The Volcanoes at Atitlán

Alexander von Humboldt called Guatemala’s Lake Atitlán “the most beautiful lake in the world,” and it’s difficult to disagree with him.
 

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As you might have guessed, some of the pointy mountains are volcanoes, but so is the lake. As noted when we looked at another volcano in the region, El Salvador’s Ilopango, you really have to watch out for volcanoes that leave nothing but a big hole in the ground when they explode.

Guatemala's many volcanoes.  I marked the Atitlan area in red.  (Map:  INSIVUMEH)

Guatemala’s many volcanoes. I marked the Atitlán area in red. (Map: INSIVUMEH)

Lake Atitlán caldera

Last time, we saw that El Salvador has at least twenty volcanoes. Well, Guatemala has 324 volcanic vents! These, too, are part of the Central American volcanic front that has formed in this complex geological region as the Cocos tectonic plate subducts underneath the Caribbean plate.

According to Oregon State volcanologists, there have been four periods of volcanic growth and caldera formation in the Atitlán region over the past 11-12 million years. The most recent one began about two million years ago, and the violent explosion that formed the caldera underneath Lake Atitlán happened 84,000 years ago.

With an estimated tephra volume of 72 cubic miles (300 cubic kilometers), this caldera eruption was much larger than Iopango’s pre-1000 AD blast. It blanketed a region that now stretches from Florida to Ecuador in very thick deposits that geologists call the Los Chocoyos ash. in The ash is very light in color and is exposed in dramatic cliffs near Lake Atitlán today, where strong earthquakes have caused landslides.

As far as anyone knows, no supereruption is brewing at Lake Atitlán right now. Indeed, the major current concern here is pollution.

However, studies show that there is likely still magma underneath the caldera and that Lake Atitlán will have another eruption at some point in the future.

Later volcanic activity filled in part of the 84,000-year-old caldera.  (Source)

Later volcanic activity filled in part of the 84,000-year-old caldera. That’s how those pointy mountains around today’s lake formed. (Source)

Three stratovolcanoes

After the Los Chocoyos event, smaller eruptions build three large volcanic cones in the Lake Atitlán caldera. First came San Pedro, and after it quieted down, Tolimán. Neither has erupted in recent times, that is, since the last Ice Age some 10,000-11,000 years ago. However, they still are hazardous because of landslides.

The active cone now is Atitlán, not to be confused with the lake bearing the same name. It sits on the southern rim of the old caldera and has had numerous explosive eruptions over the last 3,000 years, most of them fairly strong at VEI 2 and 3. Atitlán’s last confirmed eruption was in the 1850s.
 

Monitoring volcanic hazard

Landslides and lahars also occur at Atitlán Volcano, but there are other hazards present. Since the days of the conquistadors, geologists say, Atitlán has shown an eruption pattern of six clusters: 1469, 1505, 1579, 1663, 1717, and the 1850s. Such a frequent eruption pace in a popular tourist area poses obvious risks.

Too, there are many Mayan villages in the area, some of whose residents still follow the traditional ways. And to make matters worse, economic pressures have forced villagers to farm lands higher and higher on the flanks of the volcano. Any future eruptions will certain hit these people very hard.
 

US Geological Survey

Per the US Geological Survey, various volcanic hazards are present at volcanoes like Atitlán. They even include tsunamis in Lake Atitlán!


 

Experts who have studied this volcano, and who also notice a resemblance between Atitlán Volcano and Fuego, another very active Guatemalan fire mountain, think that an eruption at Atitlán could put up to 40,000 people at risk. The USGS says:

Atitlán Volcano will erupt again leading to tephra fall, pyroclastic flows, lava flows, lahars, and/or debris avalanches. The area around the volcano is also prone to slope failures and mudflows caused by seismic activity and heavy rains. The best way to cope with volcanic hazards, as with any hazard, is through advance planning of emergency response and, for the long term, consideration of volcanic hazards in future land-use and facility location in order to mitigate the effects of the potential activity at Atitlán Volcano.

Unfortunately, Guatemala is not one of the top ten wealthiest nations worldwide, and the country has other volcanoes that pose even greater risks. They’re doing what they can with very limited resources.

With outside aid from such experts groups as Geoscientists Without Borders, Guatemala is building a monitoring network for its most dangerous volcanoes. But for now, I can’t find any indication online that volcanologists have set up any type of monitoring network on Atitlán. Hopefully that is just a failure on my part, and if everyone is really lucky, monitoring will be in place there before the volcano reawakes.

Hope is a wonderful thing…but knowledge and preparation are even better.



Categories: Sunday morning volcano

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