Geologists at Ecuador’s Geophysical Institute outlined what they said are the three most likely scenarios for the Cotopaxi volcano, which entered an eruptive phase in April. It is the first time that the government has allowed publication of the possible outcomes of an eruption during current activity for what has been called one of the most dangerous volcanoes in the world.
The first scenario, the institute says, involves a slow rise of magma within the volcano’s central vent as pressure builds in the magma chamber several kilometers beneath Cotopaxi. At some point, there will be an explosion which will send pyroclastic and lahar flows down the side of the volcano and hurl volcanic rocks up to five kilometers from the crater.
According to the institute, most of the outflow and damage would be contained within Cotopaxi National Park, although some lahars would flow along river beds to nearby communities. The eruption would be accompanied by a roar from the explosion that would be heard in a radius of 20 kilometers. In this scenario, there would be weeks, maybe months, for preparation because of the gradual build-up.
The second scenario, less likely according to the institute, would be similar to the 1877 eruption, which killed thousands in a radius of 75 kilometers. There would be a violent eruption that would be heard for 50 kilometers and the expulsion of large amounts of lava accompanied by lahars that would flow 200 kilometers from the crater. Large rocks would be thrown 10 to 20 miles from the volcano. The eruption would be sudden and provide little advance warning.
A third scenario, considered the least likely, is that the activity would recede and the volcano would enter a quiet phase but would remain active.
A retired U.S. geologist who studied Cotopaxi in the early 1990s says there is a fourth possibility, although he considers it remote. “About 4,400 years ago, Cotopaxi had one of the most violent eruptions anywhere in the world in the last 10,000 years,” says George Lassiter, a part-time Cuenca expat. “The explosion destroyed the top 5,000 meters of the mountain and had outflows of 400 and 500 kilometers. The results of that would be catastrophic but I think it is very, very unlikely that we would see a recurrence.”