8. Physical Processes in Geothermal Areas

  1. William H. K. Lee
  1. John W. Elder

Published Online: 18 MAR 2013

DOI: 10.1029/GM008p0211

Terrestrial Heat Flow

Terrestrial Heat Flow

How to Cite

Elder, J. W. (1965) Physical Processes in Geothermal Areas, in Terrestrial Heat Flow (ed W. H. K. Lee), American Geophysical Union, Washington, D.C.. doi: 10.1029/GM008p0211

Author Information

  1. Institute of Geophysics and Planetary Physics, University Of California, San Diego

Publication History

  1. Published Online: 18 MAR 2013
  2. Published Print: 1 JAN 1965

ISBN Information

Print ISBN: 9780875900087

Online ISBN: 9781118668825

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Keywords:

  • Convection of water in the crust;
  • Heat transfer measuremenls;
  • Hydrothermal system;
  • Physical processes in geothermal areas;
  • Transport mechanism

Summary

The role of the movement of water and, to a lesser extent, magma in the flow of heat within the Earth, primarily in or just below the crust, is considered. The surface distribution of heat flow shows two major regions: normal areas, covering more than 99% of the surface, with heat flux of 1.5 μcal/cm2 sec; and thermal areas, in which the heat flux is an order of magnitude or more greater. Models based on radioactive heat transferred by thermal conduction and radiation give an adequate description of normal areas. In thermal areas, it is necessary to invoke mass transfer. At the surface, the heat flow is discharged as radiation, by warming the ambient air or water, or as water vapor produced by flashing or by evaporation at the water table. The water-vapor mechanism predominates in land thermal areas. Specific reference is made to the Tuscan steam zone of Italy. Beneath land thermal areas, a body of freely circulating hot water is identified and discussed in terms of convection in a porous medium. Such a hydrothermal system can transfer heat several orders of magnitude faster than thermal conduction. Model experiments are compared with the Taupo hydrothermal systems of New Zealand. Thermal areas derive their energy from sources at depth. It is suggested that these sources arise from the upper mantle by penetrative convection. Within the lower mantle a highly disordered free convective motion is envisaged. The great unknown is the rheological nature of the mantle.