Geothermal Map of North America, 2004

The Geothermal Map of North America is based on terrestrial heat flow as the primary determination for the earth's crustal/lithospheric thermal conditions. Heat flow is the measure of earth's transfer of energy and represents the expression of heat sources within the earth. It is a key indicator of the potential availability of heat as a usable resource. This map illustrates heat transfer from lithospheric to local (individual geothermal system) scales.

Three types of heat flow data points are included on the map and used for contours that range from 15–150 milliwatts per square meter. They are shown by different symbols because they may not be comparable on a point-by-point basis, but the regional comparisons are useful. Heat flow data is from published heat flow values with strict criteria that limit the numbers of such data. Bottom hole temperature (BHT) data is from Canadian, United States, and Mexican oil and gas wells. Heat flow was estimated using BHT data and thermal conductivities where they could be appropriately determined. Western Geothermal Database data is heat flow from industry thermal gradient measurements in areas expected to have high heat flow. In geothermal systems, the gradients are often more than 75 degrees C per kilometer, and heat flow is more than 120 milliwatts per square meter. The basemap is from the U.S. Geological Survey's The National Map for GTOPO30 (shaded relief; province, state, and country boundaries; and rivers); Esri sample data for place-names and city locations; and General Bathymetric Chart of the Oceans (GEBCO) data. Other data included is Holocene volcanoes and hot springs. View the U.S. map data.

Purchasing Information: American Association of Petroleum Geologists (AAPG) Bookstore, map item #423. E-mail the bookstore.