- Volcanic geothermal prospects with surface manifestations can be very striking with hot ground temperatures, steam releases from the ground itself, and fumaroles continuously expelling gases and fluids. Ground surface temperature measurements have exceeded 100°C in some locations.
- Thermal streams can exist with runoff down erosional or volcanic channels.
- Depending in the reservoir and upflow depths and surrounding rock lithologies, these fluid outflows may have lost temperature so that the surface temperatures can be significantly reduced from the subsurface temperatures at depth. Inflows of meteoric water (rain) and any seawater flows can also reduce the surface fluid temperatures. For this reason, the geochemical testing of these fluids would be used to identify the relative water sources and the dissolved minerals compositions could provide data about mineral dissolution temperatures in the thermal systems.
- The location of these surface manifestations is often where fault and fracture systems provide permeable pathways from the subsurface. Aerial surveys could be used to identify lineaments and gross surface features for subsequent more detailed ground geological surveys.
- Ground surveys would be able to obtain data about exposed lithologies, stratigraphies, faults and fault orientations associated with these surface manifestations as a “preview” of what might lie beneath the surface.
- Surface geological fieldwork would be a precursor to potential geophysical fieldwork.
