04-BS-14 · December 2015
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams December 2015 — 04-BS-14, Geology. Closed-book, 3 hours. Five questions constitute a complete paper: Questions 1-4 are mandatory and one of Questions 5-7 must be chosen; every question (5, 6, and 7) is answered here as a complete study resource. Marks for each sub-part are printed as given in the source; totals are transcribed as printed, not forced to a uniform 20.
Reference texts: Marshak, Earth: Portrait of a Planet (structural geology, relative dating, weathering, glacial and fluvial landforms, mineralogy/igneous classification); Goodman, engineering-geology mapping methods (strike and dip, cross-cutting relationships); Freeze & Cherry, Groundwater (water table, zones of aeration/saturation, well hydraulics).
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 | Geological types of mass wasting include: | a) Falls, slides/slumps, earth flows/mudflows, creep | These are the standard classes of mass wasting, distinguished by material type (rock/debris/earth/mud) and mechanism (fall = free fall/bounce, slide = coherent movement on a surface, flow = fluid-like deformation, creep = imperceptibly slow downslope movement). (b) confuses mass wasting with structural-geology terms (plunge, strike, dip); (c) lists glacial erosional landforms; (d) is a joke option. |
| 2 | Which of the following is mafic? | c) Basalt | Mafic rocks are Fe/Mg-rich, silica-poor (<52% SiO₂) and dark-coloured. Basalt is the fine-grained extrusive equivalent of gabbro. Granite and rhyolite are felsic (silica-rich, light); andesite is intermediate. |
| 3 | Which is the incorrectly labeled drainage pattern (figure of five block diagrams)? | d) Circumferential drainage | The panel labelled “d” shows streams radiating outward in all directions from the summit of a volcanic cone — this is the textbook definition of radial drainage. Circumferential (annular) drainage instead shows streams flowing in concentric rings around a dome or basin, following belts of weaker rock; it does not radiate from an apex. The other four panels are correctly labelled: (a) dendritic (tree-like branching on uniform-resistance rock), (b) rectangular (streams following orthogonal joint/fault sets), (c) trellis (parallel main streams with short right-angle tributaries, controlled by alternating resistant/weak ridges as the caption “ridges of resistant rock” confirms), (e) deranged/“confused” drainage (irregular network with lakes and swamps, typical of recently glaciated terrain with no established gradient). |
| 4 | Furthest south glaciers have advanced in North America (end-moraine evidence)? | d) Southern edge of Illinois | Pre-Illinoian/Illinoian ice sheets pushed the farthest south of any Pleistocene advance in North America, with terminal moraines mapped into southern Illinois (roughly the Ohio River confluence area), well south of the Wisconsinan limit (roughly the Ohio-Missouri river valleys further north) and far south of the 49th parallel. |
| 5 | Order in which a seismograph detects body and surface waves after an earthquake? | a) P-wave → S-wave → L-wave | P-waves (compressional, travel fastest through solid and liquid) arrive first, S-waves (shear, slower, cannot travel through liquid) arrive second, and surface (Love/Rayleigh, L-) waves, which travel only along the Earth’s surface at the slowest speed but usually carry the most damaging energy, arrive last. |
| 6 | The map shown (Nile delta, fan-shaped with smooth arcuate coastline, barrier islands, marsh/saltflat, mostly abandoned distributaries) is an example of a ____ dominated delta. | c) Wave | The Nile delta is the classic wave-dominated delta: incoming Mediterranean wave energy reworks and smooths the river-supplied sediment into a smooth, arcuate (fan) shoreline with barrier/beach-ridge islands, in contrast to the birdfoot (stream-dominated, e.g. Mississippi) or funnel-shaped, tidal-flat-fringed (tide-dominated, e.g. Ganges-Brahmaputra) end-members. |
| 7 | The most widespread metamorphic rocks exposed at the Earth’s surface are formed by: | a) Regional metamorphism | Regional metamorphism affects enormous volumes of crust in orogenic (mountain-building) belts under broadly elevated heat and directed pressure, producing the vast exposed areas of schist, gneiss and slate seen in shield and mountain terranes. Contact and hydrothermal metamorphism are localized (around plutons/hydrothermal systems); burial metamorphism is low-grade and volumetrically minor at outcrop; impact metamorphism is rare. |
| 8 | When does permanent rock deformation occur? | a) once its elastic limit is surpassed | Below the elastic limit, stress is fully recoverable (strain returns to zero on unloading). Beyond it, deformation becomes permanent — either ductile (plastic flow) or brittle (fracture), depending on temperature, confining pressure and strain rate — independent of lithification state or tectonic setting alone. |
| 9 | 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, high confining pressure and slow/prolonged strain rates — conditions typical of deep crustal levels in active orogens. Shallow depth, low pressure/temperature and rapid strain instead favour brittle fracture. |
| 10 | 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. | A mineral is defined by (i) naturally occurring, (ii) inorganic, (iii) a definite (or a range of) chemical composition, and (iv) an ordered internal crystalline structure. A rock is any consolidated (or unconsolidated, e.g. sediment) aggregate of one or more minerals (or mineraloids/glass). The other options swap the two definitions or garble them. |
| # | Statement | Answer | Why |
|---|---|---|---|
| 1 | In locations with continuous permafrost the active layer never melts. | False | The active layer is by definition the surface zone that thaws seasonally each summer, even where the permafrost beneath it is continuous and never thaws; if it never melted it would simply be part of the permafrost, not an active layer. |
| 2 | Silicates are, after carbonates, the second most abundant minerals in the crust of the Earth. | False | Silicate minerals make up roughly 90–95% of the Earth’s crust by volume/mass — they are overwhelmingly the most abundant mineral group, not second to carbonates (which are a minor fraction, concentrated in limestone/dolostone). |
| 3 | 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 unit capable of storing and transmitting usable quantities of groundwater; an aquiclude/aquitard is the low-permeability unit that confines/retards flow. |
| 4 | 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 (or a perched water table/fracture) intersects the land surface and water flows out of the ground, not into it. |
| 5 | Oxbow lakes form when a mature meandering stream cuts off a meander. | True | As a meander loop migrates and tightens, 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. |
| 6 | Drumlins and roches moutonnées have the same overall shape, however drumlins are composed of till while roches moutonnées are composed of rock. | True | Both are streamlined, asymmetric (gently sloped up-glacier, steeper down-glacier) landforms elongated parallel to ice flow; drumlins are depositional, moulded from unsorted glacial till, while roches moutonnées are erosional bedrock knobs (abraded on the up-glacier stoss side, plucked on the down-glacier lee side). |
| 7 | 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 and thrust faults (hanging wall up) accommodate crustal shortening/compression. |
| 8 | 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, the erosion (entrainment) velocity is lowest for medium-to-fine sand; below that grain size, cohesion between fine silt/clay particles raises the critical erosion velocity again, so a silt grain in fact requires a higher velocity to entrain than sand does, even though it is easier to keep in suspension once entrained. |
| 9 | Quartz is a three dimensional arrangement of silica tetrahedra, while biotite is a chain-like arrangement. | False | Quartz is correctly a three-dimensional framework (tectosilicate) of fully shared SiO₄ tetrahedra. Biotite mica, however, is a sheet silicate (phyllosilicate), not a chain silicate — chain structures (single/double) describe pyroxenes and amphiboles instead. |
| 10 | A mineral’s color and streak are always a consistent and reliable property for identification. | False | Colour is notoriously unreliable because trace impurities and weathering can shift it widely for the same mineral (e.g. quartz occurs in many colours). Streak is more diagnostic than colour but is still not universally “always” reliable (e.g. it is uninformative for minerals harder than the streak plate); the absolute qualifier makes the statement false. |
