Seismicity increases at MachÃn in Colombia

Undated image of Cerro MachÃn in Colombia.

I just picked up on this story over on the Volcanism Blog, but I want to post it here too. MachÃn, in Colombia, has experienced a sharp increase in seismicity at the volcano - maintaining the Yellow status for the volcano. 54 earthquakes were recorded at the volcano over the weekend, prompting the INGEOMINAS to raise the alert status. The volcano had a swarm in 2008 that did not lead to any eruption - but remember, better to be safe than sorry. If MachÃn were to erupt, it would join Galeras and Huila as erupting volcanoes in Colombia.

Not much is known about MachÃn, located only 22 km / 14 miles from the city of Ibagué (pop. ~500,000). The last known eruption (well, dateable eruption) was in ~1180 A.D. (+/- 150 years) and over the last 4,000 years, the volcano has produced at least seven eruptions. Typically they are explosive events, producing ash falls, pyroclastic flows and lahars - par for the course for the Colombian volcanoes.

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Erik, does anyone have any idea on the SO2 levels that this volcano might put out? Chaiten was silica rich and sulphur poor - it probably didn't turn down the climate thermostat at all.

I very much appreciate you noting the last time this volcano erupted.

For a while I've been wondering what volcanoes that haven't erupted in a long time might be coming back to life.

Volcanoes that having been sleeping for a long time often produce more destructive eruptions than those that erupt more frequently.

And also I'd appreciate seeing an explosive index for the prior eruptions of Machin (if anyone can find it).

By Thomas Donlon (not verified) on 08 Dec 2009 #permalink

Thomas - to my knowledge, unless there are some remote sensing satellite sulfur dioxide data, there isn't any sulfur dioxide numbers for Machin. However, there is indeed a general pattern where longer repose times between eruptions lead to larger eruptions - this is not always the case, but a generality. I wasn't able to find any VEI numbers, likely because the last eruptions were not observed by anyone and we really don't know the full extent of these events.

What was the VEI of Pinatubo? If I remember correctly it hadn't erupted in 500 years or so; certainly not in any written historical record.

By Catherine Clark (not verified) on 08 Dec 2009 #permalink

This is the same case of Chaitén, that was known locally as the "Cerro Chaitén", but not much as a volcano. Even the photos are very similar. It could be very interesting if this behavior leads to an eruption.

By Guillermo (not verified) on 08 Dec 2009 #permalink

From what we've seen in the past few years to decades, volcanic eruptions tend to be extremely different, even at volcanoes that have not erupted for long time. Some are highly explosive - like Pinatubo or Chaitén - whereas others are relatively minor in terms of explosivity - like Huila and Montserrat. It might well happen that if MachÃn were to come back to life, that it will produce some phreatomagmatic activity followed by the quiet extrusion of a lava dome. The main problem then would be from collapse of parts of the dome, which would generate pyroclastic flows. That would be a significant hazard, but certainly not a cataclysmic eruption capable of impacting global climate.
By the way, for the fans of apocalyptic scenarios, there's a nice headline in this article, which deals with Yellowstone's magma "plume":
Bon appetit!

Hi Erik,

INGEOMINAS has had Machin in "yellow" for several years now following detection of swarm activity (including some LF earthquakes), uplift and some changes in fumarole temperatures and chemistry! I'm not sure why the Columbian press (followed by the rest of the world!) got especially excited about last weekend's swarm. Although it was the largest recorded at the volcano this year, was modest in size compared with last year's activity.
Machin is certainly a volcano to be concerned about!,...its last eruption (also its smallest) was the the size of the 1991 Pinatubo blast!
While we're on the topic of Columbian volcanoes,...Huila began chugging with numerous LF earthquakes overnight.


By Rodger Wilson (not verified) on 09 Dec 2009 #permalink

Thanks for that information Rodger ... I will update the article to match that info. It is odd what the press picks up on sometimes. I'm getting increasingly fascinated by Machin, especially if it does have such large eruptions.

Hi Erik,

I vaguely remember at the onset of the Chaiten eruption that some experts claimed that the lava that previously erupted from Chaiten 9,000 yrs ago didn't contain much SO2 because it was instead silica rich.

Does anyone know if there is a correlation between type of magma and SO2 production?

Part of me thinks that I heard there was. Another part of me ( the uninformed part ) is willing to believe that there isn't a strong connection between magma and what gasses might be associated with it.

Is Rhyolite then normally deficient in SO2? I've read some reports that Yellowstone ( a Rhyolitic volcano ) emits a huge amount of CO2 ( Carbon Dioxide ) - and so does the Long Valley caldera. Do these volcanic systems also emit much SO2 (Sulfur Dioxide)? I don't remember hearing much about high SO2 emissions from those volcanic systems.

If there is a connection then between the type of magma and type of gas released ... then it would be helpful to know from the geological record what magma erupted at Machin in the past. Do geological maps show if the rock in the area is rhyolitic, or basaltic or andesitic?

(Now I've got to crack open my volcano books and make sure that my impression is correct: that basaltic rock is formed from gently flowing lava, andesitic can be highly explosive, and rhyolite of course is often the most explosive of all magmas.)

I appreciate you taking so much time to help out this volcano novice.

Sorry for waiting so long to make this post ... it isn't near the top of the page so maybe it won't be read or answered by the other knowledgeable readers.

By Thomas Donlon (not verified) on 10 Dec 2009 #permalink

The three lava domes of Cerro MachÃn are dacitic, so pretty much the same stuff as can be found at Pinatubo and Mount St. Helens (although St. Helens has also erupted basalt and andesite throughout it's geological history).

I don't really know anything about there being a relationship between SO2 emissions and the main type of volcanic material that's erupted. If we look at Toba, a rhyolitic volcano, we see that there is evidence of high SO2 emissions. Chaitén is rhyolitic as well, but it didn't erupt a lot of SO2. Maybe it has to do with specific circumstances in the Earth's crust below the volcano, rather than 'magma X always produces a little/a lot of SO2'?

By Gijs de Reijke (not verified) on 10 Dec 2009 #permalink

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