Thursday, September 23, 2010

PBS Nova explores the Toba supervolcano eruption 75000 years ago

“Mystery of the Megavolcano”, part of the PBS Nova series, was aired on Sept. 21, 2010. The best link seems to be this.

A megavolcano is more commonly called a supervolcano. The huge dimples in the Earth, up to a 100 miles across, have only been discovered in the past few decades.

The film shows the efforts of four independent geologists around the world to trace a suspected massive eruption in the distant past. Examination of Greenland ice samples showed the emission of sulfuric acid about 75000 years ago, consistent with a supervolcano eruption about the time that homo sapiens was almost wiped out.

Examination of oxygen isotopes in the ocean shows enormous ocean cooling about this time. The first thought was the supervolcano could have been in Iceland.

But investigation led to Lake Toba, over 100 km long, in Indonesia. This may have been the largest supervolcano in the world and its explosion may have precipitated an ice age. Apparently this is a different volcano from Krakatoa, about which several films have been made, concerning its 1883 eruption; this was a borderline “supervolcano”.

The documentary covered briefly the US supervolcanoes, Yellowstone and Mono Lake. Since Yellowstone (which moves east gradually) erupts every 600000 years, we are about due. And a supervolcano eruption would be a civilization challenging “Event”, spreading ash over an entire continent, maybe leading to a prolonged “winter”.

Wikipedia attribution link for Labe Toba aerial view, p.d.

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