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← GeographyWhich effect arises from a lahar encountering a constricted river valley located downslope?
A)Backwater flooding above the constriction✓
B)Increased tephra deposition in distal areas
C)Elevated atmospheric sulfur dioxide levels
D)Accelerated glacial basal sliding rate
💡 Explanation
Backwater flooding occurs because the valley constriction acts as a hydraulic control, causing the lahar to pool upstream via flow retardation, rather than moving freely. Therefore, flooding occurs; distal deposition is not directly linked to river constrictions.
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