HAWAII NATURE NOTES
THE PUBLICATION OF THE
NATURALIST DIVISION, HAWAII NATIONAL PARK
AND THE HAWAII NATURAL HISTORY ASSOCIATION

THE HAWAIIAN VOLCANO OBSERVATORY

The Hawaiian Volcano Observatory was established in 1912 by Dr. T. A. Jaggar, of the staff of the Massachusetts Institute of Technology, and for the first seven years of its existence it operated on funds provided by the Institute from its Whitney Fund for research in geophysics and by the Hawaiian Volcano Research Association. The latter, which is still in existence, is a group of persons, largely residents of Hawaii and principally business men, who are actively interested in the study of volcanoes. In 1919 the administration of the Volcano Observatory was taken over by the United States Weather Bureau, which was then charged by Congress with the responsibility for earthquake investigations in the United States. In 1924 the Observatory passed to the U. S. Geological Survey, in 1935 to the National Park Service, and in 1948 back to the Geological Survey. It is currently a part of the Geological Survey's volcano investigation program.

The original location of the Volcano Observatory was the site now occupied by the Volcano House. The Whitney Laboratory of Seismology, which still houses the Observatory's principal seismograph, is a concrete vault beneath the western end of the Volcano House. It can be inspected by visitors. When the present Volcano House was built in 1941, the Observatory was transferred to what is now the Park Museum and Administration Building, and in 1948 to a building on the western rim of Kilauea caldera at Uwekahuna. Dr. Jaggar continued as Director of the Observatory until his retirement in 1940, when he was succeeded by R. H. Finch, who in turn was succeeded in February 1951 by G. A. Macdonald.

Since 1912, Kilauea and Mauna Loa volcanoes have been under constant close observation by members of the Observatory staff. The purpose of the studies by the Volcano Observatory have two general aspects, the humanitarian or practical aspect and the strictly scientific. The two are difficult to separate, because a phase that belongs to pure science today may become of great practical importance within a few years. In general, the scientific aspects of the Observatory program are directed toward an understanding of the subsurface structure of the volcanoes, the nature and properties of the magma, how the volcano behaves, and why. The humanitarian aspects include prediction of eruptions and of the course of lava flows once the eruption has started, issuing of warnings of danger from lava flows, and direction of efforts to deflect flows from important areas, for example by aerial bombing (Plate 12).

An example of one phase of the Observatory's program that is of purely scientific importance at present but may become of great practical importance in the future is the investigation of the volcanic gases and their relation to the magma and effects on surrounding rocks. A large proportion of the natural deposits of metallic ores were formed either directly or indirectly by emanations (gaseous or liquid) given off by intrusive bodies of magma. The known ore bodies are being mined out, and the finding of new deposits is becoming ever more difficult. The location of new deposits is becoming the province of the trained scientist rather than that of the old-fashioned prospector, and demands an ever better understanding of how they were formed. The effects of the magmatic emanations are being studied in old ore deposits all over the world and the composition and properties of the emanations deduced from indirect evidence, but the only places the emanations themselves can be studied directly is at active volcanoes and hot springs.

The work of the Volcano Observatory includes visual observations of the volcanic eruptions and keeping of a complete diary of the activity, collection of gas and lava samples, determination of temperatures of liquid and soldifying lava and of the gases liberated in fumaroles, measurement of the width of many cracks about Kilauea caldera as they open and close, the operation of several tilt-meters and a series of magnetometer stations on Kilauea and the slopes of Mauna Loa, and a net of five seismograph stations.

Very early in the history of the Observatory it was found that the ground surface on the slopes of the volcano was constantly tilting in one direction or another, and it was soon shown that this tilting correlated with activity of the volcanoes. Preceding eruption the whole volcano swells up, as though it were being inflated like a big balloon. This produces an outward tilting on its sides. Following the eruption the volcano contracts and the slopes tilt inward. This swelling and tilting can be measured by leveling, of the sort done in ordinary surveying. By leveling from sea-level at Hilo, it was found that during the interval from 1912 to 1921 a bench mark near the Observatory apparently rose about 3 feet. Releveling in 1927, after the great collapse and steam explosions of 1924, showed that the same bench mark had lowered 3.5 feet, while a bench mark near the rim of Halemaumau had gone down about 13 feet. Ordinarily, however, the tilting of the ground surface is measured not by leveling, but by sensitive pendulums known as tilt-meters. Such tilt-meters in operation by the Observatory are capable of indicating an angle of tilt of less than one-tenth of a second. (A tilt of one-tenth of a second would displace the top of a pole ten miles high about a quarter of an inch). Volcanic tilt of many seconds of arc has been measured on the tilt-meters. Strong outward tilting of the ground surface, especially when combined with numerous earthquakes, is a good indication of magma rising in the volcano and the possibility of impending eruption.

Magnetometer measurements by the Volcano Observatory were started early in 1950. A magnetometer is an instrument used to measure the strength of the earth's magnetic attraction at any given locality. The strength of the earth magnetism depends on several factors. One cause of decrease in the strength of magnetism is rise in temperature of the underlying rock. As magma rises beneath the surface the surrounding rocks are heated up, and their magnetism decreases. It is hoped that this decrease in magnetism can be detected long enough before the magma reaches the surface to given an additional basis for prediction of eruptions, and to supply information on the rate of rise of bodies of hot magma in depth. However, the program is still too new at the date of writing (1950) to have yielded definite results.

A seismograph is a device to record earthquakes. The essential portion of most seismographs is a pendulum. Because of its inertia, during earthquakes a freely suspended pendulum tends to stand still while the earth moves under it. The effect is nearly the same at it would be if the earth were still and the pendulum vibrating. This apparent movement of the pendulum is recorded in various ways—by direct mechanical means, by directing a beam of light onto photographic paper, or electrically. Most of the seismographs operated by the Volcano Observatory consist of two pendulums, each weighing about 200 pounds, suspended in nearly horizontal positions in such a way that one is affected by north-south earth vibrations, and the other by east-west vibrations. Extending outward from the pendulum is a long boom which connects to the short arm of a magnifying lever. The movement of the end of this magnifying lever is about 115 times as great as the actual earth movement. At the end of the lever is a fine writing point which rests on smoked paper on a rotating drum. So long as the earth is quiet the writing point draws a straight line on the smoked paper, but when an earthquake occurs the pendulum vibrates with respect to the ground and the recording drum, and the line drawn on the smoked paper is wiggly (Figure 5).

FIGURE 5. Portion of a record from the vertical seismograph on December 9 and 10, 1950, showing part of the earthquake swarm during relaxation of pressure beneath Kilauea Volcano in early December. During the three hours of total time represented in the figure approximately 130 distinct earthquakes, most of them small, can be counted on the original record. The numbers mark the hours from 1600 on December 9 to 0300 on December 10, Hawaiian time. Records of two large earthquakes appear near the bottom. On the one to the left P marks the arrival of the Preliminary waves and S the arrival of the Secondary and Surface waves, which arrive almost simultaneously for local earthquakes.

Two of the seismograph stations operated by the Volcano Observatory are located close to the rim of Kilauea caldera. One of these, the Whitney Laboratory, has been in continuous operation since 1912. A third station is located on the eastern slope of Mauna Loa at 6,700 feet altitude. Another station is at the St. Joseph's School in Hilo, and the fifth at Konawaena School in Kealakekua. The instruments record strong earthquakes from all over the earth, but are designed principally to record nearby earthquakes, most of which are related to volcanic activity. Each earthquake consists of several types of vibrations (Figure 5), which travel through the rock at different known speeds.

By identifying on the record the times of arrival of the different types of vibration, and carefully measuring the interval of time between them, the distance from the station at which the earthquake originated can be calculated. Then by using the distances of origin from several stations, the epicenter and depth of origin of the earthquake can be located. Any marked increase in the number of earthquakes indicates a restlessness of the volcano in which the earthquakes originate, and the location of the earthquake indicates what portion of the volcano is involved. Commonly an eruption of either volcano is preceded by a series of earthquakes. These earthquakes begin at a depth of 25 to 30 miles, but as the series progresses the places of origin get gradually closer to the surface and often shift laterally, finally centering at a place close to the site of the coming eruption. Thus earthquakes are of great value to the volcanologist in predicting coming activity.

FIGURE 6. Graph showing activity of Kilauea and Mauna Loa volcanoes. The large amount of activity at Kilauea is very largely the result of the Halemaumau lava lake. (Modified after Stearns and Macdonald, 1946).