Sea Level and Dry Land
Several terms are used to describe the changing relationships between sea level and dry land. When the term "relative" is used, it means change relative to a fixed point in the sediment pile. The term "eustatic" refers to global changes in sea level relative to a fixed point, such as the centre of the earth, for example as a result of melting ice-caps. The term "steric" refers to global changes in sea level due to thermal expansion and salinity variations. The term "isostatic" refers to changes in the level of the land relative to a fixed point in the earth, possibly due to thermal buoyancy or tectonic effects; it implies no change in the volume of water in the oceans. The melting of glaciers at the end of ice ages is one example of eustatic sea level rise. The subsidence of land due to the withdrawal of groundwater is an isostatic cause of relative sea level rise. Paleoclimatologists can track sea level by examining the rocks deposited along coasts that are very tectonically stable, like the east coast of North America. Areas like volcanic islands are experiencing relative sea level rise as a result of isostatic cooling of the rock which causes the land to sink.
On other planets that lack a liquid ocean, planetologists can calculate a "mean altitude" by averaging the heights of all points on the surface. This altitude, sometimes referred to as a "sea level", serves equivalently as a reference for the height of planetary features.
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Famous quotes containing the words sea, level, dry and/or land:
“All the morning we had heard the sea roar on the eastern shore, which was several miles distant.... It was a very inspiriting sound to walk by, filling the whole air, that of the sea dashing against the land, heard several miles inland. Instead of having a dog to growl before your door, to have an Atlantic Ocean to growl for a whole Cape!”
—Henry David Thoreau (1817–1862)
“If there is a price to pay for the privilege of spending the early years of child rearing in the driver’s seat, it is our reluctance, our inability, to tolerate being demoted to the backseat. Spurred by our success in programming our children during the preschool years, we may find it difficult to forgo in later states the level of control that once afforded us so much satisfaction.”
—Melinda M. Marshall (20th century)
“The inhabitants of the Cape generally do not complain of their “soil,” but will tell you that it is good enough for them to dry their fish on.”
—Henry David Thoreau (1817–1862)
“Within the regions of the air,
Compassed about with heavens fair,
Great tracts of land there may be found
Enriched with fields and fertile ground;
Where many numerous hosts
In those far distant coasts,
For other great and glorious ends,
Inhabit, my yet unknown friends.”
—Thomas Traherne (1636–1674)