A lesson in defining “extinct”

Toni Feder’s Issues and Events news item about the High-Altitude Water Cherenkov Gamma-Ray Observatory under construction in Mexico (Physics Today, October 2013, page 22 ) begins by describing the site as “nestled at 4100 m on the slopes of Sierra Negra, an extinct volcano.” However, as the picture accompanying her piece or a cursory examination in Google Earth makes clear, the site is not on the slopes of Sierra Negra. It sits in the saddle between Sierra Negra and its much larger companion Pico de Orizaba, also known as Citlaltépetl. Sierra Negra, a minor flank cone of that larger volcanic system, may now be extinct, but Pico de Orizaba (http://www.volcano.si.edu/volcano.cfm?vnum=1401-10= ) absolutely is not. It is dormant at best, having erupted as recently as 1846.

To compound the issue, the photograph shows that the observatory site is built squarely in front of an obviously young lava flow. Now, I’m sure that site selection was done with due attention to natural hazards, but as long as astronomers insist on building expensive observatories on top of volcanoes, there needs to be clear understanding and common vocabulary between astronomers and geologists. “Extinct” is a troublesome word when applied to a volcano.