Major Volcanoes of the World

Santamaria

Volcán Santa María is a large active volcano in the Western Highlands of Guatemala, close to the city of Quetzaltenango. Its eruption in 1902 was one of the three largest eruptions of the 20th century, and the third large eruption of that one year, after Mount Pelée in Martinique and Soufrière in St. Vincent. It was also one of the five biggest eruptions of the past 200 (and probably 300) years.
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 Santa María and look down on the ongoing eruptions at Santiaguito, 1,200m below, a situation which may be unique in the world.

Geological history
Santa María 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 Santa María 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.