Clear cutting and its effects on landslides

Above image source:  http://landslides.usgs.gov/html_files/landslides/slides/landslideimages.htm

        Over the years, many case studies have proven that the mass removal of large trees and vegetation has a had a drastic increase on the probability of landslides occurring (Heiken, 1997). These studies have laid out several mechanisms of clear cutting that have contributed to the increase:

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Large trees provide strong root structures that penetrate fragile cracks in the underlying bedrock and anchor the soil.

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Old growth trees natural have large leaf surface areas which cause much water transfer. The water is drawn up from the soil and eventually transpired back to the atmosphere.

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Forests create a canopy of foliage high up in the air to help dissipate rain fall over large areas.

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Heavy logging machinery damages precious topsoil and decreases its ability to absorb water.

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Logging slash (leftover tree limbs) or debris blocks natural drainage basins.

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Anytime large amounts of vegetation are removed from an area the delicate root systems eventually die off which leaves the soil vulnerable to over saturation.

Above image source:  http://landslides.usgs.gov/html_files/landslides/slides/landslideimages.ht

      A study done by Richard Meehan was conducted in 1991 and a few of his conclusions were as followed:  "The frequency of mass erosion [landslides, debris flows, earthflows, etc] is strongly linked to the type and intensity of land treatment in the basin. Although most mass movements are associated with roads and their drainage systems, many originate on open slopes after logging has raised soil water tables and decreased root strength." [Meehan, 1991 page 194] He also stated that:  "The increase in mass movement due to clear cutting varies widely, ranging from 2-4 times in Oregon and Washington...to 31 times in the Queen Charlotte Islands... An increase of 6.6 times...is probably closer to the norm." [Meehan, 1991, page 194]

 

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Clear cutting and Its Effects on Landslides

Future Environmental Hazards

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