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The hydrologic cycle is the continuous, solar- and gravity-driven circulation of water between the ocean, atmosphere and land. Solar heating drives evaporation of ocean and land-surface water into vapour, supplemented by transpiration from plants (together "evapotranspiration"). As moist air rises and cools — often forced upward over mountains — water vapour undergoes condensation into cloud droplets, which grow and fall as precipitation (rain or snow). Reaching land, precipitation either becomes surface runoff, flowing downslope through streams back to the ocean, or infiltrates into the soil and rock, becoming groundwater that flows slowly (governed by Darcy's law) through the subsurface, eventually discharging to streams, springs, wetlands, or directly to the ocean. Water is temporarily stored as snow/ice, in lakes, or as groundwater, but over hydrologic timescales the system is a closed loop with no net gain or loss of water.

37. Three types of glaciers

Alpine (valley) glaciers form in mountainous terrain and flow down a pre-existing river valley from a high-elevation accumulation zone (often a cirque); they are relatively small, are topographically confined by the valley walls, and carve distinctive U-shaped valleys, cirques, arêtes and horns. Continental ice sheets are vast, sub-continental-scale domes of ice (e.g. Antarctica, Greenland, or the former Laurentide Ice Sheet) that bury pre-existing topography entirely and flow outward from a thick central dome under their own weight, independent of underlying valleys; they produce regional-scale erosional and depositional landscapes (till plains, drumlin fields, outwash plains). Piedmont glaciers form where one or more alpine glaciers emerge from confining mountain valleys onto an adjacent lowland and spread out into a broad, fan-shaped lobe (e.g. the Malaspina Glacier, Alaska) — confined upstream like an alpine glacier but unconfined and spreading like an ice sheet downstream.

38. Glacial erosional and depositional features

Erosional features (produced by abrasion and plucking): Cirques, amphitheatre-shaped hollows carved at the head of an alpine glacier by rotational plucking and abrasion; arêtes and horns, knife-edge ridges and pyramidal peaks left where cirques on opposing sides of a divide erode headward toward each other; U-shaped (glacial trough) valleys, formed as a glacier widens and deepens a former V-shaped stream valley, truncating interlocking spurs.

Depositional features (produced where the glacier or its meltwater deposits sediment): Moraines (terminal, lateral, ground), ridges or blankets of unsorted till marking a former ice margin, side, or base; drumlins, streamlined, elongated hills of till moulded parallel to ice-flow direction beneath moving ice; eskers, sinuous ridges of stratified sand and gravel deposited in subglacial or ice-marginal meltwater tunnels.

39. Bowen's Reaction Series

Bowen's Reaction Series (N.L. Bowen) describes the order in which silicate minerals crystallize from a cooling, differentiating basaltic magma, along two parallel branches that converge at low temperature. The discontinuous branch consists of distinct ferromagnesian (Fe/Mg-bearing) mineral species crystallizing in sequence, each reacting with the remaining melt to form the next: olivine → pyroxene → amphibole → biotite mica, each step an abrupt change in crystal structure. The continuous branch consists of plagioclase feldspar, crystallizing continuously across the same temperature range but with smoothly changing composition — from Ca-rich (anorthite) at high temperature to Na-rich (albite) at low temperature, as Ca²⁺ is progressively replaced by Na⁺ in the lattice. Both branches converge at low temperature in the final minerals to crystallize: K-feldspar, muscovite mica, and finally quartz, the last mineral to form. The series predicts crystallization order (and hence igneous textures such as zoned plagioclase) in a cooling magma, and — because minerals crystallizing further from surface conditions are also chemically least stable there — it parallels the Goldich weathering-stability series: olivine weathers fastest, quartz slowest.

40. Four types of volcanoes

Shield volcanoes are broad, gently sloping domes built almost entirely of low-viscosity basaltic lava flows (e.g. Mauna Loa); fluid, gas-poor magma produces predominantly effusive rather than explosive eruptions. Composite volcanoes (stratovolcanoes) are tall, steep-sided cones built of alternating layers of viscous, intermediate-to-felsic (andesitic–dacitic) lava flows and explosive pyroclastic material (e.g. Mount Fuji, Mount St. Helens); higher-viscosity, gas-rich magma produces episodic explosive eruptions between lava flows, making these the most hazardous volcano type. Cinder cones are small, steep, conical hills of loose pyroclastic fragments (cinders/scoria) ejected from a single vent during a short-lived, moderately explosive eruption of gas-rich basaltic–andesitic magma; they are the simplest, shortest-lived volcano type. Lava domes form when highly viscous, silica-rich (rhyolitic–dacitic) magma is too stiff to flow far and instead piles up over the vent as a bulbous mass; trapped gas makes lava domes prone to sudden, violent collapse and explosive pyroclastic flows.

41. Permafrost profile and seasonal temperature–depth graph

A permafrost profile has three zones. The active layer is the near-surface zone that thaws each summer and refreezes each winter; its thickness (typically decimetres to a few metres) is set by the depth to which the summer warm wave penetrates. Below it, the permafrost table marks the top of the permafrost proper — ground that remains at or below 0°C continuously for at least two consecutive years — which extends down to the depth where the geothermal heat flux from below finally warms the ground back above 0°C, the base of permafrost. Below that lies ordinary unfrozen ground, following the normal geothermal gradient. On a temperature–depth graph, the summer curve is warm (above 0°C) at the surface and cools with depth, crossing 0°C at the base of the active layer; the winter curve is very cold at the surface and warms with depth; the two curves converge at the depth of zero annual amplitude (typically 10–20 m) on the mean annual ground temperature, which is below 0°C. Below that depth a single curve follows the geothermal gradient, warming steadily to 0°C at the base of permafrost.

42. Distinguish the following (2 marks each)

a. Joints and faults. A joint is a fracture in rock along which there has been no measurable displacement parallel to the fracture surface; a fault is a fracture (or fracture zone) along which the two sides have moved measurably relative to one another. Both form from brittle failure under stress, but a fault represents accommodated shear displacement, while a joint is purely an extensional/dilational break.

b. Unconformity and non-conformity. An unconformity is a general term for any buried erosional surface representing a gap in the rock/time record; a nonconformity is one specific type of unconformity, in which sedimentary rock rests directly on eroded igneous or metamorphic (crystalline) basement rock. (The other specific types are disconformity — parallel sedimentary-over-sedimentary — and angular unconformity — horizontal-over-tilted/folded sedimentary.)

c. Polymorphic and isomorphic. Polymorphism describes two or more minerals sharing the identical chemical composition but crystallizing in different structures (e.g. diamond and graphite, both pure carbon). Isomorphism describes minerals with different but chemically similar compositions that share the same crystal structure and can substitute for one another in a solid-solution series (e.g. the olivine series, forsterite Mg₂SiO₄ to fayalite Fe₂SiO₄, where Mg²⁺ and Fe²⁺ freely substitute).

d. Elastic and plastic strain. Elastic strain is temporary and fully recoverable — the material returns to its original shape when the stress is removed (Hooke's-law regime). Plastic strain is permanent deformation that remains after the stress is removed, occurring once the material's elastic (yield) limit has been exceeded and it flows rather than fractures.

e. Dyke and sill. A dyke (dike) is a tabular igneous intrusion that is discordant — it cuts across the existing layering/foliation of the host rock. A sill is a tabular igneous intrusion that is concordant — it is injected parallel to, and follows, the existing bedding or layering of the host rock.

43. Groundwater travel time and piezometric pressure beneath a landfill

Approach. Compute the hydraulic gradient from the two water-table elevations, use Darcy's law for the specific discharge, divide by porosity to get the average linear (seepage) velocity that actually carries a solute, then divide the travel distance by that seepage velocity. For part (b), treat the water table (210 m) as the constant hydraulic head at the landfill location and apply h = z + u/γ_w at the piezometer intake elevation.

1. Hydraulic gradient. $i = \dfrac{\Delta h}{L} = \dfrac{210 - 203}{1500\ \text{m}} = 4.667\times10^{-3}$ (dimensionless).
2. Darcy (specific discharge) velocity. $v = -Ki \Rightarrow |v| = (5\times10^{-4}\ \text{m/s})(4.667\times10^{-3}) = 2.333\times10^{-6}\ \text{m/s}$.
3. Seepage (average linear) velocity. $v_s = \dfrac{v}{n} = \dfrac{2.333\times10^{-6}}{0.30} = 7.778\times10^{-6}\ \text{m/s}$ — this is the actual average speed of water (and an advected solute) moving through the pore space.
4. Travel time. $t = \dfrac{L}{v_s} = \dfrac{1500\ \text{m}}{7.778\times10^{-6}\ \text{m/s}} = 1.929\times10^{8}\ \text{s}$. Converting: $t = \boxed{6.11\ \text{years}}$ (using 1 yr = 3.1558×10⁽\ s).
5. Piezometric pressure. Treating the water table (210 m) as the hydraulic head h at the landfill and applying $h = z + u/\gamma_w$ at the piezometer intake ($z=205$ m): $u = \gamma_w(h-z) = (9.81\ \text{kN/m}^3)(210-205\ \text{m}) = \boxed{49.05\ \text{kPa}}$.