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Coastlines are a dynamic interface between land and sea. Coastlines preserve evidence of many process from the past, going back hundreds, thousands, even millions of years. Coastlines are shaped by an ongoing series of processes involving daily wind and wave action, tides, occasional storms and superstorms, earthquakes, and massive tsunamis. Coastlines reflect process of their origin including erosion of bedrock features, and are influenced by regional geology, geography, and climate.
Understanding coastline dynamics is important considering that about 75% of the worlds megacities are on coastlines. According to the United Nations. presently about 40% of the world’s population lives within 100 kilometers of the coast, with hundreds of millions living in low-lying coastal areas (below about 10 meters elevation).
Wave erosion is persistent and intense, especially when storm waves combine with high tides. As a result, coastal landforms are generally delicate, and short-lived features. The sediment supply to coasts are offset by erosion rates along shorelines. Sediment supply is influenced by climate factors and geography, and can vary significantly from place to place, season to season, and by isolated events, such as changes caused by a massive superstorm (Figure 12.2).
Figure 12.1. New York, the largest coastal city in North America. More than 12 million people in the US live in regions within 3 meters above current sea level.