18-Geol-B4 Geomorphology and Pleistocene Geology · December 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Geological Engineering, 04-Geol-B4 Geomorphology and Pleistocene Geology, December 2014. Closed book; no calculators or electronic aids permitted. 3 hours, 80 marks: Part 1 is 11 multiple-choice items (any 10 count, 2 marks each, 20 marks); Part 2 is 10 short-essay items (any 8 count, 5 marks each, 40 marks); Part 3 is 4 compulsory point-form items of varying value (20 marks).
Reference texts: Easterbrook, Surface Processes and Landforms, 2nd ed. (weathering, soils, fluvial, coastal and karst geomorphology); Benn & Evans, Glaciers and Glaciation, 2nd ed. (glacier mass balance, glacial erosion/deposition, isostasy); Fulton (ed.), Quaternary Geology of Canada and Greenland, Geological Survey of Canada (Pleistocene glacial history and engineering significance of Canadian surficial deposits); Mollard & Janes, Airphoto Interpretation and the Canadian Landscape (drainage-pattern and terrain interpretation).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Answer: (B) illuviation. In a soil profile, eluviation is the removal (leaching) of fine particles and soluble/colloidal material from an upper horizon (typically the A horizon), and illuviation is the accumulation of that same material lower in the profile (typically the B horizon, e.g. as clay skins, iron/aluminum oxide, or carbonate accumulation). The question describes the receiving, accumulating zone, which is illuviation by definition — the two terms are a matched pair describing opposite ends of the same vertical transfer process.
Answer: (D) the firn line. The firn line (equilibrium line) is the elevation on a glacier's surface at the end of the melt season above which net accumulation (snow input exceeds melt) occurs and below which net ablation (melt exceeds input) occurs; it is the surface trace of the equilibrium line altitude (ELA). The bergschrund is a crevasse at the head of a cirque glacier (a structural feature, not a mass-balance boundary); a dolin (doline) is a karst sinkhole, unrelated to glaciology; the snow limit is a broader climatic concept (the elevation above which snow persists year-round regionally) rather than the specific glacier-surface boundary asked for.
Answer: (C) total relief. The Mohr-Coulomb shear-strength criterion is τf = c' + σn' tanφ', with the effective normal stress σn' = σn − u reduced by pore pressure u; slope angle enters through the infinite-slope form of the driving and resisting stresses. Cohesion (c'), pore pressure (u), and friction angle (φ') are explicit terms, and slope angle sets the geometry of both the driving shear stress and the effective normal stress. "Total relief" (the overall vertical extent of a landscape or slope) is a topographic descriptor, not a term that appears in the Coulomb strength equation itself.
Answer: (A) baseflow. Baseflow is the sustained, slowly-varying component of stream discharge fed by groundwater seepage into the channel; it persists between precipitation/snowmelt events and defines the relatively flat, low portion of a hydrograph, distinct from the sharply peaked stormflow/quickflow response and the recession limb (the falling limb of a single flood peak, not a constant value).
Answer: (B) isostacy. Isostatic (glacio-isostatic) depression is the downward flexure of the lithosphere in response to the mass load of an ice sheet, with compensating post-glacial rebound (isostatic uplift) once the ice is removed — the process responsible for raised marine terraces and emerged shorelines across much of glaciated Canada. Eustacy is a global sea-level change (unrelated to local crustal loading); mass balance is the glacier's own accumulation/ablation budget, not a crustal response.
Answer: (B) the Hjulström diagram. The Hjulström diagram plots critical stream velocity against grain diameter on log-log axes, with separate curves for erosion (entrainment) and deposition (settling); the erosion curve rises again for the finest (clay) sizes because cohesive, densely-packed clay particles resist entrainment despite their small size, while the deposition curve falls monotonically with grain size. This is the standard tool for predicting whether a given flow will erode, transport or deposit a given grain size.
Answer: (D) debris fan: well-sorted silt. Debris fans (alluvial/debris-flow fans at the mouths of steep tributary channels) are characteristically POORLY sorted, matrix-supported mixtures spanning boulders to fines, deposited rapidly by high-energy sediment-gravity flows — the opposite of "well-sorted silt." The other four pairings are correct: abyssal plains accumulate pelagic clay, barchans are wind-formed sand dunes, kames are built of stratified glacifluvial drift, and moraines are composed of unsorted till.
Answer: (A) the active layer. The active layer is the surface layer above perennially frozen ground that thaws each summer and refreezes each winter; its thickness and behaviour (frost heave, thaw settlement, solifluction) are the primary engineering concern in permafrost terrain. Discontinuous permafrost describes a regional distribution pattern (not a seasonal zone), and the firn layer is a glaciological term for compacted, multi-year snow, unrelated to ground ice.
Answer: (D) glacimarine deposits. Flocculation is the clumping of fine clay particles into larger, faster-settling aggregates driven by cation exchange when fresh, sediment-laden meltwater meets saline water; it is therefore most pronounced where a freshwater glacial outflow enters the sea (glacimarine settings). Glacilacustrine (freshwater lake) settings lack the ionic strength needed for strong flocculation, so the marine option is the better answer of the two superficially similar choices.
Answer: (C) karren. Karren (Karst solution grooves/lapies) are sharp, jagged, closely-spaced solution runnels and ridges etched into exposed limestone by acidic rainwater/runoff along joints and bedding planes. Dolins are closed karst depressions (sinkholes); dripstone and travertine are depositional carbonate features (speleothems and spring deposits, respectively); yardangs are wind-eroded ridges in arid terrain, unrelated to limestone dissolution.
Answer: (A) beaches. "Shingle" is the standard term for a coarse gravel/cobble beach deposit, and wave swash/backwash characteristically imbricates ("shingles," like roof tiles) the clasts and organizes them into elongate, shore-parallel, tabular to wedge-shaped beach ridges — exactly the geometry described. Eskers are also linear ridges but are composed of stratified sand and gravel deposited in a subglacial/englacial conduit, not imbricated coarse clasts; debris flows and solifluction lobes produce lobate, poorly-sorted masses rather than shingled linear ridges.
