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ORIGINAL

Geomorphometric comparison of submarine channel-levee complexes with fluvial river systems: observations from the Indus R. Prerna 1

&

Kotha Mahender 2

Received: 21 October 2019 / Accepted: 7 April 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract An analogy between submarine channels and fluvial rivers has existed for long, especially on the basis of planform and morphometry. Underlying this broad resemblance are the minute disparities that shape and control these systems. In order to observe and quantify the variations between submarine channels and subaerial rivers, we present a first-ever geomorphometric investigation of one single system, where the fluvial river is compared with its offshore counterpart from source-to-sink. With exhaustive data from the submarine fan, parameters like longitudinal profile, width, sinuosity, slope and planform of the Indus Fan channel-levee complex (CLC) are estimated and compared on the basis of the same parameters estimated for the fluvial Indus River. Our new data analyses offers key insights into the variable geomorphometric patterns prevalent from the source of the Indus River until the margins of the submarine Indus Fan. Channel width and sinuosity vary from high-to-low downstream in the submarine system and from low to high in the fluvial basin. Characteristic depositional features of either system are mutually exclusive. Longitudinal profiles of the submarine fan and the river basin do not conform—principally due to the difference in intensity of erosional and depositional processes active in both regions. These differences are primarily attributed to a single-point (canyon-fed) distributary flow and a multi-point (tributary-fed) cumulative flow source system, and density contrasts between river flows and turbidity currents. By quantifying this variation, our attempt is to dissuade the long-standing morphometric analogy between fluvial rivers and submarine channels. Keywords Submarine channels . Fluvial river . Geomorphometric comparison . Indus . Channel-levee complex (CLC)

Introduction Rivers are formed when headwaters flowing downstream gradually gain momentum and converge under the influence of gravity. These headwaters mostly generate from meltwater or springs/lakes and enhance their erosive capability by gaining stream velocity. The process results in the genesis of an expansive stream network with one major channel called as the river. When such sediment-saturated rivers drain into the sea, streams of turbidity currents are often initiated. If the right conditions prevail, these currents, usually denser than the

* R. Prerna [email protected]; [email protected] 1

National Centre for Polar and Ocean Research, Headland Sada, Vasco-da-Gama, Goa, India

2

School of Earth, Ocean and Atmospheric Sciences, Goa University, Taleigao Plateau, Goa, India

ambient flow, could incise the seafloor and deposit coarser sediments at the bottom while forming fine-grained sediment deposits called levees on the channel flanks. The lan