A hypsometric curve is the one which represents the histogram of the elevations in a given geographical area or location. The histogram of the hypsometric curve is a cumulative distribution function of the land elevations (altitude or depth) with respect to a reference point. This curve shows such a distribution with two maxima where one represents the land elevations of altitude i.e. elevations above the sea level and the other one represents the elevations of the depth i.e. the elevations below the sea level. The below diagram shows a two-dimensional hypsometric curve with the bimodal distribution i.e. hypsometric curve with two peaks.
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Hypsometry and Hypsometric Curve
Hypsometry is the measurement of the land elevations which is relative to the sea level. The representation of such a measurement is the hypsometric curve. The hypsometric curve defines the elevations of the earth’s surface in the form of cumulative distribution. And the graph given above in the form of a two-dimensional histogram shows the elevation on the vertical y-axis and the area above the corresponding elevation is shown on the x-axis. It is clearly visible from the figure that the hypsometric curve is the cumulative height frequency curve of the Earth’s surface. Thus, in simple terms hypsometry is the calculation or the measurement of the land elevations and the hypsometric curve is the graphical representation of the frequency distributions (cumulative) of the elevations of the earth’s surface.
A hypsometric curve calculation plots the relative area against the relative height to show the land area that exists at different points of elevation on the surface of the earth. The elevations on the earth can be either positive or negative depending on the elevation point either being measured in terms of altitude above the sea level or the depth below the sea level. Hence, because of this the hypsometric curve calculation delivers a graph or histogram with two local maximum values. So, the representation is bimodal showing the two maximum values on land surface and beneath the sea. This is different from the surface on other planets of the solar system where the hypsometric curve calculation shows typical unimodal properties. The unimodal properties are because there are no oceans on the surface of other planets of the solar system or any such significant water bodies.
As is clear from the given definitions, hypsometry is the measurement of the high risen or highly deep points on the earth surface and hypsometry is the graphical representation of the same. As clearly visible, the hypsometric curve gives two humps of maxima in the cumulative distribution of elevation in Earth’s surface, one at 100 metre and another at 4700 metres which indicate the correlations with the mean level of the lowland continental areas and the deep sea-floor. The interesting thing about the hypsometric analysis of Earth’s surface is that it supports the theory that the crust of the Earth’s surface consists of simatic materials under the ocean and of sialic materials above the ocean i.e. the surface of the continents.
The elevation of the Earth’s crust in the form of histogram is shown below in the given diagram:
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The hypsometric curve when required to be represented in a non-dimensional or standardized form can be represented by scaling the elevation and the area by the maximum values. The hydrologists or geomorphologists can find a way to understand and assess the similarity of the watersheds from the non-dimensional hypsometric curve, which is one of the several characteristics that the curve is used to understand. The hypsometric integral is the summary of the shape of the hypsometric curve. Hence, the hypsometric integral is a terrain analysis factor reflecting from the landform erosion stage.
The curve has three parameters to fit the different hypsometric relations, as described by Arthur Strahler:
y = [((d-x)/x).(a/(d-a))]x
In the given equation, a, d and z are the mentioned fitting parameters. The research using the two-dimensional landscape models has been called the general applicability fitting to fit into the equation as well as the capability of the curve in dealing with scale-dependent effects.
The hypsometric curves are usually commonly used in limnology. In limnology, the relationship between the surface area of the lake and the depth is represented by the curve and is used to calculate the total lake volume. The graphs of the curve will be used to predict other different characteristics of the lakes like productivity, dilution of the incoming chemicals and the potential mixing for the water.
From the given article a sufficient amount of information is provided for the hypsometry and hypsometric curve. The hypsometric curve is the graph showing the cumulative frequency distribution of the elevation points on Earth’s surface on both the land above the sea level and on the surface below the sea level. Thus, in conclusion, a hypsometric curve is a graph which shows two peaks of local maxima representing the elevation distribution in terms of altitude above the point of reference and the elevation distribution in terms of the depth below the point of reference.