Basaltic Scoria Research Articles

Airfield pavement construction using basalt aggregate

75,000 m3 oc concrete were required for the Fast Exit Taxiway and Apron works for development of Wideawake airfield on Ascension Island. Locally available construction materials were used wherever possible because of the remote location. The pavement contractor obtained some 250,000 tonnes of concrete aggregate by quarrying basalt from aa lava flows associated with highly vesicular basalt scoria ejected during Strombolian-type eruptions. The methods used for ground investigation, material assessment and development include the innovative use of geostatistical techniques for resource evaluation.

The Te Rere and Okareka eruptive episodes — Okataina Volcanic Centre, Taupo Volcanic Zone, New Zealand

Abstract The Te Rere and Okareka eruptive episodes occurred within the Okataina Volcanic Centre at c. 21 000 and 18 000 yr B.P., respectively. The widespread rhyolitic pumice fall deposits of Te Rere Ash (volume 5 km3) and Okareka Ash (6 km3) are only rarely exposed in near‐source areas, and locations of their vent areas have been uncertain. New exposures and petrographic and chemical analyses show that the Te Rere episode eruptions occurred from multiple vents, up to 20 km apart, on the Haroharo linear vent zone. The Okareka episode eruptions occurred from vents since buried beneath the Tarawera volcanic massif. Eruption of the rhyolitic Okareka pumice fall was immediately preceded by a small basaltic scoria eruption, apparently from vents close to those for the following rhyolite eruptions. Dacitic mixed pumices scattered within the rhyolite pumice layers immediately overlying the scoria were formed by mixing of the basalt and rhyolite magmas. The Te Rere and Okareka pyroclastic eruptions were both foll...

Volc�n Quizapu, Chilean Andes

Quizapu is a flank vent of the basalt-to-rhyodacite Holocene stratocone, Cerro Azul, and lies at the focus of a complex Quaternary volcanic field on the Andean volcanic front. The Quizapu vent originated in 1846 when 5 km3 of hornblende-dacite magma erupted effusively with little accompanying tephra. Between ∼ 1907 and 1932, phreatic and strombolian activity reamed out a deep crater, from which 4 km3 of dacite magma identical to that of 1846 fed the great plinian event of 10–11 April 1932. Although a total of >9 km3 of magma was thus released in 86 years, there is no discernible subsidence. As the pre-plinian crater was lined by massive lavas, 1932 enlargement was limited and the total plinian deposit contains only ∼ 0.4 wt % lithics. Areas of 5-cm and 1-cm isopachs for compacted 1932 fallout are about half of those estimated in the 1930's, yielding a revised ejecta volume of ∼9.5 km3. A strong inflection near the 10-cm isopach (downwind ∼110 km) on a plot of log Thickness vs Area1/2 reflects slow settling of fine plinian ash — not of coignimbrite ash, as the volume of pyroclastic flows was trivial (<0.01 km3). About 17 vol.% of the fallout lies beyond the 1-cm isopach, and ∼ 82 wt% of the ejecta are finer than 1 mm. A least 18 hours of steady plinian activity produced an exceptionally uniform fall deposit. Observed column height (27–30 km) and average mass eruption rate (1.5x108 kg/s) compare well with values for height and peak intensity calculated from published eruption models. The progressive “aeolian fractionation” of downwind ash (for which Quizapu is widely cited) is complicated by the large compositional range of 1932 juvenile pumice (52–70% SiO2). The eruption began with andesitic scoria and ended with basaltic scoria, but >95% of the ejecta are dacitic pumice (67–68% SiO2); minor andesitic scoria and frothier rhyodacite pumice (70% SiO2) accompanied the dominant dacite. Phenocrysts (pl>hb∼opx>mt>ilm∼cpx) are similar in both abundance and composition in the 1846 (effusive) and 1932 (plinian) dacites. Despite the contrast in mode of eruption, bulk compositions are also indistinguishable. The only difference so far identified is a lower range of δ D values for 1846 hornblende, consistent with pre-eruptive degassing of the effusive batch.

The 1989 submarine eruption off eastern Izu Peninsula, Japan: ejecta and eruption mechanisms

The submarine eruption of a new small knoll, which was named “Teishi knoll”, off eastern Izu Peninsula behind the Izu-Mariana arc occurred in the evening of 13 July 1989. This is the first historic eruption of the Higashi-Izu monogenetic volcano group. The eruption of 13 July followed an earthquake swarm near Ito city starting on 30 June. There were subsequent volcanic tremors on 11 and 12 July, and the formation of the Teishi knoll on the 100 m deep insular shelf 4 km northeast of Ito city. There were five submarine explosions, which were characterized by intermittent domelike bulges of water and black tephra-jets, which occurred within 10 min on 13 July. Ejecta of the eruption was small in volume and composed of highly crystalline basalt scoria, highly vesiculated “pumice”, and lithic material. Petrographical features suggest that the “pumice” was produced by vesiculation of reheated wet felsic tuff of an older formation. The Teishi knoll, before the eruption, was a circular dome, 450 m across and 25 m high, with steep sides and a flat summit. Considerations of submarine topographic change indicate the knoll was raised by sill-like intrusion of 106 m3 of magma beneath a 30 m thick sediment blanket. This shallow intrusion is assumed to have started on 11 July when volcanic tremors were observed for the first time, but there was no indications of violent interaction between wet host sediments and intruding magma. The submarine eruption of 13 July appears to have been Friggered by a major lowering of the magma-column. The basalt scoria, having crystal-contents of more than 60%, is assumed to be derived from the cooled plastic margin of the shallow intrusive body. However, glassy scoria, which would indicate the interaction between hot fluidal magma and external water, was not observed. A scenario for the 1989 submarine eruption is as follows. When rapid subsidence of the hot interior of the intrusive magma occurred, reduced pressure caused the implosion of cooled plastic magma, adjacent pressurized, hot host material, and wet sediment. The mixing of these materials triggered the vigorous vapor explosions.

New light on caldera evolution—Askja, Iceland

The large multiple-caldera volcanic system of Askja, central Iceland, is composed principally of subglacial basaltic hyaloclastite-pillow-lava formations and postglacial basaltic scoria and flows. Traditionally, such calderas are believed to be formed by downfaulting and ring-fracture collapse. Whereas this certainly applies to the smaller A.D. 1875 caldera, the older main caldera may have developed positive relief during subglacial construction of laterally confined hyaloclastite ridges above erupting fractures. This is supported by the evidence of a large negative gravity anomaly that reaches minima over the marginal low-density ridges but which is less negative within the caldera, where relatively dense postglacial lavas are believed to cover a more limited hyaloclastite succession beneath the caldera floor.

The welded air-fall tuff layer at Krafla, northern Iceland: A composite eruption triggered by injection of basaltic magma

A composite welded tuff layer surrounding the Krafla volcanic center in northern Iceland was erupted when the caldera was formed during the last interglacial period in Iceland, 70 to 100 thousand years ago. The stratigraphic units of the up to 50 m thick layer are: silicic ash, basaltic scoria, intermediate vitrophyre, intermediate welded and agglutinated spatter, and intermediate densely welded tuff. Stratigraphic and petrochemical study of the layer suggests that it was formed by an initial explosive eruption of silicic magma triggered and immediately followed by basaltic magma, both erupting in Plinian activity. The eruption continued with Strombolian activity producing incompletely mixed silicic/basaltic pyroclastics. Most of the layer is made up of this, apparently intermediate, heterogeneous welded tuff. Welding within the layer is the result of the different solidus temperatures of basalt and dacite; after deposition, the silicic component is being kept above its softening point by the hotter but solid basaltic component. Isopleth and isopach maps of the layer indicate a source area in the southeastern part of the caldera. Estimated DRE volume of the layer is 2.4 km 3 which accounts for a 50–55-m subsidence of the 45-km 2 caldera floor. Drill hole data from within the southern margin of the caldera reveals the layer at a depth of 290 m, which indicates accumulation of about 13.5 km 3 of volcanic rocks since its formation.

Fracture fillings and intrusive pyroclasts, Inyo Domes, California

Fractures containing juvenile magmatic pyroclasts were encountered during drilling into a 600‐year‐old feeder dike beneath the Inyo Domes chain, California. The Inyo Domes consist of a north‐south trending, 10‐km‐long chain of domes, rhyolitic tuff rings, and phreatic craters. Boreholes were cored through the 51‐m‐diameter conduit of Obsidian Dome, the largest of the Inyo Domes, and through an unvented portion of the intrusion (dike) 1 km to the south. Pyroclast‐bearing fractures were intersected in both holes: (1) 7‐ to 40‐cm‐thick fractures in welded basaltic scoria and quartz monzonite country rock are adjacent to the conduit at depths of 400–411 m and 492–533 m; they contain gray, clastic deposits, which show truncated cross bedding and convolute bedding; (2) adjacent to the dike, massive fracture fillings occur at depths of 289–302 m (129 m east of the dike) and 366–384 m (95–87 m east of the dike). The fracture fillings consist of mineral clasts derived from the quartz monzonite, quartz monozonitic and basaltic lithic clasts, and juvenile glass pyroclasts. Angular mineral components are present in the same ratio as in the surrounding quartz monzonite country rock. Juvenile glassy and hyalocrystalline pyroclasts make up from less than 1% up to 22% of the deposits. They consist of blocky obsidian clasts, equant, blocky glass pyroclasts with vesicularities of 0–30%, and small pumices with vesicularities of 30–40%. Intrusive pyroclasts differ from erupted pyroclasts in their generally lower vesicularity, higher crystallinity, and the presence of solution pits and clay coatings indicative of prolonged contact with water. The presence, orientation, and texture of fracture fillings strongly resemble those of propped, man‐made hydrofractures. We interpret these fractures as naturally occurring hydrofractures. The apparently horizontal fracture orientations may have been controlled by perturbations of maximum principal stress by the dikes or by preexisting sheet fractures in the quartz monzonite country rock. Assumption of elastic moduli and fracturing properties for the Sierran basement rock allows calculation of fluid overpressures 5 to 9 MPa in excess of overburden stress. These overpressures are consistent with either vapor exsolution from decompressed magma or rapid heating of groundwater. However, the textural and chemical similarity of the pyroclasts to phreatomagmatic tephra that appears late in the explosive eruption sequence suggests that heating of groundwater by the dike/conduit caused the fracturing. Such fracturing around volcanic conduits may play an important role in the development of hydrothermal circulation.

Morne Patates volcano, southern Dominica, Lesser Antilles

AbstractMornes Patates is the youngest volcano in Dominica occupying a depression on the southwestern flank of a larger stratovolcano, Morne Plat Pays. Within the depression an arcuate ridge, apparently of acid andesite lavas, has been cored and largely buried by the explosive emplacement of two acid andesite domes and their associated pyroclastic deposits, mainly block-and-ash flow deposits. A basaltic scoria horizon, exposed on the northern side of the depression, has a14C age of 28450 ± 1500 years B.P. and is not seen on the volcano itself, which suggests that the domes and pyroclastic rocks are younger than this. A14C age of 450 ± 90 years B.P. from a block-and-ash flow deposit from the Morne Patates dome apparently confirms this and the youthful morphology also suggests a young age. The angular shape of the depression and the steep submarine slopes are consistent with an origin as a lateral gravity slide rather than a caldera collapse. Vigorous fumarolic activity and swarms of local earthquakes suggest that magma exists at depth (several kilometres) beneath the Morne Patates–Morne Plat Pays area.

Clay mineralogy of a Dystrandept and a Haplaquod from Northland, New Zealand

Abstract Two soil sampies (Ap1 and Bw3 horizons) from a Dystrandept (Papakauri) developed on basaltic scoria and two sampies (Bh1 and Bs2 horizons) from a Haplaquod (One Tree Point) on dune sands, Northland, New Zealand were analysed for their clay mineral composition by a combination of mt!thods. Absence of allophane was confirmed in the Papakauri Dystrandept. Instead, hydrous alumina and allophane-Iike constituents contributed to the “andic” nature of the soH. Predominance of allophane in the Bs2 horizon clay of the One Tree Point Haplaquod, but existence of lower amounts of this constituent (20% at most) in the Bhl horizon clay was interpreted as an indication that the continued supply of the complexing organic matter from the overlying horizons suppresses the formation of allophane. The abundance of volcanic glass in the fine sand from the Haplaquod indicated that the major parent materials were finely comminuted volcanic ejecta which primarily contributed 10 the formation of the non-crystalline clay ...

The Effect of Crushed Basalt Scoria on the Cation Exchange Properties of a Highly Weathered Soil

AbstractSoil from the surface horizon of a highly weathered soil (Acrohumox) from tropical Queensland was mixed with crushed basaltic cinders and incubated in a moist condition for 12 months in the laboratory. The cation exchange capacity (CEC) increased from 9 to 14 meq/100 g in direct relationship to the rate of application and degree of fineness of the scoria, as well as to the duration of incubation. The increase in CEC was accompanied by an increase in exchangeable calcium, magnesium, and potassium. The results suggest that crushed basaltic scoria could be successfully used to prevent cation nutrient losses from highly weathered soils of the tropics.

Rotomahana—Waimangu eruption, 1886: base surge and basalt magma

Abstract Steam explosions ejecting country rock and lake-floor sediments from Rotomahana-Waimangu accompanied eruption of basaltic scoria from Tarawera Volcanic Complex during the early morning of 1886 June 10. The near-source Rotomahana ejecta displays wave-like internal bed forms typical of base surge eruption mechanisms. Deposition occurred from high velocity, steam-fluidised density currents, which carried ejecta laterally outwards from the base of a large vertical eruption column. The surges extended at least 6 km west of the source and passed over steep hills that rise to 350 m above the eruptive vents. Controversy has existed as to whether basalt magma was erupted from craters in the previously highly active Rotomahana hydrothermal area. New exposures clearly demonstrate that basalt was erupted from Waimangu in 1886; pre-1886 basic scorias outcrop in the Rotomahana area; much near-source Rotomahana ejecta consists of little or non-altered rock. These data are consistent with the existence of a cont...

Partially Fused Granite Blocks from Mt. Elephant, Victoria, Australia

Petrological and chemical evidence is presented to show that small patches of brown glass found in blocks of granite erupted in basaltic scoria at Mt. Elephant are the result of the partial fusion of biotite and quartz. The glass has moderate SiO2 (63–66 per cent), high AI2O3 (17.5–19 per cent), high FeO (3.8–5.2 per cent) and very high K2O (7.0–7.8 per cent) relative to Na2O (3.3–3.7 per cent) and is similar in composition to many high K alkali syenites and trachytes.

Petrology of kaersutite-bearing ultramafic and mafic inclusions in Iki Island, Japan

Kaersutite-bearing peridotite, clinopyroxenite, gabbro and hornblendite inclusions up to 5 cm in size and megacrysts of kaersutite, andesine and titanomagnetite occur in alkali basalt scoria at Takenotsuji, Iki Island, Japan. New analyses are presented for seven kaersutite-bearing basaltic rocks, three inclusions, three clinopyroxenes and six kaersutites.

Glaciation in Taylor Valley, Antarctica, Older Than 2.7 Million Years

Potassium-argon dates for three samples of basaltic scoria from Taylor Valley, on the west side of McMurdo Sound, indicate that the basalt, which antedates and postdates major glaciations, is at least 2.7 million years old.

SONIC VELOCITY AND PENETRABILITY OF SIMULATED LUNAR ROCK DUST

Theoretical considerations are given for the design of an ultrasonic pulsing system for noncohesive dusts. In addition, measurements of less than one percent error of sonic velocity were made in volcanic rocks of different textures. Pumice containing elongate vesicles exhibits marked sonic anisotropy. In contrast, basaltic scoria with approximately equidimensional vesicles exhibits sonic isotropy. These anisotropy contrasts may be significant in interpreting Surveyor return data and in evaluating lunar base requirements. Sonic velocity with a simultaneous recording of porosity in rock dusts under ambient conditions ranges from 150 m/sec (500 ft/sec) to 700 m/sec (2,100 ft/sec). Absolute measurements of shear strength, using the vane‐type shear tester, were made at critical density obtained by vibrating the simulated lunar dust samples for specified time periods. Relative shear strengths were also compared at maximum density obtained by long‐period vibration of dust samples. Comparson of stress curves of dusts of different grain shapes indicates that relatively little strain occurs before the plastic zone of the stress curve is reached for volcanic dust consisting of angular glass shards. For purpose of shear strength analysis, grain shapes may be grouped as spherical, prismatic, and vesiculate. Shearing resistance curves are analyzed for each of these groups, and the vesiculate shapes have the highest shear strengths at critical density. Moreover, the sliding habit during shear appears to reflect the shape of the grains. Grain shape is apparently a first‐order parameter affecting shear strength of dust particles &gt;0.1 mm in diameter. Adhesion effects due to hard vacuum ([Formula: see text] to [Formula: see text] torr) are small but measurable for the grain sizes considered. At equivalent porosities, vacuum at [Formula: see text] torr apparently does not markedly influence the peak shear strength of dust composed of vesiculate particles greater than 0.1 mm in diameter. Once sonic velocity and shear strength data are obtained by a lunar probe or astronaut, practical studies can be made on bearing capacity, trafficability, and lunar base construction.

Volcanic risk in Northland

Abstract In Northland, Quaternary volcanism is concentrated in the Bay of Islands and Whangarei Volcanic Districts. Basaltic scoria cones and flows predominate, and there is a rhyolite dome near Kaikohe with nearby warm and hot springs and gas vents. It is from the eastern and southern edges of both volcanic districts, where Holocene basaltic cones and flows are concentrated, that new cones and flows can be expected in the future, at the rate of roughly one in every 1,000 to 2,000 years. Roughly 10 square miles of land is likely to be devastated by each eruption. The likelihood of a hydrothermal eruption is much less than that for basalt, and damage by covering the land with country rock will probably be confined to an area of a few square miles around the crater. The eruptive potential of rhyolitic lava and ash is low, and dacitic volcanism in the Whangarei Volcanic District is considered to be extinct.