University of Miami Division of Marine Geology and Geophysics
May 30, 2023
The Lower East Rift Zone Under Puna Geothermal Venture's Drill Operation is Sinking due to Subsidence.
Falk Amelung, Professor of Geophysics from the University of Miami Division of Marine Geology and Geophysics provides his comments on the Draft Environmental Impact Statement of the Puna Geothermal Venture Repower project.
In simple terms, the article highlights four important points that are not adequately addressed in the Draft Environmental Impact Statement (draft EIS) of the Puna Geothermal Venture (PGV) Repower project. Firstly, the draft EIS lacks a plan to monitor seismic activity in the PGV area, despite the potential for induced seismicity due to PGV operations. The injection of water can increase pore fluid pressure and potentially trigger earthquakes. The author recommends the operation of a bore-hole seismic network at PGV to accurately monitor and assess induced seismicity.
Secondly, the draft EIS fails to address the hazards posed by propagating underground dikes. The 2018 dike eruption in the PGV area, and the subsequent injection of heavy mud, raise questions about appropriate response measures and potential unintended consequences. The draft EIS should include a discussion on how propagating dikes can impact wells and propose an eruption response plan.
Thirdly, the impact of geothermal exploration on dike propagation is not adequately explored in the draft EIS. The study cited in the draft EIS only considers the origin of the dike and not its eruption location. The presence of cooling contraction cracks resulting from heat extraction can weaken the rock and affect the path of dikes. This effect should be estimated and discussed in the draft EIS.
Lastly, the statement in the draft EIS that there have been no significant changes in deformation patterns or trends due to human activity in the PGV area is incorrect. Analysis of InSAR time series data reveals a linear ground displacement feature, suggesting subsidence at a rate of 2-3 cm/year, starting when PGV resumed production in 2020. This subsidence may be caused by water extraction and cooling of the hot rock. The observed subsidence emphasizes the need for comprehensive research and high-quality seismic monitoring to fully understand the extent and significance of these effects.
Overall, the article highlights the need for further investigation, independent monitoring, and comprehensive assessment of the potential impacts of PGV operations, including seismic activity, dike propagation, and subsidence.