Tonga Geothermal Screening
Geothermal screening assessment identifies 43.3% prospective land reaching 185°C by 5.5 km depth in Tonga.
Key Geothermal Metrics
Primary baseline screening criterion
Minimum drill depth for high enthalpy
Maximum modeled temperature
Average to 5 km depth (15°C surface)
Hot territory within 50 km transmission
Thermal volume in place (>80°C baseline)
Depth vs. Temperature Matrix (% Land Area)
Proportion of national territory exceeding target isotherm at specified depth
| Isotherm | 3.0 km | 4.0 km | 5.0 km | 6.0 km | 7.0 km | 8.0 km |
|---|---|---|---|---|---|---|
| 150°C | 12% | 33.4% | 48.2% | 67.3% | 91.2% | 99.2% |
| 175°C | 10.4% | 27.5% | 44.1% | 56.7% | 71.9% | 100% |
| 200°C | 10% | 22.9% | 40.6% | 50.9% | 65.7% | 78.4% |
| 225°C | 10.5% | 22% | 28.8% | 44.6% | 55% | 60.5% |
| 250°C | 8.4% | 15.8% | 23.4% | 29.2% | 43.1% | 49.7% |
4-Stage Geothermal Resource & Infrastructure Funnel
Progressive screening from gross national territory down to grid-connected & populated prospective zones
Geological Setting & Subsurface Parameters
Lithology, basement thickness, stress and thermal boundary constraints
| Median Depth to 200°C Isotherm | 5.2 km |
| Best 10th Percentile Depth to 200°C | 3.9 km |
| Median Temperature at 5 km Depth | 208.9 °C |
| Best 10th Percentile Temp at 5 km | 270.2 °C |
| Median Sediment Thickness | 0.4 km |
| Sediment / Hard-Rock Well Share | 21.6% |
| Territory Under 1 km Sediment Cover | 82.3% |
| Lithostatic Pressure at 5 km Depth | 134.2 MPa |
| Moho Crustal Discontinuity Depth | 40.7 km |
| Thermal Lithosphere Thickness | 118.9 km |
| Curie Temperature Isotherm Depth | 14.5 km |
| Model Temperature Spread Uncertainty (200°C) | ±1 km |
Transmission Grid & Demand Colocation
Infrastructure interconnectivity and urban power demand proximity
| High-Voltage Transmission Network Length | 455 km |
| Land Area Within 25 km of Grid | 54.4% |
| Land Area Within 50 km of Grid | 68.6% |
| Land Area Within 100 km of Grid | 75.2% |
| Average Proximity to Nearest Substation / Line | 19.6 km |
| Urban Centers (>10,000 Population) | 10 |
| Total Urban Population | 1.4 M |
| Prospective Resource Colocated Near Demand (>1M Pop) | 45.1% |
Target Sensitivity & Deep EGS Upside
Sensitivity of prospective resource area to adjusted depth and temperature thresholds
Global Peer Benchmarking (vs. 278 Assessed Jurisdictions)
Relative ranking distribution of Tonga across 11 standardized geothermal indicators
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Analytical Geothermal Assessment & Discussion: Tonga
Subsurface thermal interpretation, model uncertainty, infrastructure colocation, and resource quality analysis
Resource Overview
Geothermal assessment for Tonga indicates volcanic_arc geological controls governing subsurface heat transport, yielding 43.3% of land area reaching the baseline target of 185°C at 5.5 km depth.
Uncertainty & Model Variance
Thermal inversion across Tonga shows consistent model convergence with constrained standard deviations across deep crustal layers.
Grid & Infrastructure Colocation
National electrical transmission coverage positions approximately 68.6% of prospective geothermal ground within 50 km of existing high-voltage corridors.
Geological & Basement Setting
Subsurface lithology is characterized by volcanic arc dynamics with median sediment thickness of 0.4 km and crustal thickness of 40.7 km.
Stored Heat Volume
Accessible thermal energy in place between 3 km and 7 km depth above 80°C totals 130.1 Zettajoules (ZJ).
Peer Comparison
Benchmarked against 237 global assessment jurisdictions, Tonga demonstrates competitive positioning across heat flow, infrastructure, and basement competence indicators.
Target Sensitivity Analysis
Screening at 150°C baseline at 5.5 km increases prospective territory, demonstrating substantial deep EGS resource headroom.
Screening Methodology, Parameters & Limitations
This screening assessment for Tonga is generated from Geothermal Radar Data Pack 2026.1 utilizing global 0.1° hex-grid thermal inversion across 8 model cells (land area: 747 km²). Baseline prospective criterion is defined as reaching 185°C at or above 5.5 km depth with surface temperature normalized to 15°C.
- Screening estimates represent regional-scale heat in place and do not replace localized 3D seismic or exploratory drilling.
- Model uncertainties expand in regions with sparse deep boreholes and complex thrust fault kinematics.
- Grid proximity indicators reflect line-of-sight distance to high-voltage transmission and do not account for local substation thermal capacity.
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