Investigation of Flexural bulge of the Indian Plate for Controls on
Landscape Evolution
Abstract
The morphology of a river channel is driven by multiple forcing factors
that can be either external or internal. The internal factors, such as
the variation in rock strength, lineament orientation, and fracture
density can be an impelling force in the landscape evolution of a slow
uplifting terrain. The spatial variation in the internal factors may
result in heterogeneity in fluvial erosion rates, which may produce
false signals of active tectonics in a terrain. The Himalayan orogeny
has resulted in an upward flexure in the Indian crust known as a
peripheral forebulge. The uplifted Vindhayan plateau is proposed as the
depiction of this flexure. The bending of the Indian plate has resulted
in the generation of tensile forces in this area. These forces have
resulted in the formation of large-scale lineaments, which are roughly
aligned parallel to the axial plane of the forebulge. This study
highlights the role of lineaments, rock strength, and fluvial
erodibility in the tectonics of forebulge. We used N-type Schmidt hammer
to measure the intact rock strength of lithologies met in the Vindhayan
plateau. We calculated the Normalized steepness index (Ksn) to assess
the fluvial erodibility of the channels. We calculated swath profiles
and local relief distribution to understand topographic variation.
Further, we looked at the knickpoint distribution and tried to correlate
it with major lineaments and lithological boundaries. Finally, we tried
to understand the relationship between the lineament distribution and
regional tectonics of the forebulge. We find that there is a significant
difference in fluvial erodibility between the weakest and strongest
lithologies. We observed that the lineaments act as the conduits for
rapid erosion and knickpoint formation. The Ksn values are relatively
high where we encountered the hard lithologies, resulting in the
formation of vertical knickpoints (waterfalls). We have observed a
correlation between, Rock strength variation, topographic relief,
knickpoints, and Normalized steepness index. Our results suggest that
spatial variation in rock strength and lineament pattern is playing a
crucial role in the landscape evolution of the Vindhayan plateau. We
finally propose a model to relate lineament orientations and
lithological variations with slow uplift of the forebulge.