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How are rift valleys different from ramp valleys?
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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.
While rift valleys and ramp valleys may appear similar to a casual observer, they are formed by fundamentally different tectonic processes.1
- Rift Valleys: These are formed by crustal extension. As lithospheric plates diverge, the brittle crust fractures, causing a central block of crust—known as a graben—to subside or drop down between two or more normal faults. They are typically associated with divergence zones and seafloor spreading.23
- Ramp Valleys: These are formed by crustal shortening. In this process, blocks of crust are thrust toward one another and pushed up onto an intervening crustal block. The weight of this encroaching material forces the central block downward, creating the valley.12
Key differences include:
* Escarpments: Rift valleys feature sharply defined escarpments, whereas the edges of ramp valleys are generally less sharply defined.1
* Surrounding Terrain: While both are bounded by high ground, the mountains surrounding a ramp valley can be higher than those bordering a rift valley because they are formed by the active thrusting of material.1
* Longevity: Ramp valleys are often ephemeral features because they tend to fill rapidly with debris eroded from the adjacent mountains.1