SUMMARY / RELATED TOPICS

Avalanche

An avalanche is an event that occurs when a cohesive slab of snow lying upon a weaker layer of snow fractures and slides down a steep slope. Avalanches are triggered in a starting zone from a mechanical failure in the snowpack when the forces of the snow exceed its strength but sometimes only with gradual widening. After initiation, avalanches accelerate and grow in mass and volume as they entrain more snow. If the avalanche moves fast enough, some of the snow may mix with the air forming a powder snow avalanche, a type of gravity current. Slides of rocks or debris, behaving in a similar way to snow, are referred to as avalanches; the remainder of this article refers to snow avalanches. The load on the snowpack may be only due to gravity, in which case failure may result either from weakening in the snowpack or increased load due to precipitation. Avalanches initiated by this process are known as spontaneous avalanches. Avalanches can be triggered by other loading conditions such as human or biologically related activities.

Seismic activity may trigger the failure in the snowpack and avalanches. Although composed of flowing snow and air, large avalanches have the capability to entrain ice, rocks and other surficial material. However, they are distinct from slushflows which have higher water content and more laminar flow, mudslides which have greater fluidity, rock slides which are ice free, serac collapses during an icefall. Avalanches are not rare or random events and are endemic to any mountain range that accumulates a standing snowpack. Avalanches are most common during winter or spring but glacier movements may cause ice and snow avalanches at any time of year. In mountainous terrain, avalanches are among the most serious objective natural hazards to life and property, with their destructive capability resulting from their potential to carry enormous masses of snow at high speeds. There is no universally accepted classification system for different forms of avalanches. Avalanches can be described by their size, their destructive potential, their initiation mechanism, their composition and their dynamics.

Most avalanches occur spontaneously during storms under increased load due to snowfall and/or erosion. The second largest cause of natural avalanches is metamorphic changes in the snowpack such as melting due to solar radiation. Other natural causes include rain, earthquakes and icefall. Artificial triggers of avalanches include skiers and controlled explosive work. Contrary to popular belief, avalanches are not triggered by loud sound. Avalanche initiation can start at a point with only a small amount of snow moving initially. However, if the snow has sintered into a stiff slab overlying a weak layer fractures can propagate rapidly, so that a large volume of snow, that may be thousands of cubic meters, can start moving simultaneously. A snowpack will fail; the load is straightforward. However, the strength of the snowpack is much more difficult to determine and is heterogeneous, it varies in detail with properties of the snow grains, density, temperature, water content. These properties may all metamorphose in time according to the local humidity, water vapour flux and heat flux.

The top of the snowpack is extensively influenced by incoming radiation and the local air flow. One of the aims of avalanche research is to develop and validate computer models that can describe the evolution of the seasonal snowpack over time. A complicating factor is the complex interaction of terrain and weather, which causes significant spatial and temporal variability of the depths, crystal forms, layering of the seasonal snowpack. Slab avalanches form in snow, deposited, or redeposited by wind, they have the characteristic appearance of a block of snow cut out from its surroundings by fractures. Elements of slab avalanches include the following: a crown fracture at the top of the start zone, flank fractures on the sides of the start zones, a fracture at the bottom called the stauchwall; the crown and flank fractures are vertical walls in the snow delineating the snow, entrained in the avalanche from the snow that remained on the slope. Slabs can vary in thickness from a few centimetres to three metres.

Slab avalanches account for around 90% of avalanche-related fatalities in backcountry users. The largest avalanches form turbulent suspension currents known as powder snow avalanches or mixed avalanches; these consist of a powder cloud. They can form from any type of snow or initiation mechanism, but occur with fresh dry powder, they can exceed speeds of 300 kilometres per hour, masses of 10000000 tonnes. In contrast to powder snow avalanches, wet snow avalanches are a low velocity suspension of snow and water, with the flow confined to the track surface; the low speed of travel is due to the friction between the sliding surface of the track and the water saturated flow. Despite the low speed of travel, wet snow avalanches are capable of generating powerful destructive forces, due to the large mass and density; the body of the flow of a wet snow avalanche can plough through soft snow, can scour boulders, earth and other v

Andrzej Zgutczyński

Andrzej Zgutczyński is a former Polish footballer, a striker. During his club career he played for Mazur Ełk, Lech Poznań, Bałtyk Gdynia, Legia Warszawa, Górnik Zabrze, AJ Auxerre, Cercle Dijon Football, CS Meaux, he earned 5 caps for the Poland national football team and participated in the 1986 FIFA World Cup, where Poland reached the second round. His brother is former footballer Dariusz Zgutczyński. Andrzej Zgutczyński at 90minut.pl Andrzej Zgutczyński at WorldFootball.net

Sixth Federal Electoral District of Chiapas

The Sixth Federal Electoral District of Chiapas is one of the 300 Electoral Districts into which Mexico is divided for the purpose of elections to the federal Chamber of Deputies and one of 12 such districts in the state of Chiapas. It elects one deputy to the lower house of Congress for each three-year legislative period, by means of the first past the post system; the Sixth District of Chiapas is located in the centre of the state and covers the municipalities of Acala, Chiapa de Corzo, Chicoasén, Las Rosas, Nicolás Ruiz, San Lucas, Soyaló, Suchiapa and Venustiano Carranza, plus the southern and western parts of the municipality of Tuxtla Gutiérrez. The district's head town, where results from individual polling stations are gathered together and collated, is the city of Tuxtla Gutiérrez. Between 1996 and 2005, the Sixth District had a different configuration; the head town was Chiapa de Corzo and it covered the following municipalities: Acala, Chiapa de Corzo, Ixtapa, Nicolás Ruiz, San Lucas, Soyaló, Totolapa and Venustiano Carranza, all of which are still part of the district, plus: Bochil, La Concordia, Villa Corzo.

L Legislature 1976–1979: Leonardo León Cerpa LI Legislature 1979–1982: Alberto Ramón Cerdio Bado LII Legislature 1982–1985: LIII Legislature 1985–1988: LIV Legislature 1988–1991: Romeo Ruiz Armento LV Legislature 1991–1994: LVI Legislature 1994–1997: Rafael Ceballos Cancino LVII Legislature 2000–1999: Roberto Albores Guillén 1999–2000: Agustín Santiago Albores LVIII Legislature 2000–2003: Roberto Domínguez Castellanos LIX Legislature 2003–2006: Roberto Aguilar Hernández LX Legislature 2006–2009: Héctor Narcía Álvarez