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Why can trench-type mountains such as the Andes remain high while subduction continues?
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continental landform
Davis's proposed landscape-development states. The morphology shown is not actually time-indicative. For example, A could be a gully system in soft sediment or a canyon such as the Royal Gorge in Colorado, which is millions of years old. The ridge-ravine topography of B would normally develop under humid conditions, but the river meandering on alluvium indicates a prior or extraneous non-humid aggrading mechanism. The riverine plain of C implies a complex history of planation and aggradation in a current fluvial mode.
Trench-type mountains, such as the Andes, remain high despite ongoing subduction due to several key geological mechanisms that counteract the erosional and tectonic forces of the subduction zone.
- Crustal Thickening and Shortening: The high elevation of the Andes is largely maintained by significant crustal thickening resulting from crustal shortening. As the South American Plate moves westward, the stable continental interior is underthrust beneath the mountain belt, effectively squeezing and thickening the crust.12
- Isostatic Buoyancy: According to the principle of isostasy, high mountain ranges are supported by low-density "roots" that extend deep into the underlying mantle, similar to an iceberg floating in water. This buoyancy helps maintain the high elevation of the range.34
- Episodic Uplift: While subduction is a continuous process, the resulting uplift often occurs in discrete, intense episodes. These events may be triggered by intervals of stronger plate convergence that compress the thermally weakened crust, forcing it upward.5