The initiation and growth of gullies in Madagascar: are humans to blame?

Wells, Neil A.; Andriamihaja, Benjamin

doi:10.1016/0169-555x(93)90002-j

Cited by 56 publications

(87 citation statements)

References 39 publications

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“…Gullies are considered one of the worst environmental problems in crystalline basement rock areas of tropical regions, where they are frequent and can reach large dimensions (Wells and Andriamihaja, 1993;Xu, 1996;Coelho Netto, 1997). In these areas, gully erosion is responsible for several environmental impacts, such as soil losses, destruction of properties and natural habitats, silting of reservoirs and groundwater drawdown (Lal, 1990;Xu, 1996;Bacellar, 2000).…”

Section: Introductionmentioning

confidence: 99%

Controlling factors of gullying in the Maracujá Catchment, southeastern Brazil

Bacellar

Netto

Lacerda

2005

Earth Surf Processes Landf

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Hundreds of gullies ('voçorocas') of huge dimensions (up to 400-500 m long, 150 m wide and 50 m deep) are very common in the small Maracujá Catchment in southeastern Brazil. These erosional features, which occur with an uneven intensity throughout the area, started due to bad soil management practices at the beginning of European settlement, at the end of the 17th century, and nowadays are still evolving, but at a slower rate. As surface soils are usually very resistant to erosion, the outcrop of the more erodible basement saprolites seems to be an essential condition for their beginning. An analysis of well known erosion controlling factors was performed, aiming to explain the beginning and evolution of these gullies and to understand the reasons for their spatial distribution. Data shows that geology and, mainly, geomorphology are the main controlling factors, since gullies tend to be concentrated in basement rock areas with lower relief (domain 2) of Maracujá Catchment, mainly at the fringes of broad and flat interfluves. At the detailed scale (1:10 000), gullies are more common in amphitheatre-like headwater hollows that frequently represent upper Quaternary gullies (paleogullies), which demonstrate the recurrence of channel erosion. So, gullies occur in areas of thicker saprolites (domain 2), in places with a natural concentration of surface and underground water (hollows). Saprolites of the preserved, non-eroded hollows are usually pressurized (confined aquifer) due to a thick seal of Quaternary clay layer, in a similar configuration to the ones found in hollows of mass movement (mudflow) sites in southeastern Brazil. Therefore, the erosion of the resistant soils by human activities, such as road cuts and trenches ('valos'), or their mobilization by mudflow movements, seem to be likely mechanisms of gullying initiation. Afterwards, gullies evolve by a combination of surface and underground processes, such as wash and tunnel erosion and falls and slumps of gully walls.

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Section: Introductionmentioning

confidence: 99%

Controlling factors of gullying in the Maracujá Catchment, southeastern Brazil

Bacellar

Netto

Lacerda

2005

Earth Surf Processes Landf

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“…This seasonality causes the degradation of the soils prone to lavakization. During the dry periods cracks appear in the sparsely covered upper soil layer and the intensive rainfall of the wet season could reach the lower unstable soil layer through them (Wells and Andriamihaja, 1993). In this case erosion could initiate a lavaka suddenly within a few days (Cox et al, 2004).…”

Section: Climatic Features Of Madagascar and The Effect Of Precipitatmentioning

confidence: 99%

“…However, it has been noted that there are several lavakas in uninhabited areas as well (Mietton et al, 2014). Distinct research groups agree upon that lavaka formation requires a specific combination of lithology, weathering profile, topography and seasonal climate (Wells and Andriamihaja, 1993;Cox et al, 2004Cox et al, , 2010Randriamanga et al, 2006;Zavada et al, 2009). Cox et al (2004) and Zavada et al (2009) interpreted lavaka as a primary response of the unstable landscape to recent tectonic activity.…”

Section: Introductionmentioning

confidence: 99%

“…1). Some of them have pillars of regolith on their bottoms (Wells and Andriamihaja, 1993). Lavakization (the formation and development of this type of gullies) starts abruptly with small cracks in the soil that develop rapidly to larger gullies with steep walls, and a relatively flat bottom.…”

Section: Introductionmentioning

confidence: 99%

“…This area is termed as the lavaka-prone area (hereafter referred to as LPA) and is characterised by highly weathered soils with a top layer that is more resistant to erosion (Cox et al, 2010). Lavakas are mostly formed in convex slopes covered by thin vegetation (grassland) and shrub patches (Wells and Andriamihaja, 1993). (after ONE, 2008a) with the lavaka-prone area (red line; Cox et al, 2010) Numerous publications mention that climate is controlling the process of lavakization because of the occurrence of heavy rainfalls followed by dry seasons (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Landscape evolution and climate in Madagascar: lavakization in the light of archive precipitation data

Szabó

Raveloson

Székely

2015

CIG

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ABSTRACT. In Madagascar, soil erosion is significant even when it is compared to world averages. A resulting special geomorphic feature is a form of gully erosion known as lavaka that appears in the highlands of the country. Lavakization (the generation and development of these features) is due to rather unique multifactorial environmental conditions. Among many factors (geology, soil composition, human activities, etc.)

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Pacific Rim Steeplands

Gómez

Page

2010

Sediment Cascades

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The initiation and growth of gullies in Madagascar: are humans to blame?

Cited by 56 publications

References 39 publications

Controlling factors of gullying in the Maracujá Catchment, southeastern Brazil

Controlling factors of gullying in the Maracujá Catchment, southeastern Brazil

Landscape evolution and climate in Madagascar: lavakization in the light of archive precipitation data

Pacific Rim Steeplands

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