04-BS-14 · December 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. National Exams, December 2018 — 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 candidate chooses four items from the bank of items 34–44. Marks: Q1 = 20, Q2 = 10, Q3 = 30 (item 31 = 10, item 32 = 6, item 33 = 14), 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 item is settled by returning to the defining relationship behind the term — composition for igneous names, process for weathering and erosion, geometry for folds and faults, and stress state for deformation style — rather than by recognising a familiar phrase.
1. (d) Andesite. The adjective “andesitic” names an intermediate bulk composition, roughly 53–63 per cent silica, dominated by plagioclase with amphibole or pyroxene. Andesite is the fine-grained (volcanic) rock of that composition and is therefore andesitic by definition. Granite and rhyolite are felsic (granitic); basalt is mafic (basaltic).
2. (c) Wave. The map accompanying the item is the Nile delta — the textbook arcuate, smoothly convex delta front with barrier islands, marshes and abandoned distributaries behind it. That smooth, sediment-redistributed shoreline and the small number of active distributaries are the signature of wave domination. A stream (fluvial) dominated delta such as the Mississippi keeps a ragged bird’s-foot outline; a tide-dominated delta such as the Ganges–Brahmaputra is dissected into elongate, tide-parallel sand ridges.
3. (a) Once its elastic limit is surpassed. Below the elastic limit, strain is fully recovered when stress is removed. Beyond it the rock deforms permanently — plastically if warm and confined, by fracture if cool and unconfined. Lithification and plate-margin location influence where deformation happens, not the criterion for permanence.
4. (b) Radioactive dating. Precambrian rocks are older than about 541 Ma, so the only practical numerical method is radiometric dating using long-lived parent isotopes such as U–Pb in zircon, Rb–Sr or K–Ar. Carbon-14, with a half-life of 5730 years, is exhausted after roughly 50,000 years and tree rings extend back only millennia.
5. (b) Basal slip. Glaciers move by internal (plastic) deformation of ice, by basal slip (sliding on a lubricating water film at the bed), and by deformation of soft subglacial sediment. Basal slip is the only listed mechanism from that set.
6. (a) Folded anticlines and synclines. Orogeny is driven by horizontal shortening, which buckles originally flat-lying layered rocks into alternating upfolds (anticlines) and downfolds (synclines). Horsts and grabens are the products of extension, not shortening.
7. (d) Biologic activity, expansion from unloading, frost wedging. The phrase “in place” restricts the answer to weathering mechanisms operating without transport: root and burrowing activity, sheeting joints formed as overburden is removed, and ice growth in fractures. Option (a) describes erosion, which by definition involves removal.
8. (b) Pleistocene Epoch. The most recent glaciation, including the Wisconsinan advance that shaped most of Canada, falls in the Pleistocene, about 2.6 Ma to 11.7 ka. The Pliocene precedes it, the Permian is Paleozoic, and the Proterozoic hosts far older glaciations.
9. (d) Along plate margins. Relative motion between plates is accommodated in narrow boundary zones, so seismicity, faulting and folding concentrate there. Cratonic interiors are comparatively rigid and quiet.
10. (b) A fold in which older flanking strata dip toward the axis. A syncline closes downward: the youngest beds occupy the core and the limbs dip inward toward the axial trace, so the older flanking beds dip toward the axis. Option (d) inverts this and describes an anticline.
11. (c). A mineral is a naturally occurring, inorganic, crystalline solid whose constituent atoms are bonded in a regular, repetitive internal structure and which has a definite chemical composition; a rock is a lithified or consolidated aggregate of one or more minerals. Options (a) and (b) simply exchange the two definitions.
12. (d) Chemically bonded in a regular crystalline structure. The defining property of a mineral is long-range crystalline order maintained by ionic, covalent or metallic bonding. Ionic radii and charges deliberately differ within a structure — that is what allows charge balance and substitution.
13. (c) A few metres. Coseismic slip in a large earthquake is metre-scale; the 1964 Alaska event and the 2011 Tohoku event reached the upper metres-to-tens-of-metres range. Kilometres of slip accumulate only over geological time at millimetres-to-centimetres per year.
14. (d) Erosion. Erosion is the removal and transport of weathered material by a mobile agent. Ablation is loss of glacier mass, and solifluction is a specific slow downslope flow of water-saturated soil over permafrost.
15. (b) Esker. An esker is the sinuous ridge of stratified sand and gravel deposited in an ice-walled meltwater tunnel and left standing when the ice melts. Drumlins are streamlined till hills, kettles are depressions left by buried ice blocks, and valley trains are outwash bodies confined between valley walls.
16. (c) Erode the continental landscape and transport and deposit sediments. Glaciers are geological agents: they abrade and pluck bedrock and redeposit the debris as till and outwash. The climate and sea-level effects in the other options are indirect consequences, and (a) has the sign of the sea-level effect backwards.
17. (a) Dissolution, hydrolysis and oxidation. Dissolution removes soluble minerals such as calcite and halite; hydrolysis converts feldspars to clays and releases dissolved silica and cations; oxidation attacks iron-bearing silicates and sulphides. Hydration and carbonation are usually treated as special cases of the first two.
18. (b) Cooler temperatures and low confining pressures. Brittle failure is promoted by low temperature, low confining pressure, high strain rate and the presence of fluids at high pore pressure. Both clauses of (b) point the same way; option (c) is true but incomplete, giving only one of the two controls.
19. (d) Very much slower; vastly more. Alpine glaciers advance at metres to hundreds of metres per year, orders of magnitude slower than streamflow in the same valley, yet ice supports clasts of any size without sorting and therefore carries a far greater and far coarser sediment load.
20. (d) Horizontally directed, compressive stresses. Folding requires layer-parallel shortening. Horizontal extension produces normal faults and grabens; vertical stretching thins rather than buckles a layered sequence.
| Item | Answer | Item | Answer |
|---|---|---|---|
| 1 | d — Andesite | 11 | c |
| 2 | c — Wave | 12 | d |
| 3 | a | 13 | c — a few metres |
| 4 | b — Radioactive dating | 14 | d — erosion |
| 5 | b — Basal slip | 15 | b — esker |
| 6 | a | 16 | c |
| 7 | d | 17 | a |
| 8 | b — Pleistocene | 18 | b |
| 9 | d — plate margins | 19 | d |
| 10 | b | 20 | d |
