Hypsometry

Abstract: The interaction between tectonism and erosion produces rugged landscapes in actively deforming regions. In the northwestern Himalaya, the form of the landscape was found to be largely independent of exhumation rates, but regional trends in mean and modal elevations, hypsometry (frequency distribution of altitude), and slope distributions were correlated with the extent of glaciation. These observations imply that in mountain belts that intersect the snowline, glacial and periglacial processes place an upper limit on altitude, relief, and the development of topography irrespective of the rate of tectonic processes operating.

Abstract: The frequency distribution of depths in ocean basins has been determined using the most recent American and Russian oceanographic charts as sources and a computer for data processing. Data have been complied for individual ocean basins and marginal seas, and also for nine different physiographic provinces, including, for example, ‘ocean basin,’ ‘rise and ridge’ and ‘continental shelf and slope.’ The summary result differs little from a hypsometric curve drawn by Murray and Hjort in 1912. Considering both land and sea, by far the most common levels are approximately at sea level and at about 5 km, the general depth of ocean floor. The compilation by physiographic provinces leads to a new understanding of the hypsometric curve, even though it does not change the shape. The distribution of depths in the ocean basin province is singly peaked and symmetrical. The distribution in the rise and ridge province is similar, but the mean depth is about 1 km less. This can be interpreted as indicating that one province is merely the elevated equivalent of the other, a conclusion which generalizes the field observation that some localized oceanic rises and ridges are formed by ephemeral bulges in the mantle under a normal oceanic crust. Most occurrences of depths between sea level and the deep sea floor have been produced by the formation of rises and ridges rather than by the deposition of sediment derived from continents. The development and collapse of rises and ridges may have caused substantial fluctuations in sea level during geological time.

Abstract: Hypsometry has historically been used as an indicator of geomorphic form of catchments and landforms. Yet there has been little work aimed at relating hypsometry to landform process and scale. This paper uses the SIBERIA catchment evolution model to explore linkages between catchment process and hypsometry. SIBERIA generates results that are qualitatively and quantitatively similar to observed hypsometric curves for physically realistic parameters. However, we show that not only does the hypsometry reflect landscape runoff and erosion process, but it is strongly dependent on channel network and catchment geometry. We show that the width to length ratio of the catchment has a significant influence on the shape of the hypsometric curve, though little on the hypsometric integral. For landforms dominated by fluvial sediment transport, the classic Strahler ‘mature’ hypsometric curve is only generated for catchments with roughly equal width and length. Narrow catchments show a hypsometric curve more similar to Strahler's ‘monadnock’ form. For landscapes dominated by diffusive transport, the simulated hypsometric curve is concave-down everywhere, this being consistent with curves reported for some example catchments in France. Because the transition between diffusive dominance to fluvial is scale-dependent, with larger catchments exhibiting greater fluvial dominance, then the hypsometric curve is a scale-dependent descriptor of landforms. Experimental results for simulated landforms from a small-scale rainfall-erosion simulator are reported. It is shown that SIBERIA yields satisfactory fits to the data, confirming its ability to predict the form of the hypsometric curve from a simple model of geomorphic processes. © 1998 John Wiley & Sons, Ltd.