geology from Stanford University in 1967.
During the following four decades, he
studied volcanoes around the world as
an employee of the U.S. Geological
Survey. Now retired, Duff leads field
trips, consults about geothermal energy,
and writes books and articles for the
general audience. Duff and his wife,
Anne, spend summers in the lake country
of northwestern Wisconsin and winters in
Flagstaff, Arizona.