Displacement of the south flank of Kilauea Volcano; the result of forceful intrusion of magma into the rift zones

Abstract

Seismic evidence has long indicated that the south flank of Kilauea Volcano is mobile. Examination of triangulation, trilateration, and leveling data obtained throughout the 20th century shows that the south flank of Kilauea has been displaced upward and away from the rift zones by as much as several metres. The amount of horizontal displacement approximates the probable amount of dilation that accompanies the intrusion of magma as dikes in the rift zones and is greatest for p~riods of most intense intrusive activity, as evidenced by the frequency of eruptions. Displacement and seismic events on the south flank take place soon after intrusive activity, indicating that the displacement is the result of forceful intrusion in the rift zones, not the cause of relatively passive intrusion. The dikes are thought to be nearly vertical or to dip steeply southward, on the basis of both interpretation of seismic and displacement data for Kilauea itself and comparison with dikes exposed in older, eroded Hawaiian shield volcanoes. In contrast to the south flank, seismic and geodetic data indicate that the north flank is virtually immobile. This contrast is believed to reflect the fact that Kilauea was built on the south slope of Mauna Loa and was consequently influenced by the gravitational stress system of Mauna Loa, which favors displacement away from the volcanic edifice. The north flank of Kilauea is effectively buttressed by Mauna Loa, whereas thr south flank is unbuttressed and free to move away from the edifice when prompted by forceful intrusion of magma. The active part of the east rift zone of Kilauea has apparently migrated several kilometres southward with time. This is shown by the location of recent vents and by the location of the axis of a positive gravity anomaly along the north edge of the active part of the rift zone. The southward migration helps explain several features of the geometry of the east rift zone, particularly its prominent bend near Kilauea Caldera. The southwest rift zone and the caldera also show some evidence of southward migration. The Hilina fault system is considered to be a gravity-controlled system not directly related to the rift zones. Gravitational instability resulting from uplift and seaward displacement is eventually relieved by normal faulting along the seaward part of the south flank. The Hilina faults are thought to bottom at shallow depth without interseeting magma reservoirs, except possibly along part of the lower east rift zone, where the fault system impinges upon the rift zone. Strains have been accumulating within the Hilina system throughout this century, and a high level of instability may have been reached. We anticipate a subsidence event in the not too distant future, possibly similar to the damaging events of 1823 and 1868. (While this paper was in press, such an event occurred on November 29, 1975.) I ACKNOWLEDG ENTS Most staff members of the Haw iian Volcano Observatory took part in the 1970, 197 , and 1973 surveys; we thank them all, especially R. T. Okamura, ...

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“…La polaridad de progresión de la actividad volcá-nica en la fractura en la erupción de 1730 podría deberse a que, a niveles ya muy superficiales, se superpongan dos mecanismos: Por una parte un proceso autoalimentado que obliga a la fractura, una vez iniciada su apertura por el efecto de cuña de la presión hidráulica del magma (Swanson et al, 1976;Hardee, 1982), a progresar en un sentido, originando un plano de ruptura intercalado forzadamente entre los di-ques que componen el eje estructural con un frente de avance de bajo ángulo en la dirección de propagación, lo que haría que el conducto eruptivo intersectase a la superficie en lugares cada vez más alejados del punto inicial de emisión.…”

A single‐force model for the 1975 Kalapana, Hawaii, Earthquake

“…The prevolcanic oceanic crust, located at about 7 km depth and lubricated by an accumulation of deep-sea sediments, has been suggested as the slide plane [Furumoto and Kovach, 1978;Crosson and Endo, 1982;Lipman et al, 1985]. Swanson et al [1976] noted that the entire south flank of Kilauea is mobile and had undergone extensions of several meters in the la.st century previous to the 1975 earthquake. On the basis of displacement measurements, seismicity, and field observations, they concluded that the zone of dilatation or "tear-away zone" separating the south flank from the remaining volcano is composed of the southwest ri(t zone; the east rift zone, and the Koae fault system (see Figure 1).…”

Three‐dimensional seismic velocity structure of Mauna Loa and Kilauea volcanoes in Hawaii from local seismic tomography

“…Hawaii is one of the most seismically active regions in the world and has been serving as a natural laboratory for studying the interactions between seismic and magmatic processes for the past few decades [e.g., Swanson et al, 1976;Lipman et al, 1985;Hill and Zucca, 1987;Rubin et al, 1998;Cayol et al, 2000;Hill et al, 2002;Amelung et al, 2007;Brooks et al, 2008]. The U.S. Geological Survey Hawaiian Volcano Observatory (HVO) operates an extensive seismic network (pink triangles in Figure 1) to measure and study the ongoing activity on the Island of Hawaii.…”