Coastal cliffs and platforms

Abstract

Introduction Our individual perceptions of the coastline are clearly related to our local coastal geomorphology. On global and regional scales coastal morphology often correlates closely with tectonic setting (Inman & Nordstrom, 1971). Frequently, major geomorphic contrasts exist between the subdued coastlines along passive continental margins and the rugged coastlines along convergent plate boundaries. Along most coastlines, modern (active) coastal landforms are similar to their Pleistocene counterparts, which suggests that current tectonic and coastal processes have been fairly uniform over extended periods of recent geological time (Lajoie, 1986 see also Chapter 12). Many exposed coastlines along passive continental margins, such as the southeast and Gulf coasts of the United States or parts of the northeast coast of Australia, for example the Gold Coast, consist of a low-relief coastal plain, bordered offshore by a wide continental shelf (see Chapters 2 and 4). These relatively stable coasts are also characterized primarily by meso- and macrotidal conditions, energy dissipation and depositional landforms, such as wide sandy beaches and dunes (see Chapter 4), as well as offshore barrier islands or bars (or a barrier reef in the case of northeastern Australia see Chapter 8). In marked contrast to the Atlantic coast of the United States and Canada, the Pacific Coasts of North and South America are active margins, and are either present or former collision coasts, where two plates have collided. Even a casual glance at almost any individual segment of this coastline will immediately reveal striking differences in coastal landforms and geological history. In addition to seismicity and vulcanism, collision coasts or active margins are characterized by deep-sea trenches offshore, narrow continental shelves, coastal mountains and often uplifted marine terraces.