Published on: 11/27/2020 2:16:02 AM

Hypsographic/ metric curve was devised by Kossinna and later on modified by Sverdrup in 1942 is a tool of oceanographers to demonstrate the bottom configuration with reference to the sea level. Hypsographic curve refers to a graphical representation used to show the share of the earth's land area that is at various heights above or below sea level.

The curve suggests that most of the earth's land area is located at predominantly two levels. In contrast to the normal distribution curve, the vast majority of the earth's land area is a little over sea level, while a little less, but still considerable, proportion of the remaining land is located at about 5,000 M below sea level. The hypsometric curve has been attributed to the significant difference in the densities of the material that make up the continents and the sea bed.

Hypsographic curve is a double skewed graph which represents 2 variables.

(a) Average elevation above sea level & avg depth

(b) Average Profile of the ocean bottom with reference to their ariel occupancy

X axis has % surface area of the earth, Y axis has average height & depth of the ocean.

The graph connects the highest point on the land with the deepest point in the ocean hence it represents. the average profile of the crust. It is more useful for oceanographers because

(a) Shows average profile of the bottom relief features e.g. - continental shelf / slope / rise, abyssal plains

(b) shows ariel occupancy of the primary relief of the ocean bottom

(c) shows average depth of such reliefs

But it is not much suitable for geomorphologists because it does not show the average profile of continental relief features. This graph also contains a cumulative frequency graph on the Y axis which shows demonstration of continental masses at different altitude and depth below the sea level. This graph can be drawn for a regional sea or at local to global level. It helps in projecting the average profile of the ocean. which can be used by navigators, oceanic researchers.

The Curve and the isostatic control

The nature of the hypsographic curve representing the height of land and the depth of sea can be explained when we consider the densities of the rocks which constitute the earth. Thus, curve demonstrates the efficacy of isostatic control by assuming Airy's theory of isostatic compensation and density difference of continental and oceanic rocks. The abundance of silica, sodium and potassium, aluminium, silicates are found in the continental rocks, with an average density of 2.72 to 2.81 gms per cm3 and the abundance of the iron, calcium and magnesium elements are present in oceanic rocks with the average density of more than 2.81 gm. per cm3. The application of this concept proves the particular accentuated nature of the curve, otherwise, "we shall have to presume that all the highest chains are today maintaining their altitude by unexhausted tangential compression, and the exceptional sagging of the oceanic deeps, their depth, by persistent tension, which is rather unlikely"