El Reventador is one of the most active volcanoes in Ecuador and has been in near continuous eruption since 2008. The name translates variously as The Exploder, The Burster, The Destroyer and occasionally as The Ripper depending on context. I chose the latter for the title of this post. Our Spanish speakers are invited to kick me back into play should I have wandered too far afield (highly likely).
It is part of the Andean Volcanic Belt, the Northern Volcanic Zone, which stretches from Ecuador in the south to Columbia in the north. The Ecuador portion of the zone has at least 24 and perhaps as many as 55 stratovolcanoes in various states of activity. El Reventador is one of the eastern most volcanoes in the zone.
Generally, the volcanoes are andesitic basalt stratovolcanoes which erupt some combination of andesite, basalt, dacite, occasionally rhyolite. Eruptive products include pyroclastic flows, lava, tephra and ash. Magma is highly silica, in many cases approaching 50%. The zone is littered with flank collapses and calderas. As these volcanoes sit quite high in the Andes, there are snow packs on the flanks of the cones, which in turn lead to significant lahars during eruptive episodes.
The capital city of Ecuador, Quito sits on the flank of Pichincha volcano, which is also active. Cotopaxi, yet another stratovolcano that sits some 50 km south of Quito is showing current signs of unrest, with an eruption possible in the not so distant future. Cotopaxi has erupted some 50 times since the mid 18th Century and is considered a most dangerous mountain. Pichincha had major eruptions in 1553, 1660 and most recently in 1999. It also occupies a caldera.
This is clearly a very active and very dangerous piece of real estate.
For its part, El Reventador is some 95 km NE of Quito. Its active cone occupies the remains of at least two flank collapses. The mountain tops out above 3,500 m. The Volcano Discovery web site suggests that the mountain started building some 400,000 years ago and suffered its first flank collapse to the east toward the Amazon Basin some 30,000 years ago. That collapse moved and deposited some 20 km3 of debris and left a 4 km diameter caldera. A second flank collapse took place some 20,000 years ago and deposited some 8 km3 of debris downhill toward the Amazon basin.
You can find webcams here: http://volcano-webcams.com/m/Reventador
The largest observed eruption of El Reventador took place in 2002, starting in November. It ended three months later with an overall VEI of 4. Ash fell up to 200 km west of the volcano, dusting Ecuador’s capital of Quito nicely. Pyroclastic flows traveled some 8 km from the crater. The eruption touched some 2 million people at some level. I have found no reports of dead due to the eruption, mostly due to the volcano’s somewhat remote location, though there were serious injuries reported for a few people.
The 2002 eruption took place after a period of quiet lasting between 27 – 34 years (depending on source). It was remarkable for being a very short trigger, with only six hours of precursory earthquakes before the initial blast, though there was some unrest noted a month earlier in October which is thought to be the beginning of the new magma intrusion into the reservoir. http://www.buffalo.edu/news/releases/2002/11/5946.html
The mechanism driving the 2002 eruption is believed to have been a magma intrusion into a homogeneous andesite reservoir starting around October 2002. The reservoir is thought to sit some 11 km below the volcano. The new basalt mixed with and destabilized the andesite crystal mush of the existing reservoir.
There were three eruptive periods since the 2002 explosion, 2004, 2007, and the current eruptive period starting in 2008. The middle eruptions were classified as VEI 2 eruptions ejecting ash, pyroclastic and lava flows. The 2002 eruption was preceded some three months by seismic swarms thought to be the introduction of new magma into the reservoir.
Current activity started in July 2008 and has been nearly continuous since it first started. This activity has led some volcanologists to conclude that magmatic recharge of the reservoir below the volcano is frequent and is in turn responsible for the frequent eruptions of the volcano. Activity has included frequent explosions, lava flows, dome building, pyroclastic flows, ash and tephra ejection and deposits. http://www.sciencedirect.com/science/article/pii/S0377027308001005
Historic eruptions for the last 600 years have been in the VEI 2 – 3 range.
Nominally, El Reventador could be described as a standard back arc subduction volcano based on the Nazca Plate subducting under South America, building the Andes. However, this volcano is more interesting than that, apparently being built in a compressional tectonic zone, which was not thought to be conducive to growth of large active volcanic systems.
A 2005 study entitled “Volcanism in compressional tectonic settings: Is it possible” by Tibaldi explores the tectonics surrounding EL Reventador. http://onlinelibrary.wiley.com/doi/10.1029/2004GL021798/full
The volcano sits on an area that is littered with faults, most originally of the strike slip variety. Fault lines are generally oriented north – south. Over the lifetime of the volcano, action of the faults have changed from generally strike slip north – south motion to compressional thrusting and folding of the mountain range underneath and to the west of the volcano. This is not a normal behavior or location for a large, active volcanic edifice, which also makes El Reventador a rather unique and surprising volcano.
The activity of the multiple faults allowed a pathway for magma to find its way to the surface for the last 400,000 years or so sufficient to build and operate a vigorously active volcano.
One of the fortunate things about Reventador is its remote location. However fortunate for people that live in its immediate vicinity, it is not nearly as good a deal for the over two million that live within 100 km from it.
The action of its reservoir suggests that the longer the time between eruptions, the worse those eruptions will be, that is until the mountain rebuilds itself to the point where a flank collapse is possible.
This is a dangerous volcano capable of moving many km3 of material in a single eruption. It should be treated with a great deal of respect.