“Shrubs on warm ground” – Chaparrastique or Volcán de San Miguel in El Salvador

Chaparrastique volcano.    Photo: Gump Stump, Wikimedia Commons

Chaparrastique volcano. Photo: Gump Stump, Wikimedia Commons

When I first heard news on a volcano erupting in El Salvador last winter, I was somewhat shocked that even the smallest country of Central America (and with the highest population density) 3 would have to deal with volcano monitoring and hazard mitigation, above all other problems they have on their heads – while your mind comes up with summer sun, palms and white Pacific beach upon mention of El Salvador. I am not a volcanologist nor any earth scientist, but have gathered some interesting information on the Chaparrastique volcano on the internet for you.

El Salvador is located in one of the most seismologically active regions on earth, situated atop three tectonic plates. The motion of these plates causes the area’s destructive earthquake and volcanic activity. The Volcanic

Source: MTU volcanoes page

Source: MTU volcanoes page

Cordillera in El Salvador is a line of volcanoes parallel to the coast and the offshore subduction zone. Virtually all the subsoil of the country (over 90%) is composed of volcanic materials.

Geological research of the early seventies, made by the German Mission, recognized up to 700 eruptive centers in El Salvador. The GVP Catalog has El Salvador with 18 individual volcanoes and three volcanic fields, however, based on geological investigations and recent field surveys in the Volcanic Cordillera scientists determined 23 active volcanoes and five volcanic fields. At present, only a few volcanoes have continued activity (outgassing and exceptionally ash) such as the Santa Ana volcano, the San Salvador volcano, volcano San Miguel and Izalco volcano.1

Aulacorhynchus prasinus, the cousin from Costa Rica. - Wikimedia, Kati Fleming

Aulacorhynchus prasinus, the cousin from Costa Rica. – Wikimedia, Kati Fleming

Chaparrastique aka Volcán de San Miguel Bosotlan aka Los Perolitos

Chaparrastique rises from an elevation of approximately 100 m on the eastern coastal plain of El Salvador to a hight of 2132 m a.s.l. With respect to its relief and beautiful symmetry it is the most impressive volcano of El Salvador. Northeast of the volcano (ca 15 km) lies the city of San Miguel (population ~300,000), which is the center of commercial activity of the eastern half of El Salvador.

Structurally, San Miguel volcano lies on the southern fault of the Central American graben at an intersection with NW-SE faults, which are evident by the alignment of radial fissures that erupted lava flows in 1844 and 1855.

The local name, Chaparrastique, means “shrub landscape on warm ground” indicating the importance to the locals of certain plants for preventing soil erosion and keeping moisture; Los Perolitos probably refers to hot springs. Coffee tree plantations and agaves characterize the slopes of Chaparrastique up to the tree line.

A subspecies of the Emerald toucanet, Aulacorhynchus prasinus volcanius, is endemic to this volcano. 2


Chaparrastique has a broad, deep crater complex, which has frequently changed morphology during historic eruptions. Its summit crater has a diameter of about 1 km. Presently the crater is observed to have concentric faults with collapse benches surrounding an internal crater of approximately 0.2 km in diameter. When viewed from the west the summit of the volcano presents a very rugged morphology. It is also apparent, from the change in slope, that the summit has suffered collapse or it has been destroyed by a violent eruption. Later eruptions up to the present continue to fill in the old crater.

Photo MARN, 2008 (?)

Photo MARN, 2008 (?)

There is very little information about the petrology of San Miguel volcano, due to a lack of studies on the subject. However Meye-Abich (1956) notes that older lavas of San Miguel commonly are olivine-pyroxene basalts, while more recent lavas such as the 1844 lava flow on the northwest side of the volcano present a more andesitic composition.8

Eruption history

Chaparrastique, view of the internal crater.

View of the internal crater of San Miguel volcano. High temperature fumaroles periodically cause small phreatic eruptions that deposit thin layers of ash on the surrounding vegetation. Photo by Carlos Pullinger, 1994.8

The first records of rumbling and degassing activity began in 1586 after 107 years of dormancy; the first historical eruption ocurred in 1699 with a lava flow from an open vent on the SSE flank. From then on, eruptions are reported roughly every 10-20 years, producing mafic lavas and tephras in mostly small VEI events. They were often just ash and gas emissions, but also a number of fissure and flank vent eruptions with effusive lava streams, blocking the nearby roads.5 Her eruptions are generally of strombolian nature, lasting from several days to months. The location of radial fissures and flank vents has migrated higher on the edifice during historical time, and the most recent activity has consisted of minor ash eruptions from the summit crater.6 Ash fall associated with historic flank eruptions has been reported up to 20 km from the volcano, and fell on the city of San Miguel in 1931. In 1976, small scale fountaining occurred in the summit crater and produced minor ash fall within a few km of the crater. Recently, small debris flows composed mostly of scoria have caused property damage on the northwestern flank of the volcano. Based on its historic activity and its current seismicity, gas emission and rock alteration, San Miguel is perhaps El Salvador’s most likely candidate for hazardous activity.7

Last Eruption 2013

Chaparrastique 30/12/2013. Photo MARN official Facebook page.

Chaparrastique 30/12/2013. Photo MARN official Facebook page.

RSAM during and after eruption Dec. 2013  Station VSM. Source SNET (green date line by the author)

RSAM during and after eruption Dec. 2013 Station VSM. Source SNET (green date line by the author)

From early December an increase in seismic activity alerted volcanologists that Chaparrastique’s quiet period of 37 years may be over. On 29th December an over 5 km high ash plume confirmed the fact. Until evening Aeropuerto Internacional El Salvador had cancelled most of its flights and several thousand people in a 3 km radius danger zone were evacuated.9

MARN’s webcam video of the onset of the 2013 eruption:

It was a shortlived eruption as seismicity decreased substantially over the following two days, although gas and slight ash emissions have been reported on and off since.1 However, from early January on there where fluctuations in seismicity that signalled the volcano had not gone back to sleep.

Current Situation

There is rarely a volcano teasing the population living around it as badly as Chaparrastique does. In May 2014 seismicity increased to RSAM values similar as before the eruption in December last year. Volcanologists soon began to warn that a new eruption could not be ruled out.

RSAM May 2014  Station VSM. Source SNET (green date line by the author)

RSAM May 2014 Station VSM. Source SNET (green date line by the author)

Steam clouds and slight ash emissions increased and so did the general seismicity. From June 27-30 the RSAM rose to values that were coming near those reached by an eruption. Ash and gas emissions got stronger and more frequent. A bit lower now, but still a very high risk of eruption – this situation must be nerve-wrecking for the locals, especially for those who have plantations on the slopes of the volcano.

RSAM June 2014  Station VSM. Source SNET

RSAM June 2014 Station VSM. Source SNET

RSAM values

These are the scale everyone is looking to for assessment of the state of affairs at the volcano. Yet I doubt that many know how those figures come about. I have read up on the subject but it is very complex. Basically, they are a computation of various data from seismographs, tilt and deformation measurements that results in a… let’s call it activity index. (This is my interpretion of what I read, please correct me if I am wrong).

What next?

So, if and when the volcano will erupt again is anybody’s guess, but sure it will. If it does, it will again affect about 15.000 people, and square kilometers of coffee plantations. The main nuisance will be the amounts of ash destroying crops and buildings. The other danger are the lahars that are to expect. The area is already at very high risk for landslides, which shows in the regular reports on expected rain fall and landslide susceptibility.10

Chaparrastique 30/12/2013. Photo MARN official Facebook page.

Chaparrastique 30/12/2013. Photo MARN official Facebook page.


If you want to keep an eye on Chaparrastique:






6 http://www.volcano.si.edu/volcano.cfm?vn=343100




10 https://twitter.com/MARN_Oficial_SV

Some further reading




49 thoughts on ““Shrubs on warm ground” – Chaparrastique or Volcán de San Miguel in El Salvador

  1. I made this to show the variation of melt viscosity according to temperature and water content.
    This is for an andesitic type of melt.
    I picked up a correlation from the reference in the title bar.
    usually you get only a graph according to one parameter. As you can see both parameters play but water content is really the important parameter.

  2. Thank you, Granyia for an interesting article 🙂

    & thank you also to Chryphia for the article on curved subduction zones 🙂

    • Perhaps local stories didn’t count for Clovis volcanologists, and the first seismograph was installed in 1480… 😉

    • Well, on May 13 1479, Christopher Columbus marries Felipa Perestrelo Moniz (Italian on her father’s side) and receives as dowry her late father’s maps and papers charting the seas and winds around the Madeira Islands and other Portuguese possessions in the Ocean Sea.


      Elsewhere, Pál Kinizsi made a name for himself in his performance at the Battle of Breadfield in 1479. (From the way it reads, it was pretty much a rout. Many of the remaining Turks that fled were killed by locals who had an issue with the marauding that they had been engaged in.)

      This was about 2 years after Vlad III, Prince of Wallachia had died.

    • Now, joke aside: that was my own wording of the first entry in the table of Eruption history, and I had thought about it, too. There is one explanation. This is the entry:

      1586 | Gassing, after 107 years of inactivity | Ponce (1586), Sapper & Fear (1933), […]

      Ponce probably wrote in his ‘Annals of Demonic Occurrences’ in 1586 that an evil Mountain-Demon who had slept for 107 years, had woken up again breathing poison out of the mountain. Sapper&Fear boldly interpreted that als volcanic activity in 1933. So, if Ponce didn’t say what happened in 1479, and nobody else gave a record of the event, no one will ever know until they start analysing the tephra.

  3. Yes. But then, is not all history, that has not been researched and proved by scientists in modern times, folklore? We take a lot for true that cannot directly be proved anymore, the evidence being (mostly written) records from olden times.

  4. Sorry for being cantankerous. My heel hurts and I can’t quite doze off. Pisser of a day trying to rebuild connectors and the friken IT rep leaves before I can have her check the interfaces. Oh, and the heat stress factor was about 107 deg F today while I was squatting in what little shade there was doing the gear swap out.

  5. Heads up all Hekla fans. Since many of you may be (maybe) on vacation, here is one for the record. Place is in zone that seems lie mid-between Hekla and Vatnafjöll, but putting it in real contest, is too close to Hekla´s main crack, to close for comfort. So far (12 hrs) no further
    unrest or quakes have appeared. This could be rouge one, but I think depth gives the clue …
    02.07.2014 23:48:57 64,013 -19,488 / 9,9 km / 2,3 R / 99,0 / 9,1 km ANA of Hekla

    • Another reason for Hekla, or anywhere else, to do something spectacular is that I’m going on a camping holiday to Scotland tonight and won’t be near an internet connection for 10 days! Hekla has certainly been restless these past few weeks.

      • Yep. Been watchin´ with one eye
        Exactly reason I put this here 😉 So you can see when you come back; hopefully (?) 🙂 beeing delayed by the huge ashcloud drifting down to Scotland 🙂 But History (past 4-5 eruptions or so) show this clears in a day or two. So just stay put and enjoy … travel by rail … *wicked smile*

          • Well, probably week to ten days but could stretch out like some months, effusive
            exposivly over in a day or two )

            Carl is right (side comment, below/abowe)

      • No, American are going banning all to enter next, or leave
        thats only way preventing anything happening on international jet travelling

    • That seems to be on the FZ between the Hreppar and Tröllaskagi microplates along their common transform that leads to the defacto triple junction near Bardabunga and the plume.

  6. OT Alert

    Wrightsville Beach is a town in New Hanover County, North Carolina, United States. Wrightsville Beach is just east of Wilmington and is part of the Wilmington Metropolitan Statistical Area…The town consists of a four-mile-long beach island, an interior island called Harbor Island, and pockets of commercial property on the mainland.

    Wrightsville beach and surf cam


    Company is coming…

    • There always are.

      The messed up part is that if one of them suffers a mishap, the USCG has to go out in that crap to retrieve them. Erratic high gusty winds are not the place to be buzzing around in a helicopter.

      To give you an idea of the environment. Not far from here is where the coast guard does it’s boat training for operating in high seas. The natural weather and wave patterns make it a reliable place to find nasty swells. (Up around Hatteras)

      On the plus side, it’s not a very old storm, so it hasn’t had a chance to build up a monster storm surge. However, according to the Fleet Weather Center out of Norfolk VA, out in the storm proper, the seas are up to about 26 feet wave height.

      WWNT30 KNGU 040000


      MAX SEAS 26FT NEAR 33.0N6 076.8W1.

      Pulling out the checksums since it can be confusing, the max seas are at the position 33.0°N – 076.8°W.

      Now, if there was a threat to the surfers from hostile invasion, there are a few thousand Marines nearby at Camp Lejeune… provided they are not tied up in sensitivity training.

      Sorry, but I am old school. I don’t give a shit how sensitive a war-fighter is. Their job is to break stuff and kill people. That’s what they are hired for. It’s their job.

      I want them on that wall. Despite the movie being geared to show the hard core military in a bad light, the Col Jessup speech is dead on accurate and I fully support the sentiment. Additionally, the Tom Cruise casting was quite accurate as a self centered myopic shitbag.

      • I guess I should amplify.

        I also have a great deal of appreciation for my dog. I know that should anyone try to enter my house to harm me or my family, that dog will do everything in it’s power to prevent that, even if it means it’s life. Now, don’t get me wrong, I am not equating Marines to dogs, but they have that same loyalty and dedication to duty. They perform their task with un-nerving fury. That’s what I like about them. They are reliable. You can sleep well at night knowing that they are on duty.

        As for the dog, he’s got my back. The game-plan is that in the ruckus and uproar of the dog dealing with the intruder, I will have time to get my shotgun and cover his back and provide assistance as needed. About the only way you can get that sort of coverage from a cat is if you pick it up and throw it at the intruder… provided that it has an evil temperament.

        As for the Marines… yeah, we squids may take great jest as being their taxi service, but if you put them on the beach, God help anyone that gets in their way.

        A brutal and heartless point of view? Yeah, it is. But they are Marines. That’s what I want in a sentry. If you don’t like it, you can politely pound sand up yer arse.

        In the afore mention movie link, Col Jessup’s mistake was in not processing the non-performer out of the service. I’ve made similar recommendations for students who had become “administrative burdens.” In a nutshell, Ron White’s punchline applies. “You can’t fix stupid”.

        Now, an aside. One thing that media heads bandy about is the “Thank you for your service” mantra. Appreciated, but don’t use that as a flag that you can drape over yourself in order to make yourself look like some sort of patriot. As the Col Jessup character noted, pick up a gun and man a post. To me, the statement has taken on the meaning of a trite pandering quip in order to win favor. Cover our backs with your action or STFU. A simple “thanks” would do nicely. As for my service, all I did was ride around looking for and evaluating radars. There’s not a whole lot of valor in that, but it was my job and I did it. Actual combat vets may have a different take on it, but that is just my opinion.

        About the only exciting thing that happened was when I told (upon asking) what it was I was looking at to the weapons officer. ‘What’s that?’, “A fire control radar” ‘what’s it doing?’ → “Looking at us” at which point he nearly shit his pants.

        (and yes, I did have my jammers on standby and a defensive recommendation ready for combat and the bridge, but the odds of them actually taking a shot at us were pretty slim from a geopolitical point of view.)

        • “sensitivity training” – Oh, they do that
          Weeping or crying?
          *now I be banned enterin U S of A forever*

        • Dunno, when those idjit flyboys got tangled up in Tailhook, they made everyone attend training about it. Admiral Boorda was preparing to fry every one of the B/S monkeys from the aviation community but oddly, “committed suicide”. (assisted suicide in my opinion) Allegedly, it was over a combat decoration that he wore, but his commanding officer at the time it was awarded has stated that he was fully entitled to wear it.

          His suicide was by self inflicted shotgun to the chest, on the sidewalk, in front of his residence. I had met Admiral Boorda while on one of my previous ships. He was not a tall person at all. How he could manage the shot while being of such small stature is beyond me.

  7. Since June, Ambang volcano on Sulawesi (Indonesia) had a few shallow and deep earthquakes a day. Today they increased fourfold in numbers. PVMBG increased the alert level from normal to Waspada (watch) today.

    From GVP: The compound Ambang volcano is the westernmost of the active volcanoes on the northern arm of Sulawesi. The 1795-m-high stratovolcano rises 750 m above lake Danau. Several craters up to 400 m in diameter and five solfatara fields are located at the summit. Ambang’s only known historical eruption, of unspecified character, took place in the 1840s.”


  8. Well, we are about at the point where the approaching front is gonna grab Arthur up by the short-hairs and sling his arse out into the North Atlantic. You can barely see the effects of that front on the outer feederband to the Northwest starting to take effect as it shuffles the precipitation to the Northeast.

    I’m just guessing, but Arthur is going to go extratropical pretty fast. (transition to a cold-core low rather than a warm-core low) When that happens, the driving force will no longer be the warm moist air convecting up into those feeder storms, but will be the temperature differential of the two opposing air masses.

  9. ATTN: Carl, something you may find of interest, or alarm.

    …“He [Yoshihiro Kawaoka] took the 2009 pandemic flu virus and selected out strains that were not neutralised by human antibodies. He repeated this several times until he got a real humdinger of a virus,” said one scientist who was present at Professor Kawaoka’s talk.

    “He left no doubt in my mind that he had achieved it. He used a flu virus that is known to infect humans and then manipulated it in such a way that it would effectively leave the global population defenceless if it ever escaped from his laboratory,” he said.

    “He’s basically got a known pandemic strain that is now resistant to vaccination. Everything he did before was dangerous but this is even madder. This is the virus,” he added.


    • Astonishing that he was allowed to do that with no more than local instituional level approval, and at low containment level for the risk. They had top level containment there – why the low level?

      Unlikely he will be allowed to publish the data.
      It does illustrate the ease with which these viruses can be turned into a weapon.

      Ebola is on the loose – thats the current big threat. And H5N1 in the far east is a continuing threat.- not ‘if’ it mutates to spread human to human, its ‘when’

      • One of the things that determines how deadly a pathogen is, is how fast it incapacitates the host. It’s not going to be quite as dangerous if it puts the host down before it can spread to others.

        But in the modern era, humans can fly and cover more ground.

  10. Idjitz… the world is full of full blown Idjitz…
    A certain person I know liked to experiment with combining Marburg and H1N1…

    • Odd, not more than a month ago a paper came out that exonerated fracking. Interesting note in this one’s abstract:

      “Although thousands of disposal wells operate aseismically, four of the highest-rate wells are capable of inducing 20% of 2008-2013 central US seismicity. ”

      So, they picked four wells that would give them the data they were after? That sounds a lot like selection bias to me.

      Also from the abstract:

      – Author Affiliations

      1 Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA.
      2 Department of Geological Sciences, University of Colorado, Boulder, CO, USA
      3 Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, USA.
      4 U.S. Geological Survey, Menlo Park, CA, USA.

      3 and 4… and possibly 2 are the only ones that have any credentials in my opinion. As for #1, what the hell does someone invested in Atmospheric Sciences have to do with it? Could it be that it supports their AGW agenda? The people involved in that field of study have a poor record of research integrity. (Just look at Michael “Piltdown” Mann and his torturing of data to get a hockey stick with “Mike’s Nature Trick“)

      From a geological point of view, I would much rather have a thousand sub Mag 4.0 quakes that a single Mag 7.5. In general, those fracking induced quakes release accumulating strain. Strain that is going to be there whether you frack or not. Give it enough time, it will snap anyway. Simple choice, something manageable or something catastrophic.

    • As for the “fault,” well, everyone is always looking to lay blame at someone’s feet. Check it out.

      Section 1422 requires states to meet EPA’s minimum requirements for UIC programs. Programs authorized under section 1422 must include construction, operating, monitoring and testing, reporting, and closure requirements for well owners or operators. Enhanced oil and gas recovery wells may either be issued permits or be authorized by rule. Disposal wells are issued permits. The owners or operators of the wells must meet all applicable requirements, including strict construction and conversion standards and regular testing and inspection.

      Section 1425 allows states to demonstrate that their existing standards are effective in preventing endangerment of USDWs. These programs must include permitting, inspection, monitoring, and record-keeping and reporting that demonstrates the effectiveness of their requirements.

      Note that record keeping aspect of it. The well operator is not allowed to exceed the permitted pressure that the well is licensed to operate at. That pressure is determined by the fracture gradient of the strata that it is drilled into. Violate that too often and your permits are revoked and the EPA gets to extract assloads of cash from your company. That’s why they do the inspections… to see if they can siphon cash out of the company.

      … so, if some quakes are triggered by the injection, is it the company’s fault, or the regulating agency? (rhetorical question)

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