18-Geol-B4 Geomorphology and Pleistocene Geology · December 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Geological Engineering, 04-Geol-B4 Geomorphology and Pleistocene Geology, December 2017. Closed book; no calculators or electronic aids permitted. 3 hours, 80 marks: Part 1 is 12 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: (A) eluviation. A pedafer (a soil order dominated by iron/aluminum sesquioxides and clay rather than calcium carbonate, typical of humid climates) has its A horizon as the zone from which fine particles and soluble/colloidal material are washed downward — the removal process is eluviation. Illuviation is the matched opposite process, the ACCUMULATION of that same material lower in the profile (typically the B horizon), so it names the receiving zone, not the source zone the question describes.
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 regional climatic concept rather than the specific glacier-surface boundary asked for.
Answer: (B) base level. Base level is the lowest elevation to which a stream can theoretically erode its bed — ultimately sea level for a stream draining to the ocean, or a local base level such as a lake or a resistant rock sill for a tributary or interior stream. As a channel profile approaches base level, gradient and stream power fall toward zero and vertical incision effectively ceases, leaving lateral (meandering) processes to dominate. Baseflow and recession limb are hydrograph terms (about discharge over time, not erosional limit), and "competence" describes the largest particle size a stream can move, not an elevation limit.
Answer: (E) total relief. The Mohr-Coulomb shear-strength criterion for slope stability is τf = c' + (σn − u)tanφ', where the effective normal stress σn' = σn − u is reduced by pore pressure u. Normal stress, pore pressure, cohesion (c') and friction angle (φ') are all explicit terms in the equation. "Total relief" (the overall vertical extent of a landscape) is a topographic descriptor that does not itself appear in the strength criterion.
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 response and from the recession limb (the falling limb of one particular flood peak, not a steady minimum value).
Answer: (C) 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) flocculation. Flocculation is the clumping of fine clay particles into larger, faster-settling aggregates, driven by cation exchange when fresh, sediment-laden glacial meltwater mixes with saline seawater; it is therefore the dominant depositional process for fine-grained sediment in glacimarine environments. Terminal settling and siltation describe simple gravitational settling without the ionic aggregation mechanism, saltation is a bedload transport mode (not a fine-sediment depositional process), and eluviation is a soil-horizon leaching process unrelated to marine sedimentation.
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: (B) facets. Facets are the flat, planar surfaces ground onto a clast (commonly by glacial abrasion against the ice/bed interface, or by wind abrasion in a desert pavement) as one face is worn against a fixed abrading surface; a clast with several such planar faces meeting at edges is described as faceted. Loess (wind-blown silt) and tillite (lithified till) are sediment/rock types, not clast-surface features, and "stosses" refers to the streamlined stoss-and-lee form of a whole outcrop or landform, not a pebble-scale facet.
Answer: (E) eustacy. Eustacy (eustatic sea-level change) is a GLOBAL change in sea level caused by a change in the total volume of water held in the ocean basins (glacio-eustasy: water locked up in growing ice sheets during glacials, released during interglacials) or a change in ocean-basin capacity; because it reflects the total ocean-water budget it is felt worldwide. Isostacy (isostasy), by contrast, is a LOCAL/regional crustal response to loading (e.g. subsidence under an ice sheet, rebound after it melts) and does not by itself change the global sea-surface volume.
Answer: (C) increased downstream erosion. Channelization (straightening, deepening, lining or otherwise engineering a natural channel, typically for flood control or drainage) shortens the channel and steepens its gradient, which increases flow velocity and stream power; because the channel now carries the same water and sediment load faster and with more energy, the reach immediately downstream of the channelized section experiences increased erosion (channel incision, bank erosion, headward-migrating knickpoints) as the stream adjusts toward a new equilibrium profile. It does not typically create distributaries or wadis (both are unrelated landform outcomes), and it increases — not reduces — the erosive/transport capacity delivered downstream.
Answer: (D) Sangamon. The Sangamon interglacial (the North American term, correlative with the European Eemian) was the interglacial stage immediately preceding the Wisconsinan glaciation, and paleoclimate proxies (e.g. deep-sea oxygen-isotope records, fossil pollen assemblages) indicate its temperatures were comparable to, or slightly warmer than, the present (Holocene) interglacial. The Wisconsinan is the most recent GLACIAL stage, not an interglacial; the Holocene is the CURRENT interglacial, not the "previous" one; the Cordilleran refers to the western North American ice-sheet complex (a glacial-source region, not a time period); the Huronian is a Precambrian glacial episode, far older than the Pleistocene glacial-interglacial cycle the question addresses.
