04-BS-14 · May 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams May 2016 — 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 1–4 mandatory). On Question 4 only the first four (4) answered sub-questions are normally marked; all seven (25–31) 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, rock mechanics, mineralogy); Goodman, engineering-geology mapping methods (strike and dip, three-point problem, apparent dip, structure contours); Freeze & Cherry, Groundwater (aquifers/aquicludes, permafrost, active layer).
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 | The best way to determine the age of a pre-Cambrian rock: | b) Radioactive dating | Pre-Cambrian rocks (>541 Ma) predate essentially all index fossils and any organic material datable by carbon-14 (which is useful only to ~50,000 years and only on organic carbon). Radiometric (radioactive) dating of long-lived isotope pairs (U-Pb, K-Ar, Rb-Sr) is the only method that reaches billion-year timescales. Tree rings (dendrochronology) span at most a few thousand years. |
| 2 | Which of the following is mafic? | c) Basalt | Mafic rocks are Fe/Mg-rich and silica-poor (<52% SiO₂), dark-coloured; basalt is the fine-grained extrusive equivalent of gabbro. Granite and rhyolite are felsic (silica-rich, light-coloured); andesite is intermediate composition. |
| 3 | Furthest south glaciers have advanced in North America (from end-moraine evidence): | d) Southern edge of Illinois | The pre-Illinoian/Illinoian continental ice sheets reached their maximum southern extent in the U.S. Midwest, with end moraines mapped as far south as southern Illinois (~37°N) — the southernmost limit of Pleistocene continental glaciation in North America. The other options are all well north of this true limit. |
| 4 | Following an earthquake, a seismograph detects Body Waves and Surface Waves in the order of: | a) P-wave → S-wave → L-wave | P-waves (compressional, fastest, ~6–8 km/s in crust) always arrive first, followed by the slower S-waves (shear, ~3.5–4.5 km/s, cannot travel through liquids), with the surface (Love/Rayleigh, “L”) waves — which travel only along the surface at roughly S-wave speed or slower but by a longer path — arriving last and carrying most of the damaging shaking energy. |
| 5 | The most widespread metamorphic rocks exposed at the Earth’s surface are formed by: | a) Regional metamorphism | Regional metamorphism affects enormous volumes of crust over broad areas during mountain-building (orogenesis), producing the vast metamorphic terranes exposed in continental shields and orogenic belts. Contact and hydrothermal metamorphism are localized (metres to a few km around an intrusion or vent); burial metamorphism is low-grade and volumetrically minor by comparison; impact metamorphism is rare and localized to craters. |
| 6 | When does permanent rock deformation occur? | a) Once its elastic limit is surpassed | Below the elastic limit (yield point) rock strain is fully recoverable (elastic behaviour); once stress exceeds that limit the rock accumulates permanent (plastic or brittle/fracture) strain that does not reverse on unloading. Deformation is a material-strength property, not tied to being on a plate margin or fully lithified. |
| 7 | When do rocks succumb to ductile deformation? | a) At great depth under active mountain belts with high confining pressure and low strain rates or prolonged strain | Ductile (plastic) behaviour is favoured by high temperature and confining pressure (both increase with depth) and by slow/prolonged strain rates, which allow crystal-plastic mechanisms (dislocation glide/creep, recrystallization) to operate. Shallow depth, low temperature/pressure and rapid strain (fault zones, impact rims) instead favour brittle fracture. |
| 8 | Which of the following best defines a mineral and 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 correctly captures both defining criteria: a mineral requires long-range crystalline order (a defined internal atomic arrangement), while a rock is simply a naturally occurring, consolidated aggregate of one or more minerals (or mineraloids/glass). The other options swap or garble these two definitions. |
| 9 | The physical removal of dissolved or disaggregated rock from the site of weathering by wind, water, or ice is termed | d) Erosion | Erosion is, by definition, the transport-driven removal of weathered material away from its source; ablation refers specifically to mass loss from a glacier surface (melting/sublimation), solifluction is a specific slow mass-wasting process on saturated, thawing soil, and recidivism is not a geological term. |
| 10 | ___ is one of the three ways a glacier can move over its bed. | b) Basal slip | Glaciers move by (1) internal deformation/creep of the ice itself, (2) basal slip — sliding on a thin film of meltwater at the ice–bed interface, and (3) subglacial sediment deformation (bed deformation). Frost heaving, morainal sliding and crevassal slip are not recognized glacier-motion mechanisms. |
| # | Statement | Answer | Why |
|---|---|---|---|
| 11 | In locations with continuous permafrost the active layer never melts. | False | The active layer is, by definition, the surface zone that thaws each summer and refreezes each winter, sitting directly above the permafrost table; if it never thawed it would simply be part of the permafrost itself, not an active layer. |
| 12 | Engineering solutions for problems with permafrost include thermosyphons and insulation to aid in melting of permafrost. | False | Thermosyphons (passive two-phase heat pipes) and insulation are used to preserve permafrost — extracting ground heat in winter and blocking heat gain in summer — specifically to prevent thaw settlement beneath foundations, pipelines and roadbeds, not to promote melting. |
| 13 | An aquifer is an impermeable layer which serves as a confining layer above an aquiclude which has the capacity for transmitting groundwater. | False | The definitions are reversed. An aquifer is a permeable, saturated unit capable of storing and transmitting usable quantities of groundwater; an aquiclude (or aquitard) is the low-permeability unit that confines or retards flow. |
| 14 | A spring is a place where the groundwater flows into the ground. | False | A spring is a natural point of groundwater discharge — where the water table, a perched aquifer, or a fracture network intersects the land surface and water flows out of the ground, the opposite of what is stated. |
| 15 | Oxbow lakes form when a mature meandering stream cuts off a meander. | True | As a meander loop migrates and tightens (increasing sinuosity), the stream eventually cuts through the narrow neck during a flood, abandoning the loop as a crescent-shaped oxbow lake isolated from the active channel — the classic mature-meandering-stream landform. |
| 16 | Drumlins and roche moutonnees have the same overall shape however drumlins are composed of till with and roche moutonnees are composed of rock. | True | Both are streamlined, elongate, asymmetric hills moulded by moving ice, with their long axes parallel to ice flow. This shared form is what the statement intends. Drumlins are depositional, moulded from unsorted glacial till. Roches moutonnées are erosional bedrock knobs. Note that the asymmetry is reversed between the two: a drumlin has its blunt, steeper end up-glacier and tapers down-glacier, while a roche moutonnée is smoothly abraded on its gentle up-glacier (stoss) side and plucked steep on its down-glacier (lee) side. |
| 17 | Normal faults are caused by extensional tectonic forces and reverse faults are caused by compressional tectonic forces. | True | Normal faults (hanging wall down relative to footwall) accommodate crustal extension/thinning; reverse faults (hanging wall up) accommodate crustal shortening/compression. This is the standard Andersonian fault classification by stress regime. |
| 18 | The water velocity required to mobilize a grain of silt is greater than that which will mobilize a grain of sand. | True | The Hjulström–Sundborg diagram shows the minimum erosion (entrainment) velocity occurs for fine-to-medium sand (≈0.2–0.5 mm); both coarser grains (more mass/friction to overcome) and finer grains such as silt and clay (cohesive, mutually attracting particles that resist plucking and lie within the boundary sublayer) require a higher critical velocity to entrain than sand does — a well-known counter-intuitive result of cohesion. |
| 19 | Quartz is a three dimensional arrangement of silica tetrahedra, while biotite is a chain-like arrangement. | False | Quartz is correctly described as a fully polymerized, three-dimensional (tektosilicate) framework of SiO₄ tetrahedra. Biotite, however, is a sheet silicate (phyllosilicate) — tetrahedra linked in continuous two-dimensional sheets — not a chain-like (inosilicate) structure; chain silicates are pyroxenes (single chain) and amphiboles (double chain). |
| 20 | A mineral's color and streak are always a consistent and reliable property for identification. | False | Colour is notoriously unreliable: trace-element impurities and lattice defects let a single mineral species (e.g. quartz, corundum, fluorite) show many colours. Streak is more diagnostic (it strips away surface alteration/impurity tinting) but is still not always reliable — many silicates, especially light-coloured or very hard ones, give a white/colourless streak regardless of hand-sample colour, so it cannot discriminate them. |
