Geology topics
Source-linked reports with geographic coverage including Kilauea Volcano.
Brief excursions of magnetic field differences between a base station and two satellite station magnetometers show only slight correlation with ground tilt at Kilauea Volcano. This result suggests that only transient, localized stresses occur during prolonged periods of deformation and that the volcano can support no large-scale pattern of shear stresses.
Lava from the Mauna Ulu eruption on Kilauea Volcano entered the sea on the south coast of the Island of Hawaii three times from 1969 to 1971. Two of these flows were investigated underwater by divers, one while lava was actively flowing. The June 1969 flow entered the sea as a narrow flow of aa. Below sea level, the flow maintained continuity and flowed at least several hundred meters to a depth beyond 70 m. Several cylindrical flow lobes about 1 m in diameter and about 10 to 15 m long emerged from the side of the aa flow at a depth of about 25m. Underwater investigations, combined with subaerial observations, revealed that the March–May 1971 flow produced a distinct lava delta composed of subaerial pahoehoe lava resting on a submarine sequence of steeply dipping foreset-bedded volcanic sand and rubble that includes conformably dipping cylindrical lava tongues. Most of the pahoehoe streams pouring over the sea cliff are quenched and shattered to glassy sand and rubble that in turn is further fragmented by vigorous wave action and avalanching. In some places, however, larger pahoehoe flows maintain coherence across the cliff and through the surf zone to feed submarine lava tongues. Underwater, these active lava tongues emitted a roaring noise as lava flowed inside their outer black glassy walls. Periodically, cracks exposed the brightly incandescent lava within, and pillow-like buds and toes grew from the top and sides of the lava tongue. Only a small amount of steam was generated underwater. Water temperature close to the active tongues was elevated only 2.5°C.
Note: This paper is dedicated to Aaron and Elizabeth Waters on the occasion of Dr. Waters' retirement. Three types of chemically similar pahoehoe flows were observed to form during the 1969–1971 Mauna Ulu eruption. (1) A cavernous type called shelly pahoehoe, characterized by fragile gas cavities, small tubes, and buckled fragments of surface crust, was deposited when gas-charged lava welled out of the source fissure with little or no accompanying fountaining. (2) A comparatively smooth-surfaced, dense type, characterized by surface channels and only a few large cavities, formed from voluminous flows of partly degassed fallout away from the foot of lava fountains more than 100 m high. (3) A relatively dense type, characterized by hummocky surfaces with abundant low tumuli and overlapping pahoehoe toes and lobes, formed when largely degassed lava issued from tubes after flowing underground for several kilometers or more. Shelly pahoehoe is rarely found in the geologic record, but the other two types occur commonly. These three types of pahoehoe, which are completely intergradational, can be related qualitatively to the relative gas content and mode of flowage of the lava. The present surface of Kilauea is underlain mostly by hummocky, tube-fed pahoehoe.
The amount of water and sulfur in pumice erupted during periods of vigorous activity during the 1969-71 Mauna Ulu eruption varied inversely with fountain height because of degassing during the fountaining. The pumice lost about 0.05 wt percent water and 0.003 wt percent sulfur during fountaining to heights of 400-540 m. Analyses suggest that the initial volatile content of Mauna Ulu lava was greater immediately preceding periods of high fountaining than during weak activity between those periods or after the last high fountains on December 30, 1969. Water and sulfur were systematically depleted during nearly isothermal flowage in lava tubes. Rapidly quenched samples of dipped melt show losses of about 0.03-0.04 wt percent water and 0.007-0.008 wt percent sulfur during flowage for several hours through a distance of 12 km. Glassy skins on cooled pahoehoe flows contain about 0.002-0.003 wt percent less sulfur than quenched melt at comparable distances from the vent, because of continued degassing under natural cooling conditions. Chlorine shows similar but less well defined trends. Pumice erupted in high fountains becomes more strongly oxidized than the parent magma, because of mixing with air while still at high temperatures.
Since February 1969 Alae Crater, a 165-m-deep pit crater on the east rift of Kilauea Volcano, has been completely filled with about 18 million m 3 of lava. The filling was episodic and complex. It involved 13 major periods of addition of lava to the crater, including spectacular lava falls as high as 100 m, and three major periods of draining of lava from the crater. Alae was nearly filled by August 3, 1969, largely drained during a violent ground-cracking event on August 4, 1969, and then filled to the low point on its rim on October 10, 1969. From August 1970 to May 1971, the crater acted as a reservoir for lava that entered through subsurface tubes leading from the vent fissure 150 m away. Another tube system drained the crater and carried lava as far as the sea, 11 km to the south. Much of the lava entered Alae by invading the lava lake beneath its crust and buoying the crust upward. This process, together with the overall complexity of the filling, results in a highly complicated lava lake that would doubtless be misinterpreted if found in the fossil record.
During the course of an electromagnetic survey about Kilauea Volcano in Hawaii, an unusual amount of low-frequency noise was observed at one recording location. Several weeks later an eruption occurred very close to this site. The high noise level appeared to be associated in some way with the impending eruption.
Kilauea Volcano has erupted lava from its summit caldera and from two rift zones that extend from the summit towards the east and south-west. Lavas erupted from the summit of the volcano differ from each other principally in their content of olivine and define lines of ‘olivine control’ on magnesia variation diagrams. Lavas erupted on the rift zones may be similar in composition to the summit lavas or may be differentiated by processes that involve minerals other than olivine. All of the differentiated lavas have less than 6·8 per cent MgO and plot off the extension of olivine control lines for the summit lavas. Prehistoric vents (before A.D. 1750) from which differentiated lavas have been erupted are found on the east rift zone and in the western Koae fault zone adjacent to the south-west rift zone; historic vents for differentiated lavas are confined to the east rift zone. Twenty-one new analyses are presented for several of the east rift differentiates and for the newly discovered differentiates adjacent to the south-west rift zone. The differentiates have MgO as low as 3·9 per cent and SiO 2 as high as 56 per cent; both extremes are found in the prehistoric lavas adjacent to the south-west rift. Detailed petrochemical studies suggest the following conclusions: The chemical composition of magma erupted at Kilauea summit varies with the date of eruption. Lavas erupted before 1750, during the eighteenth and nineteenth centuries, and in the twentieth century form groups that can be distinguished chemically. On a lesser scale, each Kilauea summit eruption in the twentieth century has a chemistry that is distinctive with respect to the chemistry of every other summit eruption. During late prehistoric time pockets of differentiated magma were formed within the rift zones by separation of the liquid remaining after partial crystallization of bodies of summit magma. This process presumably is still going on within the east rift zone, but the more recently separated liquids have not yet been erupted to the surface. The relative time at which these differentiated magmas were produced can be estimated from calculations based on their chemical compositions, which show that the differentiates could lie on the liquid line of descent for Kilauea summit magma of prehistoric composition but not on any liquid line of descent for younger summit magmas. Lava from some eruptions, notably the early part of the 1955 eruption on the lower east rift, has the composition of the liquid fraction as it is generated within the rift. Lava compositions of other eruptions, including those of the later lavas of 1955, are best explained by mixing of magma supplied from a central reservoir beneath Kilauea summit with the differentiated liquid in the rift. Lava from each summit eruption is unique chemically, so it is possible to recognize its presence or absence as components of mixing in such mixed lavas. It appears that summit magma of composition characteristic of the 1952 and 1961 Halemaumau eruptions contributed to the composition of the mixed lavas produced in the latter part of the 1955 eruption. Summit magma of 1961 composition is alone sufficient to explain the composition of mixed lavas erupted in 1960 and 1961. In rift lavas erupted from 1962 to 1965, the composition of lava erupted in Halemaumau in 1967, in addition to the 1961 composition, is a component of mixing, and it is the dominant summit component in the composition of the two 1965 eruptions. The proportion of summit magma to differentiated magma needed to explain the composition of lavas erupted on the upper east rift increases from 1961 to 1965; this increase indicates that the differentiated magma was being diluted and used up by repeated flooding of this part of the rift zone by magma supplied from the central reservoir. The fact that components of ‘summit composition’ appear in rift eruptions before they appear undiluted in Halemaumau suggests that the central reservoir is vertically zoned. Rift eruptions are fed from lower levels where younger magma is available, and summit eruptions are fed from the relatively older magma above. The chemical distinction between lava of successive summit eruptions implies that significant convective mixing of magma does not take place throughout the central reservoir. The unique and uniform composition of lava of each successive summit eruption also suggests that summit eruptions end when all of the magma of one composition has been erupted. The magma erupted from the upper levels of the reservoir during one cycle is continually replaced from below by younger magma of different composition. In order for eruption to be renewed in Halemaumau, new magma from the mantle must be held in storage at intermediate levels before it attains an ‘eruptive state’. The hypothesis presented in 2–4 above permits qualitative predictions concerning future lava compositions. The composition of the next lava to be erupted in Halemaumau is expected to be distinct from that of the 1967 eruption, and this composition will presumably be identified in rift eruptions occurring between 1967 and the time of its appearance in Halemaumau. Differentiates of prehistoric age also were apparently formed in the same way as those of historic age, but the mixing cannot be described quantitatively because of poor control on the stratigraphy and the compositions of erupted lavas. One lava in the Koae group, that from Yellow Cone, appears to be a mixture of a picritic magma (12 per cent MgO) with a differentiated liquid with less than 2·5 per cent MgO and nearly 60 per cent SiO 2 .
On 5 November 1967 Kilauea volcano began erupting lava from vents on the floor of its summit pit crater. Halemaumau, 170 meters deep. This eruption ended nearly 2 years of the quiescence that followed a short lived eruption on the east rift zone of Kilauea in December 1965 (1). The 1967-68 eruption was the first activity in Halemaumau since July 1961 (2). The eruption ceased on 13 July 1968 following 31 separate phases of fountaining separated by short periods of quiescence. Six weeks after the end of the summit eruption, a short eruption occurred on the upper east rift zone of Kilauea. As the article goes to press there have been four eruptions, all of the upper east rift zone. The last of the four began in May 1969 and have just completed its seventh phase. The article summarizes the eruption in Halemanumau and complements an article Fiske and Kinoshita on the deformation that preceded the eruption (3). The methods of study and the instrumentation used during the eruption are the same as those discussed in the earlier article. The locations of all seismographs tiltmeter stations and bench marks are shown in Fig. 1.
Ocean-bottom photographs from 18 stations and dredge hauls from 35 stations adjacent to the Island of Hawaii indicate that basaltic pillow lava and pillow fragments are the dominant rock type on the crest and flanks of the submarine rift zone ridges, whereas glassy basalt sand and scoria are the dominant type on the submarine flanks of the volcanoes directly downslope from land. These relations indicate that three major rock units comprise different levels of the volcanoes depending on the site of eruption: (1) pillow lavas and pillow fragments are dominant below sea level and are erupted from deep-water vents; (2) hyaloclastite rocks (vitric explosion debris, littoral cone ash, and flow-foot breccias) mantle the pillowed base of the volcano, and are erupted from shallow-water vents, subaerial vents in water-soaked ground, or are produced where subaerial lava flows cross the shoreline; and (3) thin subaerial lava flows make up the visible, subaerial shield volcano, are built atop the clastic layer, and are erupted from subaerial vents. This three-fold structure is similar to the table mountains of Iceland that are built by eruption beneath glacial ice. Large-scale slumping in the clastic layer may modify the submarine slopes of the volcanoes as well as produce faulting and downslope movement of parts of the overlying shield volcano. The slope change produced where the gentler shield meets the steeper pillowed pile can be recognized beneath sea level in the older volcanoes, where it has been submerged by regional subsidence.
Submarine pillow basalts from Kilauea Volcano contain excess radiogenic argon-40 and give anomalously high potassium-argon ages. Glassy rims of pillows show a systematic increase in radiogenic argon-40 with depth, and a pillow from a depth of 2590 meters shows a decrease in radiogenic argon-40 inward from the pillow rim. The data indicate that the amount of excess radiogenic argon-40 is a direct function of both hydrostatic pressure and rate of cooling, and that many submarine basalts are not suitable for potassium-argon dating.
An electrochemical device was used to measure the fugacity of oxygen ( f O2 ) in holes drilled through the crust of Makaopuhi lava lake, Kilauea Volcano, Hawaii. Results obtained within 6 months of the lake formation show that log f O2 normally varies linearly with the reciprocal of the absolute temperature, and that chemical changes occurring in the cooling tholeiitic basalt are reflected in the f O2 values measured in the holes.
The 1959 summit eruption of Kilauea Volcano, Hawaii, filled the crater of Kilauea Iki with a lake of lava 365 feet deep. Temperatures of the erupting basalt ranged between 1060° and 1190°C. Temperatures down a 12.7-foot-deep hole, drilled into the crust of the lake 5 months after cessation of eruptive activity, agree with calculated temperatures based on the heat equation. The cooling effect of rainfall is pronounced only in the upper 3½ feet of the crust.