18-Geol-B2 Terrain Analysis · December 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 2017 — 04-Geol-B2 Terrain Analysis. Three-hour, open-book exam; approved Casio/Sharp calculator permitted. The paper prints SIX questions; per the instructions only the first five as they appear in the answer book are marked (100 points total), but all six are answered below so the set stands as a complete study resource.
Reference texts: Lillesand, Kiefer & Chipman, Remote Sensing and Image Interpretation (7th ed.) — primary reference for spectral/spatial/radiometric resolution, radar imaging geometry, Landsat sensor comparisons, and image-interpretation elements (Q1, Q2, Q3, Q5); Sabins, Remote Sensing: Principles and Interpretation (3rd ed.) — radar depression-angle geometry, albedo, atmospheric correction, Landsat 8 TIRS (Q1, Q2, Q5); Mollard, J.D. & Janes, J.R., Airphoto Interpretation and the Canadian Landscape (Energy, Mines and Resources Canada, 1984) — the exam's own required reference for the stereopair interpretation questions (Q4, Q6); Van Zuidam, Terrain Analysis and Classification Using Aerial Photographs — slope-form and karst terrain-classification context (Q1, Q6).
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.
a) Points # 1 and 2 [5 marks]. On a karst plateau, the most common isolated closed-depression features are dolines (sinkholes): roughly circular-to-oval, closed depressions with no surface outflow channel, formed by dissolution of the underlying carbonate (limestone/dolomite) bedrock or by collapse of a cave roof. Diagnostic photo evidence: a closed, bowl- or funnel-shaped depression visible in stereo relief with no connecting drainage channel entering or leaving it; a distinct tonal/vegetation contrast between the depression floor (often darker, wetter, or more densely vegetated where moisture and fine sediment collect) and the surrounding drier plateau surface; and, where several occur together, a characteristic clustered, "pockmarked" spatial pattern rather than the branching pattern of ordinary stream valleys. If points 1 and 2 sit close together and are similar in size/shape, they most likely represent two dolines of a developing sinkhole field.
b) Between points # 6 and # 7 [5 marks]. A linear or curvilinear feature running between two points on karst terrain, terminating without a visible continuation, is most consistent with a solution-widened joint/karst (blind) valley or a swallow-hole (stream-sink) system: a stream channel is traceable up to a point where it abruptly disappears (the swallow hole, where surface flow sinks into the carbonate bedrock via an enlarged joint or cave entrance) with no channel resuming further along the expected downstream trend. Diagnostic evidence: a normal, well-defined drainage channel with typical fluvial tonal/textural signature over part of its length, an abrupt termination (rather than the gradual attenuation and disappearance into overbank sediment typical of purely alluvial systems) at a point coinciding with a small closed depression or vegetation anomaly, and no channel continuation reappearing downstream on the same trend.
c) Point # 10, and how it formed [5 marks]. An isolated feature distinct from the smaller dolines of (a) — larger, often irregular in outline, sometimes with steep or collapsed margins — is most consistent with either an uvala (a large, compound closed depression formed by the lateral coalescence of several adjacent dolines as continued dissolution widens and eventually breaches the intervening bedrock walls) or a collapse sinkhole (formed where continued dissolution enlarges an underlying cave/void until its roof can no longer support itself and catastrophically collapses, producing a steep-walled depression, often with a talus of collapsed blocks visible on its floor). The formation mechanism in both cases is the same underlying process — groundwater circulating through joints and bedding planes progressively dissolves the soluble carbonate bedrock, enlarging voids until either surface coalescence (uvala) or roof failure (collapse sinkhole) produces the larger closed landform; which of the two applies is read from whether point #10 shows a smooth compound-doline outline (uvala) or steep, block-strewn collapse margins (collapse sinkhole) on the actual plate.
d) How the pocket stereoscope aids feature identification [5 marks]. A pocket stereoscope lets the interpreter view a stereopair — two overlapping photos of the same ground taken from slightly different flight positions — with each eye seeing only its own photo, so the brain fuses them into a single three-dimensional stereo model with vertical exaggeration (typically ≈3–4× true relief for standard airphoto overlap/base-height ratios). This is essential for karst interpretation because closed depressions, collapse sinkholes, and subtle relief breaks are often nearly invisible in plan-view tone/texture alone on a single (monoscopic) photo, but become immediately and unambiguously obvious as true negative relief once viewed in stereo — the exaggerated vertical relief also makes it possible to distinguish a genuine collapse feature (steep true relief) from a merely darker-toned flat area that could otherwise be mistaken for a depression from tone alone, and to judge relative depth/size between adjacent dolines that a single photo cannot convey.
