Cerro Hudson

To introduce this week’s volcano, here’s a news report of its last eruption (VEI 2, in October 2011):


That was rough on the sheep, but it was a relatively small eruption for this million-year-old volcano, which is much older than many volcanoes.

An explosive volcano

No one even knew Cerro Hudson was there until it had a VEI 3 eruption in 1971.

Scientists now know that Chile’s Cerro Hudson cuts loose on a plinian scale at times, with a VEI 5 eruption (Mount St. Helens 1980 size) in 1991 and two VEI 6 eruptions (Pinatubo 1991 size) in the distant past.

And even further back, some 6,700 years ago, it also had a violent eruption. At first the experts thought this one formed Hudson’s current 10-km-wide caldera, but they couldn’t find evidence of massive pyroclastic flows that would happen during such an eruption. Current thinking is that Hudson probably had a phreatomagmatic eruption (think “water” when you see “phreato”). The volcano was covered in ice when it erupted. This is what a VEI 3 phreatomagmatic eruption (Ruapehu in New Zeland, 1995 and 1996) looks like:


Cerro Hudson’s eruption back in around 4700 BC was probably much bigger, but it didn’t form the caldera all by itself. Volcanologists think that the present caldera is the result of a series of collapse events dating back to before the end of the last ice age.

Volcanic hazards

Hudson’s 1991 eruption caused (PDF) heavy ashfall that affected local infrastructure and water supplies. It eventually reached the Falkland Islands (of note, Cerro Hudson is on the other side of South America from the Falklands).

Ash from Cerro Hudson's 1991 eruption.  (NASA)

Ash from Cerro Hudson’s 1991 eruption. (NASA)


This eruption also released a lot of sulfur dioxide, which is what killed over a million sheep and harmed local crops and other vegetation.

Are there other unrecognized volcanoes out there? In a word, yes. Scientists are looking for them, partly because of the hazard, of course, but also to add to the world database of volcanoes. The more we understand about volcanoes, the better we can protect ourselves from and learn to live with them.


More on Cerro Hudson from the Global Volcanism Program; from SERNAGEOMIN (Chile’s geological agency) in Spanish.

Categories: Sunday morning volcano

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