Giétro Glacier
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The Giétro Glacier or Giétroz Glacier () is a 4 km long valley
glacier A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
located in south-western
Switzerland Switzerland, officially the Swiss Confederation, is a landlocked country located in west-central Europe. It is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland ...
. The 1818 Giétro Glacier catastrophe, which led to a lake outburst flood, is one of the most famous and most disastrous historical cases in the
Swiss Alps The Alps, Alpine region of Switzerland, conventionally referred to as the Swiss Alps, represents a major natural feature of the country and is, along with the Swiss Plateau and the Swiss portion of the Jura Mountains, one of its three main Physica ...
.


Description

The Giétro Glacier lies on the northern side of the
Pennine Alps The Pennine Alps (, , , ), sometimes referred to as the Valais Alps (which are just the Northern Swiss part of the Pennine Alps), are a mountain range in the western part of the Alps. They are located in Italy (the Aosta Valley and Piedmont) an ...
in the Swiss canton of
Valais Valais ( , ; ), more formally, the Canton of Valais or Wallis, is one of the cantons of Switzerland, 26 cantons forming the Switzerland, Swiss Confederation. It is composed of thirteen districts and its capital and largest city is Sion, Switzer ...
. It is located in the upper Bagnes Valley, south of
Martigny Martigny (; , ; ) is the capital city of the district of Martigny (district), Martigny, cantons of Switzerland, canton of Canton of Valais, Valais, Switzerland. It lies at an elevation of , and its population is approximately 20,000 inhabitants ( ...
and
Verbier Verbier () is a village located in south-western Switzerland in the canton of Valais Valais ( , ; ), more formally, the Canton of Valais or Wallis, is one of the cantons of Switzerland, 26 cantons forming the Switzerland, Swiss Confederatio ...
. The length of the glacier is 4.45 km (2017) and its area is 5.3 km2 (2017). The glacier is fed by the snows of Mont Blanc de Cheilon (3,870 m) and La Ruinette (3,875 m). On the upper part, the glacier is relatively flat. It descends to the north on the side of Mont Rouge du Giétro and then curves to the west between Le Pleureur and Mont Rouge. On the lower part, the glacier reaches a steepness of 40% forming a large number of
crevasse A crevasse is a deep crack that forms in a glacier or ice sheet. Crevasses form as a result of the movement and resulting stress associated with the shear stress generated when two semi-rigid pieces above a plastic substrate have different rate ...
s. The terminus is located at about 2,750 metres. Part of the glacier is linked to the Cheilon Glacier through the Col du Cheilon (3,243 m). The water generated by the glacier ends in the Lake Mauvoisin (artificial lake) and then reaches the Dranse de Bagnes, a tributary of the Rhone.


Glacier catastrophes

The Giétro Glacier is known to have caused many deaths in the valley during historical times. The earliest known
glacial lake outburst flood A glacial lake outburst flood (GLOF) is a type of outburst flood caused by the failure of a dam containing a glacial lake. An event similar to a GLOF, where a body of water contained by a glacier melts or overflows the glacier, is called a jà ...
was recorded in 1595, and caused 140 deaths. More recently in 1818 a similar lake outburst flood occurred killing 44 people. In the latter case a hole was drilled through the glacier to limit the level of waters. After an increase of the glacier during the "
Year Without a Summer The year 1816 is known as the Year Without a Summer because of severe climate abnormalities that caused average global temperatures to decrease by . Summer temperatures in Europe were the coldest of any on record between 1766 and 2000, resultin ...
", an ice cone started to form in 1816 in the valley. It was created by the accumulation of the falling
serac A serac () (from Swiss French ''sérac'') is a block or column of glacial ice, often formed by intersecting crevasses on a glacier. Commonly house-sized or larger, they are dangerous to mountaineers, since they may topple with little warning. ...
s of the terminus. A lake was formed but it emptied on 27 May 1817 without causing any fatalities. In April 1818 the lake measured about 2 km in length. On 10 May 1818, the engineer Ignaz Venetz was called by the canton. To stop the rapid rise of waters, he decided to drill a hole through the ice. The work began one day later. A tunnel was drilled from the two sides, about 20 metres above the level of the lake. An avalanche of ice occurred on 18 May but without any casualties. A secondary tunnel was then drilled for safety reasons. A week later the level of the lake reached 10 metres below the tunnel. On 27 May an enormous piece of ice detached itself from the cone in the lake and floated to the surface while making terrible noise; everybody escaped. They went back to work two days later. The 198 metre-long hole was completed on 4 June. Other large pieces of ice detached from the cone and floated back. The waters finally reached the level of the hole on 13 June, 22:00. They continued to rise until 14 June, when the level of the lake began to fall because of the erosion of the hole by the waterfall. Some water also ran out from the base of the cone. Only two men stayed in place; Venetz warned the inhabitants of the valley of the danger. On the morning of 16 June, terrible noises and violent detonations were heard. The cone began to crack. A group of British tourists and a drawer from Lausanne visited the place with Venetz. In the afternoon, Venetz and the workers escaped to the heights of Fionnay. Finally, at 16:30, the dam broke and 18 million m3 of water invaded the valley. Half an hour later the lake was empty. The flood reached the village of Bagnes 10 minutes later; the alert was given to Martigny before 18:00, but too late. The wave invaded Martigny-Bourg a few minutes later. The rise of the waters was observed along the Rhone, at 19:00 in Saint-Maurice and at 23:00 on
Lake Geneva Lake Geneva is a deep lake on the north side of the Alps, shared between Switzerland and France. It is one of the List of largest lakes of Europe, largest lakes in Western Europe and the largest on the course of the Rhône. Sixty percent () ...
.


See also

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List of glaciers in Switzerland This is a non-exhaustive list of the major glaciers in Switzerland. It contains their surface area, their lengths since the start of measurement and the most current year, their height and their outflow. Most of them are retreating and many wil ...


References


External links

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Swisstopo Swisstopo is the official name for the Swiss Federal Office of Topography, Switzerland's national mapping agency. The current name was made official in 2002. It had been used as the domain name for the homepage of the instituteswisstopo.admi ...
maps
Swiss glacier monitoring network
{{DEFAULTSORT:Gietro Glacier Glaciers of Valais Bagnes Glacial lake outburst floods