04-BS-14 · December 2019
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. National Exams, December 2019 — 04-BS-14 Geology. Three hours, closed book, one approved Casio or Sharp calculator. Four questions constitute a complete paper: Questions 1, 2 and 3 are mandatory, and on Question 4 the first four answers appearing in the answer book are marked. Marks: Q1 = 20 (1 mark/item, 20 MC items), Q2 = 10 (11 True/False items), Q3 = 30 (item 32 = 10, item 33 = 5, item 34 = 15), Q4 = 40 (four items at 10 marks each). Total = 100 marks.
Reference texts.
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.
Approach. Each statement is tested against the formal definition of the term it uses; where a statement contains two clauses, both must hold for the statement to be true.
21. True. Iceland straddles the Mid-Atlantic Ridge, and it sits above the Iceland mantle plume (hot spot) at the same time — the unusually thick, subaerial crust of Iceland is exactly the product of a hot spot supplying extra magma to a divergent boundary.
22. False. The active layer is defined as the near-surface zone that thaws every summer and refreezes every winter; it exists above continuous permafrost as well as discontinuous permafrost. What never thaws is the permafrost beneath it. In the Canadian Arctic the active layer is simply thin (commonly 0.3–1 m in fine-grained soils), and its seasonal thaw is precisely what governs foundation, pipeline and slope design in the North.
23. False. The order is reversed: silicates, not carbonates, are by far the most abundant mineral group in the crust (roughly 90 per cent by volume), because silicon and oxygen are the two most abundant crustal elements. Carbonates are volumetrically minor by comparison, however conspicuous they are in sedimentary basins.
24. False. The two definitions have been exchanged. An aquifer is the permeable, saturated unit that has the capacity to transmit usable quantities of groundwater; an aquiclude (or aquitard) is the low-permeability unit that confines it. As written, the statement makes the aquifer the confining layer and the aquiclude the transmissive one, which is backwards.
25. True. Wegener's and later plate-tectonic evidence for Pangaea is exactly this list: the jigsaw fit of the continental margins (especially South America–Africa), matching fossil assemblages (Mesosaurus, Glossopteris) on continents now separated by ocean, orogenic belts that align across the present ocean gap (Appalachians–Caledonides–Scandinavian mountains), and striated tillites of the same Permo-Carboniferous glaciation on southern-hemisphere continents now widely separated and at different latitudes.
26. True. As a meander loop grows, the narrowing neck is eventually breached during a flood, the stream adopts the shorter course, and the abandoned loop is sealed off by deposition at both ends, leaving a crescent-shaped oxbow lake that gradually fills with fine sediment and organic matter.
27. True. The focus (hypocentre) is the point at depth where rupture initiates; the epicentre is its vertical projection onto the Earth's surface, and it is normally the point of greatest shaking intensity for a shallow event.
28. True. In a normal fault the hanging wall moves down relative to the footwall, lengthening the section, which requires a horizontal least principal stress, i.e. extension. In a reverse (thrust) fault the hanging wall rides up, shortening the section under horizontal compression.
29. True. A porphyritic texture, and by extension a porphyry, is defined by two distinct crystal-size populations — large phenocrysts set in a finer-grained (or glassy) groundmass — recording two stages of cooling: slow growth at depth followed by rapid quenching on eruption or shallow emplacement.
30. True. Graphite and diamond are polymorphs of pure carbon. Diamond's tetrahedral, covalently bonded 3-D lattice gives it extreme hardness; graphite's sheet structure of covalently bonded hexagonal layers held together only by weak van der Waals forces gives it softness and a slippery cleavage — the same composition, wholly different physical properties, because of the different structure.
31. True. Quartz is a tectosilicate (framework silicate) in which every oxygen of the SiO4 tetrahedron is shared between two tetrahedra in three dimensions. Biotite is a phyllosilicate (sheet silicate) built of continuous two-dimensional layers of tetrahedra sharing three of their four oxygens, which is why it cleaves into thin, elastic flakes while quartz has no cleavage at all.
| Item | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Answer | T | F | F | F | T | T | T | T | T | T | T |
