Lehman survey

Spontaneous potential or SP methods can be used for a variety of tasks. SP is considered to be caused by three different sources. Electromotive sources are caused by something moving, such as water leaking through a dam. Electro-chemical sources are related to chemical contrasts in the subsurface, such as those found near landfill leachate. Electro-thermal forces are caused by thermal contrasts in the subsurface. Significant work has been done with electro-thermal investigations of geothermal resources in Iceland.