Geochemical Tracer An environmentally benign chemical that is injected to trace fluid movement through the geothermal...

Geothermal Gradient The increase in temperature with depth below the surface, usually reported in units of °C/km.

Geyser A rare type of hot spring that periodically discharges a fountain of hot water and steam (or sometimes just...

Gneiss Metamorphic rock that forms under intense pressure and high temperature and that is made of quartz, feldspar,...

Granite Light colored, coarse grained, intrusive rock with a felsic (silica-rich) composition that is mostly made of...

Granitoid A generic term referring to hard, coarsely crystalline plutonic rock that is produced by intrusion of magma...

Heat exchanger A device or engineered system that is used to transfer thermal energy in soil, rock or produced fluid...

Heat Mining The process of extracting geothermal heat by the heating of initially cold water that flows through...

Helium Isotopes Helium gas is a trace constituent of groundwater and thermal fluids, and the ratio of 3He to 4He can...

Hot Dry Rock Hot crystalline rock with essentially no porosity and lacking producible hot water. Geothermal production...

Hydraulic Fracture A rock-hosted tensile fracture that is created by injection of fluid under high pressure.

Hydraulic Gradient The slope on the water table which promotes horizontal fluid flow in permeable rock units.