Kilauea's East Rift Zone Research Articles

Fluid-inclusion evidence for past temperature fluctuations in the Kilauea East Rift Zone geothermal area, Hawaii

Heating and freezing data were obtained for fluid inclusions in hydrothermal quartz, calcite, and anhydrite from several depths in three scientific observation holes drilled along the lower East Rift Zone of Kilauea volcano, Hawaii. Compositions of the inclusion fluids range from dilute meteoric water to highly modified sea water concentrated by boiling. Comparison of measured drill-hole temperatures with fluid-inclusion homogenization-temperature ( T h) data indicates that only about 15% of the fluid inclusions could have formed under the present thermal conditions. The majority of fluid inclusions studied must have formed during one or more times in the past when temperatures fluctuated in response to the emplacement of nearby dikes and their subsequent cooling. The fluid-inclusion data indicate that past temperatures in SOH-4 well were as much as 64°C hotter than present temperatures between 1000 and 1500 m depth and they were a maximum of 68°C cooler than present temperatures below 1500 m depth. Similarly, the data show that past temperatures near the bottoms of SOH-1 and SOH-2 wells were up to 45 and 59°C, respectively, cooler than the present thermal conditions; however, the remainder of fluid-inclusion T h values for these two drill holes suggest that the temperatures of the trapped waters were nearly the same as the present temperatures at these slightly shallower depths. Several hydrothermal minerals (erionite, mordenite, truscottite, smectite, chlorite-smectite, chalcedony, anhydrite, and hematite), occurring in the drill holes at higher temperatures than they are found in geothermal drill holes of Iceland or other geothermal areas, provide additional evidence for a recent heating trend.

Episode 49 of the Pu'u 'O'o-Kupaianaha eruption of Kilauea volcano-breakdown of a steady-state eruptive era

The Pu'u 'O'o-Kupaianaha eruption (1983-present) is the longest lived rift eruption of either Kilauea or neighboring Mauna Loa in recorded history. The initial fissure opening in January 1983 was followed by three years of episodic fire fountaining at the Pu'u 'O'o vent on Kilauea's east rift zone ∼19km from the summit (episodes 4–47). These spectacular events gave way in July 1986 to five and a half years of nearcontinuous, low-level effusion from the Kupaianaha vent, ∼ 3km to the cast (episode 48). A 49th episode began in November 1991 with the opening of a new fissure between Pu'u 'O'o and Kupaianaha. this three week long outburst heralded an era of more erratic eruptive behavior characterized by the shut down of Kupaianaha in February 1992 and subsequent intermittent eruption from vents on the west flank of Pu'u 'O'o (episodes 50 and 51). The events occurring over this period are due to progressive shrinkage of the rift-zone reservoir beneath the eruption site, and had limited impact on eruption temperatures and lava composition.

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.

Development of lava tubes in the light of observations at Mauna Ulu, Kilauea Volcano, Hawaii

During the 1969–1974 Mauna Ulu eruption on Kilauea's upper east rift zone, lava tubes were observed to develop by four principal processes: (1) flat, rooted crusts grew across streams within confined channels; (2) overflows and spatter accreted to levees to build arched roofs across streams; (3) plates of solidified crust floating downstream coalesced to form a roof; and (4) pahoehoe lobes progressively extended, fed by networks of distributaries beneath a solidified crust. Still another tube-forming process operated when pahoehoe entered the ocean; large waves would abruptly chill a crust across the entire surface of a molten stream crossing through the surf zone. These littoral lava tubes formed abruptly, in contrast to subaerial tubes, which formed gradually. All tube-forming processes were favored by low to moderate volume-rates of flow for sustained periods of time. Tubes thereby became ubiquitous within the pahoehoe flows and distributed a very large proportionof the lava that was produced during this prolonged eruption. Tubes transport lava efficiently. Once formed, the roofs of tubes insulate the active streams within, allowing the lava to retain its fluidity for a longer time than if exposed directly to ambient air temperature. Thus the flows can travel greater distances and spread over wider areas. Even though supply rates during most of 1970–1974 were moderate, ranging from 1 to 5 m3/s, large tube systems conducted lava as far as the coast, 12–13 km distant, where they fed extensive pahoehoe fields on the coastal flats. Some flows entered the sea to build lava deltas and add new land to the island. The largest and most efficient tubes developed during periods of sustained extrusion, when new lava was being supplied at nearly constant rates. Tubes can play a major role in building volcanic edifices with gentle slopes because they can deliver a substantial fraction of lava erupted at low to moderate rates to sites far down the flank of a volcano. We conclude, therefore, that the tendency of active pahoehoe flows to form lava tubes is a significant factor in producing the common shield morphology of basaltic volcanoes.

Deep, slim hole, diamond drilling program proves effective for geothermal assessment in Hawaii

The Hawaii State legislature, in 1988, funded a deep, slim-hole, diamond core drilling program, known as the Scientific Observation Hole (SOH) program, stimulate geothermal development and confirm the geothermal resources of This program was designed by the Hawaii Natural Energy Institute (HNEI) at the University of Hawaii at Manoa to assess the geothermal resources of the Kilauea East Rift Zone (KERZ) on the Big Island of Hawaii. The program is funded by the Hawaii Department of Business, Economic Development, and Tourism and managed by HNEI. To assess the geothermal potential of the KERZ, a fence of four holes, three of which were drilled, were sited along the long axis of the KERZ within existing Geothermal Resource Subzones. These holes were located to provide stepout drill coverage between existing and planned geothermal production wells, and to pair the SOHs with production wells to test for permeability across the rift zone. Successful drilling techniques and casing procedures were devised as the rock section became known and its characteristics noted. Above 130°C (270°F) a complex stearate was added to the drilling fluids to maintain lubricity. Above 165°C (330°F) a mixture of soda ash, high temperature polymer, complex stearate, and sepiolite virtually eliminated high torque and vibration problems frequently associated with high temperature drilling. The core and other data from the SOHs have proven to be extremely valuable for both active developers in siting production wells, and in the understanding of the subsurface geologic conditions. The first hole drilled, SOH-4, provided thermal and permeability conditions along the eastern portion of the TruelMid-Pacific Geothermal Venture's lease, and was instrumental in the proposed location of True's #2 site. SOH-4 was drilled to a total depth of 2,000.1 m (6,562 ft) and recorded bottom hole temperatures of 306.1°C (583°F) at a depth of 1,950.7 m (6,400 ft). The second hole, SOH-I, effectively defined the northern extent ofthe Puna Geothermal Venture's (PGV) HGP-AlPGV reservoir, doubled the proven reservoir size, and provided sufficient data to the lending institution for continued project funding. SOH-l was drilled to a total depth of 1,684.3 m (5,526 ft) and recorded a bottom hole temperature of 206.1°C (403°F). The third hole, SOH-2, was drilled on a PGV lease to a total depth of 2,073.2 m (6,802 ft), recorded a bottom hole temperature of 350.6°C (663°F), and may have intersected a potential reservoir at a depth of approximately 1,490 m (4,900 ft).

Buffered and unbuffered dike emplacement on Earth and Venus: implications for magma reservoir size, depth, and rate of magma replenishment

Models of the emplacement of lateral dikes from magma chambers under constant (buffered) driving pressure conditions and declining (unbuffered) driving pressure conditions indicate that the two pressure scenarios lead to distinctly different styles of dike emplacement. In the unbuffered case, the lengths and widths of laterally emplaced dikes will be severely limited and the dike lengths will be highly dependent on chamber size; this dependence suggests that average dike length can be used to infer the dimensions of the source magma reservoir. Probable examples on Earth of the unbuffered case are flanking rift zones on shield volcanoes such as the Hawaiian Kilauea East Rift Zone, in which the dikes of average widths of less than a meter extend for several km from the central part of the edifice. In contrast, emplacement of lateral dikes in the constant driving pressure (buffered) case can produce dikes which have sizes and widths which are very large, and are independent of chamber size. For relatively shallow magma chambers, buffered emplacement is expected to produce graben of relatively fixed length which are associated with eruptive fissures and long, large volume lava flows. A decline in magma supply rate and loss of pressure buffering during the later stages of such eruptions may give rise to caldera formation/collapse events. Deeper dikes are not likely to erupt but will produce surface graben of variable length. Therefore, edifices or dike swarms which show an extremely wide variation in fracture or dike lengths are likely to have been formed in buffered conditions. On Earth, the characteristics of many mafic-dike swarms suggest that they were emplaced in buffered conditions (e.g., the Mackenzie dike swarm in Canada and some dikes within the Scottish Tertiary). On Venus, the distinctive radial fractures and graben surrounding circular to oval features and edifices on many size scales and extending for hundreds to over a thousand km are candidates for dike emplacement in buffered conditions.

Aeromagnetic study of the Island of Hawaii

An aeromagnetic study of the Island of Hawaii provides new insight on magnetic properties of subsurface rock and geologic structure. On a regional scale, spectral‐depth analysis delineates two shallow magnetic zones, each roughly 1.5 km thick, lying at a depth of 1 km. One zone (of unknown origin) lies in the center of the island and correlates with a regional magnetic high. The other zone coincides with pronounced magnetic lows paralleling Kilauea's active east rift zone. These magnetic lows probably depict rocks chemically altered by hydrothermal fluids, in which titanomagnetite has been destroyed. Analysis of magnetic terrain effects indicates that magnetization also decreases with depth within Mauna Kea and Mauna Loa. We estimate that magnetization is reduced by about half at a depth of 1 km. The magnetic method is particularly useful in delineating the lateral extent of local shield structures, such as rifts, summit calderas, pit craters, and vent fissures. Rifts possess characteristic magnetic patterns, primarily long‐wavelength linear magnetic low zones. We propose alteration processes reduce magnetizations along the flanks of rifts. On the other hand, along young rifts (e.g., Kilauea's east rift zone), short‐wavelength magnetic anomalies probably reflect slowly cooled, unaltered intrusions. Altered rock may also produce magnetic lows that help define buried summit calderas.

Differentiation and magma mixing on Kilauea's east rift zone

The lavas of the 1955 east rift eruption of Kilauea Volcano have been the object of considerable petrologic interest for two reasons. First, the early 1955 lavas are among the most differentiated ever erupted at Kilauea, and second, the petrographic character and chemical composition of the lava being erupted changed significantly during the eruption. This shift, from more differentiated (MgO=5.0–5.7%) to more magnesian (MgO=6.2–6.8%) lava, has been variously interpreted, as either due to systematic excavation of a zoned, differentiated magma body, or to invasion of the differentiated magma by more primitive magma, followed by rapid mixing and eruption of the resulting hybrid magmas. Petrologic examination of several nearvent spatter samples of the late 1955 lavas shows abundant evidence for magma mixing, including resorbed and/or reversely zoned crystals of olivine, augite and plagioclase. In addition, the compositional ranges of olivine, plagioclase and groundmass sulfide are very large, implying that the assemblages are hybrid. Core compositions of olivine phenocrysts range from Fo85 to Fo77. The most magnesian olivines in these samples must have originally crystallized from a melt containing 8.0–8.5% MgO, which is distinctly more magnesian than the bulk composition of the late 1955 lavas. The majorelement and trace-element data are either permissive or supportive of a hybrid origin for the late 1955 lavas. In particular, the compositional trends of the 1955 lavas on plots of CaO vs MgO, and the virtual invariance of Al2O3 and Sr in these plagioclase-phyric lavas are more easily explained by magma mixing than by fractionation. The pattern of internal disequilibrium/re-equilibration in the late 1955 spatter samples is consistent with reintrusion and mixing having occurred at least twice, during the latter part of the 1955 eruption. Plagioclase zonation preserves possible evidence for additional, earlier reintrusion events. Least-squares modelling the mixing of early 1955 bulk compositions with various summit lavas±olivine pick the 1952 summit lava as most like the primitive component. The results also indicate the primitive component had MgO=7.5–8.0%, corresponding to liquidus temperatures of 1165–1175°C. The absence of Fe-Ti oxide phenocrysts in the late 1955 lavas implies that the cooler component of the hybrid had T>1110°C. Thus the thermal contrast between the two components may have been as much as 55–65°C, sufficient to produce the conspicuous disequilibrium effects visible in the spatter samples.

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.

Phreatomagmatic and phreatic fall and surge deposits from explosions at Kilauea volcano, Hawaii, 1790 a.d.: Keanakakoi Ash Member

In or around 1790 a.d. an explosive eruption took place in the summit caldera of Kilauea shield volcano. A group of Hawaiian warriors close to the caldera at the time were killed by the effects of the explosions. The stratigraphy of pyroclastic deposits surrounding Kilauea (i.e., the Keanakakoi Ash Member) suggests that the explosions referred to in the historic record were the culmination of a prolonged hydrovolcanic eruption consisting of three main phases. The first phase was phreatomagmatic and generated well-bedded, fine fallout ash rich in glassy, variably vesiculated, juvenile magmatic and dense, lithic pyroclasts. The ash was mainly dispersed to the southwest of the caldera by the northeasterly trade winds. The second phase produced a Strombolian-style scoria fall deposit followed by phreatomagmatic ash similar to that of the first phase, though richer in accretionary lapilli and lithics. The third and culminating phase was phreatic and deposited lithic-rich lapilli and block fall layers, interbedded with cross-bedded surge deposits, and accretionary lapilli-rich, fine ash beds. These final explosions may have been responsible for the deaths of the warriors. The three phases were separated by quiescent spells during which the primary deposits were eroded and transported downwind in dunes migrating southwestward and locally excavated by fluvial runoff close to the rim. The entire hydrovolcanic eruption may have lasted for weeks or perhaps months. At around the same time, lava erupted from Kilauea's East Rift Zone and probably drained magma from the summit storage. The earliest descriptions of Kilauea (30 years after the Keanakakoi eruption) emphasize the great depth of the floor (300–500 m below the rim) and the presence of stepped ledges. It is therefore likely that the Keanakakoi explosions were deepseated within Kilauea, and that the vent rim was substantially lower than the caldera rim. The change from phreatomagmatic to phreatic phases may reflect the progressive degassing and cooling of the magma during deep withdrawal: throughout the phreatomagmatic phases magma vesiculation contributed to the explosive interaction with water by initiating the fragmentation process: thereafter, the principal role of the subsiding magma column was to supply heat for steam production that drove the phreatic explosions of the final phase.

Horizontal ground deformation patterns and magma storage during the Puu Oo eruption of Kilauea volcano, Hawaii: episodes 22?42

Horizontal ground deformation measurements were made repeatedly with an electronic distance meter near the Puu Oo eruption site approximately perpendicular to Kilauea's east rift zone (ERZ) before and after eruptive episodes 22–42. Line lengths gradually extended during repose periods and rapidly contracted about the same amount following eruptions. The repeated extension and contraction of the measured lines are best explained by the elastic response of the country rock to the addition and subsequent eruption of magma from a local reservoir. The deformation patterns are modeled to constrain the geometry and location of the local reservoir near Puu Oo. The observed deformation is consistent with deformation patterns that would be produced by the expansion of a shallow, steeply dipping dike just uprift of Puu Oo striking parallel to the trend of the ERZ. The modeled dike is centered about 800 m uprift of Puu Oo. Its top is at a depth of 0.4 km, its bottom at about 2.9 km, and the length is about 1.6 km; the dike strikes N65° E and dips at about 87°SE. The model indicates that the dike expanded by 11 cm during repose periods, for an average volumetric expansion of nearly 500 000 m3. The volume of magma added to the dike during repose periods was variable but correlates positively with the volume of erupted lava of the subsequent eruption and represents about 8% of the new lava extruded. Dike geometry and expansion values are used to estimate the pressure increase near the eruption site due to the accumulation of magma during repose periods. On average, vent pressures increased by about 0.38 MPa during the repose periods, one-third of the pressure increase at the summit. The model indicates that the dikelike body below Puu Oo grew in volume from 3 million cubic meters (Mm3) to about 10–12 Mm3 during the series of eruptions. The width of this body was probably about 2.5–3.0 m. No net long-term deformation was detected along the measured deformation lines.

Introduction to Special Section on How Volcanoes Work: Part 2

The special section on “How Volcanoes Work” is a collection of some of the nearly 300 papers presented at the Hawaii Symposium on How Volcanoes Work, held in Hilo in January 1987 [Tilling, 1987a]. The response of the symposium participants to the invitation to submit their papers for consideration in the special section exceeded expectations. In all, more than 70 manuscripts were received, reviewed, and handled following regular JGR editorial procedures.Part 1 of the special section, composed of the papers that were processed and accepted in time to meet the production schedule, was published in the December 1987 issue of the Journal of Geophysical Research‐Solid Earth and Planets [Tilling, 1987a]. Even though part 1 contained only eight papers, it nonetheless provided a representative sampling of the multidisciplinary nature of the investigations undertaken to improve our understanding of volcanic systems. The papers published in part 1 included ground deformation studies on caldera systems [Dzurisin and Yamashita, 1987; Mortensen and Hopkins, 1987], geochemical and observational studies of the lava fountains and of volcanic fume during the 1983–1984 activity of Pu'u 'O'o in Kilauea's east rift zone [Crowe et al., 1987; Head and Wilson, 1987], magmatic crystal stratigraphy and theoretical petrology [Pearce et al., 1987; Russell, 1987], dynamics of active lava lakes [Tilling, 1987b], and seismic evidence for a subcrustal intrusive complex beneath the Island of Oahu, Hawaii [ten Brink and Brocher, 1987].

Origin of differentiated lavas at Kilauea Volcano, Hawaii: Implications from the 1955 eruption

Kilauea's 1955 eruption was the first major eruption (longer than 2 days) on its east rift zone in 115 years. It lasted 88 days during which 108 × 106 m3 of lava was erupted along a discontinuous, 15-km-long system of fissures. A wide compositional range of lavas was erupted including the most differentiated lavas (5.0 wt% MgO) from a historic Kilauea eruption. Lavas from the first half of the eruption are strongly differentiated (5.0–5.7 wt% MgO); later lavas are weakly to moderately differentiated (6.2–6.7 wt% MgO). Previous studies using only major-element compositions invoked either crystal fractionation (Macdonald and Eaton 1964) or magma mixing (Wright and Fiske 1971) as models to explain the wide compositional variation in the lavas. To further evaluate these models detailed petrographic, mineralogical, and whole-rock, major, and trace element XRF analyses were made of the 1955 lavas. Plagioclase and clinopyroxene in the early and late lavas show no petrographic evidence for magma mixing. Olivines from both the early and late lavas show minor resorption, which is typical of tholeiitic lavas with low MgO contents. Core-to-rim microprobe analyses across olivine, augite, and plagioclase mineral grains give no evidence of disequilibrium features related to mixing. Instead, plots of An/Ab vs distance from the core (D) and %Fo vs (D)4.5 generated essentially linear trends indicative of simple crystal fractionation. Least-squares, mass-balance calculations for major- and trace-element data using observed mineral compositions yield excellent results for crystal fractionation (sum of residuals squared <0.01 for major elements, and <5% for trace elements); magma mixing produced less satisfactory results especially for Cr. Furthermore, trace-element plots of Zr vs Sr, Cr, and A12O3 generate curved trends indicative of crystal fractionation processes. There is no evidence that mixing occurred in the 1955 lavas. Instead, the data are best explained by crystal fractionation involving a reservoir that extends at least 15 km along Kilauea's east rift zone. A dike was intruded into the rift zone from the summit reservoir eight days after the eruption started. Instead of causing magma mixing, the dike probably acted as a hydraulic plunger forcing more of the stored magma to be erupted.

Voluminous submarine lava flows from Hawaiian volcanoes

The GLORIA long-range sonar imaging system has revealed fields of large lava flows in the Hawaiian Trough east and south of Hawaii in water as deep as 5.5 km. Flows in the most extensive field (110 km long) have erupted from the deep submarine segment of Kilauea's east rift zone. Other flows have been erupted from Loihi and Mauna Loa. This discovery confirms a suspicion, long held from subaerial studies, that voluminous submarine flows are erupted from Hawaiian volcanoes, and it supports an inference that summit calderas repeatedly collapse and fill at intervals of centuries to millenia owing to voluminous eruptions. These extensive flows differ greatly in form from pillow lavas found previously along shallower segments of the rift zones; therefore, revision of concepts of volcano stratigraphy and structure may be required.

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.

Geothermal resources assessment in Hawaii

Report prepared for Western States Cooperative Direct Heat Resource Assessment under grant No. DOE DE-ACO3-80SF10819, Feb. 1985.

The financing of a demonstration geothermal project

The State of Hawaii started a geothermal exploration program, focused in the Kilauea East Rift Zone of the Island, in the late 1960s. The urgent demand for alternate energy created by the global petroleum disruptions of the 1970s encouraged Federal energy agencies to join the Hawaii team to drill, on the first attempt, a successful deep well, and construct a 3 MW wellhead generator. The costs were high, especially for the generator, but this timely demonstration of a viable geothermal resource has encouraged private developers.

Hydrogen isotope systematics of submarine basalts

The D/H ratios and water contents in fresh submarine basalts from the Mid-Atlantic Ridge, the East Pacific Rise, and Hawaii indicate that the primary D/H ratios of many submarine lavas have been altered by processes including (1) outgassing, (2) addition of seawater at magmatic temperature, and (3) low-temperature hydration of glass. Decreases in δD and H 2O + from exteriors to interiors of pillows are explained by outgassing of water whereas inverse relations between δD and H 2O + in basalts from the Galapagos Rise and the FAMOUS Area are attributed to outgassing of CH 4 and H 2. A good correlation between δD values and H 2O is observed in a suite of submarine tholeiites dredged from the Kilauea East Rift Zone where seawater (added directly to the magma), affected only the isotopic compositions of hydrogen and argon. Analyses of some glassy rims indicate that the outer millimeter of the glass can undergo lowtemperature hydration by hydroxyl groups having δD values as low as −100. δD values vary with H 2O contents of subaerial transitional basalts from Molokai, Hawaii, and subaerial alkali basalts from the Society Islands, indicating that the primary δD values were similar to those of submarine lavas. Extrapolations to possible unaltered δD values and H 2O contents indicate that the primary δD values of most thoteiite and alkali basalts are near −80 ± 5: the weight percentages of water are variable, 0.15–0.35 for MOR tholeiites, about 0.25 for Hawaiian tholeiites, and up to 1.1 for alkali basalts. The primary δD values of −80 for most basalts are comparable to those measured for deep-seated phlogopites. These results indicate that hydrogen, in marked contrast to other elements such as Sr, Nd, Pb, and O, has a uniform isotopic composition in the mantle. This uniformity is best explained by the presence of a homogeneous reservoir of hydrogen that has existed in the mantle since the very early history of the Earth.

Focal mechanisms and locations of earthquakes in the vicinity of the 1975 Kalapana Earthquake aftershock zone 1970–1979: Implications for tectonics of the south flank of Kilauea Volcano, Island of Hawaii

The November 29, 1975, Kalapana earthquake of magnitude 7.1 on the south flank of Kilauea Volcano, Hawaii, represents a major rift tectonic event. It is generally understood that the earthquake resulted from movement on a nearly horizontal fault plane, with the crustal block south of Kilauea's east rift zone moving south‐southeastward up to several meters. Well‐recorded earthquakes on the south flank of Kilauea from 1970 to 1979 were analyzed and focal mechanisms determined to obtain a better understanding of the details of south flank tectonics. Included are a large number of earthquakes from the aftershock sequence of the 1975 earthquake. Hypocenters are distributed in a subplanar zone that dips 2° to 3° to the west at a depth of about 8–9 km depth. We interpret this pattern to coincide with a portion of the slip plane of the Kalapana earthquake and to be consistent with the notion of the slip plane occurring in a weak layer at the top of the old oceanic crust. Focal mechanisms are remarkably constant throughout this time period, both before and after the 1975 event, and closely agree with the mainshock mechanism. P axis azimuths and slip vectors for the low‐angle fault planes are normal to the middle and lower east rift zones of Kilauea. There is suggestion of a change in the orientation of P axes from shallower to steeper plunge at the time of the Kalapana earthquake. Such a change is consistent with a general reduction in the horizontal compressional stress normal to the rift zone at the time of the large earthquake. No other evidence of precursory reorientation of the stress field was found and the precise predictability of this event remains in doubt. However, a general model of the tectonics of the volcanic rift system is now available that satisfies a number of geological and geophysical observations.

Focal mechanisms of earthquakes related to the 29 November 1975 Kalapana, Hawaii, earthquake: The effect of structure models

abstractInitial focal mechanism determinations for the 29 November 1975 Kalapana, Hawaii, earthquake indicated discrepancy between the mechanism determined from teleseismic data by Ando and the mechanism determined using data from the local U.S. Geological Survey network surrounding the epicenter region. The resolution of this difference is crucial to correctly understand this earthquake, as well as to understand the tectonics of the south flank of Kilauea volcano. When a model with a low-velocity layer at the base of the crust is used for projection back to the focal sphere for the local network mechanisms, the discrepancy vanishes. To further investigate this result, focal mechanisms were determined using several contrasting models for a set of well-recorded earthquakes. A large number of these earthquakes have mechanisms identical to the main shock when the low-velocity layer model is used. Dispersion of P and T axes is also minimized by use of this model. A low-angle slip direction, favored for the main shock and typical of most other solutions, exhibits remarkable stability normal to the east rift zone of Kilauea. Our results suggest a tectonic model, similar in nature to that proposed by Ando, in which the south flank of Kilauea consists of a mobile block of crust which is relatively free to move laterally on a low-strength zone at about 10 km depth. Forceful injection of magma along the rift zones provides the loading stress which is released by catastrophic failure in the weak, horizontal layer in a cycle of perhaps 100 yr.