04-BS-14 · May 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams May 2018 — 04-BS-14, Geology. Closed-book, 3 hours; candidates may use only a Casio or Sharp-approved calculator. Four questions constitute a complete exam paper (Questions 1–3 mandatory). On Question 4, per the exam notes only the first four (4) answers as they appear in the answer book are normally marked; all nine (35–43) are answered here as a complete study resource. Total marks for the exam = 100.
Reference texts: Marshak, Earth: Portrait of a Planet (mineralogy, rock textures, Bowen's Reaction Series, structural geology, drainage patterns, glacial/periglacial landforms, plate tectonics, relative dating and unconformities); Goodman, engineering-geology mapping and mass-wasting methods; Freeze & Cherry, Groundwater (Darcy's law, hydraulic head, advective transport).
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.
| # | Item | Answer | Why |
|---|---|---|---|
| 1 | Which is a mafic rock? | c) Basalt | Mafic rocks are Fe/Mg-rich, silica-poor (<52% SiO₂) and dark; basalt is the fine-grained extrusive mafic rock. Granite and rhyolite are felsic; andesite is intermediate. |
| 2 | Furthest south North American glacial advance (end moraine evidence) | d) Southern edge of Illinois | The pre-Illinoian/Illinoian ice sheets pushed as far south as central–southern Illinois (~37–38°N), the southernmost limit of continental glaciation reached in North America — well south of the 49th parallel or the Great Lakes basin. |
| 3 | Seismic wave arrival order after an earthquake | a) P-wave→S-wave→L-wave | P-waves (compressional) travel fastest and arrive first, followed by the slower S-waves (shear), followed by the still-slower surface (Love/Rayleigh, "L") waves, which usually cause the most damage despite arriving last. |
| 4 | One of the three ways a glacier moves over its bed | b) Basal slip | A glacier moves by internal (creep) deformation of the ice, basal sliding (slip) at the ice–bed interface (often lubricated by meltwater), and deformation of a soft subglacial till bed; "frost heaving," "morainal sliding" and "crevassal slip" are not recognized glacier-flow mechanisms. |
| 5 | Most widespread metamorphic rocks exposed at Earth's surface | a) Regional metamorphism | Regional (dynamothermal) metamorphism affects vast belts of crust at convergent plate margins and orogenic belts, producing by far the largest exposed volume of metamorphic rock; contact and hydrothermal metamorphism are localized to the margins of individual intrusions. |
| 6 | Flat-lying strata bent during mountain building | a) Folded anticlines and synclines | Horizontal compression during orogeny buckles originally flat sedimentary/volcanic layers into paired up-folds (anticlines) and down-folds (synclines); horsts/grabens are extensional fault structures, not folds. |
| 7 | Physical removal of weathered rock by wind/water/ice | d) Erosion | Erosion is the entrainment and transport of already-disaggregated or dissolved material away from its weathering site; "ablation" refers specifically to glacial ice/snow loss, and the other options are not standard terms. |
| 8 | Dissolution/decomposition of minerals and rocks | b) Chemical weathering | Chemical weathering breaks down minerals via dissolution, hydrolysis and oxidation, altering their composition; mechanical weathering instead disaggregates rock without changing its chemistry. Hydrolysis is one specific chemical-weathering reaction, not the general term asked for. |
| 9 | Why plutonic (depth-emplaced) rocks are seen at the surface | b) Erosion of overlying rocks due to uplift | Tectonic uplift brings deeply emplaced plutons toward the surface, and prolonged erosion then strips away the overlying country rock to expose the pluton — a slow, continual process, not a catastrophic upheaval or ongoing intrusion. |
| 10 | Principal causes of mechanical fragmentation of in-place rock | d) Biologic activity, expansion from unloading, frost wedging | These are the classic physical-weathering agents that break rock apart in place (root wedging, sheeting/exfoliation from unloading, freeze–thaw); erosion and transport instead move already-fragmented debris away. |
| 11 | Three major chemical weathering processes | a) Dissolution, hydrolysis, and oxidation | These are the fundamental reaction types that alter mineral structure/composition at Earth-surface conditions; the other option lists mix in unrelated or sedimentary/diagenetic processes. |
| 12 | Till landform tied to continental (not alpine) glaciation | b) Drumlin | A drumlin is a streamlined, elongate hill of till moulded beneath a moving ice sheet, and drumlin fields are a hallmark of continental glaciation (e.g. the Peterborough and Guelph drumlin fields of the Laurentide Ice Sheet in Ontario). Moraines are also till, but they form at the margins of alpine and continental glaciers alike, so "not with alpine glaciers" rules them out; a cirque is an alpine erosional hollow and outwash is sorted meltwater sediment, not till. |
| 13 | Most recent Pleistocene glacial episode in North America | a) Wisconsinan | The Wisconsinan glaciation (ending ~11,700 years ago) is the last of the North American Pleistocene ice advances; Kansan is an older, informally-named stage, and "Indianan"/"Dakotan" are not standard glacial-stage names. |
| 14 | Geologic-time interval within Earth's most recent "Ice Age" | b) Pleistocene Epoch | The informal "Ice Age" refers to the Quaternary glaciations, whose glacially active portion is the Pleistocene Epoch (2.58 Ma–11.7 ka); the Proterozoic and Permian had their own, far older glaciations, and the Pliocene predates the main Northern-Hemisphere ice sheets. |
| 15 | Where most crustal deformation occurs | d) Along plate margins | Relative motion between rigid plates concentrates folding, faulting and seismicity at their boundaries; plate interiors are comparatively undeformed and aseismic. |
| 16 | Definition of a syncline | b) A fold in which older flanking strata dip toward the axis | In a syncline the youngest beds occupy the trough at the fold's core while progressively older beds flank it, dipping inward toward the axis — the mirror image of an anticline (older beds central, dipping away from the axis). |
| 17 | Best definition distinguishing a mineral from a rock | c) In a mineral the constituent atoms are bonded in a regular, repetitive, internal structure; a rock is a lithified or consolidated aggregate of minerals | This is the standard pairing: crystallinity (an ordered atomic arrangement) defines a mineral, while a rock is any consolidated aggregate of one or more minerals. |
| 18 | What minerals' constituent atoms/ions are | d) Chemically bonded in a regular crystalline structure | Minerals are defined by a fixed, orderly, three-dimensional atomic arrangement held together by chemical bonding, not by uniform size/charge, one fixed packing geometry, or shared protons. |
| 19 | What silicate igneous rocks make up | b) Bulk of the Earth's crust and mantle | Silicate minerals (feldspars, pyroxenes, olivine, quartz, micas) dominate both the crust and the silicate mantle by volume; the core is metallic (Fe-Ni), not silicate. |
| 20 | Cause of explosive volcanic eruptions | a) Violently escaping gases evolve suddenly to drop the magma density and propel molten magma from the chamber | Explosive eruptions occur when dissolved volatiles (H₂O, CO₂) exsolve rapidly as confining pressure drops, expanding and fragmenting the magma; this is favoured by viscous, gas-rich, silica-rich magmas that trap gas rather than release it passively, unlike fluid basaltic magma at a seafloor vent. |
