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California Heat Flow Data: Glossary

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Common Abbreviations

  • H.F. - heat flow, given in mW/m2
  • H.P. - heat production, given in µW/m3.
  • hyd - no data, hydrologic disturbance due to ground water flow.
  • N/A - data is not available.

Heat Flow

The values of heat flow in this database represent measurements of the conductive component of heat transferred through the Earth's crust to the surface. The units of measurement are in milliWatts per square meter (mW/m2), which represent the amount of energy passing through a unit area. The most common approach to determining the heat flux from the Earth involves measuring temperatures in a borehole and measuring the thermal conductivity of the rock penetrated by the borehole. The temperature measurements are used to calculate the rate of temperature change with depth, which is usually referred to as the vertical temperature gradient and is reported in degrees Celsius per kilometer (°C/km). The thermal conductivity is a measure of the ability of the material (in this case rock or soil) to transport heat and is reported in Watts per meter-degrees Kelvin(W/m•K). These two quantities are multiplied together to determine heat flow. Future versions of this database will include links to the temperature and thermal conductivity data from each site.


The location of each borehole is given in decimal degrees of latitude and longitude.


The maximum depth of each borehole in meters relative to the ground surface.


The elevation of the ground surface at each site in meters above mean sea level.

Heat Production

Heat production is a measurement of the volumentric heat generation in the rock penetrated by a borehole due to the decay of radiogenic isotopes of Potassium, Uranium and Thorium. It is reported in units of microWatts per cubic meter (µW/m3). Understanding the distribution of this naturally-occuring heat source is necessary in using heat-flow measurements to estimate thermal conditions deep in the Earth's crust and mantle.

Common Name

The complete name for a site. The types of boreholes used for heat-flow measurements include oil wells, water wells, geothermal wells, and scientific holes drilled expressly for the purpose of measuring heat flow and other Earth properties.


An abbreviated designation for the scientific publication in which the heat-flow measurement was reported. Clicking on the abbreviation will bring you to a complete reference for the publication. These publications usually provide more detailed information of the site, including plots of subsurface temperature and thermal conductivity.


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