Scientific Observation Hole

Liz bagging drilling fragments from SOH #2, 3/25/91.

A geothermal experiment by the University of Hawaii proved that the Kilauea East Rift Zone held geothermal potential. From 1990 to 1991, the Scientific Observation Hole (SOH) program operated three geothermal test wells in Puna, Hawaii:

  • SOH-1: Lower Kilauea East Rift Zone
  • SOH-2: Lower Kilauea East Rift Zone
  • SOH-4: Between Puna Geothermal Venture and True/Mid-Pacific geothermal wells

Continuously cored, these exploratory slim holes ranged in depth from 5,500 to 6,800 feet. As for SOH-3, it was planned, but never drilled.

The data showed that a ten-mile interval along the Kilauea East Rift Zone held favorable high temperatures, as shown in the following:

Geothermal Well Temperature F (C) Total Depth Drilled (feet)
SOH-1 403 5,526
SOH-2 662 6,802
SOH-4 583 6,562
Map of Kilauea East Rift Zone
As the map of lower Puna, Hawaii Island, shows, SOH-4 operated in the Puna Forest Reserve, southwest of Pahoa, SOH-1, north of Puna Geothermal Venture’s power plant, and SOH-2, further east, west of Kapoho. All of these wells were built in historically volcanic areas (e.g. in 2018, lava from the Kilauea eruption flowed to the Puna Geothermal Venture power plant).

These holes provided data for the following:

  • Assessing the geothermal potential of those areas.
  • Determining rock types, alteration, and structures within the rift zones, the depth to potential geothermal reservoirs, the depth and composition of groundwater, and the temperature of rock and fluids at depth.

The Hawaii Natural Energy Institute (HNEI) operated SOH. HNEI is a division of the School of Ocean and Earth Science and Technology, University of Hawaii at Manoa.

Project Photographs

John Deymonaz and Governor’s advisory commission were examining cores at SOH-1, 11/8/90.

General Information

man pouring rocks
A drill crew member operates the drilling rig and collects core samples from SOH-1.

Data, Core Samples, and Scientific Analysis

Visual Core Descriptions

  • SOH-1: volumes 1A | 2A | 3A
  • SOH-2: volumes 2 | 3
  • SOH-4: volumes 1A | 1B | 2A | 2B

Drill bits (front) and boxes of core samples (back)

Core Photographs of Scientific Observation Hole #1

Core Photographs of Scientific Observation Hole #2

Core Photographs of Scientific Observation Hole #4

The SOH #1 site, 11/8/90.

Environmental Aspects


man with students surrounding him
John Deymonaz shows students from Iliahi Elementary School core samples from SOH #2.


– Alice Kim, Information Coordinator

Updated: August 6, 2020
Created: August 6, 2020