(a) Waves are responsible for modifying the coastal geomorphology. Justify the statement giving suitable examples and neat…

(a) Waves and coastal geomorphology

Coastal geomorphology is predominantly sculptured by wave energy through continuous mechanical action and sediment redistribution. While tides, wind, and river influxes act as secondary agents, waves supply the primary kinetic energy that drives shoreface dynamics. Wave transformation in shallow water governs this evolution: low-energy constructive waves with dominant swash deposit material to build wide berms, whereas high-energy destructive waves with strong backwash erode the coast. As waves encounter irregular coastlines, wave refraction concentrates wave energy on headlands and dissipates it in bays. Concurrently, oblique wave approach generates longshore drift, mobilizing littoral sediment along the shore.

Through hydraulic action, abrasion, and attrition, waves carve distinctive erosional landforms. Headland attack initiates sea caves along structural weaknesses, which breach into sea arches and eventually collapse into isolated sea stacks and stumps (seen along the rocky, headland-and-bay Konkan and Malabar coasts). At the base of cliffs, notch development promotes mass wasting, forming extensive wave-cut platforms. Depositional landforms emerge where refracted wave energy declines; longshore currents construct sand spits, baymouth bars and barrier bars (the bars enclosing Kerala's backwaters, the Chilika spit and Sriharikota island fronting Pulicat Lake), while tombolos tie offshore islands to the mainland, and broad progradational beaches develop, exemplified by Chennai's Marina Beach, which accreted where the harbour breakwaters trap northward littoral drift.

(b) Remote Sensing and GIS in Groundwater Delineation

Remote Sensing (RS) and Geographic Information Systems (GIS) provide a multi-criteria spatial framework to evaluate groundwater potential zones (GWPZ) by integrating hydrogeological surface indicators. Multispectral and microwave sensors (such as Landsat-8/9, Sentinel-1/2, and ASTER DEM) are processed to delineate rock types, structural lineaments (faults, fractures), drainage networks, slope gradients, and land-use/land-cover (LULC) patterns. Lineaments identified from satellite imagery mark zones of enhanced secondary porosity and permeability, while drainage density and digital elevation models indicate surface runoff versus infiltration capacity.

Within the GIS platform, these parameters are converted into thematic raster layers. Using Multi-Criteria Decision Analysis, such as the Analytical Hierarchy Process (AHP), weights and ranks are assigned to each layer based on hydrogeological significance:

GWPI = Σ (Wᵢ × Rᵢ)

where Wᵢ is the layer weight (e.g., lineament density, lithology) and Rᵢ is the internal class rank. The resulting continuous index is categorized into very high, high, moderate, and poor groundwater potential zones. This spatial model is subsequently validated against Central Ground Water Board (CGWB) observation well yields and piezometric head data. In India, NRSC's 1:50,000 groundwater prospects maps prepared under the Rajiv Gandhi National Drinking Water Mission, now served through Bhuvan, apply exactly this approach, and GRACE satellite gravity data add a regional view of groundwater storage change.

(c) Thrust Geometries in Compressional Regimes

In compressional tectonic regimes where maximum principal stress (σ₁) is horizontal, contraction is accommodated by thrust systems comprising sub-horizontal flats along incompetent décollement layers connected by inclined ramps cutting across competent strata.

Kinematic thrust progression yields distinct structural configurations:

1. Imbricate Fan: A series of curved thrust splays branching off a basal decollement and dipping toward the hinterland. If splays terminate upward blindly, it forms a blind imbricate; if they breach the surface, it forms an emergent imbricate fan with a dominant foreland vergence.
2. Duplex Structures: Formed when a package of rock (a horse) is completely bounded by a floor thrust (sole thrust) below and a roof thrust above. As successive horses are accreted, they stack vertically into an antiformal stack or culminations, accommodating high crustal shortening.
3. Triangle Zones and Passive Roof Duplexes: Characterized by conjugate thrusting where a foreland-directed floor thrust interacts with a back-thrust (hinterland-verging passive roof thrust), creating a wedge-shaped zone at the deformation front, as described from foreland fold-thrust belts such as the Canadian Rockies and the Potwar–Salt Range front.
4. Fault-Fold Relationships: As displacement occurs over non-planar fault planes, slip over ramps generates fault-bend folds, whereas fault propagation folding develops ahead of an advancing, blind thrust tip. In the Himalaya these geometries are seen together: the Lesser Himalayan duplex beneath the MCT sheet, imbricate splays of the MBT and MFT, and fault-propagation anticlines in the Siwaliks above the blind frontal thrust.