This is the final post in the series on mapping in geothermal energy. We will focus on environmental and hazard mapping. In order to make any geothermal development sustainable, we must reduce its environmental impact and mitigate potential hazards. Even though emissions associated with geothermal exploration and development are small compared to fossil fuel power plants, there are other environmental concerns to be considered. The major environmental concerns associated with geothermal energy exploration and development includes:
It’s good to note that the importance of each varies depending on the phase of geothermal development. For example feasibility- chemical pollution, visual effects, noise; plant construction – surface disturbances, noise, visual impact, ecological impacts and disposal of waste; and power plant operation – induced seismicity, subsidence, and noise.
Environmental mapping in geothermal energy includes land subsidence, impact on natural manifestations and induced seismicity (I will talk about induced seismicity seismic geo-hazards). Land subsidence associated with geothermal energy production can occur due to fluid withdrawal without balanced reinjection. We can map this using satellite interferometric synthetic aperture radar (InSAR) and from subsidence leveling surveys. InSAR has been recently applied to image structures with a lateral outflow of thermal fluids by showing areas of subsidence associated with fluid production and areas of uplift related to the injection. Land subsidence has been observed in New Zealand (max event 400mm/year,) and Tuscany, Italy (max event 250mm/y).
Geothermal production can impact natural manifestations due to subsurface pressure changes. This can result in a decrease or increase in the activity of thermal manifestations. Examples of increase thermal manifestation include Craters of the Moon, (Karapiti), Wairakei and Mokai, Tirohanga Road Craters in New Zealand. An increase in soil temperatures has been observed in Reykjanes, Iceland. Monitoring of thermal manifestations have been carried out using thermal infrared imagery (TIR) and an example from Iceland can be seen below.
Most medium to high-temperature geothermal resources are located in tectonically active regions. Thus increasing the chances of geo-hazard occurrences. These are hazards related to geological phenomena and includes, seismic and volcanic events and mass flow movements (landslides and debris flows). Geo-hazard mapping is important in order to identify potential hazard zones and aid in the development of mitigation measures.
Seismic events are related to ground motions caused by earthquakes (natural or induced). Hazard mapping and analysis of these events try to determine the location of potential earthquakes, identify past events, locate active faults and potential areas of associated hazards (landslides, liquefaction and ground deformation). On January 13th, 2001, a magnitude 7.6 earthquake was recorded in El Salvador which affected the Ahuachapán and Berlín.
Reinjection of water into the reservoir or hydraulic fracturing (for Enhanced Geothermal Systems, EGS) can induce seismicity. Seismic monitoring has been done and is recommended for producing geothermal fields. This often results in a seismic map showing distribution, intensity, and location of seismic monitoring stations. Induced earthquakes occurred in Switzerland on two occasions:
A protocol for handling induced seismicity due to EGS can be found here.
Image 3: Induced seismicity at sites of geothermal projects Soultz‐sous‐Forêts, Landau i. d. Pf. resp. Insheim, Unterhaching, and Basel (red circles) in comparison with natural tectonic earthquakes (white circles) from June 2000 to March 2011, Switzerland. (From Grünthal, 2014)
A volcanic hazard refers to any potentially dangerous volcanic process (e.g. lava flows, pyroclastic flows, ash). Typically, volcanic hazards increase the closer we are to an eruptive center. However, in the case of a geothermal power plant, we have to consider long-range associated events with these hazards such as ash falls and ballistic impacts (volcanic bombs and blocks). Understanding and mitigating these hazards require mapping past events (locations and affected zones), constant monitoring of volcanic activity and development of an emergency management plan. The most recent event was the eruption of the Kilauea Volcano that began on May 3, 2018. It resulted in the closure of the Puna Geothermal plant (Ormat Technologies) where lava eventually damaged numerous buildings, blocked an access road and covered 3 geothermal wells.
Mass movements are described as movements of soil and rock debris down slopes in response to the pull of gravity. These are affected by a number of internal and external factors. Internal factors include rock type; slope angles; altered ground; and the presence of faults. External factors include heavy rains, seismic and volcanic activities. A number of movements exist, the most common in geothermal areas are landslides and rockfalls. On January 5, 1991, a deadly landslide occurred at the Zunil I geothermal field (Western Guatemala) covering an area containing active fumaroles, access road and drill pad for one of 6 productions wells in the field. In order to mitigate against such events, detailed surficial geology and slope stability maps are necessary. This should also include information on landslides scars, alteration zones, faults, fractures, etc. Landslide hazard zonation maps have been created and an example from the Mindanao Geothermal Production Field in the Philippines can be seen below. The selection of drill pads, siting of buildings and layout and construction of steam pipes should avoid areas of the obvious potential for these hazards.
Even though the environmental impacts of geothermal energy utilization is small, there are still environmental impacts to be considered and managed. Here I covered those aspects that we can ‘map’, but others exist that focuses on showing data using charts and graphs. Geo-hazards can be natural or induced and can have severe impacts on geothermal utilization like in Zunil, Guatemala, and Switzerland. This shows the importance of environmental and hazard mapping including monitoring for geothermal exploration and development.
This concludes our series on mapping as an important tool in geothermal energy exploration and development. We hope that you enjoyed the series and learned something you can apply to your geothermal project. If you have any questions or comments feel free to contact us here or directly at [email protected].
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