets the ocean, the sediment falls to the bottom, forming deltas. Some of the most spectacular deltas include the Mississippi Delta in the United States, the Yangtze Delta in China, and the Ganges Delta in Bangladesh and India. These areas are incredibly fertile due to the large amount of nutrients deposited by the rivers, making them vital for agriculture and for human settlements. However, deltas are dynamic environments. While some deltas are being built up by new deposits of sediments, others are gradually being eroded by the sea, causing their coast to retreat.

Erosion along cliffs and beaches is most dramatic during intense weather such as winter storms and typhoons. Even though these extreme events are relatively rare, they can rapidly alter our coastlines and the overall shaping of our planet's surface. So, the serene beaches we enjoy on sunny days are actually shaped by immense forces like waves, tides and powerful storms, all of which underscore the importance of water in sculpturing the Earth's surface. In the next module, we'll look at the journey of water from rain to groundwater, exploring how it shapes landscapes and sustains life.