Question 1 of 3: Part 1 — Multiple Choice

Question 1: Part 1 — Multiple Choice (20 marks)

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.

1.1 — Weathered residue overlying bedrock

Answer: (A) regolith. Regolith is the general blanket of unconsolidated, weathered rock and mineral material -- both residual (formed in place) and locally reworked -- that mantles fresh, unweathered bedrock. Talus is a specific TRANSPORTED accumulation of coarse rockfall debris at a cliff base (a type of colluvium, not the general weathered mantle). Silicrete and calcrete are specific INDURATED (cemented) weathering hardpans -- silica-cemented and calcium-carbonate-cemented respectively -- not the general residual layer itself. Flocs are aggregated fine clay particles formed by ionic clumping in a depositional setting, unrelated to in-situ weathering.

1.2 — Boundary between ablation and accumulation zones

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.

1.3 — Theoretical lower limit of vertical river erosion

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.

1.4 — The most recent glacial period

Answer: (E) Wisconsinan. The Wisconsinan is the most recent North American Pleistocene glacial stage, ending approximately 11,700 years ago at the onset of the Holocene. The Holocene is the CURRENT interglacial (post-glacial) epoch, not a glacial period. Kansan and Nebraskan are OLDER, pre-Illinoian North American glacial stages that precede the Wisconsinan by several full glacial-interglacial cycles. Sangamon is the INTERGLACIAL stage that immediately preceded the Wisconsinan glaciation, not itself a glacial period.

1.5 — Constant minimum discharge

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).

1.6 — Grain size vs. stream velocity

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.

1.7 — Fine sediment deposition in a glacimarine setting

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.

1.8 — Seasonally freeze-thaw zone in permafrost

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.

1.9 — Flat surfaces on pebbles/cobbles

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.

1.10 — Crustal depression and rebound during glacial cycles

Answer: (E) isostacy (isostasy). Isostasy is the local/regional flexural response of the lithosphere to a changing surface load -- the crust is DEPRESSED under the growing mass of an ice sheet and REBOUNDS (uplifts) once that load is removed by deglaciation; this glacio-isostatic adjustment is still measurably ongoing today across previously glaciated Canada (e.g. the Hudson Bay lowlands). Eustasy is the GLOBAL change in sea level from a change in total ocean-water volume -- a water-budget effect, not a crustal deformation. Mass balance is the glacier's OWN accumulation-minus-ablation budget, an internal glaciological quantity rather than a crustal response. Refraction (wave bending) and neap (a tidal range term) are unrelated processes.

1.11 — Effect of channelization

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.

1.12 — Previous interglacial as warm as present

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 (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 Huronian is a Precambrian glacial episode, far older than the Pleistocene cycle the question addresses; the Blancan is a North American Land Mammal Age spanning roughly the late Pliocene to early Pleistocene (~4.75-1.8 Ma), a faunal biostratigraphic stage rather than a climatic interglacial, and it predates the Sangamon/Wisconsinan/Holocene sequence by a wide margin.