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Geophysical characterization of the bedrock and regolith in the Pranmati basin critical zone, Uttarakhand Himalaya.

The Earth's critical zone (CZ) is the thin, outermost layer of the planet earth that extends from the top of vegetation to the bottom of groundwater. The study of soil and CZ is a major growing research as its crucial for the aspects like functioning of watershed, crop production and its significance for the sustainability of life on Earth. The Electrical Resistivity Tomography (ERT) survey done at the Pranmati Basin CZO in Uttarakhand has revealed shallow subsurface structure linked to slope variations. Lower Ratgaon site, with a slope <5°, has thicker alluvium (20-25m) than upper Ratgaon (5-7m, slope 15°-20°). Being located at the Baijnath Klippen the compressional tectonic stresses increase bedrock fractures, enhancing water infiltration, facilitating weathering and increased regolith deposition. The study hypothesize that the Bedrock fracture systems facilitate weathering and play a key role on the evolution of deep critical zone.

Horizontal slices of the resistivity image at different depths for the Ratgaon site

Cartoon showing influence of tectonic forces and the subsurface water pathways on the regolith and bedrock 

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