The position and height of the sea relative to land, that is relative sea level, determines the location of shorelines. Though global fluctuations in sea level may result from the growth and melting of continental glaciers and large-scale changes in the configuration of continental margins and ocean floors, many regional processes result in rise or fall of relative sea level that affect one coastline and not another. These include: thermal expansion of ocean waters, changes in meltwater load, crustal rebound from glaciation, uplift or subsidence in coastal areas related to various tectonic processes (e.g., seismic disturbance and volcanic action), fluid withdrawal, and sediment deposition and compaction. Variations in relative sea level also may result from geodetic changes such as fluctuations in the angular velocity of Earth or polar drift. Tide-