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: Sea Level
Famous quotes containing the words sea, level, dry and/or land:
“Now I am powerless
to draw back
for the sea is cyclamen-purple,
cyclamen-red, colour of the last grapes,
colour of the purple of the flowers,
cyclamen-coloured and dark.”
—Hilda Doolittle (1886–1961)
“Ambivalence reaches the level of schizophrenia in our treatment of violence among the young. Parents do not encourage violence, but neither do they take up arms against the industries which encourage it. Parents hide their eyes from the books and comics, slasher films, videos and lyrics which form the texture of an adolescent culture. While all successful societies have inhibited instinct, ours encourages it. Or at least we profess ourselves powerless to interfere with it.”
—C. John Sommerville (20th century)
“There is something about poverty that smells like death. Dead dreams dropping off the heart like leaves in a dry season and rotting around the feet; impulses smothered too long in the fetid air of underground caves. The soul lives in a sickly air. People can be slave-ships in shoes.”
—Zora Neale Hurston (1891–1960)
“We grant no dukedoms to the few,
We hold like rights and shall;—
Equal on Sunday in the pew,
On Monday in the mall.
For what avail the plough or sail,
Or land or life, if freedom fail?”
—Ralph Waldo Emerson (1803–1882)