SUMMARY / RELATED TOPICS

Erosion

In earth science, erosion is the action of surface processes that removes soil, rock, or dissolved material from one location on the Earth's crust, transports it to another location. This natural process is caused by the dynamic activity of erosive agents, that is, ice, air, plants and humans. In accordance with these agents, erosion is sometimes divided into water erosion, glacial erosion, snow erosion, wind erosion, zoogenic erosion, anthropogenic erosion; the particulate breakdown of rock or soil into clastic sediment is referred to as physical or mechanical erosion. Eroded sediment or solutes may be transported just a few millimetres, or for thousands of kilometres. Natural rates of erosion are controlled by the action of geological weathering geomorphic drivers, such as rainfall; the rates at which such processes act control. Physical erosion proceeds fastest on steeply sloping surfaces, rates may be sensitive to some climatically-controlled properties including amounts of water supplied, wind speed, wave fetch, or atmospheric temperature.

Feedbacks are possible between rates of erosion and the amount of eroded material, carried by, for example, a river or glacier. Processes of erosion that produce sediment or solutes from a place contrast with those of deposition, which control the arrival and emplacement of material at a new location. While erosion is a natural process, human activities have increased by 10-40 times the rate at which erosion is occurring globally. At well-known agriculture sites such as the Appalachian Mountains, intensive farming practices have caused erosion up to 100x the speed of the natural rate of erosion in the region. Excessive erosion causes both "on-site" and "off-site" problems. On-site impacts include decreases in agricultural productivity and ecological collapse, both because of loss of the nutrient-rich upper soil layers. In some cases, the eventual end result is desertification. Off-site effects include sedimentation of waterways and eutrophication of water bodies, as well as sediment-related damage to roads and houses.

Water and wind erosion are the two primary causes of land degradation. Intensive agriculture, roads, anthropogenic climate change and urban sprawl are amongst the most significant human activities in regard to their effect on stimulating erosion. However, there are many prevention and remediation practices that can curtail or limit erosion of vulnerable soils. Rainfall, the surface runoff which may result from rainfall, produces four main types of soil erosion: splash erosion, sheet erosion, rill erosion, gully erosion. Splash erosion is seen as the first and least severe stage in the soil erosion process, followed by sheet erosion rill erosion and gully erosion. In splash erosion, the impact of a falling raindrop creates a small crater in the soil, ejecting soil particles; the distance these soil particles travel can be as much as 0.6 m vertically and 1.5 m horizontally on level ground. If the soil is saturated, or if the rainfall rate is greater than the rate at which water can infiltrate into the soil, surface runoff occurs.

If the runoff has sufficient flow energy, it will transport loosened soil particles down the slope. Sheet erosion is the transport of loosened soil particles by overland flow. Rill erosion refers to the development of small, ephemeral concentrated flow paths which function as both sediment source and sediment delivery systems for erosion on hillslopes. Where water erosion rates on disturbed upland areas are greatest, rills are active. Flow depths in rills are of the order of a few centimetres or less and along-channel slopes may be quite steep; this means that rills exhibit hydraulic physics different from water flowing through the deeper, wider channels of streams and rivers. Gully erosion occurs when runoff water accumulates and flows in narrow channels during or after heavy rains or melting snow, removing soil to a considerable depth. Valley or stream erosion occurs with continued water flow along a linear feature; the erosion is both downward, deepening the valley, headward, extending the valley into the hillside, creating head cuts and steep banks.

In the earliest stage of stream erosion, the erosive activity is dominantly vertical, the valleys have a typical V cross-section and the stream gradient is steep. When some base level is reached, the erosive activity switches to lateral erosion, which widens the valley floor and creates a narrow floodplain; the stream gradient becomes nearly flat, lateral deposition of sediments becomes important as the stream meanders across the valley floor. In all stages of stream erosion, by far the most erosion occurs during times of flood when more and faster-moving water is available to carry a larger sediment load. In such processes, it is not the water alone

Salem Township, Clarion County, Pennsylvania

Salem Township is a township in Clarion County, United States. The population was 881 at the 2010 census; the township is bordered to the west by Venango County. The unincorporated community of Lamartine is in the western part of the township, along Pennsylvania Route 208, which leads east 5 miles to Knox and southwest 5 miles to Emlenton on the Allegheny River; the eastern half of Kahle Lake, a reservoir on Mill Creek, is in the township north of Lamartine. According to the United States Census Bureau, Salem Township has a total area of 16.3 square miles, of which 16.0 square miles is land and 0.27 square miles, or 1.73%, is water. As of the census of 2000, there were 852 people, 311 households, 250 families residing in the township; the population density was 53.0 people per square mile. There were 349 housing units at an average density of 21.7/sq mi. The racial makeup of the township was 99.06% White, 0.12% Native American, 0.23% Asian, 0.59% from two or more races. Hispanic or Latino of any race were 0.47% of the population.

There were 311 households, out of which 35.7% had children under the age of 18 living with them, 69.8% were married couples living together, 6.8% had a female householder with no husband present, 19.6% were non-families. 15.8% of all households were made up of individuals, 9.0% had someone living alone, 65 years of age or older. The average household size was 2.74 and the average family size was 3.06. In the township the population was spread out, with 26.8% under the age of 18, 6.0% from 18 to 24, 30.5% from 25 to 44, 23.5% from 45 to 64, 13.3% who were 65 years of age or older. The median age was 39 years. For every 100 females there were 100.9 males. For every 100 females age 18 and over, there were 95.0 males. The median income for a household in the township was $35,385, the median income for a family was $37,375. Males had a median income of $32,321 versus $23,393 for females; the per capita income for the township was $15,742. About 9.2% of families and 11.3% of the population were below the poverty line, including 18.6% of those under age 18 and 10.4% of those age 65 or over.

Salem Township listing at Clarion County Association of Township Officials

Li Eventi di Filandro Et Edessa

Li Eventi di Filandro Et Edessa is an opera by Marco Uccellini based on a libretto by Gaddo Gaddi. It was first performed at the Teatro del Collegio dei Nobili in Parma in 1675. Creonte, king of Egypt is at war with Artaserse, King of Persia, but Artaserse’s son prince Laoconte is in love with Edessa, daughter of Creonte. Laoconte sends his trusted friend Filandro of Lydia to Edessa, but he falls in love with her himself. Edessa in turn falls in love with him, they return to Egypt where they live in hiding. Laoconte comes to Egypt to press his own suit but Creonte imprisons him, whereupon the Persians invade and conquer Egypt. Although the libretto has survived, Uccellini’s score has not. Carlo Andrea Clerici, Carlo Antonio Riccardi, Francesco Castelli, Giovanni Battista Pezzali, Pauolo Castelli, Giorgio Martinelli, Francesco Folchi, Giovanni Matteo Gentilini, Francesco Orsi, Federico Sudari, Francesco Bardi, Pauolo Pasquale, Stefano Odoardi