Summary geological report and index log of the Scientific Observation Hole #2 on the Kilauea East Rift Zone, Hawaii

Abstract

The Scientific Observation Hole (SOH) program is a multifaceted core drilling project. The overall project goals are to provide data for volcanic research, to aid in evaluating the commercial geothermal potential along the east rift zone (ERZ) of Kilauea volcano, and to utilize the sites for long-term monitoring. The volcanic and stratigraphic sequence penetrated by SOH-2 is dominated by subaerial and submarine basaltic lava flows. Thin tephra units and rare carbonate sediments interbed with the flows. Basaltic and diabase intrusive bodies cut through these formations. Olivine and plagioclase are the common phenocrysts in the basalts. The diabase may constitute an important stratigraphic marker horizon that can help to tie SOH-2 to future drilled sections along the lower east rift zone (LERZ). The transition from subaerial to submarine formations is within the interval of 1669-1909 feet, suggesting 1387-1627 feet of subsidence. Argillic alteration grades into propylitic alteration with increasing depth. Secondary minerals occur as fracture fillings, amygdules, and replacements after glass and primary groundmass minerals, and mainly include smectite clays, zeolites, analcime, secondary feldspars, sulfides, and a variety of silica minerals. Epidote occurs below 5900 feet. Below 4800 feet the hole permeated an interval with a geothermal gradient on the order of 13.7 degrees F/100 feet. A maximum temperature of 661 degrees F was encountered at 6782 feet.