A gully is a landform
created by running water, eroding
sharply into soil
, typically on a hillside. Gullies resemble large ditch
es or small valley
s, but are metres to tens of metres in depth and width. When the gully formation is in process, the water flow rate
can be substantial, causing a significant deep cutting action into soil.
The earliest known usage of the term is from 1657. It originates from the French word ''goulet'', a diminutive form of ''goule'' which means ''throat''. It is possible that the term is connected to the name of a type of knife used at the time, a ''gully-knife.''
Formation and consequences
Gully erosion is the process by which gullies are formed. Hillsides are more prone to gully erosion when they are cleared of vegetation, through deforestation
or other means. The eroded soil
is easily carried by the flowing water after being dislodged from the ground, normally when rainfall
falls during short, intense storms such as during thunderstorms
A gully may grow in length by means of headward (i.e. upstream) erosion
at a knick point
. This erosion can result from interflow
as well as surface runoff
Gullies reduce the productivity of farmland
where they incise into the land, and produce sediment
that may clog downstream waterbodies
. Because of this, much effort is invested into the study of gullies within the scope of geomorphology
, in the prevention of gully erosion, and in restoration of gullied landscapes. The total soil loss from gully formation and subsequent downstream river sedimentation
can be sizeable.
Gullies can be formed or enlarged by a number of human activities.
Artificial gullies are formed during hydraulic mining
when jets or streams of water are projected onto soft alluvial deposits
to extract gold
or tin ore
. The remains of such mining methods are very visible landform features in old goldfield
s such as in California
and northern Spain. The badland
s at Las Medulas
for example, were created during the Roman period by hushing
or hydraulic mining
of the gold-rich alluvium with water supplied by numerous aqueducts tapping nearby rivers. Each aqueduct
produced large gullies below by erosion of the soft deposits. The effluvium was carefully washed with smaller streams of water to extract the nuggets
and gold dust.
Gullies are widespread at mid- to high latitudes on the surface of Mars
, and are some of the youngest features observed on that planet, probably forming within the last few 100,000 years. There, they are one of the best lines of evidence for the presence of liquid water
on Mars in the recent geological past, probably resulting from the slight melting of snowpacks on the surface or ice in the shallow subsurface on the warmest days of the Martian year. Flow as springs from deeper seated liquid water aquifers
in the deeper subsurface is also a possible explanation for the formation of some Martian gullies.
[Malin M. C. and Edgett K. S. (2000) Science, 288, 2330–2335.]
File:A gully (Budanova Gora) 1.jpg|A gully in Saratov Oblast, Russia.
File:A gully (Budanova Gora) 3.jpg|Inside the gully (to the left) in Saratov Oblast, Russia.
File:Voçoroca (23 12 24S - 48 47 59W) - REFON 3.JPG|''Voçoroca'' (Portuguese for gully) in Avaré, Brasil
* – a narrow gully with a steep gradient in a mountainous terrain
* - gully in Scotland or Northern England in rock
* – a shallow channel cut into soil by erosion from flowing water
* ''Oxford English Dictionary''
Category:Environmental soil science
Category:Canyons and gorges