2. 1| Application of Volcanological Observations to Geothermal Exploration
Topic Outlines
Introduction
Tectonic setting
Origin of magmas and,
Magma chambers
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3. 3
Chapter One
Chapter
Objectives
Having completed this chapter, you should be able to:
understand the dichotomy in technological approaches of
volcanology and geothermal energy
know the strategy that bridges the gap left between the
two aspects.
understand the relationship between plate tectonics,
earthquakes and volcanoes.
4. Introduction
• Volcanology, discipline of the geologic sciences that is concerned with all
aspects of volcanic phenomena.
• Classify volcanic eruptions according to the physical and chemical properties
of their magma.
• From it we learn about the different kinds of volcanic eruptions.
• Volcanology deals with the formation, distribution, and classification of
volcanoes as well as with their structure and the kinds of materials ejected
during an eruption.
5. • A volcano is an opening in a planet or moon’s crust through which molten rock,
hot gases, and other materials erupt. Or a state or situation which is liable to erupt
into anger or violence.
• Volcanoes often form a hill or mountain as layers of rock and ash build up from
repeated eruptions.
• Volcanoes are classified as active, dormant, or extinct. Active volcanoes have a
recent history of eruptions; they are likely to erupt again. Dormant volcanoes have
not erupted for a very long time but may erupt at a future time. Extinct volcanoes
are not expected to erupt in the future.
Introduction
6. • A geothermal resource can be defined as a reservoir inside the Earth from
which heat can be extracted economically (cost wise less expensive than or
comparable with other conventional sources of energy—such as
hydroelectric power or fossil fuels) and utilized for generating electric
power or any other suitable industrial, agricultural or domestic
application in the near future.
• They are clean, renewable, and reliable energy sources, making them an
advantageous replacement for fossil fuels.
Introduction
8. • Geothermal energy is an important and promising alternative energy
resource that has shown continual growth throughout this century.
• Because the world's highest temperature—and perhaps most abundant—
geothermal resources are associated with active volcanic regions,
• this course develops a framework for exploration and development of
geothermal resources in volcanic areas.
• by linking modern volcanological concepts to aspects of geothermal
energy.
Introduction
9. • Volcanology has largely been an outgrowth of the larger discipline of geology and,
like geology, is mostly a qualitative or "inexact" science.
• In contrast, much of the supporting science of geothermal energy has evolved from
engineering methods that were developed in the petroleum industry; hence, it is
intrinsically more quantitative and has a very different technical language.
• This traditional dichotomy in technological approach has, we believe, hindered
progress in both exploration for and developments of geothermal systems in
volcanic areas.
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Introduction
13. • Many of the complexities and unknown subsurface characteristics of a
volcanic geothermal field can be constrained:
• through careful field observation, mapping, sample studies, and the
integration of related geophysical and hydrogeochemical data.
• Many geothermal exploration projects in volcanic areas have suffered from
the lack of important volcanological observations and interpretations.
1.1| Application of Volcanological Observations to Geothermal Exploration
14. • Geologic maps: present spatial and temporal information on the
composition, orientation, and evolution of earth materials and structures.
• Digital geologic maps: facilitate quantitative assessment of earthquake,
volcanic, and landslide hazards, deformation and eruption rates, subsurface
structure, petrologic modeling, surface processes, and climate change
through time.
1.1| Application of Volcanological Observations to Geothermal Exploration
15. What Geologists must use for developing geothermal resource?
• Geologists must use what is known about volcanoes,
1) their structure, eruption phenomena, and composition, to reveal
necessary information about:
2) the heat sources and settings of groundwater—key factors in
formation of a hydrothermal system.
1.1| Application of Volcanological Observations to Geothermal Exploration
16. • Good geological mapping includes:
topographic maps,
aerial photographs,
satellite photographs,
plane table surveying,
tape and brunton traverses, and panoramic viewpoints/birds’ view.
systematic descriptions of tephra deposits and rocks are vital,
especially for core logs from exploration holes.
Integration of data is necessary
1.1| Application of Volcanological Observations to Geothermal Exploration
17. What has to be integrated?
• In applying volcanological observations, one should integrate:
1) the observations (for example, mapping and sample analyses) with other
information,
2) surface springs and fumaroles, water chemistry and hydrology, and
3) geophysical surveys, including gravity, electrical resistivity, seismicity,
and heat flow.
• Geologist, hydrochemists, geophysicists and reservoir engineers, must talk to
each other and work as teams to successfully develop geothermal resources.
18. A basic methodology for geothermal exploration in volcanic fields
• A basic methodology for geothermal exploration in
volcanic fields was developed in 1983 by an
international team of experts for the Latin
American Energy Development Organization
(OLADE, 1983).
• The field approach involves:
• learning everything possible about a volcano
or volcanic field:
• including structure, structural setting,
eruption phenomena, composition, and
ages of eruptions (see illustration).
Flow diagram showing steps of the OLADE
methodology for a geothermal project.
19. Field Approach
• The geological and physical volcanological approach involves the three steps
outlined here;
• These steps are undertaken at the same time as the hydrogeochemical
sampling but before geophysical surveys.
1) Evaluation of Available Information about the Area to Be Studied
(literature review)
2) Field and Laboratory Investigations
3) Detailed Field and Laboratory Studies: Geology and Volcanology
20. 1) Evaluation of available Information about the area to be studied
• The initial phase of a project, all existing information is collected and
evaluated, including:
topographic and geological maps at large and small scales
regional geological syntheses, including stratigraphy, structural geology,
and history of volcanism;
satellite images and aerial photography;
all published and unpublished reports on geology, geochemistry,
geophysics, hydrology and meteorology.;
information on the presence and characteristics of hot springs,
fumaroles, and hydrothermal alteration;
information on drillholes or coreholes from any source, including water
well drilling, petroleum drilling, and coring by mining companies;
21. 2) Field and laboratory investigations
• Field and laboratory investigations should be designed to answer specific
questions regarding:
a) the possible presence of shallow thermal anomalies,
b) regional hydrologic conditions, and
c) the na ture of thermal manifestations.
• These include:
• Identify those areas where there are episodes of recent volcanism.
22. 2) Field and laboratory investigations
• Evaluate the relative quantities of silicic and mafic or intermediate volcanic
products.
• Define, on a regional scale, the present relationship between the volcanic
structure and the regional tectonic framework.
• Identify phreatic explosion craters.
• Systematically collect samples of all lithologic types for laboratory analysis,
including petrographic and chemical analyses.
• Collect lithic clasts (xenoliths) from pyroclastic units for petrographic analysis.
• Determine the absolute ages of representative lithologic units.
• Study (in preliminary form) all possible reservoir and cap rock units.
23. 3) Detailed Field and Laboratory Studies: Geology and Volcanology
Detailed field and laboratory studies begin with
(a) interpretation of aerial photography,
(b) preliminary identification of faults and volcanic structures,
(c) hypotheses concerning the regional volcanotectonic setting, and
(d) integration of information from existing maps.
Following this work, a detailed field study is needed.
24. Detailed field study comprises of the followings four steps
1) A search for thermal anomalies in the upper crust which involves:
• mapping and sampling young volcanic eruption sequences, especially
rock types indicative of shallow magma bodies.
• all areas of hydrothermal manifestations, both fossil and active, are
mapped and sampled in conjunction with hydrogeochemical sampling.
• all volcanic structures are mapped, including craters, domes, phreatic
craters, and associated faults.
25. Detailed field study comprises of the followings four steps
2) In areas with surface hydrothermal manifestations:
• potential caprock are mapped and sampled, and their origin is determined.
• In volcanic zones, the search for phreatic explosion craters is emphasized.
3) The extent of potential geothermal reservoirs can be estimated through:
• A study of lithic clasts (xenoliths) in pyroclastic deposits; these clasts
provide information on the nature of rock units underlying the volcano.
26. • Identification and mapping of recent faults. This effort is essential
because active faults frequently represent zones of fracture permeability.
• Determination of the degree of hydrovolcanic activity responsible for
pyroclastic deposits in the volcanic field.
• This work may identify aquifers beneath the volcano during recent
eruptions.
• These aquifers could be current hydrothermal reservoirs
27. 4) In tropical countries where soils form rapidly and outcrop are soon
covered by vegetation, geological mapping is considerably more difficult.
• In these situations, several additional approaches are necessary:
• Landform mapping: These maps are based primarily on the interpretation of
aerial photographs and satellite images, especially in young volcanic fields.
The interpretations are field checked along road cuts, stream bottoms, and
shorelines, as well as in quarries.
• Side-looking airborne radar (SLAR) imagery: Such images are extremely
useful in mapping faults and volcanic landforms in tropical areas, although
they may be relatively expensive to acquire.
28. • If you look at a map showing the distribution of earthquakes around the
world, it shows that they tend to be concentrated along well-defined belts.
• Correspondingly, maps of tectonic plate boundaries are primarily produced
using earthquake locations.
• We can also can see from the distribution of volcanoes around the world that
most lie on plate boundaries too, in particular a region a called the Pacific
Ring of Fire around the edge of the Pacific Plate.
1.2| Tectonic setting, origin of magmas and magma chambers
35. Volcanoes need magma (molten rock) – how to get molten rock in
the solid planet?
o Temperature increases with depth, but the same with melting
temperature
Decompression:
– hot spot
– mid-ocean ridge
– continental rift
Hydratation:
– subduction
36.
37. • There are three settings where volcanoes typically form:
constructive plate boundaries
destructive plate boundaries
hot spots
Volcanoes do not typically occur at transform boundaries. One of the reasons
for this is that there is little or no magma available at the plate boundary.
1.2| Tectonic setting, origin of magmas and magma chambers
