The San Salvador Volcano (also known as Quezaltepeque or El Boquerón) is a stratovolcano situated northwest to the city of San Salvador. The crater has been nearly filled with a relatively newer edifice, the Boquerón volcano. San Salvador is adjacent to the volcano and the western section of the city actually lies among its slopes. Due to this close proximity, any geological activity of the volcano, whether eruptive or not, has the potential to result in catastrophic destruction and death to the city. Despite this, the volcano is iconic of the city, and several TV and radio antennas are situated on the El Picacho peaks and the crater of Boqueron. El Picacho, the prominent peak is the highest elevation (1,960 metres altitude).
Geology San Salvador is the result of subduction as the Cocos plate subducts under the Caribbean plate. More than 90% of subsurface lithology is from the Cenozoic and Quaternary periods, pointing to relatively young volcanic activity. Since 600 CE, there have been six volcanic eruptions: 640 CE ± 30 years, 1200 CE, 1575 CE, 1658-1659 CE, an unconfirmed eruption in 1806 CE, and 1917 CE. Eruptions have been episodic for the past 70,000 years. Most eruptions are violent to effusive, erupting pumice, pyroclastic material, and basalt. Most past eruptions have not been voluminous. One exception was an eruption between 40-30 kyr that deposited a tephra layer that 1 meter thick within 10 kilometers of the volcano.
1917 eruption
The most recent eruption occurred on 7 June 1917. Rated as a VEI-3 on the volcanic explosivity index, it was classified as a Strombolian-type eruption that erupted ash on the SW slope of the volcano as well as a basaltic lava flow. At 6:55pm local time, a strong 6.5 magnitude earthquake struck San Salvador. About 35 minutes later at 7:30pm local time, another large 6.4 earthquake struck the city. These earthquakes were devastating to San Salvador with heavy damage to most buildings and fires that raged out of control. Shortly after the second earthquake, the eruption began. Several fissures opened on the northwest flank of the volcano. The crater lake at the summit was completely evaporated within a month. The eruption created the small scoria cone (Boqueroncito) which is (≈30–40 m) high. Activity continued intermittently until it ended in November 1917.
Boquerón edifice
The main edifice, known as the Boquerón edifice, formed between 700 and 1,000 years ago, filling up a former caldera. The crescent-shaped ridge on the northeast side of the volcano is a remnant of the caldera rim. The lavas of the Boquerón edifice contain more alkali elements and iron oxide than the lavas of the older edifice. Around 800 years ago, the present day crater was formed in a violent explosion. The crater, which gives it the present name (Boquerón means "big mouth" in Spanish) is 1.5 km in diameter and 500m deep. Within the crater around the upper walls, crops are cultivated by the locals who live on the volcano. The magma chamber which the volcano sits upon contains a number of fissures which protrude along the flanks and sides of the volcano. The northwest (N40W) fissure has been the most active recently, with such significant eruptive events, such as the Loma Caldera eruption which buried the ancient village of Ceren and the eruption of El Playon (1658–71) which buried the town of Nexapa. The citizens relocated to Nejapa and nowadays the eruption is celebrated annually. The most recent eruption in 1917 caused a flank eruption on the volcano along the N40W fissure. During this eruption, the crater lake inside the Boquerón evaporated and a cinder cone appeared, christened 'Boqueroncito'.
Gallery
See also List of volcanoes in El Salvador
References
Sources Williams, H., and Meyer-Abich, H., 1955 Volcanisim in the southern part of El Salvador: University of California Publication in geological Sciences v. 32 pp1–64 Sofield. D., Eruptive history and volcanic hazards of Volcan San Salvador, in Rose W.I. et al., Natural Hazards in El Salvador: Bolder, Colorado, Geological Society of America Special Paper 375, pp 147–158. Fairbrothers G E., Carr M J., and Mayfield F G., Temporal Magmatic Variation at Boqueron Volcano, El Salvador. Contrib. Mineral. Petrol. v 67, pp 1–9 (1978)
External links
Topographical hazard zonation maps regarding the volcano and the city Archived 17 May 2014 at the Wayback Machine
