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Galeras

2007 Schools Wikipedia Selection. Related subjects: Geology and geophysics

                   Galeras
   Galeras, March 1989
   Elevation     4,276 metres (14,029 feet)
   Location      Colombia
   Range         Andes
   Coordinates   1°13′0″N, 77°22′0″W
   Type          Stratovolcano
   Last eruption 2005

   Galeras (Urcunina among the indigenous people) is a volcano in
   Colombia, near the city of Pasto. Its summit lies 14,029 feet (4276 m)
   above sea level. It has erupted frequently since the Spanish conquest,
   and in 1993, an eruption killed nine people, including five scientists
   who had descended into the volcano's crater to sample gases .

Geological history

   Galeras has been an active volcano for at least a million years. Two
   major caldera-forming eruptions have occurred, the first about 560,000
   years ago in an eruption which expelled about 15 cubic kilometres of
   material, and the second some time between 40,000 and 150,000 years
   ago, in a smaller but still sizable eruption of 2km³ of material.
   Subsequently, part of the caldera wall has collapsed, probably due to
   instabilities caused by hydrothermal activity, and later eruptions have
   built up a smaller cone inside the now horseshoe-shaped caldera.

   At least six large eruptions have occurred in the last 5000 years, most
   recently in 1886, and there have been at least 20 small to medium sized
   eruptions since the 1500s. In light of its violent eruption history and
   proximity to the 450,000 people of Pasto, Galeras was designated a
   Decade Volcano in 1991, identifying it as a target for detailed study
   as part of the United Nations' International Decade for Natural
   Disaster Reduction.

1993 eruption

   Galeras had become active in 1988 after 10 years of dormancy. In 1993,
   the volcano erupted when several volcanologists were inside the crater
   taking measurements. The scientists had been visiting Pasto for a
   conference related to the volcano's designation as a Decade Volcano.
   Six were killed, together with three tourists on the rim of the crater.
   Stanley Williams was one of the survivors. He suffered serious injuries
   after being struck by lava bombs, but was rescued from the crater some
   hours later.

   Williams later wrote a book about his ordeal, entitled Surviving
   Galeras. However, controversy has since surrounded many of his claims.
   Detractors claim that his aim was to glorify himself, to the extent of
   claiming to be the only survivor among those on the mountain that day,
   when in fact seven others survived. It is also claimed that Williams
   ignored clear signs that an eruption was imminent, thus placing himself
   and others in danger unnecessarily.

Current activity

   Space radar image of Galeras Volcano
   Enlarge
   Space radar image of Galeras Volcano

   Activity at a low level has continued at Galeras, with small explosions
   occasionally dusting nearby villages and towns with ash. The volcano
   has continued to be well studied, and predictions of eruptions at the
   volcano have improved. One phenomenon which seems to be a reliable
   precursor to eruptive activity is a low-frequency seismic event known
   as a 'tornillo'. These have occurred before about four-fifths of the
   explosions at Galeras, and the number of tornillo events recorded
   before an eruption is also correlated with the size of the ensuing
   eruption.

   More than 100 minor tremors were felt during a major eruption in April,
   2002, although no damage or injury was reported. An eruption in
   November 2005 forced an evacuation of the dangerous area surrounding
   the volcano and about 9400 people from nearby villages (mostly farmers)
   were ordered to leave. The city of Pasto, about 9 km from the volcano,
   was blanketed by a layer of ash after the volcanic explosion, forcing
   the residents to don goggles and face masks.

   Numerous minor tremors and ash emissions since March, 2006, culminated
   on Wednesday, July 12, 2006 in three explosive eruptions, producing an
   ash and gas column reaching an altitude of 8 kilometers. Rock falls and
   pyroclastic flows were reported from towns as distant as Consacá, 11.4
   kilometers west of the main crater. The Colombian government has
   repeatedly ordered evacuations to temporary shelters, of more than 8500
   people residing in the highest risk areas surrounding the volcano ,
   with hopes of eventual assistance toward permanent relocation.
   Retrieved from " http://en.wikipedia.org/wiki/Galeras"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
