04-BS-14 · Undated paper

Question 2 of 4: True and False (10 marks)

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

Paper format. National Exams, May 2019 — 04-BS-14 Geology (every page carries the header "National Exams May 2019"). 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 (20 multiple-choice items), Q2 = 10 (10 true/false items), Q3 = 30 (item 31 = 10, item 11 = 6, item 12 = 14), Q4 = 40 (four items at 10 marks each). Total = 100 marks.

Source and numbering notes. Two printed numbering slips are kept exactly as printed so the items can be matched to the paper: on page 8 the two Question 3 items that follow item 31 are numbered "11" and "12", and the Question 4 bank on page 9 is numbered 13–24 rather than continuing from 31. Every printed item is answered, including all twelve Question 4 items, not merely the four an examinee would select.

Reference texts.

Marshak, S., Earth: Portrait of a Planet — general physical geology (rock cycle, plate tectonics, structural geology, glaciation, mass wasting, streams).
Tarbuck, E. J. & Lutgens, F. K., Earth: An Introduction to Physical Geology — igneous-structure and alpine-glaciation block diagrams of the type reproduced in Question 3, Bowen's Reaction Series, volcano forms.
Goodman, R. E., Engineering Geology: Rock in Engineering Construction — engineering-geological description of rock masses, weathering, discontinuities and slope stability.
Freeze, R. A. & Cherry, J. A., Groundwater — aquifers, aquitards/aquicludes, springs and the subsurface limb of the hydrologic cycle.

Question 2: True and False (10 marks)

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. 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.

22. 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.

23. 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.

24. False. The direction of flow is reversed. A spring is a place where groundwater flows out of the ground and discharges naturally at the surface — where the water table intersects the land surface, or where a permeable unit perched on an impermeable one (an aquitard, or a perched water table over a clay lens) crops out on a hillside. Water flowing into the ground describes infiltration and recharge, not a spring.

25. 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.

26. False. The two materials have been swapped. A drumlin is a streamlined hill of till moulded beneath moving ice, with its blunt, steep end facing up-ice and a gently tapering tail pointing down-ice. A roche moutonnée is a knob of bedrock, smoothed and striated by abrasion on its gentle up-ice (stoss) side and quarried by plucking into a steep, jagged down-ice (lee) side. The two are not even the same shape in detail: their asymmetry faces opposite ways relative to the ice-flow direction. Drumlin fields across southern Ontario and the Prairies are typical Canadian examples.

27. 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.

28. True. On the Hjulström diagram the critical erosion velocity has its minimum for fine to medium sand (about 0.1–0.5 mm). Silt (0.004–0.0625 mm) needs a higher velocity to be mobilised than sand, because the small, platy grains are held by cohesion and lie within the smooth viscous sublayer at the bed, where they are sheltered from the flow. Once entrained, however, silt stays in suspension down to much lower velocities than sand. So the statement, silt needs more velocity than sand, is correct.

29. 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.

30. False. Colour is notoriously the least reliable identification property — trace-element impurities let a single mineral species (e.g. quartz, corundum, fluorite) occur in almost any colour. Streak is considerably more consistent because it exposes a thin, unweathered, finely powdered surface, but even streak is not universally diagnostic (many silicates streak white regardless of hand-specimen colour), so "always" is too strong a claim for either property.

Question 2 — answer key
Item	21	22	23	24	25	26	27	28	29	30
Answer	F	F	F	F	T	F	T	T	T	F

Topic. Definitions in permafrost engineering, mineralogy, hydrogeology, glacial geomorphology, sediment transport and fault mechanics.

Key relations. Active layer thaws seasonally; permafrost does not. Silicates outnumber every other mineral group in the crust. Aquifer transmits, aquiclude confines. Springs discharge groundwater. Drumlin = till, roche moutonnée = bedrock. Hjulström: sand is the easiest grain size to erode.

Why this works. A true/false item in this subject almost always turns a genuine definition on one hinge — a swapped pair of terms (23, 26), a reversed direction (24), a reversed order of abundance (22) or an absolute qualifier such as "never" or "always" (21, 30). Locating that hinge produces both the answer and the one-line justification that earns the mark.

Common pitfall. Assuming that bigger grains are always harder to move (28): cohesion makes silt and clay harder to erode than sand.

Source. Freeze & Cherry, Groundwater, ch. 2 (aquifers, aquitards, springs); Marshak, Earth: Portrait of a Planet, chapters on minerals, glaciers, streams and faults.

← Question 1 Next: Question 3 →