04-BS-14 · May 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams May 2017 — 04-BS-14, Geology. Closed-book, 3 hours; candidates may use only a Casio or Sharp-approved calculator. Three questions constitute a complete exam paper (Questions 1–3 mandatory). On Question 3, per the exam notes only the first two (2) answers as they appear in the answer book are normally marked; all eight (65–72) are answered here as a complete study resource. Total marks for the exam = 100.
Reference texts: Marshak, Earth: Portrait of a Planet (relative dating, unconformities, plate tectonics, glacial and fluvial landforms, mass wasting, mineralogy, rock textures, Bowen's Reaction Series, volcanoes); Goodman, engineering-geology mapping methods; Freeze & Cherry, Groundwater (permeability/porosity context for weathering and drainage).
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 | Instantaneous fault displacement during earthquakes | c) Several meters | Coseismic slip on a single rupture typically spans decimetres to a few metres (up to ~10–20 m in the very largest megathrust events); millimetre-scale motion describes interseismic creep, and kilometre-scale offsets describe cumulative geologic-time displacement, not one earthquake. |
| 2 | Most recent Pleistocene glaciation in North America | a) Wisconsin | The Wisconsinan (Wisconsin) glaciation, ending ~11,700 years ago, is the last of the North American Pleistocene glacial stages; Kansan, Nebraskan and "Dakotan" name older/earlier (or non-standard) advances. |
| 3 | Geologic period within Earth's most recent "Ice Age" | b) Pleistocene Epoch | The informal "Ice Age" refers to the Quaternary glaciations, of which the Pleistocene Epoch (2.58 Ma–11.7 ka) is the glacially active portion; the Proterozoic and Permian are far older eras with their own separate glaciations, and the Pliocene predates the main Northern-Hemisphere ice sheets. |
| 4 | Where most crustal deformation occurs | d) Along plate margins | Plate boundaries concentrate the relative motion between rigid plates, so nearly all folding, faulting, seismicity and mountain building is localized there; plate interiors are comparatively aseismic and undeformed. |
| 5 | Stress causing folding of flat-lying strata | d) Horizontally directed, compressive stresses | Folding shortens and thickens a rock layer, which requires horizontal shortening — i.e. compression; extensional (stretching) stresses instead produce normal faulting and thinning, not folds. |
| 6 | How elastic deformation differs from plastic/brittle | d) It is reversible/recoverable; rocks snap back when stress is removed | Elastic strain is, by definition, fully recovered on unloading (Hooke's law regime); plastic strain is permanent, and brittle failure fractures the rock — neither reverses. |
| 7 | Conditions favouring brittle over plastic deformation | b) Cooler temperatures and low confining pressure | Brittle fracture dominates near the surface where low temperature and low confining pressure prevent crystal-plastic flow mechanisms from operating; high temperature/pressure at depth instead favours ductile (plastic) behaviour. |
| 8 | When permanent rock deformation occurs | a) Once its elastic limit is surpassed | Below the elastic (yield) limit strain is fully recoverable; once stress exceeds it, the rock accumulates permanent plastic or brittle strain. This is a material-strength threshold, unrelated to lithification state or plate-margin location. |
| 9 | Conditions for ductile deformation | a) Great depth, high confining pressure, low strain rates or prolonged strain | High temperature and pressure (both increasing with depth) plus slow/sustained strain allow crystal-plastic mechanisms (dislocation glide/creep, recrystallization) to accommodate strain smoothly; shallow, cold, rapidly strained rock instead fractures. |
| 10 | 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 (core) and the older, flanking beds dip inward toward the axis — the mirror image of an anticline, where the older beds are central and dip away from the axis. |
| 11 | Best definition of mineral vs. rock | c) In a mineral atoms are bonded in a regular, repetitive structure; a rock is a lithified aggregate of minerals | This is the standard textbook pairing: crystallinity (ordered atomic structure) defines a mineral, while a rock is any consolidated aggregate of one or more minerals (or mineraloids/glass). |
| 12 | 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, a single packing geometry, or shared protons. |
| 13 | What silicate igneous rocks make up | b) The 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. |
| 14 | Cause of explosive volcanic eruptions | a) Violently escaping gases drop magma density and propel magma from the chamber | Explosive eruptions occur when dissolved volatiles (mainly H₂O and CO₂) exsolve rapidly as pressure drops, expanding violently and fragmenting/propelling the magma; this is favoured by viscous, silica-rich magmas that trap gas rather than let it escape passively. |
| 15 | Principal causes of mechanical fragmentation in place | d) Biologic activity, expansion from unloading, frost wedging | These are the classic physical (mechanical) weathering agents that break rock without changing its chemistry, acting where the rock sits; erosion/transport instead move already-fragmented material away. |
| 16 | Three major chemical weathering processes | a) Dissolution, hydrolysis, and oxidation | These are the fundamental chemical reactions that alter mineral structure/composition (dissolving soluble minerals, breaking silicate bonds with water, oxidizing Fe/Mn-bearing minerals); the other lists mix in physical/sedimentary processes. |
| 17 | Main direct geologic effect of glaciers | c) Erode the continental landscape and transport/deposit sediments | Glaciers are geomorphic agents: they scour and pluck bedrock (erosion) and carry that debris to be deposited as till/outwash; they do not directly raise sea level by depressing crust or reduce marine productivity. |
| 18 | Alpine glacier motion and sediment load vs. streams | d) Very much slower; vastly more | Glacial ice flows at metres–to–tens-of-metres per year, orders of magnitude slower than stream flow, yet ice can entrain and carry boulders and till loads (by volume and clast size) far exceeding what a stream of comparable cross-section can transport. |
| 19 | Where abrasion and plucking occur in a glacier | d) The basal, sliding zone | Erosion requires the ice to be in contact with and moving over bedrock, which happens at the base where sliding occurs; the surface brittle zone and internal flow zone do not touch the substrate. |
| 20 | Erosional feature specific to alpine glaciation | b) U-shaped valley | Alpine glaciers widen and deepen pre-existing V-shaped stream valleys into a characteristic U-shaped cross-section; kames and lateral moraines are depositional, not erosional, features. |
| 21 | Definition of a fjord | c) A stream valley deepened by glacial erosion, that floods as sea level rises | A fjord is a glacially over-deepened valley (originally fluvial) later inundated by the sea (or by isostatic subsidence plus eustatic rise); option (a) reverses the mechanism (glacial rebound raises land, it does not sink a valley). |
| 22 | Definition of glacial drift | b) The sedimentary materials outwash and till | "Drift" is the umbrella term for all sediment deposited directly or indirectly by glacial ice — till (unsorted, ice-deposited) and outwash (sorted, meltwater-deposited) together, not a flow process or advance. |
| 23 | False statement about glacial deposits | d) "Glacial erratics are blocks too large for the glacier to move" — FALSE | Erratics are, by definition, transported by the glacier (sometimes over great distances) and deposited far from their bedrock source; the statement's premise contradicts the definition. (a), (b) and (c) are all accurate. |
| 24 | What drumlin fields contain | d) Smooth, tapering, asymmetric ridges of till shaped beneath a continental ice sheet | Drumlins are streamlined till landforms with a blunt, steep stoss (up-ice) end and a tapering lee end, moulded subglacially by moving ice — not meltwater mounds, striated bedrock, or plucked depressions. |
| 25 | Description that does NOT apply to stratified drift | d) "Rock flour deposited directly from advancing ice" | Material deposited directly from ice (unsorted, unstratified) is till by definition; stratified drift is, by contrast, sorted and layered sediment reworked by meltwater — (a)–(c) all correctly describe it. |
| 26 | Former meltwater channel filled with sand and gravel | b) Esker | An esker is a long, sinuous ridge of stratified sand and gravel that fills a former ice-walled or subglacial meltwater tunnel, left standing in relief after the surrounding ice melts. |
| 27 | Pleistocene features significantly larger than today | b) The Great Lakes and Lake Agassiz | Meltwater ponded against retreating ice sheets formed proglacial lakes far larger than today's Great Lakes, including glacial Lake Agassiz (once the largest lake in North America, now largely drained); alpine cirques/horns and moraine belts were active but not "larger" in this sense, and fan deltas were not more extensive. |
| 28 | Best way to determine the age of a pre-Cambrian rock | b) Radioactive dating | Pre-Cambrian rocks (>541 Ma) predate virtually all index fossils and any carbon-14-datable organic material (useful only to ~50,000 years); long-lived radiometric systems (U-Pb, K-Ar, Rb-Sr) are the only method reaching billion-year ages. |
| 29 | Which rock is mafic | c) Basalt | Mafic rocks are Fe/Mg-rich, silica-poor (<52% SiO₂) and dark-coloured; basalt is the fine-grained extrusive mafic rock. Granite and rhyolite are felsic; andesite is intermediate. |
| # | Statement | Answer | Why |
|---|---|---|---|
| 30 | Pangaea evidence: continent fit, matching fossils/mountain chains separated by oceans, southern-hemisphere glaciated rocks | TRUE | These are exactly Wegener's classic lines of evidence for continental drift/Pangaea, later explained mechanistically by plate tectonics. |
| 31 | Earth's magnetic field polarity has reversed at various times in the past | TRUE | Magnetic reversals are recorded as symmetric striping in oceanic crust on either side of mid-ocean ridges and form the basis of the geomagnetic polarity timescale used to date the seafloor. |
| 32 | Continents "plow through" thinner ocean lithosphere like icebreakers, pushing it out of the way | FALSE | This describes the outdated pre-plate-tectonics "continental drift" mechanism. In plate tectonics, continental and oceanic lithosphere move together as parts of the same rigid plate; continents do not independently plow through separate oceanic crust. |
| 33 | Continental crust is generally less dense than oceanic crust | TRUE | Continental crust is felsic (~2.7 g/cm³, granitic), oceanic crust is mafic (~3.0 g/cm³, basaltic/gabbroic) — the density contrast is why continents "float" higher and why oceanic crust preferentially subducts. |
| 34 | Seafloor sediments gradually thicken away from a mid-ocean ridge | TRUE | Seafloor age increases with distance from the spreading ridge, so sediment has had progressively longer to accumulate on older crust — sediment thickness increases correspondingly away from the ridge axis. |
| 35 | The epicentre is the surface point directly above the focus | TRUE | This is the standard definition: focus (hypocentre) is the subsurface rupture point; epicentre is its vertical surface projection. |
| 36 | Earthquakes result from sudden release of elastic strain energy stored around a fault | TRUE | This is the elastic rebound theory (Reid, 1906): rock strains elastically as stress accumulates across a locked fault, then ruptures, suddenly releasing the stored energy as seismic waves. |
| 37 | Earthquake energy is felt just as strongly in distant places as near the source, regardless of magnitude | FALSE | Seismic wave amplitude attenuates with distance (geometric spreading and anelastic absorption), so shaking intensity decreases away from the epicentre for a given magnitude — distant sites feel a smaller effect. |
| 38 | S-waves can travel through both solid and liquid media | FALSE | S-waves are shear waves and require material rigidity to propagate; they cannot travel through liquids (or gases), which is how the Earth's liquid outer core was discovered (S-wave shadow zone). |
| 39 | Horizontal vibrations (strike-slip, S-waves, some surface waves) are generally more dangerous to tall buildings than vertical shaking | TRUE | Tall, flexible structures are far more vulnerable to lateral (horizontal) sway, which excites their fundamental bending modes, than to vertical up-down motion, which mainly loads them axially (a direction they are already designed to resist via gravity loading). |
| 40 | 90% of all earthquakes occur below depths of 700 km | FALSE | The opposite is true: roughly 90–95% of earthquakes are shallow-focus (<70 km), occurring in the brittle crust and uppermost mantle; 700 km is approximately the maximum depth at which any earthquake occurs (deep-focus events within subducting slabs), and they are a small minority. |
| 41 | The Richter magnitude scale is based on total energy released, as measured on a seismograph | FALSE | The Richter (local magnitude) scale is based on the logarithm of the maximum amplitude of seismic waves recorded on a standard seismograph at a fixed distance, corrected empirically — not a direct energy measurement. (Moment magnitude, Mw, is the scale actually tied to total radiated/seismic-moment energy.) |
| 42 | Unconsolidated, water-saturated soils are good foundation materials because they absorb/dampen seismic vibrations | FALSE | Loose, saturated, cohesionless soils typically amplify ground shaking and are prone to liquefaction (loss of strength under cyclic loading), making them among the WORST foundation materials seismically — the opposite of dampening. |
| 43 | The "Milankovitch discontinuity" separates Earth's mantle and outer core | FALSE | The mantle–core boundary is the Gutenberg discontinuity (~2,900 km depth). Milankovitch cycles refer to orbital-forcing cycles (eccentricity, obliquity, precession) that drive long-term climate/glaciation, not a seismic-velocity discontinuity. |
| 44 | All atoms of the same element have the same atomic number | TRUE | Atomic number (proton count) is the defining property of an element by convention; isotopes of the same element share atomic number but differ in neutron count (mass number). |
| 45 | Graphite and diamond have the same chemical composition and different crystal structures | TRUE | Both are pure carbon (C) polymorphs: diamond's tetrahedral sp³ bonding gives extreme hardness, while graphite's layered sp² sheets bonded by weak van der Waals forces give softness and cleavage into flakes. |
| 46 | Diamond and quartz are both minerals composed of a single element | FALSE | Diamond is a single-element mineral (carbon), but quartz is a compound, SiO₂ (silicon dioxide) — two elements, not one. |
| 47 | Mineral lustre is broadly classified as either metallic or opaque | FALSE | The standard classification is metallic vs. non-metallic (further subdivided as vitreous, pearly, silky, resinous, dull, etc.); "opaque" describes light transmission, not lustre category, and is a separate property. |
| 48 | Colour is one of the most diagnostic properties of minerals | FALSE | Colour is notoriously unreliable because trace impurities can radically change it (e.g. quartz appears clear, purple, pink, or smoky); streak, hardness, cleavage, and crystal habit are far more diagnostic identification properties. |
| 49 | As silicate tetrahedra link into larger units, more oxygens are shared and the negative charge per silicon decreases | TRUE | An isolated SiO₄⁴⁻ tetrahedron carries charge −4; as tetrahedra polymerize (chains→sheets→framework) by sharing corner oxygens, the net unshared (unbonded) charge contributed per silicon atom progressively decreases, consistent with Bowen/Goldich series mineral chemistry. |
| 50 | Calcite and dolomite are both carbonate minerals | TRUE | Calcite (CaCO₃) and dolomite (CaMg(CO₃)₂) both belong to the carbonate mineral class, defined by the (CO₃)²⁻ anion group. |
| 51 | Rocks always weather chemically before they undergo mechanical weathering | FALSE | There is no fixed sequence; mechanical weathering commonly precedes or accompanies chemical weathering, since fracturing increases exposed surface area and accelerates subsequent chemical attack (and vice versa, chemical weathering along grain boundaries can trigger mechanical disintegration). |
| 52 | Sheeting parallel to quarry floors and rock bursts on fresh cuts/tunnels are caused by unloading | TRUE | Removing overburden (by erosion or excavation) releases confining pressure; the rock expands elastically parallel to the newly exposed surface, producing exfoliation/sheeting joints and, in high-stress rock, sudden violent rock bursts. |
| 53 | A small amount of acidity dramatically increases dissolution/chemical weathering rates | TRUE | Even mildly acidic water (e.g. from dissolved CO₂ or organic acids) sharply accelerates dissolution of carbonates and hydrolysis of silicates, since reaction rate scales strongly with H⁺ activity. |
| 54 | Chemical weathering of limestone mostly produces solid, insoluble calcium hydroxide | FALSE | Limestone (CaCO₃) reacts with carbonic acid to form soluble calcium bicarbonate, Ca(HCO₃)₂, which is carried away in solution (the mechanism behind karst dissolution) — not an insoluble hydroxide. |
| 55 | Quartz weathers readily to aluminum-rich clay minerals | FALSE | Quartz is chemically inert and highly resistant to weathering (no cleavage, strong Si–O bonds, no aluminum to form clay) — it survives as sand grains. Feldspars, not quartz, are the silicates that weather to clay minerals. |
| 56 | Feldspars decompose during weathering to clay minerals, silica, and soluble constituents | TRUE | Hydrolysis of feldspar (e.g. K-feldspar + carbonic acid → kaolinite + dissolved silica + K⁺ and HCO₃⁻ in solution) is the textbook reaction producing clay minerals. |
| 57 | High-temperature ferromagnesian minerals (olivine, pyroxene) are much LESS susceptible to weathering than quartz | FALSE | The Goldich weathering-stability series mirrors Bowen's Reaction Series in reverse: minerals that crystallize first at high temperature (olivine, Ca-plagioclase) are LEAST stable/MOST susceptible to weathering at Earth-surface conditions, because they formed furthest from equilibrium with surface temperature/pressure; quartz, crystallizing last, is the most weathering-resistant common silicate. |
| 58 | There is no geologic evidence that mid-ocean ridges spread at uniform or symmetric rates | TRUE | Spreading rates vary considerably between different ridge systems (e.g. slow Mid-Atlantic ~2–5 cm/yr vs. fast East Pacific Rise ~6–16 cm/yr) and can differ somewhat either side of a given ridge segment; magnetic-stripe widths record this variability directly. |
| 59 | Subducted seafloor penetrates and ruptures the surrounding mantle, causing the largest earthquakes as the mantle fractures | FALSE | The largest earthquakes (megathrust events, M>8.5) occur on the shallow, brittle subduction-zone interface between the overriding and subducting plates — not from the slab "rupturing" the mantle at depth; deep-focus earthquakes within the slab are a distinct, smaller-magnitude phenomenon whose mechanism (phase-transformation faulting) differs from simple brittle fracture. |
| 60 | Calcite and halite both react with dilute acids to evolve carbon dioxide | FALSE | Calcite (CaCO₃) fizzes with dilute HCl, releasing CO₂ — the standard field carbonate test. Halite (NaCl) simply dissolves in water/acid without any carbonate group to release CO₂; it does not effervesce. |
