Ambrym Island, located in Vanuatu, is home to a prominent active volcano within a 12-km-wide caldera, featuring the Benbow and Marum craters. These craters, known for their persistent lava lakes and significant volcanic gas and heat emissions, drive visible geothermal activity, including fumaroles, steaming ground, and hot springs. However, the presence of volcanic heat does not necessarily translate to a viable geothermal reservoir for power generation. This report explores Ambrym’s geothermal hotspots, past surveys, development interest, feasibility of power projects, and associated challenges and environmental concerns.

Existing Geothermal Activity and Hotspots

Ambrym’s volcanic activity fuels several geothermal phenomena, primarily driven by the volcano’s magma system. Key geothermal features include:

• Northwest Coast Springs (Sesivi/Ranon Area): Hot springs near Sesivi exhibit surface temperatures of 39–40°C with neutral to slightly alkaline pH, indicating volcanic-heated groundwater mixed with shallow meteoric water. These springs, used locally for bathing and cleaning, suggest long-term geothermal activity.
• Southwest Coast Springs (Sulphur Bay): The hottest springs on Ambrym, reaching up to 60°C, are found at Sulphur Bay. With notable flow rates (tens of liters per second) and a sulfurous odor, these low-enthalpy springs reflect volcanic gas influence but remain far below boiling temperatures.
• Fumaroles and Hot Ground: Within the caldera and near volcanic vents, fumaroles release hot steam and gases, while heated ground is prevalent. These features indicate intense volcanic heat but are not linked to a known hot water aquifer, limiting their direct usability.

Assessment: Ambrym’s geothermal features confirm the presence of volcanic heat, but the springs’ moderate temperatures (≤60°C) and geochemical profiles suggest shallow, peripherally-heated systems rather than a deep, high-temperature reservoir suitable for power generation.

Past Research and Surveys

Geothermal potential on Ambrym has been evaluated through limited but targeted studies, focusing on whether a high-temperature hydrothermal system exists:

• 1960s–70s Surveys: Early geological surveys during the New Hebrides Condominium era mapped Ambrym’s hot springs and volcanic activity but did not conduct detailed geothermal assessments.
• 2015–2016 Baseline Geothermal Survey: Conducted by Vanuatu’s Department of Geology, Mines, and Water Resources, this survey analyzed hot spring temperatures, chemistry, and isotopes. Key findings include:
  • Spring waters showed no evidence of boiling or originating from a high-temperature reservoir.
  • Geochemical geothermometers estimated subsurface temperatures well below 150°C, insufficient for efficient power generation.
  • Conclusion: Ambrym’s hot springs are peripherally-heated, with no exploitable hydrothermal reservoir, unlike Tanna Island, where a 200+°C reservoir was identified.
• Other Studies: Research on volcanic gas emissions (e.g., fluoride-related health impacts) and geophysical monitoring of magma chambers post-2018 eruption provide context but confirm that Ambrym’s heat is primarily “dry” volcanic output rather than a hot water resource. No exploration wells have been drilled due to discouraging survey results and high costs.

Summary: Scientific evidence indicates Ambrym lacks a viable high-temperature geothermal reservoir, limiting its potential for conventional geothermal power.

Government and NGO Interest

Vanuatu’s push for renewable energy includes geothermal exploration, but Ambrym has seen minimal development interest due to its uncertain resource and low electricity demand:

• National Energy Plans: Vanuatu’s National Energy Road Maps (2013–2020, 2016–2030) prioritize geothermal for islands like Efate and Tanna, where resources and demand align. Ambrym is slated for solar and wind projects, with a 2000 proposal explicitly favoring solar for rural electrification.
• 2015–2016 Survey: Government-funded research on Ambrym aimed to identify commercial geothermal targets but concluded against development due to low resource potential.
• Current Initiatives: Geothermal exploration licenses have been granted for Efate and Tanna as of 2025, but none for Ambrym. Ambrym’s energy needs are addressed through solar, wind, and diesel-hybrid systems.
• NGO and Donor Support: Organizations like the World Bank and IRENA support Vanuatu’s renewable energy transition but focus on high-potential sites. Ambrym has not attracted geothermal investment, though regulatory frameworks (e.g., 2019 Geothermal Energy Act) could support future projects if viable resources are found.

Conclusion: Ambrym remains a low-priority site for geothermal development, with government and donors favoring more promising locations and alternative renewables for the island.

Feasibility of Geothermal Electricity Projects

Developing geothermal power on Ambrym faces significant technical and economic hurdles, particularly for small-scale projects suited to the island’s modest demand:

1. Resource Temperature and Capacity:
   • Known springs (≤60°C at surface, ~100°C estimated at depth) are low-enthalpy, suitable only for inefficient binary cycle generators.
   • High-temperature (>150°C) reservoirs, critical for viable power plants, are not evident. Drilling near magma chambers to access hotter fluids is risky and may not yield a suitable aquifer.
2. Drilling and Infrastructure:
   • Drilling wells (1–2 km deep) in Ambrym’s rugged terrain requires transporting heavy equipment, building roads, and establishing stable drill pads, all at high cost.
   • Volcanic hazards (e.g., magma encounters, corrosion) increase drilling risks, with no prior test wells to reduce uncertainty.
3. Economic Viability:
   • Ambrym’s low electricity demand (met by diesel generators and solar) limits the market for a geothermal plant, which would likely exceed local needs.
   • High capital costs for a small plant (1–3 MW) result in expensive power compared to solar or hybrid systems. Exporting power via subsea cables is infeasible.
4. Scale and Design:
   • Small-scale binary plants (<1 MW) could theoretically use a ~120°C resource, but multiple wells and mini-plants across villages multiply costs.
   • A centralized plant requires a costly mini-grid, making geothermal less competitive than distributed solar or wind solutions.

Verdict: Geothermal electricity is not currently feasible on Ambrym due to low resource temperatures, high costs, and competition from cheaper alternatives. A high-temperature reservoir discovery could alter this outlook, but existing data suggest this is unlikely.

Challenges and Environmental Concerns

Geothermal development on Ambrym would face significant challenges and require careful environmental and social management:

• Volcanic Hazards:
  • Ambrym’s active volcano poses risks of eruptions, ashfall, and seismic activity, threatening infrastructure. The 2018 eruption and ongoing unrest (1–2 km Permanent Danger Zone) complicate safe project siting.
  • Drilling in a volcanic zone risks triggering tremors or encountering magma, increasing operational hazards.
• Geochemical Corrosion and Emissions:
  • Acidic volcanic fluids and gases (sulfur dioxide, fluorine) could corrode equipment, necessitating costly specialized materials.
  • Geothermal emissions would be minor compared to the volcano’s output, but protecting infrastructure from the caustic environment is a priority.
• Environmental Impacts:
  • Tapping groundwater could reduce hot spring flows, affecting local use and potential tourism at sites like Sulphur Bay.
  • Surface disturbance (roads, drill pads) may clear vegetation, impacting tropical forests and wildlife. Fluid reinjection is essential to prevent groundwater or marine pollution.
  • Environmental impact assessments, mandated by Vanuatu law, must address effects on ecosystems and coastal waters.
• Land and Community Relations:
  • Customary land ownership requires negotiations with local clans, ensuring fair benefits and respect for cultural sites tied to the volcano.
  • Community engagement is critical to avoid conflicts and provide tangible benefits (e.g., electricity access). Safety education is needed to prevent accidents near geothermal facilities.
• Financial and Project Risk:
  • High exploration costs and volcanic risks deter investors, potentially requiring government subsidies.
  • Opportunity costs are significant, as funds for geothermal could yield faster results with solar or wind projects.

Summary: Volcanic risks, environmental impacts, and social considerations, combined with financial uncertainty, make geothermal development on Ambrym highly challenging.

Final Assessment

Ambrym Island’s active volcano generates significant geothermal activity, evidenced by hot springs and fumaroles, but lacks a high-temperature reservoir suitable for electricity generation. Comprehensive surveys, notably the 2015–2016 study, confirm that Ambrym’s geothermal systems are shallow and low-enthalpy, steering government and investor focus toward islands like Efate and Tanna. Technical and economic barriers—low resource temperatures, high drilling costs, and competition from solar and wind—render geothermal power infeasible under current conditions. Volcanic hazards, environmental concerns, and community land issues further complicate development. While Ambrym’s geothermal potential remains a theoretical possibility, solar, wind, and diesel-hybrid systems are better suited to meet the island’s energy needs in the near term. Future exploration with advanced technology could revisit this potential, but any initiative must involve geoscientists and local communities to navigate the island’s unique challenges.

References

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8. Vanuatu Broadcasting and Television Corporation. (2025). Geothermal Exploration Licenses for Efate and Tanna. VBTC.vu. Retrieved from https://vbtc.vu
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