Drilling temperature wells into the floor and rim of Kilauea Crater was a project I had anticipated when Mr. John Brooks Henderson of Washington came to Hawaii and offered to help finance it. We had taken the temperature of hot cracks in many places, and found them to range from 320° Centigrade at the Postal Card Crack close to Halemaumau, down to 96° Centigrade at Sulphur Bank, and then on to lower temperatures at many cracks which yielded visible vapor in damp weather but no vapor at all in sunshine. A spectacle for tourists was a crack on the Sulphur Bank flat, where a cigar to windward or the exhaust gas of a car would nucleate the invisible vapor and cause a big puff of white “steam” to show. This phenomenon, which depends on smoke particles condensing invisible water vapor, is well known at Solfatara near Naples.
The experimental approach to finding out what the temperature of the ground really is, is to drill a hole and keep the temperature measured repeatedly with a thermometer, and to find out the thermal gradient change vertically if possible. This means to measure how much the temperature changes with depth. The whole problem concerns how much unusual heat energy is released at a place like Kilauea Crater.
With the aid of Hobart, a drilling engineer, I started at Sulphur Bank with a churn drill. We quickly discovered that we were going through intensely hard basalt, containing metallic sulfide which appeared to be pyrite but turned out to be marcasite. After drilling for several years—with four holes at Sulphur Bank, one sixty-foot hole under the observatory shop, and about twenty-five holes in the eastern part of the Kilauea floor over a surveyed map pattern—we changed to a rotary core drill using steel shot, and then changed again to a percussion drill actuated by compressed air, for shallow holes to show cross-country temperatures. Unfortunately core drilling requires large quantities of water, which we did not have, for the Hawaii National Park depends upon rainwater collected from roofs in redwood tanks. Without water cooling, rotary bits heat and expand in hot rock, stick, and are often lost.
Two seventy-foot holes, one at Sulphur Bank and the other in the middle of Kilauea floor, showed no definite thermal gradient; and in general it turned out that drill holes were dependent on steam in the cracks for their temperatures.
Heat was brought up by vapor, and in a number of ten-foot holes scattered over the Kilauea floor, the hottest were at the edge of the floor. The Postal Card Crack, near the edge of Halemaumau and 600 feet above red hot intrusives, was exceptionally hot, and it is not at all clear how the water made contact with the hot intrusive rock underneath. This place completely caved in and was lost forever within the enlarged pit of 1924. Sulphur Bank itself is at the edge of an old Kilauea floor on a shelf at a high level. The extra heat at floor edges means a wall crack between the crater fill and the confining funnel, so that hot gas comes up from intrusive lava somewhere deep down toward the center.
Thus when a mercurial thermometer was lowered, ten-foot holes would show a hot place half way down and cold rock at the bottom. Some holes had no heat at all, which meant that an inclined steam crack was cut across by the hole or that no steam crack was present. The heat supply was dependent upon vapor channels from heated rainwater, but we were never able, owing to lack of funds, to drill a hole deep enough to find the water supply which made the steam. It is a remarkable fact that the casings on three wells at Sulphur Bank emit continuously a column of steam exactly at the theoretical boiling point for this altitude, as though the groundwater were boiling only a short distance below. Dr. Allen by his analyses proved that Sulphur Bank vapor was ninety-nine percent steam and that the remainder contained fractions of a percent of sulfur and carbon dioxide, but this sulfur was enough in the course of months to coat the interior of our casings with yellow crystals over black iron sulfide. It coated the Sulphur Bank with yellow crystals of sulfur and soaked the rock below to generate brassy iron sulfide.
The result of these experiments was to exhibit the complexity of any solfatara in its relation to underground lava, and to the soakage of a volcanic country by rainfall. This is especially important for Martinique and Montserrat.
Another experiment was conducted by Emerson, who was equipped by the Observatory with chemical apparatus to make qualitative analyses of numerous Kilauea products, and he also did critical photographic work, including some photography in the infra-red. In one valuable experiment, he melted Kilauea lava in a refractory crucible at a temperature of about 1200° Centigrade until it was as fluid as honey. Allowed to chill and harden naturally, it was shiny glass like pahoehoe lava. If stirred with an iron rod, it made sprouted black needles, crystallized all through, like aa lava. Thus he proved that stirring made Hawaiian lava crystallize and sprout like fudge, or like the solidification of such metals as silver and bismuth. Sudden outbreak and stirring anywhere will convert pahoehoe to aa; but never does aa become converted physically to pahoehoe, unless flame melts it. The standing pinnacles in the midst of an aa flow, which breaks up into boulders, give evidence of the stirring process.
When Emerson’s discovery is applied to basaltic lava flows, it appears that the glassy lava of a source, when stirred by gas fountaining or by flowing, will change from its glassy condition to a sprouting and crystallizing condition. All flows are glassy pahoehoe pumice fountains at source vents, and a quarter of a mile away they become aa. Later the source pahoehoe preserves itself within a glassy skin and pours forward under glassy shells and frontal toes.
R. M. Wilson’s work supplied proof of a swelling mountain. Wilson was one of the three leading members of the topographic party of the Geological Survey. The other two were C. Birdseye and A. Burkland. Wilson, whom I had known as a student in M. I. T., was a product of Spofford’s Civil Engineering department and was to become the chief computer of the Survey in Washington. As levelman in Birdseye’s organization, he became topographic engineer of the Observatory, and produced by precise leveling and triangulation the brilliant experiment which showed [the swelling and shrinking of the mountain during fifteen years.