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Tilt records for thirteen years at the Hawaiian Volcano Observatory¹

Abstract

Analysis for thirteen years of the extraordinarily large angular tiltings of the ground on the east side of the active volcanic system of Mauna Loa and Kilauea reveals the following correlations:

1 Seasonal tilts of twenty seconds or more in a half-year vary with air temperature, easterly tilts corresponding to cold months, westerly tilts to hot months. The correlation extends to such short periods as a week. Easterly tilt is volcanically centrifugal.

2 The range of angular tilting per half-year is greater when measured gushing up of lava is greater. The gushing up of lava and easterly tilting have been regularly greater in autumn and winter.

3 There is practically no correlation between tilt and rainfall.

4 Between 1913 and 1920 there was a northeasterly tilt of about eighty seconds accumulated at Kilauea, and an elevation of about 0.6 meters in the central part of the mountain, diminishing apparently to zero in a radius of ten kilometers. This was a partial eruptive cycle, characterized by rising lava.

5 Between 1920 and 1926 there was a southwesterly tilt of about ninety-three seconds, accumulated at Kilauea, and a depression at the central part of the mountain (distinct from collapse at the pit) of about four meters, diminishing in a radius of twenty-two kilometers to 0.09 meters. This was an extraordinary half-cycle of lava subsidence plus explosive eruption with engulfment.

6 The total void computed from the engulfment and subsidence data is approximately 757 million cubic meters, of form suggesting the evacuation left by an intrusive sill of about thirty kilometers radius, swollen in the center.

7 Local earthquake frequency and centripetal tilt accompany lava subsidence, otherwiese there is little correlation between tilt and earthquakes.

8 There is perfect correlation between Kilauea lava movement and Mauna Loa lava movement, whenever the Kilauea lava pit is not sealed. The east-west tilt curve exhibited accumulation of easterly tilt preceding every Mauna Loa eruption. The north-south tilt curve followed consistently the overflow and subsidence phases of Kilauea. These facts agree with the position of the instruments, north of Kilauea and east of Mauna Loa.

9 Explanation of the correspondence between easterly tilt and lava gushing, on the one hand, and winter atmospheric mean lower temperature, on the other, is difficult. Two possible explanations are: (a) that solar heating in the summer checks volcanic radiation, whereas outward conduction is stimulated by the winter cold; (b) that a winter solstice tidal effect acts on the east-west fissure of the Hawaiian ridge, owing to a solar pull southward on the great mass of the ridge and on the equatorial protuberance; this might produce trigger stress for winter effervescence and tumescence, if the lava sponge below were in nice adjustment for gas-pressure release. Possibly both (a) and (b) work in concert.

Footnotes

¹ Published by permission of the Director of the United States Geological Survey.

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