04-BS-14 · May 2015
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams May 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. Each question is worth 20 marks.
Reference texts: Marshak, Earth: Portrait of a Planet (structural geology, relative dating, weathering, glacial and fluvial landforms); Goodman, engineering-geology mapping methods (strike and dip, three-point problem); Freeze & Cherry, Groundwater (Darcy flow, piezometers).
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.
Each item is a definitional/first-principles question, so it is answered as choice + justification rather than the numeric Given/Find/Steps shape (reserved below for Q3 and Q4.2).
| # | Item | Options | Answer | Why |
|---|---|---|---|---|
| 1) | The study of terrestrial magnetism shows that the current magnetic north is directed to: | a) geographic north b) the geographic south c) has no preferred direction | a | The present-day magnetic north pole lies close to true (geographic) north (offset by only a few degrees of declination); paleomagnetic study of the present field shows this alignment, unlike the frequent polarity reversals recorded in older rocks. |
| 2) | A volcanic arc is the result of: | a) compression of a continental plate beneath an oceanic plate b) subduction of an oceanic plate under a continental plate c) collision between two lithospheric plates d) abduction of an oceanic crust on a continental plate | b | Volcanic arcs (e.g. the Cascades) form where a denser oceanic plate is subducted beneath a continental (or another oceanic) plate; partial melting of the mantle wedge above the slab feeds the arc volcanoes. |
| 3) | The greatest ocean depths are: | a) at the mid-ocean ridges b) at passive margins c) at the hot spots d) at subduction zones | d | Subduction-zone trenches (e.g. the Mariana Trench) are the deepest points in the ocean, since the down-going slab flexes the sea floor far below the surrounding abyssal plain, unlike the shallower, spreading mid-ocean ridges. |
| 4) | A normal fault is a fault where: | a) the roof rises relative to the wall b) the roof drops relative to the wall c) the roof slides laterally along the wall d) none of these answers | b | In a normal fault the hanging wall (the roof) moves down relative to the footwall (the wall) under extension; the opposite sense (hanging wall up) defines a reverse/thrust fault. |
| 5) | An anticline has a concavity of: | a) down b) up c) sideways d) middle | a | An anticline is convex-upward (arch-shaped); its concave side faces downward. A syncline is the mirror case, concave up. |
| 6) | An artesian well is a well which: | a) always conveys without pumping b) penetrates an unconfined aquifer c) penetrates a confined aquifer d) none of these answers | c | An artesian well penetrates a confined aquifer bounded above by an aquitard; the defining feature is the confined aquifer (with a potentiometric surface above the aquifer top), not that flow is automatically at the surface. |
| 7) | Sediment transformation processes in sedimentary rocks are: | a) very fast b) diagenesis c) lithification d) 2 and 3. | d | Diagenesis (post-depositional physical/chemical/biological change) and lithification (compaction plus cementation into solid rock) together describe how loose sediment becomes sedimentary rock. |
| 8) | During major earthquakes, instantaneous displacements of occur across pre-existing faults. | a) a few kilometres b) a few millimetres c) a few metres d) a few thousand kilometres | c | Coseismic slip in major earthquakes is on the order of metres (roughly cm to several metres, up to ~10-20 m for great subduction events), not the km-scale of cumulative long-term offset. |
| 9) | Most crustal deformation occurs in active tectonic zones | a) deep within old plate interiors b) at the base of sedimentary basins c) in thick piles of unconsolidated sedimentary strata d) along plate margins | d | Strain concentrates at plate boundaries (convergent, divergent, transform) where relative plate motion is accommodated; plate interiors are comparatively rigid and aseismic. |
| 10) | Plutonic rocks are emplaced at depth yet they can be seen at the Earth's surface due mainly to | a) widespread igneous inversion b) erosion of overlying rocks due to uplift c) catastrophic violent upheavals that bring them to the surface d) continual ongoing intrusion after the magma solidifies | b | Plutons crystallize kilometres underground; they are exposed only after tectonic uplift raises them and erosion strips away the overlying rock, a slow continuous process, not a single violent event. |
| # | Statement | Answer | Why |
|---|---|---|---|
| 11) | Iceland is located over a hot spot. | True | Iceland sits at the rare intersection of the Mid-Atlantic Ridge and the Iceland mantle plume (hot spot), which is why it has anomalously voluminous, subaerial volcanism for a mid-ocean-ridge setting. |
| 12) | A sill is an intrusive formation that is parallel to the encasing rock. | True | By definition a sill is a tabular, concordant intrusion injected parallel to host bedding planes; a dike is the discordant (cross-cutting) equivalent. |
| 13) | The Earth's inner core is liquid. | False | The inner core is solid iron-nickel, kept solid by immense pressure despite very high temperature; it is the outer core that is liquid, driving the geodynamo. |
| 14) | The Earth is five hundred million years old. | False | The Earth is about 4.54 billion years old (radiometric dating of meteorites and the oldest terrestrial zircons); 500 Ma is only the early Paleozoic, roughly the Cambrian-Ordovician boundary. |
| 15) | A shield volcano has very steep slopes. | False | Shield volcanoes (e.g. Mauna Loa) are built from low-viscosity, high-fluidity basaltic lava that spreads far before solidifying, producing broad, gently-sloping profiles, the opposite of steep-sided composite/stratovolcanoes. |
| 16) | A porphyry is a rock which exhibits two significantly different grain sizes. | True | Porphyritic texture is defined by large phenocrysts set in a much finer-grained (or glassy) groundmass, recording two stages of cooling, slow at depth then rapid on/near eruption. |
| 17) | The structure of the Earth was inferred from the study of the propagation of earthquakes' seismic waves. | True | Seismology (travel times, shadow zones, S-wave cutoff in the outer core) is the primary evidence for the crust-mantle-outer core-inner core layered structure and their physical states. |
| 18) | Silicates are, after carbonates, the second most abundant minerals in the crust of the Earth. | False | Silicates are themselves the most abundant mineral group in the crust (over 90% by volume), reflecting the crust's dominant elements O and Si; carbonates are a minor fraction by comparison. |
| 19) | Quartz is a three dimensional arrangement of silica tetrahedra, while biotite is a chain-like arrangement. | False | Quartz is correctly a tectosilicate (3-D framework of SiO4 tetrahedra), but biotite is a phyllosilicate (sheet silicate, mica group); chain silicates are the pyroxene/amphibole groups, not biotite. |
| 20) | Ferromagnesian minerals are darker than non-ferromagnesian minerals. | True | Fe- and Mg-bearing (mafic) minerals such as olivine, pyroxene, amphibole and biotite are characteristically dark; felsic, non-ferromagnesian minerals (quartz, feldspar, muscovite) are light-coloured. |
