This image shows the calculated heat flow values of the Southwest United States. Heat flow measures the energy transfer (flux) through the near surface of the lithosphere. Locally, heat flow is used for such things as imaging magma chambers, while globally it can be used to determine lithospheric thickness. In this image, warmer colors (reds, oranges) indicate higher heat flow measurements, while cooler colors (yellows, greens) indicate lower heat flow measurements. Black dots are measurement points, and regions in between measurement points have been interpolated using an inverse distance weighted (IDW) calculation.

Background on heat flow:

Heat flow is calculated using Fourier’s Law, which states that the flux (heat flow) is equal to the thermal conductivity multiplied by the thermal gradient:
q = K (dt/dz)

K = thermal conductivity of the medium being measured

Global averages, in mW/m2, are as follows:

Oceanic: 101

Continental: 65

Global: 80

Thermal conductivity is the “K” of Fourier’s Law, in W/mK:

q = K (dt/dz)

Thermal conductivity data points are determined through drilled boreholes, often at the same locations as heat flow measurements. Values are based on the surrounding rock type.