| dc.description.abstract | Numerous geothermal exploration projects have taught us a fundamental axiom for geothermal
exploration in volcanic areas. Many of the complexities and unknown, subsurface characteristics
of a volcanic geothermal field can be constrained through logical deduction that is based upon
careful field observation, mapping, sample studies, and the integration of related geophysical and
hydrogeochemical data.
We believe that many geothermal exploration projects in volcanic areas have suffered from the
lack of pertinent volcanological observations and interpretations. So many clues regarding the
location and magnitude of geothermal systems are available from the volcanic structure and
deposits that one might say detailed interpretation of these observations constitutes a type of
exploration drill-hole. Therefore, we stress the need for careful field volcanology during
geothermal exploration projects in volcanic areas.
During the last 10 years, the field of volcanology has been growing rapidly; the resulting new
observations and ideas are providing us with numerous hypotheses on volcanic structure and
processes. In magma genesis, movement, and eruption phenomena, as well as volcanic structure
and thermal histories, there have been many new discoveries that have engendered a better
understanding of igneous systems and their relationship to high-grade geothermal systems. These
hypotheses and discoveries have important geothermal implications when applied to the
interpretation of volcanological observations.
Geologists must use what is known about volcanoes, their structure, eruption phenomena, and
composition, to reveal necessary information about the heat sources and settings of
groundwater—key factors in formation of a hydrothermal system. A basic approach to
exploration includes good geological mapping by whatever means is available: topographic
maps, aerial photographs, satellite photographs, planetable surveying, tape and brunton traverses,
and panoramic viewpoints. Also, systematic descriptions of tephra deposits and rocks are vital,
especially for core logs from exploration holes.
In applying volcanological observations, one should integrate the observations (for example,
mapping and sample analyses) with other information on surface springs and iv
fumaroles, water chemistry and hydrology, and geophysical surveys, including gravity, electrical
resistivity, seismicity, and heat flow. Any of these surveys by itself, without a geologic
framework, is almost useless; integrated with good geological surveys, each is valuable.
Hydrochemists, geophysicists, reservoir engineers, and geologists must talk to each other and
work as teams to successfully develop geothermal resources.
The field approach involves learning everything possible about a volcano or volcanic field,
including structure; structural setting, eruption phenomena, composition, and ages of eruptions.
Using these data, it is possible to establish hypotheses regarding the location and magnitude of
hydrothermal resources. Simply put, the volcano and its products supply information normally
gathered from the first drillholes and may provide a view of the volcano's geothermal system or
systems. The field approach is usually cost effective and defines the first step towards
prescribing the geophysical surveys and exploration drilling that will be of use. | en |
