(a) Elucidate the types of glacier and illustrate the erosional and depositional features produced by the valley-glaciers. (20…

(a) Glaciers and their landforms Glaciers are perennial ice masses that flow under gravity. Valley or alpine glaciers are confined by valley walls and move down a valley; continental ice sheets cover vast areas and flow radially from accumulation centres, controlled more by ice thickness than topography; piedmont glaciers spread out at a valley mouth like a tongue; cirque glaciers occupy bowl-shaped headwalls. In a valley glacier, ice thickens, basal pressure rises, and it deforms internally and slides over bedrock. In an ice sheet, great thickness produces radial flow and subglacial meltwater lubrication, while valley glaciers are channelled and more responsive to local slope. This distinction matters because valley glaciers concentrate erosion in a channel, whereas ice sheets distribute it over a wide area. In India, Gangotri and Siachen illustrate valley glaciers, with cirques, arêtes and U-valleys in the Himalaya.

Erosion is by abrasion, where rock fragments frozen in the ice scratch the bed, and plucking, where meltwater in joints freezes and lifts blocks. Valley-glacier erosional features include cirques, arêtes, horns, U-shaped valleys, roche moutonnée, and striations. A cross-section diagram would show a cirque at the headwall, an arête between cirques, a horn at their intersection, a broad U-valley, a smoothed roche moutonnée, and striated bedrock. Depositional features are moraines, drumlins, eskers, and outwash plains. Terminal moraine marks the snout; lateral moraines lie on the sides; medial moraines form where tributary glaciers meet; ground moraine is buried under the ice. Drumlins are streamlined hills, eskers are sinuous meltwater-channel ridges, and outwash plains are sand and gravel deposited by meltwater beyond the glacier.

(b) Meteorites Meteorites are solid fragments that reach Earth’s surface from space. Most originate from asteroid-belt bodies disrupted by collisions; lunar and Martian meteorites are ejected by impacts. Cometary material can supply meteoroids, but it rarely survives to become meteorites. They are not simply space dust; they are fragments of primitive or differentiated bodies. Compositionally, meteorites are metallic, stony, or stony-iron. Metallic meteorites are mainly Fe-Ni alloys; stony meteorites are silicate-rich; stony-iron meteorites contain significant metal and silicates.

The main classes are chondrites, achondrites, irons, and stony-irons. Chondrites are primitive stony meteorites containing chondrules and often CAIs; they include carbonaceous and ordinary types and preserve early solar-nebula material. Achondrites are igneous, lack chondrules, and come from differentiated parent bodies, including lunar and Martian rocks. Iron meteorites are metallic and show Widmanstätten patterns, likely representing cores of differentiated asteroids. Stony-irons include pallasites, with olivine crystals in a metal matrix, and mesosiderites, which are impact breccias. Diagnosis uses mineralogy, texture, chemistry, and isotopes.

(c) Rock cleavage Rock cleavage is a planar fabric, often produced by aligned minerals or repeated fractures, that allows a rock to split along parallel surfaces. It is different from bedding: bedding records deposition, whereas cleavage records deformation and may cut across bedding. Cleavage is a structural fabric, not merely the cleavage of a single mineral, though mineral alignment controls it. It generally develops perpendicular to the direction of maximum shortening and parallel to the plane of intermediate and minimum stress.

Genetically, cleavage may be fracture or joint cleavage, formed by brittle opening and closing of parallel fractures, or slippage/flow cleavage, formed by ductile slip and mineral reorientation. Slaty cleavage is a low-grade slippage cleavage, fine and perfect. Phyllitic cleavage is intermediate, with a silky sheen and less perfect splitting. Schistose cleavage is higher grade, developed by platy minerals, and splits less readily. Gneissic banding is high-grade compositional layering, not a true cleavage. Diagrams should show: (i) joint cleavage as parallel fractures; (ii) slippage cleavage as aligned mica or chlorite layers; and (iii) a stress ellipse with cleavage perpendicular to maximum shortening.

Together, glaciers, meteorites, and cleavage reveal Earth’s surface processes, solar-system history, and deep deformation.