http://www.cdc.gov/mmwr/pdf/rr/rr58e0821.pdf

We’re not ready, the Times concludes.

http://www.nytimes.com/2009/08/11/health/11docs.html

If you have a stratavolcano (the kind which explodes such as Vesuvius) sometimes lava comes out but it’s too sticky to flow.  So it forms a big solid ball, which fills from the inside with new lava, and the outside is stiff, but crumbly.  This is called a lava dome.

Lava Dome at Redoubt Volcano, Alaska, currently growing, June 8, 2009 photo

Lava Dome at Chaiten Volcano, Chile, during active eruption in 2008

The thing is, when they are still hot, these domes are unstable, especially since new lava is being forced inside.  If they collapse or burst, pyroclastic flows — the most lethal type of volcanic event — can occur.

Why is the lava sticky, you may ask?  Well sometimes it’s a temperature thing, but usually it’s because the lava is higher in silica.  In other words, the petrochemistry makes it so.  Probably the most fluid lava on earth is from the Nyiragongo Volcano in Africa, which last erupted in 2002, sending its super-fluid lava down its slopes at more than 60 miles per hour toward the nearby town of Goma, destroying 4,500 buildings and leaving 120,000 homeless.  Very low silica.  (  )

Where does the silica come from?  The volcanoes around the Pacific ring of fire are mostly formed where the pacific plate is being pushed under a continental shelf.  So the heated rock is ‘polluted’ if you will, by plate layers melted down.  Whereas Nyiragongo and the Hawaiian hot spot (Kilauea, Mauna Loa) have lavas that come from deeper in the mantle.

Nyiragongo from Goma, Republic of the Congo