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23-619: In northernmost Chile the central valley is made up of the Pampitas, a series of small flats dissected by deep valleys. Immediately south of the Pampitas, in Tarapacá Region and northern of Antofagasta Region , the Central Valley is known as Pampa del Tamarugal . Contrary to the Pampitas valleys descending from the Andes do not incise the plains but merge into the surface of Pampa del Tamarugal at

46-432: A dissected plateau . River incision is the natural process by which a river cuts downward into its bed, deepening the active channel. Though it is a natural process, it can be accelerated rapidly by human factors including land use changes such as timber harvest, mining, agriculture, and road and dam construction. The rate of incision is a function of basal shear-stress. Shear stress is increased by factors such as sediment in

69-401: A height of c . 1500 m. The westernmost portion of Pampa del Tamarugal has a height of 600 m. This western part contain a series of raised areas called pampas and basins containing salt flats . Interconnecting basins are important corridors for communication and transport in northern Chile. South of Loa River the valley continues, flanked by Cordillera Domeyko to east, until it is ends at

92-452: A stream can thus indirectly reflect accelerated crustal uplift . This is because accelerated incision may trigger accelerated erosion on the adjacent slopes creating slopes progressively steeper slopes that are in equilibrium with high erosion rates. Acacia caven Vachellia caven ( Roman cassie , aromita , aromo criollo , caven , churque , churqui , espinillo , espinillo de baado , espino , espino maulino )

115-595: Is 190 km long from north to south. The Central Valley south of Bío Bío River has been influenced by volcanism and past glaciations giving origin to the ñadis and moraines that cover parts of the valley. The natural vegetation of the central section vary from north to south. To a lesser degree vegetation also vary towards the foothills of the Andes and the Chilean Coastal Range. From Santiago to Linares thorny woodlands of Acacia caven are dominant. In Ñuble Region two sclerophyll vegetation types cover

138-671: Is also well documented as a cause of river incision. Stable material on the river bed mitigate erosion, removing this armoring layer of gravel, boulders, etc. exposes the channel bed to the erosive force of the water. "On the Russian River near Healdsburg, California, instream pit mining in the 1950s and 1960s caused channel incision in excess of 3-6 m over an 11-km length of river." Tectonics play an important role in shaping landscapes and rivers, and tectonic uplift and river incision go hand in hand. Over geologic time, as mountains rise higher, water erodes deep gorges and channels, dissecting

161-477: Is an ornamental tree in the family Fabaceae . Vachellia caven is native to Argentina , Bolivia , Chile , Paraguay , Uruguay and Rio Grande do Sul in Brazil. It grows four to five metres tall and bears very stiff and sharp white thorns up to 2 cm in length. It blooms in spring, with bright yellow flower clusters 1–2 cm (0.39–0.79 in) in diameter. Prominent occurrences of V. caven are within

184-564: The Chilean matorral of central Chile, where the species is a common associate of the Chilean Wine Palm , Jubaea chilensis . The flowers of V. caven are used as food for bees in the production of honey . The tree is used for erosion control. The tree has ornamental uses. Tannin from the seed pods is used for tanning hides. The wood is used as fuel and to make posts for fences . The chief current human use for V. caven

207-472: The Isthmus of Ofqui . (46°50' S). 35°20′07″S 70°43′48″W  /  35.33529°S 70.72998°W  / -35.33529; -70.72998 River incision River incision is the narrow erosion caused by a river or stream that is far from its base level . River incision is common after tectonic uplift of the landscape. Incision by multiple rivers result in a dissected landscape, for example

230-443: The Central Valley extends from Tiltil (33°05' S) near Santiago to Temuco (38°45' S). The Coast Range and the Andes almost merge in two locations: one between Santiago and Rancagua and another between San Fernando and Rengo . The result is the enclosure of the Central Valley into two smaller basins in the north: Santiago Basin and Rancagua Basin. The valley runs an un-interrupted length of 360 km from Angostura de Pelequén in

253-456: The bed and banks. This leads to scouring of the bed material, exposing the bedrock channel bed to erosion and thus faster rates of channel incision. The scoured bed material consists of finer sediments such as silts, sands, and gravels. The removal of these removes important aquatic habitats for salmonid species and other aquatic organisms. In many agricultural areas, rivers have been straightened and dyked for flood control and to plant crops in

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276-465: The continuation of the Central Valley is made up of a series of marine basins including Reloncaví Sound , Gulf of Ancud , and the Gulf of Corcovado that separates Chiloé Island from the mainland. Further south the valley runs as the narrow Moraleda Channel . Emerged portions include numerous small islands plus the eastern coast of Chiloé Island and Taitao Peninsula east of Presidente Ríos Lake , including

299-443: The floodplain. Normally, floods are allowed to spread out across the floodplain, allowing deposition of sediment and slowing water speeds, reducing the erosive potential of the water. Channelization concentrates flood flows down the active channel, increasing erosion. River incision due to agriculture is well-documented throughout the agricultural regions of the world, such as the Central Valley of California. In-stream gravel mining

322-619: The landscape. In some instances, such as the Sierra Nevada mountains of California, up to 1 km of incision has been shown to have occurred over the last 5 million years. "River erosion is one of the primary agents of landscape evolution. Outside of glaciated regions, rivers are responsible for sculpting uplifted terrain into arborescent valley networks and creating the relief that drives gravitational transport processes such as landsliding". Rivers and streams that cross tectonic boundaries are subject to immense geomorphic change. When an area in

345-587: The latitude of Taltal (25°17' S). It re-appears around Chañaral (26°20' S) as an isolated basin surrounded by mountains and hills. This 250 km long and up to 70 km wide basin is called Pampa Ondulada or Pampa Austral. As the Pampa Ondulada is extinguished at Copiapó River (27°20' S) in the Norte Chico region running south of this river there is no proper Central Valley , only a few narrow north–south depressions that align with geological faults . In

368-520: The latitudes of Temuco the Coast Range is subdued to such degree the Central Valley coalesces with the coastal plains. In the 110 km between Gorbea and Paillaco ( c . 39–40° S) the Central Valley is inexistent as the region is instead crossed by a series of east–west mountainous ridges and broad fluvial valleys. South of this region the Central Valley re-appears in the south to extend into Osorno and Puerto Montt (41°30' S). This southern section

391-423: The north to Bío Bío River (37°40' S) in the south. It broadens from 12 km at Molina (35°05' S) in the north to 74 km in the south at Laja (37°15' S) the relief being gently undulating. Conglomerate of Andean provenance cover large swathes of the Central Valley being less common to the west near the Coast Range. Occasionally the valley contains isolated hills and mountains made up of basement rocks. At

414-655: The northern section of the central valley vegetation is extremely scarce as result of conditions of extreme aridity in Atacama Desert . Only to the south in Atacama Region does a Chilean Matorral vegetation exist. The northern portion of the matorral is made up by the Nolana leptophylla – Cistanthe salsoloides association while the southern half by the Skytanthus acutus – Atriplex deserticola association. The main portion

437-402: The path of a river is uplifted, the river must either divert, or slowly incise into the uplifted area, creating a gorge or canyon. As a channel bed drops, the water in the surrounding aquifer runs into the stream, lowering the water table. This modifies the flow regime of a stream, and can lead to a large reduction in summer flows. Prolonged incision can lower the water table to the point where

460-552: The roots of the riparian vegetation can no longer access it for water, causing the death of the riparian forest and thus a loss of soil stability, contributing to increased sedimentation. Riparian forests are some of the most productive and diverse ecosystems on the planet and are for this reason the focus of many restoration projects throughout the United States. At low erosion rates increased stream incision may make gentle slopes to erode creating convex-up forms. Convex slopes around

483-509: The territory. These are the associations of Lithrea caustica – Peumus boldus and Quillaja saponiana – Fabiana imbricata . From Bío Bío River to the south Nothofagus obliqua becomes the dominant tree species. Only Llanquihue Lake and the Puerto Montt area are exceptions to this being respectively dominated by Nothofagus dombeyi – Eucryphia cordifolia and Nothofagus nitida – Podocarpus nubigena . South of Puerto Montt

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506-451: The water's potential to cause erosion. Traditional logging in the West coast of the United States included many practices which increased river incision. Timber removal and the associated road construction facilitate runoff and thus increased erosion and sediment delivery to streams. Increases in sediment increases the water's stream power, increasing the stream's ability to do geomorphic work on

529-430: The water, which increase its density. Shear stress t {\displaystyle t} is proportional to water mass, gravity, and WSS: where t is shear stress (N/m2), ρ is density of flowing water, g is gravity on Earth, D is average water depth, and WSS is Water Surface Slope. This is analogous to the basal shear stress commonly used in glaciology. Increases in slope, depth, or density of water increase

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