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:
“The moon is door. It is a face in its own right,
White as a knuckle and terribly upset.
It drags the sea after it like a dark crime; it is quiet
With the O-gape of complete despair.”
—Sylvia Plath (1932–1963)
“There are old heads in the world who cannot help me by their example or advice to live worthily and satisfactorily to myself; but I believe that it is in my power to elevate myself this very hour above the common level of my life.”
—Henry David Thoreau (1817–1862)
“In ten thousand years the Sierras
Will be dry and dead, home of the scorpion.”
—Gary Snyder (b. 1930)
“I’m right here to tell you, mister. There ain’t nobody gonna push me off my land. My grandpa took up this land seventy years ago. My pa was born here. We was all born on it. And some of us was killed on it. And some of us died on it. That’s what makes it ourn. Bein’ born on it. And workin’ on it. And dyin’ on it. And not no piece of paper with writin’ on it.”
—Nunnally Johnson (1897–1977)