(a) Discuss in detail, with diagrams, the landforms and features resulting from deposition by rivers. (20 marks) (b) Describe…

(a) Landforms and features of fluvial deposition

Rivers deposit sediment where competence and capacity fall, so fluvial landforms record channel energy, sediment supply, and base level. Fluvial deposition. In-channel deposits are dominated by bedload: point bars build on inner meanders, channel bars include longitudinal, transverse and oblique forms in braided or high-energy reaches, and riffle–pool sequences reflect alternating coarse riffles and fine pools. In meandering rivers, lateral erosion and point-bar accretion produce scroll bars and, when a meander neck is cut off, oxbow lakes; in braided rivers, bar migration and channel switching produce braid bars and avulsion surfaces. Overbank deposits are finer: natural levees line channels with sand and silt, crevasse splays radiate where levees breach, and floodplains accumulate mud and organic matter. Floodplain deposits often show fining-upward sequences: sand in levee and splay, silt and mud in backswamp. The diagrams show a meander scroll with abandoned channels and crescentic point-bar deposits, a levee–backswamp section with a crevasse splay, a staircase of terraces as stepped remnants of former floodplains, an alluvial fan with radial distributaries, and fining-upward floodplain deposits. Terraces are primarily erosional remnants of old floodplains, underlain by fluvial deposits, produced when base level falls or tectonic uplift incises the alluvium. Downstream fining occurs because stream power and competence decrease; hydraulic sorting keeps coarse grains in channels and fines on floodplains. Base-level rise causes aggradation, while fall causes incision and terrace formation. Alluvial fans form where gradient drops at mountain fronts; fan dynamics include progradation, avulsion, lobe stacking and fining-upward deposits. The Kosi megafan is a fluvial megafan built mainly by braided river processes, with radial drainage, channel avulsion, lobe progradation and fan surface aggradation, not a debris-flow fan. Deltas are major river deposits at base level, where distributaries split, sediment progrades, and lobes switch; deltaic deposits show progradational clinoforms and coarsening-upward sequences. Delta form depends on the balance of river, wave and tide energy: river-dominated bird’s-foot (Mississippi), wave-dominated arcuate (Nile) and cuspate (Tiber), and tide-dominated estuarine types; the Ganga–Brahmaputra (the world’s largest) and the Mahanadi are India’s best-known deltas. Indo-Gangetic plains illustrate extensive alluvial deposition, terraces, fans and deltas.

(b) Characteristics of Indian remote sensing satellites

The IRS series began with IRS-1A in 1988. Indian satellites fly in near-polar, sun-synchronous low Earth orbits at about 450–900 km, crossing each place at nearly the same local solar time (about 9:30–10:30 a.m.), which keeps illumination and viewing geometry consistent for repeat coverage and change detection. IRS-1C/1D carried LISS-III (23.5 m, 4 bands) and PAN (5.8 m) with a 24-day repeat cycle. Resourcesat-1/2 added LISS-IV (5.8 m) and AWiFS (56 m, 4 bands) for agriculture, soil moisture and wasteland mapping. LISS-III/IV and AWiFS use visible, near-infrared and shortwave-infrared bands. Cartosat-1 is a dedicated stereoscopic satellite (2.5 m) for DEMs; Cartosat-2 (about 1 m) and Cartosat-3 (0.25–0.28 m PAN, about 1.1 m multispectral) are agile high-resolution mapping satellites that can image up to 28 spots per orbit and revisit a chosen scene within days. RISAT-1 (C-band) and RISAT-2 (X-band) SAR provide all-weather data. EOS-04 (RISAT-1A, 2022) continues C-band SAR, and NISAR (NASA–ISRO, launched July 2025) carries L- and S-band SAR to measure ground deformation, landslides and glacier flow. Data are distributed through NRSC and the Bhuvan portal. These sensors support groundwater exploration, flood/drought monitoring, disaster management and land-use mapping.

(c) Normal, strike-slip and thrust faults from the stress ellipsoid

Anderson’s model uses σ1>σ2>σ3 as the stress ellipsoid axes, with σ1 the long axis and σ3 the short axis. The Mohr circle’s centre represents mean stress; failure occurs when it touches the envelope. In a normal fault, σ1 is vertical and σ3 horizontal; the fault plane dips steeply, the Mohr circle touches the failure envelope at relatively low shear stress, and focal mechanisms show extensional quadrants; the rift-bounding normal faults of the Cambay and Godavari basins are Indian examples. In a thrust fault, σ1 is horizontal and σ3 vertical; the fault is a low-angle reverse plane, the Mohr circle is shifted to high normal stress, and focal mechanisms show compression; the Main Boundary Thrust exemplifies this. In a strike-slip fault, σ1 and σ3 are horizontal while the intermediate axis σ2 is vertical; the fault plane is vertical, the Mohr circle plots intermediate normal stress, and focal mechanisms show shear; the dextral Kopili fault of Assam illustrates it. Shear fractures form at about 30° to σ1, in the plane containing σ2, so normal faults dip about 60°, thrusts about 30°, and strike-slip faults are near vertical. In fault-plane solutions, the P (compression) axis is vertical for normal faults, the T (tension) axis is vertical for thrusts, and the N (null) axis is vertical for strike-slip faults. These correspond to divergent, convergent and transform plate settings.