Slope Angle Studies From Multibeam Sonar Data on Three Seamounts in Central Indian Basin

Abstract

Abstract: Slope angles are powerful morphometric tools. Slope angle studies in manganese nodule areas using the Multi Beam Sonar (MBS) data is useful to the mining geologist. A technique to convert depth grid generated from MBS data to slope angle values data is presented here. The slope angle grid can be used to create the slope angle map. Morphology of three seamounts from Central Indian Basin and the slope angle data on them are described. The seamounts are of the heights 1000-1200 m and occupy area up to 300 sq kms. The maximum slope angle around the seamounts is 38° with average being 10°. Over 80% of the area around the seamounts will be unmineable because of higher slope angles. Introduction Study of slopes and surface processes has been integral part of the geomorphological studies since the second World War. Slopes provide a basis on which by successive combination into larger units, general geomorphology of an area can be reconstructed. It is an important aspect in establishing relationship between geomorphology and other factors of environment. Just as the study of slopes forms a basis for geomorphological study on land, it can also be effectively carried out on seafloor data. Submarine geomorphology is challenging because of inability to observe things first hand 1 " However, slope angle studies on seafloor data have evoked considerable interest in the last decade. 2, 3,4,. Slope angle maps along with accurate depth contour map are essential for deep sea mining geologist to evaluate the resources and to eliminate unfavorable areas for mining. The path of the mine head has to be predetermined for which a detailed bathymetric and slope angle map of the area is a prerequisite. This study describes the technique for developing slope angle maps from the Multi beam sonar data. Slope Angle Grid Generation With the advent of multibeam system, the quality and the coverage of seafloor area have increased many fold. To generate a depth contour map from multibeam sonar data, the data from different survey lines is merged and a combined grid of depth values is generated. The technique developed for creating a slope angle grid from the depth values grid from HYDROSWEEP system Multibeam swath bathymetric system manufactured by M/s Krupp Atlas Elektronik, Germany (See references5,6 for technical details of the equipment) is briefly described here. The slope angle grid generated from this program can be used for preparing a slope angle map of area or slope profile across the area. The program is developed on EPR 1300 computer but with necessary modifications, it can be used on any computer. The program can also be adopted for land altitude data to create slope angle grids7