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.
Read more about this topic: Eustatic
Famous quotes containing the words sea, level, dry and/or land:
“They call them the haunted shores, these stretches of Devonshire and Cornwall and Ireland which rear up against the westward ocean. Mists gather here, and sea fog, and eerie stories. That’s not because there are more ghosts here than in other places, mind you. It’s just that people who live hereabouts are strangely aware of them.”
—Dodie Smith, and Lewis Allen. Roderick Fitzgerald (Ray Milland)
“To Time it never seems that he is brave
To set himself against the peaks of snow
To lay them level with the running wave,
Nor is he overjoyed when they lie low,
But only grave, contemplative and grave.”
—Robert Frost (1874–1963)
“The knowledge of an unlearned man is living and luxuriant like a forest, but covered with mosses and lichens and for the most part inaccessible and going to waste; the knowledge of the man of science is like timber collected in yards for public works, which still supports a green sprout here and there, but even this is liable to dry rot.”
—Henry David Thoreau (1817–1862)
“Whilst all the land was ringed with bristling arms
And flames laid waste our world,
All that was left me was a little garden
And thou within it, my beloved, my comrade.”
—Stefan Zweig (18811942)