Hot stuff Geothermal power is a growing renewable energy source, which is good news for ThermaSource, Inc., a leading geothermal drilling, engineering and consulting firm, executive vice president Jim Hanson tells Ruari McCallion. No one who has watched a volcano erupt, experienced an earthquake or watched a geyser blow off steam can fail to be impressed with the power of the planet. The challenge is, as always, how to control and tap it.