The Arizona Geological Survey has a new report on the age of young volcanic rocks near the Palo Verde nuclear power plant. The report was produced over concern of geologic hazards near the generating station.
The report concerns the Sentinel – Arlington volcanic field which extends over about 50 miles from Sentinel volcanic field west of Gila Bend northeastward to Arlington volcano west of Buckeye. That puts it within 6 miles of the power plant.
Arlington Volcano is located 6 miles southeast of the power plant. Six potassium-argon radiometric dates of basalt rock samples from Arlington volcano range from 1.28- to 3.28 million years old. Although there is a two-million-year spread in the age dates, AZGS notes that the Arlington “volcano is geologically simple, consisting of a single, small, low-relief volcano with no soil horizons between flows. Most likely it was erupted in a single volcanic episode of short geologic duration (<10,000 years), …about 2.1 million years ago.
Gillespie volcano occurs about 12 miles south of the Palo Verde Nuclear Generating Station. It is a morphologically similar low shield volcano without soil horizons or multiple eruptive centers. Four of five potassium-argon dates range from 2.67- to 3.6 million years, suggesting an age of 3 million years. AZGS infers that this eruption temporarily dammed the Gila River.
The report goes on to discuss other volcanoes more distant from the Palo Verde nuclear station. The AZGS report concludes with a caveat:
“The Sentinel – Arlington volcanic field produced extensive, low relief basalt lava flows and small, gently sloping basalt shield volcanoes. Available geochronologic data suggest that the Sentinel – Arlington volcanic field has erupted intermittently over the past 1.1-3.5 Ma, with no clear migration of volcanic activity within the field. Although there is no geochronologic evidence for eruptions during the past one million years, the large range of geochronologic dates from the Sentinel volcanic field, the uncertainties inherent in many of the older potassium-argon dates, and the large number of eruptive centers, allow for the possibility of more recent activity that is as yet undocumented.”