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.
The rock cycle is the continuous set of processes that transform Earth materials among the three rock classes — igneous, sedimentary and metamorphic — and back to magma, with no fixed starting point. Igneous rock forms when magma (molten rock generated by partial melting in the mantle or lower crust) cools and crystallizes, either slowly at depth (intrusive/plutonic rock, e.g. granite, coarse interlocking crystals) or rapidly at/near the surface (extrusive/volcanic rock, e.g. basalt, fine-grained or glassy). Once exposed at the surface by uplift and erosion, any rock is broken down by weathering (mechanical disintegration and chemical decomposition) into loose sediment, which is eroded and transported by water, wind or ice and deposited in layers. Burial under successive layers causes compaction (grains pressed together, pore space reduced) and cementation (minerals precipitated from pore water bind the grains); together these lithification processes turn loose sediment into sedimentary rock (e.g. sandstone, shale, limestone). Any rock — igneous, sedimentary or already metamorphic — subjected to elevated heat and pressure without melting (typically from deep burial or tectonic activity) recrystallizes in the solid state into metamorphic rock (e.g. slate, schist, gneiss, marble), developing new mineral assemblages and often a foliated fabric. If temperature rises enough for partial or complete melting, the rock returns to magma, closing the cycle. Any pathway may be interrupted at any stage, which is why the cycle is drawn with multiple cross-linking arrows rather than a single loop.
the labelled axes/percentages of the rock-classification chart in Q3-2), which is unambiguous, rather than from the illegible caption text.
Figure Q3-1 is a coastal block diagram illustrating the rock cycle in a landscape setting, read left (offshore) to right (mountain source area) — the same processes described in Part 1:
| Box (left→right) | Structure shown |
|---|---|
| 1 (offshore, horizontal layered strata under the sea) | Sedimentary rock — horizontal, undisturbed marine strata built from accumulated offshore sediment. |
| 2 (at the shoreline/vessel symbol, where new sediment is actively settling) | Zone of active deposition — the site where sediment currently being eroded from the mountains is being laid down and will lithify into new sedimentary rock. |
| 3 (coastal plain, layered sediment exposed on land) | Sedimentary rock (uplifted, now exposed on the coastal plain) — the same lithified material as box 1, subsequently raised above sea level. |
| 4 (rugged mountain terrain, right) | Metamorphic/igneous (crystalline) rock — the uplifted mountain core exposed by erosion, the ultimate source of the sediment supplied to boxes 1–3, closing the rock-cycle loop shown in Part 1. |
Figure Q3-2 is a standard igneous-rock identification chart, plotting rock colour (light–dark) against the percentage of dark (ferromagnesian) minerals, with a middle column already labelled “Andesitic (Intermediate)” (15–40% dark minerals):
| Box | Fill-in | Why |
|---|---|---|
| Top-left (classification) | Felsic (Granitic) | Light-coloured column, <15% dark minerals — the felsic/granitic composition class. |
| Top-right (classification) | Mafic (Basaltic) | Dark-coloured column, >40% dark minerals — the mafic/basaltic composition class. |
| Bottom-left (name of rock) | Granite | Coarse-grained (phaneritic) rock of felsic/granitic composition. |
| Bottom-right (name of rock) | Gabbro | Coarse-grained (phaneritic) rock of mafic/basaltic composition. |
