ABSTRACT
Introduction The level of the sea is not constant, it is always rising and falling, either through the passing of waves (including tides), meteorological influences or gravitational effects in the form of the earth’s geoid. Longterm and significant sea level changes, however, reflect changing levels of both land and sea; eustasy refers to absolute changes in global sea level, and isostasy refers to the vertical movement of land due to local geological factors. It is the balance between these two processes at a given coastline that produces observed changes in sea level, referred to as relative sea level change, because an absolute (eustatic) rise in sea level may not be required to allow the sea to rise relative to the land. Figure 5.1 explores this balance in a simplified way, and a number of cases can be put forward to illustrate the relationship:
• Relative sea level rise will occur if (a) eustatic sea level rises whilst the land is isostatically subsiding, static or uplifting at a slower rate than eustatic rise; (b) eustatic sea level is static whilst the land is isostatically subsiding; and (c) eustatic sea level falls whilst the land is isostatically subsiding at a faster rate than eustatic fall.
