04-BS-14 · December 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams December 2017, 04-BS-14 Geology, 3 hours, CLOSED BOOK (Casio/Sharp approved calculators only). Three questions constitute a complete exam (candidates must answer Questions 1 to 3); every printed sub-part is answered, including the 5 of 9 items in Question 3 the exam does not require.
Reference texts: Marshak, Earth: Portrait of a Planet (general/structural/surficial geology); Goodman, Engineering Geology: Rock in Engineering Construction (engineering-geology, permafrost, mass wasting); Freeze & Cherry, Groundwater (aquifers, wells, water table).
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 of the following is a mafic rock? | c) Basalt | Mafic rocks are Fe/Mg-rich, silica-poor (~45–52% SiO₂); basalt is the fine-grained mafic extrusive rock. Granite and rhyolite are felsic (silica-rich); andesite is intermediate. |
| 2 | Furthest south glaciers have advanced in North America (from end-moraine evidence) | d) Southern edge of Illinois | The older Illinoian glaciation (pre-Wisconsinan) pushed farthest south of any North American ice advance, to near the confluence of the Ohio and Mississippi Rivers in southern Illinois (~37°N) — well south of the later Wisconsinan limit near the 49th parallel/Great Lakes. |
| 3 | Order in which body/surface waves are detected after an earthquake | a) P-wave → S-wave → L-wave | P-waves (compressional) travel fastest and arrive first, S-waves (shear) travel slower and arrive second, and surface (Love, "L") waves travel slowest along the surface and arrive last. |
| 4 | The pictured delta (aerial/satellite image) is an example of a ____ dominated delta | c) Wave | The photo shows a smooth, symmetric, gently scalloped seaward shoreline reworked into a cuspate point — the signature of strong wave energy redistributing sediment along the delta front (Nile-delta style), unlike the multi-fingered "birdfoot" shape of a stream-dominated delta (Mississippi-style) or the elongated, shore-parallel sand ridges of a tide-dominated delta (Ganges–Brahmaputra-style). |
| 5 | Origin of the most widespread metamorphic rocks exposed at the Earth's surface | a) Regional metamorphism | Regional metamorphism affects huge volumes of rock across orogenic belts and continental shields under combined heat and directed pressure, so it accounts for the great majority of exposed metamorphic terrain; contact, hydrothermal, burial and impact metamorphism are all comparatively localized. |
| 6 | Physical removal of dissolved/disaggregated rock from the weathering site by wind, water, or ice | d) Erosion | By definition, erosion is the transport of weathered material away from its source; ablation refers specifically to ice/snow mass loss, and "solifluction"/"recidivism" are not this process. |
| 7 | Dissolution or decomposition of minerals and rocks | b) Chemical weathering | Chemical weathering is the umbrella term for in-place mineral breakdown by dissolution, hydrolysis and oxidation; hydrolysis is only one of its three constituent reactions (see item 10), not the general term. |
| 8 | Natural source of the acidity that speeds chemical weathering | d) Organic acids from decayed plants, acid rain, and sulphuric acid from pyrite oxidation | Decomposing organic matter releases humic/carbonic acids, atmospheric CO₂/SO₂ produce acid rain, and oxidation of sulphide minerals (e.g. pyrite) generates sulphuric acid — all natural acid sources that accelerate chemical weathering. |
| 9 | Principal causes of mechanical fragmentation of rock in place | d) Biologic activity, expansion from unloading (sheeting), and frost wedging | These are the standard physical-weathering mechanisms that fracture rock without moving it; erosion/transport (option a) moves already-loosened material rather than fragmenting it in place. |
| 10 | Three major processes of chemical weathering | a) Dissolution, hydrolysis, and oxidation | These are the three fundamental chemical-weathering reaction types (carbonate/evaporite dissolution, silicate hydrolysis producing clays, and oxidation of Fe/Mn-bearing minerals). |
| # | Statement | Answer | Why |
|---|---|---|---|
| 11 | Engineering solutions for permafrost include thermosyphons and insulation to aid in melting of permafrost | FALSE | Thermosyphons (passive, one-way heat pipes) and insulation are installed to preserve the frozen state beneath foundations, roads and pipelines — preventing thaw settlement — not to aid melting. |
| 12 | An aquifer is an impermeable layer serving as a confining layer above an aquiclude, which has the capacity for transmitting groundwater | FALSE | The definitions are reversed: an aquifer is the permeable unit that transmits usable quantities of groundwater; an aquiclude (aquitard) is the impermeable/low-permeability unit that confines it. |
| 13 | A spring is a place where groundwater flows into the ground | FALSE | A spring is where the water table (or a confined aquifer under pressure) intersects the surface and groundwater flows out, not a place where surface water enters the ground. |
| 14 | Oxbow lakes form when a mature meandering stream cuts off a meander | TRUE | When a meander neck is breached (a cutoff), the stream shortcuts to a new channel and the abandoned meander loop is isolated as a crescent-shaped oxbow lake. |
| 15 | Drumlins and roche moutonnées have the same overall shape, but drumlins are composed of till and roche moutonnées are composed of rock | TRUE | Both are streamlined, asymmetric (steep-stoss/gentle-lee or the reverse) hills elongated parallel to ice flow; a drumlin is moulded glacial till, while a roche moutonnée is bedrock abraded and plucked by moving ice. |
| 16 | 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 horizontal compression/shortening. |
| 17 | The water velocity required to mobilize a grain of silt is greater than that which will mobilize a grain of sand | TRUE | On the Hjulström diagram, erosion (entrainment) velocity is a U-shaped curve with its minimum at fine sand (~0.1–0.5 mm); coarser grains need more velocity because of greater mass, but finer cohesive silt/clay also needs more velocity than sand because inter-particle cohesion resists entrainment — a well-known counter-intuitive result. |
| 18 | Aa flows are generally thinner, faster moving, and have smoother surfaces than pahoehoe flows | FALSE | The description is reversed: pahoehoe (low-viscosity, hotter, gas-poor) flows are thinner, faster, and smooth/ropy-surfaced; aa (cooler, more viscous, more crystallized) flows are thicker, slower, and have a rough, jagged, clinkery surface. |
| 19 | Dry granite melts at a higher temperature than dry basalt | FALSE | By Bowen's Reaction Series, mafic minerals (and mafic rocks like basalt) crystallize/melt at higher temperature than felsic minerals (and felsic rocks like granite); dry granite's solidus/liquidus is lower than dry basalt's, not higher. |
| 20 | Like most other liquids, water decreases in volume when it freezes | FALSE | Water is anomalous: hydrogen-bonded ice has a more open lattice than liquid water, so it is less dense and water expands (~9%) on freezing — unlike most liquids, which contract on solidifying. |
