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 | |
| 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
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.