Santiguito is the name of a dome complex that grew out of the partial flank collapse scar of the Santa Maria volcano following its VEI 6 eruption in 1902. It began erupting in 1922 and has been in near continuous eruption since its formation.
Recent activity has included pyroclastic flows, explosions and ash fall.
Web cams can be found here (courtesy Volcano Discovery): http://webcams.volcanodiscovery.com/Santiaguito
Michigan Technological University Geology Department has a presence in Guatemala assisting Guatemalan geologists with monitoring and reporting of a number of active volcanoes. http://www.geo.mtu.edu/volcanoes/Volcanoes/Index.html
Santa Maria is a 3,770 m tall stratovolcano that is part of the Sierra Madre line of volcanoes which extend NW to SE parallel to the coast of western Guatemala. It is separated from the ocean by a broad plain. The Sierra Madre is in turn part of the Central America Volcanic Arc.
The volcano dates back some 30,000 years. It went through several thousand years of eruptions that were small and frequent building the cone. Activity changed to long periods of quiet followed by emissions of small lava flows from vents on the cone. Its eruptive products are primarily dacite and andesite / basaltic andesite.
The period of quiet before the 1902 eruption was at least 500 years and may have been many thousands of years long.
The 1902 eruption was one of the three most powerful in the 20th Century, exceeded only by Katmai and Pinatubo. 1902 was a tough year for eruptions in the western hemisphere as it was the same year that Mount Pelee devastated Saint-Pierre, Martinique with pyroclastic flows killing 30,000.
The crater created by the 1902 eruption has left portions of the cone very steep and perhaps susceptible to flank collapse. To my untrained eye, it looks more like a partial flank collapse than a crater. In any event, it has been filled over the last 62 years with a dome complex and over 1 km3 of lava flows plus slide debris from the cone above it.
Lahars are a significant and ongoing hazard from this volcano.
The Santiaguito dome complex has three vents with Caliente being the currently active one. The other two dormant vents are La Mitad and El Brujo. Activity has migrated westward toward the newer Caliente vent.
Santiaguito also produces thick, blocky lavas which periodically break and produce pyroclastic flows. Extrusion of lava flows is not periodic and the activity appears to wax and wane over time.
There are nearly 120,000 within 10 km of the volcano and nearly 6.2 million within 100 km.
Two neighboring volcanoes Siete Orejas and de Cerro Quermado (Almolonga) lie less than 10 km NW and NE respectively, between Santa Maria and the closest city Quetzaltenango. Almolonga is the remains of a large stratovolcano that started building some 84,000 years ago. It went caldera leaving a 3.3 km diameter caldera. The caldera was subsequently filled with numerous lava domes, Cerro Quemado being the largest. It had a flank collapse some 1,150 years before present. Siete Orejas suffered a flank collapse to the south leaving a horseshoe shape in the volcano. That collapse is undated but thought to be in excess of 85,000 years old.
The 18 x 12 km diameter Atitlan Caldera formed some 85,000 years ago. It was subsequently filled with a lake and three stratovolcanoes. It is located some 40 km east of Santiaguito. This is clearly a very nasty volcanic part of the world.
Jessica Ball in the AGU Blogosphere has written several posts on Santa Maria, Santiaguito and their eruptions in 1902 and 1929. They are well worth poking around. I will summarize much of what she wrote in the following section.
Santa Maria woke up from a 500 year period of quiet on October 25, 1902. The eruption was preceded by seismic activity felt locally. The problem was that as that locale had no previous volcanic activity, the tectonic warnings were not heeded.
The eruption kicked off at around 1700L with noise from the volcano. Shortly after the noise ended, dark clouds were seen over the volcano. They were first thought to be a thunderstorm over the mountain. Ash described as sand started falling on nearby towns. During this initial ash fall, the prevailing wind changed.
Around 1900L a glow around the crater and lightning in the eruptive column was seen in an enormous black cloud lit with powerful electric discharges. These discharges produced thunder. As the night progressed, the eruption increased in violence and the size of pumice falling from the sky increased. Maximum intensity of the eruption was around 1100L the next morning. Intensity decreased over the next 24 hours, and the air began to clear a bit. The eruption continued in varying degree for the rest of the week as the black ash laden clouds changed to much lighter steam-dominant plumes.
Depending who you read, total material ejected was 5.5 – 10 km3, making this eruption a solid VEI6. Total coverage by the ash and pumice fall was some 273,000 km2.
Following the eruption, a new crater had formed on the flank of Santa Maria in what looks like a partial flank collapse. It measures roughly 1 by 2 km. The new crater was filled over time by water and landslides from the steeper part of the volcano above the new crater. Lahars were and still are a significant ongoing threat from the volcano.
The eruption ended up killing over 5,000 people and wiped out most of the coffee crop. Ash went as far as Mexico. The plume topped out above 28 km.
There was a lull in activity until 1922 when the Santiaguito lava dome started to grow in the new crater. It grew quickly and continuously until 1929 when it suffered a partial collapse. The collapse triggered a significant pyroclastic flow which covered at least 15 km2 near the volcano killing several hundred to as many as 5,000 people.
The dome is essentially erupting the same sort of dacite and andesite material that was erupted in 1902. Since its formation, it has produced almost 1 km3 of dacitic lavas out of several associated vents. In between the lava flows have been pyroclastic flows, vertical eruptions, and ash. These in turn keep getting turned into lahars as local rains move the loose materials down slope into local river valleys.
The volcanic system is located near the triple junction of the Cocos, North American and Caribbean plates. Crustal thickness under it is greater than 45 km.
As we saw with our previous post on the neighboring (79 km east) Volcan Fuego, the primary tectonic forces in the region are driven by the interaction of the three plates listed in the last paragraph. Cocos is subducting under the Caribbean Plate with the subduction trench as the Mid America Trench in the Pacific Ocean to the west of the Sierra Madre volcanoes. A transform fault which is the boundary between the North American and Caribbean Plates lies to the north of the volcano. https://volcanohotspot.wordpress.com/2016/04/04/continuing-eruptions-at-volcan-de-fuego-guatemala/#more-18164
The Sierra Madre is certainly a vigorously active string of active volcanoes. It includes nearly 30 volcanoes in various stages of activity, a few huge calderas and numerous examples of flank collapse and lateral blasts. As long as the tectonics continue to grind subduction into the Mid-American Trench, there is no reason to believe the activity will change much in the foreseeable future.
Santa Maria – Santiaguito has already cooked off a VEI 6 eruption just over a century ago. There is no reason to believe that another such eruption is not in the future.
One humorous (at least to me) thing I ran across looking into this is the environmentalist organization Nature Conservancy has decided that the Sierra Madre is pristine and must be saved from the ravages of mankind. Interesting perspective, that, especially given the history of massive eruptions along the range. Makes you wonder if they know that the surrounding countryside gets occasionally carpeted with tens to hundreds of cubic kilometers of ash and pyroclastic flows from the active volcanoes they are saving. Ironic? Or perhaps clueless. http://www.nature.org/ourinitiatives/regions/centralamerica/guatemala/placesweprotect/sierra-madre-volcanoes.xml