Kilauea's Summit Research Articles

Petrology of lavas from the Puu Oo eruption of Kilauea Volcano: III. The Kupaianaha episode (1986-1992)

The Puu Oo eruption has been remarkable in the historical record of Kilauea Volcano for its duration (over 13 years), volume (>1 km3) and compositional variation (5.7–10 wt.% MgO). During the summer of 1986, the main vent for lava production moved 3 km down the east rift zone and the eruption style changed from episodic geyser-like fountaining at Puu Oo to virtually continuous, relatively quiescent effusion at the Kupaianaha vent. This paper examines this next chapter in the Puu Oo eruption, episodes 48 and 49, and presents new ICP-MS trace element and Pb-, Sr-, and Nd-isotope data for the entire eruption (1983–1994). Nearly aphyric to weakly olivine-phyric lavas were erupted during episodes 48 and 49. The variation in MgO content of Kupaianaha lavas erupted before 1990 correlates with changes in tilt at the summit of Kilauea, both of which probably were controlled by variations in Kilauea's magma supply rate. These lavas contain euhedral olivines which generally are in equilibrium with whole-rock compositions, although some of the more mafic lavas which erupted during 1990, a period of frequent pauses in the eruption, accumulated 2–4 vol.% olivine. The highest forsterite content of olivines (∼85%) in Kupaianaha lavas indicates that the parental magmas for these lavas had MgO contents of ∼10 wt.%, which equals the highest observed value for lavas during this eruption. The composition of the Puu Oo lavas has progressively changed during the eruption. Since early 1985 (episode 30), when mixing between an evolved rift zone magma and a more mafic summit reservoir-derived magma ended, the normalized (to 10 wt.% MgO) abundances of highly incompatible elements and CaO have systematically decreased with time, whereas ratios of these trace elements and Pb, Sr, and Nd isotopes, and the abundances of Y and Yb, have remained relatively unchanged. These results indicate that the Hawaiian plume source for Puu Oo magmas must be relatively homogeneous on a scale of 10–20 km3 (assuming 5–10% partial melting), and that localized melting within the plume has apparently progressively depleted its incompatible elements and clinopyroxene component as the eruption continued. The rate of variation of highly incompatible elements in Puu Oo lavas is much greater than that observed for Kilauea historical summit lavas (e.g., Ba/Y 0.09 a–1 vs ∼0.03 a–1). This rapid change indicates that Puu Oo magmas did not mix thoroughly with magma in the summit reservoir. Thus, except for variable amounts of olivine fractionation, the geochemical variation in these lavas is predominantly controlled by mantle processes.

Use of Precipitation and Groundwater Isotopes to Interpret Regional Hydrology on a Tropical Volcanic Island: Kilauea Volcano Area, Hawaii

Isotope tracer methods were used to determine flow paths, recharge areas, and relative age for groundwater in the Kilauea volcano area of the Island of Hawaii. A network of up to 66 precipitation collectors was emplaced in the study area and sampled twice yearly for a 3‐year period. Stable isotopes in rainfall show three distinct isotopic gradients with elevation, which are correlated with trade wind, rain shadow, and highelevation climatological patterns. Temporal variations in precipitation isotopes are controlled more by the frequency of storms than by seasonal temperature fluctuations. Results from this study suggest that (1) sampling network design must take into account areal variations in rainfall patterns on islands and in continental coastal areas and (2) isotope/elevation gradients on other tropical islands may be predictable on the basis of similar climatology. Groundwater was sampled yearly in coastal springs, wells, and a few high‐elevation springs. Areal contrasts in groundwater stable isotopes and tritium indicate that the volcanic rift zones compartmentalize the regional groundwater system, isolating the groundwater south of Kilauea's summit and rift zones. Part of the Southwest Rift Zone appears to act as a conduit for water from higher elevation, but there is no evidence for downrift flow in the springs and shallow wells sampled in the lower East Rift Zone.

The Uwekahuna Ash Member of the Puna Basalt: product of violent phreatomagmatic eruptions at Kilauea volcano, Hawaii, between 2800 and 2100 14C years ago

Kilauea volcano's reputation for relatively gentle effusive eruptions belies a violent geologic past, including several large phreatic and phreatomagmatic eruptions that are recorded by Holocene pyroclastic deposits which mantle Kilauea's summit area and the southeast flank of adjacent Mauna Loa volcano. The most widespread of these deposits whose original distribution can be reconstructed is the Uwekahuna Ash Member of the Puna Basalt, a basaltic surge and fall deposit emplaced during two or more eruptive episodes separated by a few decades to several centuries. The first episode occurred between 2770 ± 70 and 2265 ± 50 14C yr ago. It included two major pyroclastic surges, each preceded by unusually vigorous lava fountaining from a vent near the volcano's summit. Before the second eruptive episode, 2110 ± 120 14C yr ago, plants had re-colonized the rainforest environment northeast of the summit, and at least two lava flows from Mauna Loa had buried parts of the first-episode deposits. The second episode also began with vigorous lava fountaining, followed by widespread lithic ashfall, a third major surge and finally a fourth fountaining event. Before the final pumice deposit could be significantly reworked, it was partly buried by picritic basalt flows that are unusual in Kilauea's summit area. In proximal areas, the Uwekahuna Ash Member is more than 1 m thick (locally > 5 m) and includes lithic blocks up to 0.8 m in diameter. Coarse, primarily lithic debris was deposited around the vent by laterally expanding surges; fallout deposits accumulated preferentially to the northeast under the influence of high-altitude counter-tradewinds. The area devastated by surges and originally buried by at least 15 cm of the Uwekahuna was about 420 km 2. The bulk volume of the deposits was approximately 0.3 km 3, including less than 0.1 km 3 of juvenile material. Juvenile constituents are olivine-tholeiitic basalts similar in major-element composition to typical Kilauea summit lava flows, but variations in both major elements and trace elements suggest that the eruptions tapped more than a single, uniform source region. We infer that the eruptions which produced the Uwekahuna were driven by water interacting with a fluctuating magma column. Magma withdrawal episodes may have been accompanied by large-volume submarine effusive eruptions and by summit collapse. The volume, extent and character of the Uwekahuna deposits underscore the hazards posed by relatively infrequent but potentially devastating explosive eruptions at Kilauea, as well as at other basaltic volcanoes.

Deformation of Kilauea volcano during 1982 and 1983: A transition period

A major transition in the style of deformation of Kilauea volcano occurred during the period January 1982 through November 1983. Prior to 1983, the deformation was dominated by magma intrusions, rapid extension of the summit, and seaward movement of the south flank. The pattern of activity changed to magma eruption and slowed deformation of the volcanic edifice in January 1983. An earthquake swarm in the southwest rift zone in June 1982 and an intrusion of a large dike in the east rift zone in January 1983 prepared the volcano for the eruptive sequences that continue today. We estimate the sources of surface displacements associated with these events using a least squares nonlinear inversion technique and planar dislocations. The models are constrained with measurements of line length changes and of surface height changes from tide gauges, water wells, and spirit‐level tilt data. Deformation associated with the 1982 earthquake swarm is best modeled as the emplacement of a steeply dipping dike in the upper and middle southwest rift zone extending from 2–3 km to 10–11 km depth with a width of ∼1–2 m. Tilt measurements gathered at the time of the earthquake swarm record a small deflation of Kilauea's summit; however, trilateration data indicate the summit was rapidly extending in 1982. The extension and our models are consistent with seaward slip of the south flank on a low‐angle basal thrust fault. Dislocation models of the January 1983 dike intrusion yield a 14‐ to l5‐km‐long dike along the zone of observed ground rupture. The dike extends from just below the surface to the region of the most intense rift zone seismicity at 4–5 km depth. A strong nonlinear relationship among height, dip, and width results in a suite of models that explain the data equally well. Tests of parameter sensitivity indicate that the dike width and height are the least constrained parameters; the best fit average width ranges from 1.7 to 2.8 m. Our models also include a source of contraction at ∼5 km depth that produces 40 cm of ground subsidence near Makaopuhi, the point of initiation of the intrusion. This location is consistent with geochemical and seismic evidence that indicate magma is stored in the rift zone. Residual errors for all models indicate that substantial line‐length changes are unexplained. Seaward motions of the south flank during 1982 and 1983 are not well modeled by simple dikes and summit deflations; however, attempts to constrain low‐angle faults in the south flank were only partly successful due to the limited extent of the geodetic networks.

Inferred attenuation from site effect-correctedT phases recorded on the island of Hawaii

Coda site amplification factors are used to eliminate the site effect from records of three circum-PacificT phases recorded by the Hawaiian Volcano Observatory (HVO) network on the island of Hawaii. ObservedT-phase amplitudes across the island generally decrease with increasing distance from the conversion point where acoustic waves in the SOFAR channel become seismic waves propagating through the crust. However, the decay of the observedT-phase signal across the island is not regular in regions of dense station coverage, in particular, the Kilauea caldera region. We divide the maximum observedT-phase amplitudes at a given station by the coda site amplification factor obtained for the same station and frequency band (3.0Hz); the distribution of these amplitudes reveals a smooth pattern over the entire island. The distance over which the site effect-correctedT-phase amplitude decreases by one-half, combined with the apparent velocity of propagation ofT phases across the island, allows for an approximate determination of near-surfaceQ over much of the island of Hawaii. We found a region of lowQ in the Kilauea summit area (Q≈30) and east rift zone (Q≈60) with considerably higherQ in the Kaoiki and northern portions of the island (Q≈150 to 200). The lowQ values obtained in the Kilauea summit region and east rift zone are significantly lower than estimates of codaQ in the same region, suggestingT phases may be sampling the earth's near-surface properties.

Hydrogen and oxygen isotopic compositions of waters from fumaroles at Kilauea summit, Hawaii

Condensate samples were collected in 1992 from a high-temperature (300° C) fumarole on the floor of the Halemaumau Pit Crater at Kilauea. The emergence about two years earlier of such a hot fumarole was unprecedented at such a central location at Kilauea. The condensates have hydrogen and oxygen isotopic compositions which indicate that the waters emitted by the fumarole are composed largely of meteoric water, that any magmatic water component must be minor, and that the precipitation that was the original source to the fumarole fell on a recharge area on the slopes of Mauna Loa Volcano to the west. However, the fumarole has no tritium, indicating that it taps a source of water that has been isolated from atmospheric water for at least 40 years. It is noteworthy, considering the unstable tectonic environment and abundant local rainfall of the Kilauea and Mauna Loa regions, that waters which are sources to the hot fumarole remain uncontaminated from atmospheric sources over such long times and long transport distances. As for the common, boiling point fumaroles of the Kilauea summit region, their 18O, D and tritium concentrations indicate that they are dominated by recycling of present day meteoric water. Though the waters of both hot and boiling point fumaroles have dominantly meteoric sources, they seem to be from separate hydrological regimes. Large concentrations of halogens and sulfur species in the condensates, together with the location at the center of the Kilauea summit region and the high temperature, initially suggested that much of the total mass of the emissions of the hot fumarole, including the H2O, might have come directly from a magma body. The results of the present study indicate that it is unreliable to infer a magmatic origin of volcanic waters based solely on halogen or sulfur contents, or other aspects of chemical composition of total condensates.

Hydrogen and oxygen isotopic compositions of waters from fumaroles at Kilauea summit, Hawaii

Hydrogen and oxygen isotopic compositions of waters from fumaroles at Kilauea summit, Hawaii

Petrology of gabbroic xenoliths in 1960 Kilauea basalt: crystalline remnants of prior (1955) magmatism

The 1960 Kapoho lavas of Kilauea's east rift zone contain 1–10 cm xenoliths of olivine gabbro, olivine gabbro-norite, and gabbro norite. Textures are poikilitic (ol+sp+cpx in pl) and intergranular (cpx+pl±ol±opx). Poikilitic xenoliths, which we interpret as cumulates, have the most primitive mineral compositions, Fo82.5, cpx Mg# 86.5, and An80.5. Many granular xenoliths (ol and noritic gabbro) contain abundant vesicular glass that gives them intersertal, hyaloophitic, and overall ‘open’ textures to suggest that they represent ‘mush’ and ‘crust’ of a magma crystallization environment. Their phase compositions are more evolved (Fo80-70, cpx Mg# 82-75, and An73-63) than those of the poikilitic xenoliths. Associated glass is basaltic, but evolved (MgO 5 wt%; TiO2 3.7–5.8 wt%). The gabbroic xenolith mineral compositions fit existing fractional crystallization models that relate the origins of various Kilauea lavas to one another. FeO/MgO crystal-liquid partitioning is consistent with the poikilitic ol-gabbro assemblage forming as a crystallization product from Kilauea summit magma with ∼8 wt% MgO that was parental to evolved lavas on the east rift zone. For example, least squares calculations link summit magmas to early 1955 rift-zone lavas (∼5 wt% MgO) through ∼28–34% crystallization of the ol+sp+cpx+pl that comprise the poikilitic ol-gabbros. The other ol-gabbro assemblages and the olivine gabbro-norite assemblages crystallized from evolved liquids, such as represented by the early 1955 and late 1955 lavas (∼6.5 wt% MgO) of the east rift zone. The eruption of 1960 Kapoho magmas, then, scoured the rift-zone reservoir system to entrain portions of cumulate and solidification zones that had coated reservoir margins during crystallization of prior east rift-zone magmas.

Geology of kilauea volcano

This paper summarizes studies of the structure, stratigraphy, petrology, drill holes, eruption frequency, and volcanic and seismic hazards of Kilauea volcano. All the volcano is discussed, but the focus is on its lower cast rift zone (LERZ) because active exploration for geothermal energy is concentrated in that area. Kilauea probably has several separate hydrothermal-convection systems that develop in response to the dynamic behavior of the volcano and the influx of abundant meteoric water. Important features of some of these hydrothermal-convection systems are known through studies of surface geology and drill holes. Observations of eruptions during the past two centuries, detailed geologic mapping, radiocarbon dating, and paleomagnetic secular-variation studies indicate that Kilauea has erupted frequently from its summit and two radial rift zones during Quaternary time. Petrologic studies have established that Kilauea erupts only tholeiitic basalt. Extensive ash deposits at Kilauea's summit and on its LERZ record locally violent, but temporary, disruptions of local hydrothermal-convection systems during the interaction of water or steam with magma. Recent drill holes on the LERZ provide data on the temperatures of the hydrothermal-convection systems, intensity of dike intrusion, porosity and permeability, and an increasing amount of hydrothermal alteration with depth. The prehistoric and historic record of volcanic and seismic activity indicates that magma will continue to be supplied to deep and shallow reservoirs beneath Kilauea's summit and rift zones and that the volcano will be affected by eruptions and earthquakes for many thousands of years.

Geophysical characteristics of the hydrothermal systems of Kilauea volcano, Hawaii

Clues to the overall structure of Kilauea volcano can be obtained from spatial studies of gravity, magnetic, and seismic velocity variations. The rift zones and summit are underlain by dense, magnetic, high P-wave-velocity rocks at depths of about 2 km less. The gravity and seismic velocity studies indicate that the rift structures are broad, extending farther to the north than to the south of the surface features. The magnetic data give more definition to the rift structures by allowing separation into a narrow, highly-magnetized, shallow zone and broad, flanking, magnetic lows. The patterns of gravity, magnetic variations, and seismicity document the southward migration of the upper cast rift zone. Regional, hydrologic features of Kilauea can be determined from resistivity and self-potential studies. High-level groundwater exists beneath Kilauea summit to elevations of +800 m within a triangular area bounded by the west edge of the upper southwest rift zone, the east edge of the upper east rift zone, and the Koa'c fault system. High-level groundwater is present within the east rift zone beyond the triangular summit area. Self-potential mapping shows that areas of local heat produce local fluid circulation in the unconfined aquifer (water table). The dynamics of Kilauea eruptions are responsible for both the source of heat and the fracture permeability of the hydrothermal system. Shallow seismicity and surface deformation indicate that magma is intruding and that fractures are forming beneath the rift zones and summit area. Magma supply estimates are used to calculate the rate of heat input to Kilauea's hydrothermal systems. Heat flows of 370–820 mW/m 2 are calculated from deep wells within the lower east rift zone. The estimated heat input rate for Kilauea of 9 gigawatts (GW) is at least 25 times higher than the conductive heat loss as estimated from the heat flow in wells extrapolated over the area of the summit caldera and rift zones. Heat must be dissipated by another mechanism, or the heat input rate estimates are much too high.

The 1919?1920 eruption of Mauna Iki, Kilauea: chronology, geologic mapping, and magma transport mechanisms

Utilizing historical accounts, field mapping, and photogeology, this paper presents a chronology of, and an analysis of magma transport during, the December 1919 to August 1920 satellitic shield eruption of Mauna Iki on the SW rift zone of Kilauea Volcano, Hawaii. The eruption can be divided into four stages based on the nature of the eruptive activity. Stage 1 consisted of the shallow injection of a dike from the summit region to the eventual eruption site ∼10 km downrift. During stage 2, a low ridge of pahoehoe formed in the vent area; later a large a'a flow broke out of this ridge and flowed ∼8.5 km SW at an average flow front velocity of 0.5 km/day. The eruption continued until mid-August producing almost exclusively pahoehoe, first as gas-rich overflows from a lava pond (stage 3), and later as denser tube-fed lava (stage 4) that reached almost 8 km from the vent at an average flow-front velocity of 0.1 km/day. Magma transport during the Mauna Iki eruption is examined using three criteria: (1) eruption characteristics and volumetric flow rates; (2) changes in the surface height of the Halemaumau lava lake; and (3) tilt measurements made at the summit of Kilauea. We find good correlation between Halemaumau lake activity and the eruptive stages. Additionally, the E-W component of summit tilt tended to mimic the lake activity. The N-S component, however, did not. Multiple storage zones in the shallow summit region probably accounted for the decoupling of E-W and N-S tilt components. Analysis of these criteria shows that at different times during the eruption, magma was either emplaced into the volcano without eruption, hydraulically drained from Halemaumau to Mauna Iki, or fed at steady-state conditions from summit storage to Mauna Iki. Volume calculations indicate that the supply rate to Kilauea during the eruption was around 3 m3/s, similar to that calculated during the Mauna Ulu and Kupaianaha shield-building eruptions, and consistent with previously determined values of long-term supply to Kilauea.

1992 AGU Front Range Meeting

The AGU Front Range Branch held its annual meeting on February 10, 1992, at the National Center for Atmospheric Research in Boulder, Colo. The theme of the meeting was “Our Changing Environment,” with specific emphasis on the Rocky Mountains, the Front Range, the High Plains, and the Great Basin environments.The all‐day meeting featured twenty oral presentations and five poster presentations. Most of the topics presented were related to environmental issues such as ozone depletion, emergency response applications at the Rocky Flats Plant, climatic forcing, and hydrogeology. Other papers of interest included a geophysical study of the Sand Dunes National Monument in Colorado, a paper on the impact of the 1988 forest fires on the chemistry of nonthermal groundwater at Yellowstone National Park, and a poster on the soil‐gas flux of carbon dioxide from nonventing areas of the Kilauea Summit in Hawaii. A poster and an oral presentation centered on the vulnerability of transportation and energy supply networks in the central United States to earthquakes in the New Madrid seismic zone. The field of space science was represented by two posters on recent geomagnetic behaviors and magnetospheric convection and an oral presentation on plasma density in the Earth's magnetosphere. Three Front Range Branch awards were given to students to recognize excellent presentations.

Differentiation and magma mixing on Kilauea's east rift zone: a further look at the eruptions of 1955 and 1960. Part II. The 1960 lavas

New and detailed petrographic observations, mineral compositional data, and whole-rock vs glass compositional trends document magma mixing in lavas erupted from Kilauea's lower east rift zone in 1960. Evidence includes the occurrence of heterogeneous phenocryst assemblages, including resorbed and reversely zoned minerals in the lavas inferred to be hybrids. Calculations suggest that this mixing, which is shown to have taken place within magma reservoirs recharged at the end of the 1955 eruption, involved introduction of four different magmas. These magmas originated beneath Kilauea's summit and moved into the rift reservoirs beginning 10 days after the eruption began. We used microprobe analyses of glass to calculate temperatures of liquids erupted in 1955 and 1960. We then used the calculated proportions of stored and recharge components to estimate the temperature of the recharge components, and found those temperatures to be consistent with the temperature of the same magmas as they appeared at Kilauea's summit. Our studies reinforce conclusions reached in previous studies of Kilauea's magmatic plumbing. We infer that magma enters shallow storage beneath Kilauea's summit and also moves laterally into the fluid core of the East rift zone. During this process, if magmas of distinctive chemistry are present, they retain their chemical identity and the amount of cooling is comparable for magma transported either upward or laterally to eruption sites. Intrusions within a few kilometers of the surface cool and crystallize to produce fractionated magma. Magma mixing occurs both within bodies of previously fractionated magma and when new magma intersects a preexisting reservoir. Magma is otherwise prevented from mixing, either by wall-rock septa or by differing thermal and density characteristics of the successive magma batches.

Petrology of lavas from episodes 2?47 of the Puu Oo eruption of Kilauea Volcano, Hawaii: Evaluation of magmatic processes

The Puu Oo eruption of Kilauea Volcano in Hawaii is one of its largest and most compositionally varied historical eruptions. The mineral and whole-rock compositions of the Puu Oo lavas indicate that there were three compositionally distinct magmas involved in the eruption. Two of these magmas were differentiated (<6.8 wt% MgO) and were apparently stored in the rift zone prior to the eruption. A third, more mafic magma (9–10 wt% MgO) was probably intruded as a dike from Kilauea's summit reservoir just before the start of the eruption. Its intrusion forced the other two magmas to mix, forming a hybrid that erupted during the first three eruptive episodes from a fissure system of vents. A new hybrid was erupted during episode 3 from the vent where Puu Oo later formed. The composition of the lava erupted from this vent became progressively more mafic over the next 21 months, although significant compositional variation occurred within some eruptive episodes. The intra-episode compositional variation was probably due to crystal fractionation in the shallow (0.0–2.9 km), dike-shaped (i.e. high surface area/volume ratio) and open-topped Puu Oo magma reservoir. The long-term compositional variation was controlled largely by mixing the early hybrid with the later, more mafic magma. The percentage of mafic magma in the erupted lava increased progressively to 100% by episode 30 (about two years after the eruption started). Three separate magma reservoirs were involved in the Puu Oo eruption. The two deeper reservoirs (3–4 km) recharged the shallow (0.4–2.9 km) Puu Oo reservoir. Recharge of the shallow reservoir occurred rapidly during an eruption indicating that these reservoirs were well connected. The connection with the early hybrid magma body was cut off before episode 30. Subsequently, only mafic magma from the summit reservoir has recharged the Puu Oo reservoir.

Deep Magma Body Beneath the Summit and Rift Zones of Kilauea Volcano, Hawaii

A magnitude 7.2 earthquake in 1975 caused the south flank of Kilauea Volcano, Hawaii, to move seaward in response to slippage along a deep fault. Since then, a large part of the volcano's edifice has been adjusting to this perturbation. The summit of Kilauea extended at a rate of 0.26 meter per year until 1983, the south flank uplifted more than 0.5 meter, and the axes of both the volcano's rift zones extended and subsided; the summit continues to subside. These ground-surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones. Kilauea's magmatic system is, therefore, probably deeper and more extensive than previously thought; the summit and both rift zones may be underlain by a thick, near vertical dike-like magma system at a depth of 3 to 9 kilometers.

Fluctuations in surface height of active lava lakes during 1972–1974 Mauna Ulu Eruption, Kilauea Volcano, Hawaii

An “active” lava lake is one that forms directly on top of a magma column, as opposed to an “inactive” one formed by passive ponding of lava within a preexisting crater. Two active lava lakes operating within summit craters of newly constructed volcanic shields at Mauna Ulu and Alae were the longest‐lived of any observed in a Hawaiian rift zone to date. Small‐scale fluctuations (a few to 20 m) in the height of lake surfaces are typically associated with degassing (“gas piston”) activity. Larger fluctuations, as great as 200 m, reflect major changes in eruptive activity. Measurements of surface height fluctuations of Mauna Ulu lake show gross positive correlation with variation in summit tilt, which in turn reflects the inflation‐deflation state of Kilauea's summit magma reservoir. A more tenuous conclusion is that a sympathetic variation possibly exists between surface heights of the Mauna Ulu and Alae lakes. Collectively, these observations (1) require the existence of a fully engorged, connected, open, and hydraulically efficient magma conduit system linking the summit reservoir with the lava lakes, (2) provide additional evidence for the postulated regime of “quasi‐steady‐state” magma transfer that characterized much of the eruption, (3) imply that fluctuations in lake surface reflect variation in magma supply rate to the reservoir and/or outflow rate from the Mauna Ulu‐Alae vents, and (4) suggest undetected episodes of magma intrusion or storage in Kilauea's east rift zone during 1973.

Resistivity monitoring of an active volcano using the controlled‐source electromagnetic technique: Kilauea, Hawaii

A controlled‐source electromagnetic monitoring system located near the summit of Kilauea has been in operation since mid‐1979. Prominent changes in the controlled‐source magnetic fields have been observed both preceding and following two seismic swarms that are interpreted to be related to shallow magma intrusions in August 1980 and January 1981. The vertical magnetic field (Hz) sensor nearest the sites of intrusion showed the largest field changes. All comparisons to date have been made at 1 Hz, which corresponds to a depth of penetration of several kilometers. Large and rapid vertical‐magnetic field changes were measured following the intrusion into the upper east rift of Kilauea on August 27, 1980. Similar fluctuations were measured both before and during the intrusion into the southern caldera on January 20, 1981. Located earthquakes and data from a recording tiltmeter within 2 km of the Hz sensor, which showed anomalous field changes over the January 20 event, indicate that the Hz sensor was located nearly over the zone of intrusion. The Hz field changes recorded over both the August 1980 and January 1981 intrusive events appear too large to have been caused by conductivity changes within a horizontally layered section. More probably, they were caused by relatively shallow intrusion of high‐conductivity magma into open high‐angle fractures or by establishing continuity of short sections of preexisting magma storage zones, thereby producing long linear conductors from short, normally discontinuous conductive segments.

Seismic Detection of the Summit Magma Complex of Kilauea Volcano, Hawaii

Application of simultaneous inversion of seismic P-wave arrival time data to the investigation of the crust beneath Kilauea Volcano yields a detailed picture of the volcano's heterogeneous structure. Zones of anomalously high seismic velocity are found associated with the volcano's rift zones. A low-velocity zone at shallow depth directly beneath the caldera coincides with an aseismic region interpreted as being the locus of Kilauea's summit magma complex.

Modeling the three‐dimensional structure of macroscopic magma transport systems: Application to Kilauea Volcano, Hawaii

We report the results of modeling the three‐dimensional internal structure of Kilauea's magmatic passageways. The approach uses a clear plexiglass model containing equally‐spaced levels upon which well‐located seismic hypocenters are plotted. Application of constraining geologic and geophysical criteria to this distributed volume of earthquakes permits the interpretation of seismic structures produced by fracturing in response to locally high fluid pressures. Four magma transport and storage structures have been identified within and beneath Kilauea: (1) Primary conduit. The conduit transporting magma into Kilauea's summit storage reservoir rises from the model base (14.6 km) to the 6.5 km depth level. It is a zone of intense fracturing and inferred intrusion, whose horizontal sections are elliptical in planform. Over its height, the average major axis of the component horizontal sections is 3.3 km, with an average minor axis of 1.7 km. This yields an aspect ratio of ξ = 0.52. At the 14.6 km level, the strike of the major axis is N67°E. During passage from the upper mantle through the oceanic crust, this axis rotates in a right‐handed sense, until the strike is N41°W at the 6.5 km level. (2) Magma chamber complex floor. The interval from 6.5 to 5.7 km, immediately over the primary conduit, is aseismic. This suggests differentially high fluid‐to‐rock ratios, and relatively weak pathways for further vertical transport into higher levels of the storage complex, as well as lateral leakage eastward into the Mauna Ulu staging area—for later vertical ascent beneath the upper east rift zone. Seismicity within the immediately subjacent rocks that form the top of the primary conduit (at 6.5 km) suggests that this inferred magma‐rich horizon forms the effective floor of the summit storage complex. (3) Magma chamber crown. Intense seismicity over the 1.1–1.9 km depth interval defines an elliptical region in plan view. The top of this region has a broad apex with an average major axis of 1.5 km, and an average minor axis of 1.1 km producing an aspect ratio of ξ = 0.73. This region coincides with the epicentral position of summit vertical displacement maxima during inflationary deformation and is interpreted as a region of intense diking, crowning the summit storage complex. (4) Upper east rift zone pipe. From a depth of 5.7 km, a cylindrical region of seismicity rises beneath the upper east rift zone, to the 1.9 km level, where it merges with the subhorizontal upper east rift zone duct. This pipe‐like zone has a mean diameter of 1.4 km and a vertical axis that pierces the surface of the volcano at the intersection of the Koae fracture system and the upper east rift zone. We suggest this pipe forms a principal connection between the base of the summit storage reservoir, and near‐surface storage compartments and ducts in the upper east rift zone. In this role, the pipe is suggested to have contributed heavily to Mauna Ulu's magma supply during 1969–1974. The model of magma transport and storage thus constructed provides a context in which other types of data (e.g., ground deformation and electrical conductivity) may be interpreted as well as a means of refining petrological inferences based on lava chemistry.

Three-dimensional crust and mantle structure of Kilauea Volcano, Hawaii

Teleseismic P wave arrival times recorded by a dense network of seismograph stations located on Kilauea volcano, Hawaii, are inverted to determine lateral variation in crust and upper mantle structure to a depth of 70 km. The crustal structure is dominated by relatively high velocities within the central summit complex and along the two radial rift zones compared with the nonrift flank of the volcano. Both the mean crustal velocity contrast between summit and nonrift flank and the distribution of velocities agree well with results from crustal refraction studies. Comparison of the velocity structure with Bouguer gravity anomalies over the volcano through a simple physical model also gives excellent agreement. Mantle structure appears to be more homogeneous than crustal structure. The root mean square velocity variation for the mantle averages only 1.5%, whereas variation within the crust exceeds 4%. The summit of Kilauea is underlain by normal velocity (8.1 km/s) material within the uppermost mantle (12--25 km), suggesting that large magma storage reservoirs are not present at this level and that the passageways from deeper sources must be quite narrow. No evidence is found for substantial volumes of partially molten rock (5%) within the mantle to depths of at leastmore » 40 km. Below about 30 km, low-velocity zones (1--2%) underlie the summits of Kilauea and nearby Mauna Loa and extend south of Kilauea into a broad offshore zone. Correlation of volcanic tremor source locations and persistent zones of mantle earthquakes with low-velocity mantle between 27.5- and 42.5-km depth suggests that a laterally extensive conduit system feeds magma to the volcanic summits from sources either at comparable depth or deeper within the mantle. The center of contemporary magmatic production and/or upwelling from deeper in the mantle appears to extend well to the south of the active volcanic summits, suggesting that the Hawaiian Island chain is actively extending to the southeast.« less