   #copyright

Santamaría (volcano)

2007 Schools Wikipedia Selection. Related subjects: Central & South American
Geography

                      Santa María
   Elevation     3,772 metres (12,372 feet)
   Location      Quetzaltenango Department, Guatemala
   Range         Sierra Madre
   Coordinates   14.756° N 91.552° W
   Type          Stratovolcano
   Last eruption 2006 (continuing)

   Volcán Santamaría is a large active volcano in the Western Highlands of
   Guatemala, close to the city of Quetzaltenango. Its eruption in 1902
   was the second-largest eruption of the 20th century, and the third
   large eruption of that one year, after Mount Pelée in Martinique and
   Soufrière in St. Vincent.

   The 1902 eruption blasted away most of one side of the 3,772 m tall
   mountain. Some 5.5 cubic km (1.3 cubic miles) of volcanic material was
   ejected during the 19-day eruption, and the ash column reached heights
   of up to 28 km. The eruption devastated the surrounding areas.

   In 1922, a new volcanic vent formed in the enormous crater, and formed
   a new volcano, named Santiaguito. Santiaguito has been erupting ever
   since and now forms a cone a few hundred metres tall, reaching an
   elevation of about 2,500 m. Today, it is possible to climb to the top
   of Santamaría and look down on the ongoing eruptions at Santiaguito,
   1,200m below, a situation which may be unique in the world.

Geological history

   Steam rises from Santiaguito. The area of the flank destroyed by the
   1902 eruption can be clearly seen. Lahar deposits snake down river
   valleys to the left of the image
   Enlarge
   Steam rises from Santiaguito. The area of the flank destroyed by the
   1902 eruption can be clearly seen. Lahar deposits snake down river
   valleys to the left of the image

   Santamaría is part of the Sierra Madre range of volcanoes, which
   extends along the western edge of Guatemala, separated from the Pacific
   Ocean by a broad plain. The volcanoes are formed by the subduction of
   the Cocos Plate under the Caribbean Plate.

   Eruptions at Santamaría are estimated to have begun about 30,000 years
   ago. For several thousand years, eruptions seem to have been small and
   frequent, building up the large cone of the volcano, reaching about
   1,400 m above the plain on which the nearby city of Quetzaltenango
   sits. Following the cone-building eruptions, activity seems to have
   changed to a pattern of long periods of repose followed by the emission
   of small lava flows from vents on the flanks.

   The cone built by the eruptions had a volume of about 10 km³, and
   consisted of a mixture of basalt and andesite lavas.

1902 eruption

   The first eruption of Santamaría in recorded history occurred in
   October 1902. Before 1902 the volcano had been dormant for at least 500
   years and possibly several thousand years, but its awakening was
   clearly indicated by a seismic swarm in the region starting in January
   1902. The eruption began on 24 October, and the largest explosions
   occurred over the following two days, ejecting an estimated 5.5 km³ of
   magma. The eruption was one of the largest of the 20th century,
   comparable in magnitude to that of Mount Pinatubo in 1991.

   The pumice formed in the climactic eruption fell over an area of about
   273,000 km², and volcanic ash was detected as far away as San
   Francisco, 4,000 km away. The eruption tore away much of the
   south-western flank of the volcano, leaving a crater about 1 km in
   diameter and about 300 m deep, stretching from just below the summit to
   an elevation of about 2,300 m.

   Because of the lack of previous activity at Santamaría, local people
   did not recognise the preceding seismicity as warning signs of an
   eruption. At least 5,000 people died as a result of the eruption
   itself, and a subsequent outbreak of malaria killed many more.

Santiaguito

   The volcano as seen from the nearby city of Quetzaltenango
   Enlarge
   The volcano as seen from the nearby city of Quetzaltenango

   The 1902 eruption was followed by 20 years of dormancy. In 1922, new
   eruptions began, with the extrusion of a lava dome in the crater left
   by the 1902 eruption. The dome was christened Santiaguito, and since
   then, activity has been virtually constant. Santiaguito now reaches a
   height of about 2,500 m, and has a volume of about 1 km³. From the
   summit of Santamaría, it is possible to look down on the eruptions at
   Santiaguito a mile below.

   Dome growth at Santiaguito has alternated between growth caused by the
   emission of lava flows, and inflation caused by the injection of magma
   into the middle of the dome. These dome growth types are described by
   volcanologists as exogenous and endogenous respectively. Activity has
   been concentrated at several different vents, and Santiaguito now has
   the appearance of several overlapping domes.

   Although most of Santiaguito's eruptive activity has been relatively
   gentle, occasional larger explosions have occurred. In 1929, part of
   the dome collapsed, generating pyroclastic flows which killed several
   hundred people. Occasional rockfalls have generated smaller pyroclastic
   flows, and vertical eruptions of ash to heights of a few kilometres
   above the dome are common. :]]]

Volcanic hazards at Santamaría

   A hot lahar rushes down a river valley near El Palmar in 1989
   Enlarge
   A hot lahar rushes down a river valley near El Palmar in 1989

   The areas to the south of Santamaría are considerably affected by
   volcanic activity at Santiaguito. Currently, the most common volcanic
   hazard at Santamaría is lahars, which frequently occur in the rainy
   season due to heavy rainfall on loose volcanic deposits. The town of El
   Palmar, 10 km from Santiaguito, has been destroyed twice by lahars from
   Santiaguito, and infrastructure such as roads and bridges have been
   repeatedly damaged. Lahar deposits from Santiaguito have affected
   rivers all the way downstream to the Pacific Ocean.

   Lava flows do not occur frequently from Santiaguito, and tend not to
   stretch more than a few kilometres from the dome. The magma at
   Santiaguito is rich in silica and is thus highly viscous. Flows are
   therefore very slow-moving and are of little danger to human life,
   although property damage may occur. Fast-moving pyroclastic flows can
   occur, and these may travel several kilometres from the dome.

   One hazard which could be devastating is the collapse of Santamaría
   itself. The 1902 crater has left the southern flank of the mountain
   above Santiaguito highly over-steepened, and a large earthquake or
   eruption from Santiaguito could trigger a huge landslide, which might
   cover up to 100 km². However, this is thought to be unlikely in the
   short term.

   In light of the threat it poses to nearby populations, Santamaría has
   been designated a Decade Volcano, identifying it as a target for
   particular study by volcanologists to mitigate any future natural
   disasters at the volcano.

   Retrieved from "
   http://en.wikipedia.org/wiki/Santamar%C3%ADa_%28volcano%29"
   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.
