Eustasy

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Eustasy is one of several terms that are used to describe the changing relationships between sea level and dry land. When the term "relative" is used, it connotes change that is not attributed to any specific cause.

The term "eustasy" or "eustatic" refers to changes in the amount of water in the oceans, usually due to global climatic changes. The melting of glaciers at the end of ice ages is an example of eustatic sea level rise. When the Earth's climate cools, water is evaporated from the oceans and is precipitated on land masses as permanent ice and snow. This causes sea levels to fall relative to a stable land mass.

The term "isostasy" or "isostatic" refers to changes in the level of the land masses due to thermal buoyancy or tectonic effects and implies no real change in the amount of water in the oceans. Areas like volcanic islands are experiencing relative sea level rise as a combined result of isostatic cooling of the rock (which causes the land to sink) and eustatic sea level rise from the continuing recovery from the last ice age.

Paleoclimatologists can track sea level changes by examining the rocks deposited along coasts that are very tectonically stable, like the east coast of North America.