Question 2 of 10: True/False

Question 2: True/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.

1) FALSE. Thermosyphons and insulation are installed to PRESERVE (keep frozen) the permafrost beneath a structure – passively extracting ground heat in winter and blocking heat gain in summer – not to aid its melting; uncontrolled permafrost thaw causes settlement/thaw subsidence, the problem these devices are engineered to prevent.

2) FALSE. The definitions are swapped: an aquifer is the PERMEABLE unit that transmits/yields usable groundwater; an aquiclude (or aquitard) is the low-permeability confining layer that restricts flow. As written, the statement calls the aquifer "impermeable" and the confining aquiclude "transmitting" – both backwards.

3) FALSE. A spring is where groundwater discharges (flows OUT) to the surface – the water table intersecting the ground surface, e.g. at a hillslope or valley wall – the opposite of water flowing into the ground.

4) TRUE. As a meandering stream matures, erosion on the outer bank and deposition on the inner bank tighten a meander loop's neck until the river cuts through it during a flood, abandoning the loop as a crescent-shaped oxbow lake.

5) FALSE. The composition half is right: a drumlin is till (depositional) and a roche moutonnée is bedrock (erosional). The shapes are not the same, though. Their asymmetry is REVERSED. A drumlin has its blunt, steep end facing up-ice (stoss) and tapers gently down-ice (lee). A roche moutonnée is abraded smooth and GENTLE on its stoss side and plucked into a STEEP, jagged face on its lee side. Each therefore records the ice-flow direction in the opposite sense, and that difference is what the statement hides.

6) TRUE. Normal faults accommodate crustal extension (hanging wall moves down relative to footwall); reverse (and thrust) faults accommodate crustal shortening/compression (hanging wall moves up).

7) TRUE. The Hjulström–Sundborg curve shows the minimum erosion (entrainment) velocity occurs for fine-to-medium sand; both coarser grains (need more force to move a heavier particle) and finer silt/clay (held together by cohesive electrochemical/surface-tension forces) require a HIGHER velocity to initiate motion than sand does – even though, once entrained, silt settles out again at a lower velocity than sand.

8) FALSE. The description is reversed: pahoehoe flows are the thinner, faster-moving, smooth/ropy-surfaced basaltic flows; aa flows are thicker, slower-moving, and have rough, jagged, clinkery surfaces (formed as the cooling, more viscous/gas-poor flow front breaks apart as it advances).

9) FALSE. Basalt (mafic) has a HIGHER dry melting point (roughly 1000–1200°C) than granite (felsic, roughly 650–750°C dry) – felsic magmas are richer in low-melting-point silica-alumina-alkali components, so granite melts (and crystallizes) at a lower temperature than basalt.

10) FALSE. Water is anomalous: hydrogen bonding forces the open hexagonal ice lattice to be LESS dense than liquid water, so water EXPANDS (increases in volume, ~9%) on freezing – unlike most other liquids, which contract when they solidify.