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:
“If I were as I once was, the strong hoofs crushing the sand and the shells,
Coming out of the sea as the dawn comes, a chaunt of love on my lips,
Not coughing, my head on my knees, and praying, and wroth with the bells,
I would leave no saint’s head on his body from Rachlin to Bera of ships.”
—William Butler Yeats (1865–1939)
“Adults understandably assume that the level of verbal proficiency a five-year-old displays represents his level of proficiency in all areas of functioning—if he talks like an adult, he must think and feel like one. However, five-year-olds,... belie the promise of adult-like behavior with their child-like, impulsive actions.”
—Dorothy H. Cohen (20th century)
“But oh, not the hills of Habersham,
And oh, not the valleys of Hall
Avail: I am fain for to water the plain.
Downward, the voices of Duty call—
Downward, to toil and be mixed with the main,
The dry fields burn, and the mills are to turn,
And a myriad flowers mortally yearn,
And the lordly main from beyond the plain
Calls o’er the hills of Habersham,
Calls through the valleys of Hall.”
—Sidney Lanier (1842–1881)
“The prairies were dust. Day after day, summer after summer, the scorching winds blew the dust and the sun was brassy in a yellow sky. Crop after crop failed. Again and again the barren land must be mortgaged for taxes and food and next year’s seed. The agony of hope ended when there was not harvest and no more credit, no money to pay interest and taxes; the banker took the land. Then the bank failed.”
—Rose Wilder Lane (1886–1968)