Bailey, John, and Dehn, Jonathan, 2006, Volcano monitoring using Google Earth [abs]: in Brady, S.R., Sinha, A.K., and Gundersen, L.C., Geoinformatics 2006 - Abstracts, U.S. Geological Survey Scientific Investigations Report 2006-5201, p. 25, available at http://pubs.usgs.gov/sir/2006/5201/ .
link to USGS website, containing links to the PDF on a USGS server