Electricity is now produced from geothermal energy in 21 countries, including the United States. Some visible features of geothermal energy are volcanoes, hot springs, geysers, and fumaroles. But you cannot see most geothermal energy. Usually geothermal energy is deep underground. There may be no clues above ground to what exists below ground.
Geologists use many methods to find geothermal resources.
They may study aerial photographs and geological maps. They may analyze the chemistry of local water sources and the concentration of metals in the soil. They may measure variations in gravity and magnetic fields. Yet the only way they can be sure there is a geothermal resource is by drilling wells to measure underground temperatures. The earth is a hotbed of geothermal energy.