Although volcanic activity takes place every day all around the world, few people have been killed by eruptions in recent years and thus volcanoes have not been much in the news in the past couple years. Oregon State University maintains the Volcano World site and choosing the 'Current Eruption Reports' item (first choice on the drop down menu entitled 'Volcanoes') gives you the most recent news. Scanning the page for just the last week in January 2012 provides updates on nearly two dozen volcanoes including Etna in Italy, Kilauea in Hawai'i, Krakatoa in Indonesia (site of the infamous catastrophic 1883 eruption) and active sites in Central America, Russia, Japan, West Indies, and the western Pacific island arcs. This list includes many of the volcanoes that have been newsworthy for the past few years including the Soufriere Hills on Montserrat in the West Indies, Kilauea because it keeps the tourists coming, and Mt. St. Helens because it is in a populated and accessible part of the mainland USA and scientifically because the eruptive demise of this mountain 30 years ago and its subsequent rebuilding phase is the best instrumented and studied volcano in the world.

 The most active volcano in the eastern Aleutians is Augustine Volcano on Cook Inlet south of Anchorage, Alaska. The most recent significant activity in early 2006 yieldied a large ash cloud which, depending on the wind direction, could have posed a serious problem for air travel in and out of Anchorage and Fairbanks. By August of that year the volcano was again napping and temporarily off the list of concerns. Let's start by going back 15 years to another volcano that threatened southern Alaska.

Pavlof on Wednesday, December 11, 1996. Seismicity was elevated that day, the Level of Concern Color Code was RED.

Photograph by Reeve Aleutian Airways pilots on December 11 and 12, 1996. Courtesy of Alaska Volcano Observatory.

"Current Status (Sunday, December 29, 1996): Pavlof erupted in its strongest eruption of the current episode in the early morning of December 27th, ending about eleven days of quiet. Starting on December 26th, small bursts of tremor occurred every few minutes. By about midnight tremor was continuous and the intensity of seismicity was increasing steadily... ."

Pilots reported steam plumes 28,500 feet above surface level, and an ash cloud reaching 17,000 feet. Lava fountains (defined) from the summit vents and intermittent bursts of steam and ash were also seen, and two lava flows were still active months later on the north flank. "Seismic activity could increase with little or no warning," say the volcano-sleuths up in Alaska. Here's a short AVO report on Pavlof.

The smoking mountain
Since Pavlof is in a sparsely populated region (there are just a few towns within 50 kilometers), volcanologists were mainly concerned that the ash could destroy jet engines. That's quite a contrast to Popocatepetl, the king of the Mexico City skyline (on the odd clear day, that is). El Popo is continuously active these days, in terms of its gas emissions, earthquakes, and steam-ash eruptions.

Volcanoes in the Mexican volcano belt coexist with a zone of extremely heavy population.

© David Tenenbaum.

Formally known as Popocatépetl, this giant, steep-sided volcanic cone is 55 kilometers east of Mexico City. After a 50 year quiet period, El Popo awoke in 1995 and has been percolating ever since. El Popo has erupted 17 times in the past 500 years or so, generally with something resembling the current combination of gas and ash, according to the Institute of Geophysics of the National Autonomous University of Mexico. Follow this link for a 3D map and brief explanation of the recent activity and the plate tectonic setting of the Mexican volcanic belt.

None were classic cataclysms, at least in volcanic terms. Nevertheless, in a bit of understatement, the U.S. Geologic Survey opines that "A major eruption would have serious consequences for people living in communities on the flanks of the volcano." El Popo had been essentially quiet since a series of eruptions between 1920 and 1922, but there's potential for catastrophe: According to the USGS, "more than 30 million people live within view of the volcano..."

Arizona State University geologist Stanley Williams puts it this way: "Mount Popo is phenomenally active." The volcano, he says, is putting out as much as 8,000 tons of sulfur dioxide per day, and since only three or four volcanoes around the world put out even 1,000 tons of the gas, "Popo's putting out 10 times more than a volcano that we consider a big deal."

Williams has tested a new remote sensor for carbon dioxide at Popo, and found in a preliminary measurement that the mountain is also putting out 40,000 tons of carbon dioxide per day, another astonishing measurement of the flow of magma perilously near the largest city in the world.

Williams, who has observed close to 100 active volcanoes, says "Popo is in a league of its own." During the past six years' of activity, "it has been releasing several million tons of SO2 (sulfur dioxide). It's a volcano that's full of energy, full of magma, and it's either going to be the most spectacular case of a volcano that safely let off its energy, or it's going to continue to erupt..."

An eruption -- with 30 million spectators?
Past eruptions at El Popo have put as much as 10 centimeters of volcanic ash into the Valley of Mexico, home of Mexico City, the world's largest city. And since ash is basically pulverized rock, that has the potential to crush roofs and cause panic. "Popo is capable of a very bad eruption," Williams adds, noting that Klaus Siebe of the National Autonomous University of Mexico has found ash "all over the Valley" from eruptions during the past 1,000 years.

Yikes!

Half a billion people live close enough to Earth's 1,500 active terrestrial volcanoes to be threatened by them, according to Williams. Where do volcanoes get their power?

And what can they tell us about the Earth?