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Difficulty: HardLandform Evolution by Running Water and Underground Water

A river system flowing across a mature landscape experiences sudden tectonic uplift, causing a significant base-level drop. This change reactivates intense vertical erosion, prompting the river to cut deeply into its former floodplain and leave step-like benches at identical elevations on both sides of the new valley. Which landform is produced by this geomorphic process?

  1. Paired river terracesAnswer
  2. B
    Interlocking spurs
  3. C
    Alluvial fans
  4. D
    Escarpment fault steps

Answer

Paired river terraces are formed when river rejuvenation leads to vertical downcutting into a former floodplain, creating symmetrical bench-like landforms on opposite sides of the valley.
Paired river terraces represent former floodplain levels left standing above the current channel after river rejuvenation. Tectonic uplift or a drop in sea level increases the river's gradient and kinetic energy, driving rapid vertical downcutting. As the river carves a deeper inner gorge, remnants of the old valley floor remain as flat bench-like steps at identical elevations on both sides of the valley.

Step-by-Step Solution

1
Analyze the geomorphic trigger described in the stem.
Tectonic uplift drops the base level, initiating river rejuvenation and accelerating vertical downcutting.
Rejuvenation increases the river's energy, allowing it to incise deeply into its existing channel floor.
2
Examine the spatial arrangement of the resulting valley features.
The old floodplain is abandoned above the active channel, forming flat, bench-like steps at matching elevations across the valley.
When downcutting occurs evenly across symmetrical valley sides, paired terraces are formed.
3
Match the observed features to the correct geomorphic landform.
The step-like remnants at equal heights are identified as paired river terraces.
Unpaired terraces occur with lateral meander migration, whereas equal-height benches on both sides confirm paired terraces.

Key Concept

River Rejuvenation and Terrace Formation
Estimated Time:2m 0s
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Topics

Landform Evolution by Running Water and Underground Water

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