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91.
92.
Rowland RH 《Soviet geography》1980,21(4):195-218
93.
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. 相似文献
94.
95.
John E. Bailey Andrew J. L. Harris Jonathan Dehn Sonia Calvari Scott K. Rowland 《Bulletin of Volcanology》2006,68(6):497-515
An open channel lava flow on Mt. Etna (Sicily) was observed during May 30–31, 2001. Data collected using a forward looking
infrared (FLIR) thermal camera and a Minolta-Land Cyclops 300 thermal infrared thermometer showed that the bulk volume flux
of lava flowing in the channel varied greatly over time. Cyclic changes in the channel's volumetric flow rate occurred over
several hours, with cycle durations of 113–190 min, and discharges peaking at 0.7 m3 s−1 and waning to 0.1 m3 s−1. Each cycle was characterized by a relatively short, high-volume flux phase during which a pulse of lava, with a well-defined
flow front, would propagate down-channel, followed by a period of waning flow during which volume flux lowered. Pulses involved
lava moving at relatively high velocities (up to 0.29 m s−1) and were related to some change in the flow conditions occurring up-channel, possibly at the vent. They implied either a
change in the dense rock effusion rate at the source vent and/or cyclic-variation in the vesicle content of the lava changing
its bulk volume flux. Pulses would generally overspill the channel to emplace pāhoehoe overflows. During periods of waning
flow, velocities fell to 0.05 m s–1. Blockages forming during such phases caused lava to back up. Occasionally backup resulted in overflows of slow moving ‘a‘ā
that would advance a few tens of meters down the levee flank. Compound levees were thus a symptom of unsteady flow, where
overflow levees were emplaced as relatively fast moving pāhoehoe sheets during pulses, and as slow-moving ‘a‘ā units during
backup. Small, localized fluctuations in channel volume flux also occurred on timescales of minutes. Volumes of lava backed
up behind blockages that formed at constrictions in the channel. Blockage collapse and/or enhanced flow under/around the blockage
would then feed short-lived, wave-like, down-channel surges. Real fluctuations in channel volume flux, due to pulses and surges,
can lead to significant errors in effusion rate calculations.
Editorial responsibility: A. Woods 相似文献
96.
Mary E. MacKay Scott K. Rowland Peter J. Mouginis-Mark Harold Garbeil 《Bulletin of Volcanology》1998,60(4):239-251
We use a digital elevation model (DEM) derived from interferometrically processed SIR-C radar data to estimate the thickness
of massive trachyte lava flows on the east flank of Karisimbi Volcano, Rwanda. The flows are as long as 12 km and average
40–60 m (up to >140 m) in thickness. By calculating and subtracting a reference surface from the DEM, we derived a map of
flow thickness, which we used to calculate the volume (up to 1 km3 for an individual flow, and 1.8 km3 for all the identified flows) and yield strength of several flows (23–124 kPa). Using the DEM we estimated apparent viscosity
based on the spacing of large folds (1.2×1012 to 5.5×1012 Pa s for surface viscosity, and 7.5×1010 to 5.2×1011 Pa s for interior viscosity, for a strain interval of 24 h). We use shaded-relief images of the DEM to map basic flow structures
such as channels, shear zones, and surface folds, as well as flow boundaries. The flow thickness map also proves invaluable
in mapping flows where flow boundaries are indistinct and poorly expressed in the radar backscatter and shaded-relief images.
Received: 6 September 1997 / Accepted: 15 May 1998 相似文献
97.
C25 HBI alkenes of the diatom, Haslea ostrearia, have been examined in experiments in which the algae were cultured for up to 10 days at 14–15°C at nine different salinities (15 to 40 per mil). H. ostrearia proved to be an osmotolerant organism and growth was observed at all salinities. After 10 days growth at the lowest and highest salinities of 15 and 40 per mil, the concentrations of 2,10,14-trimethyl-6-methylene-7-(3-methylpent-1-enyl)pentadec-9-ene, which was the only HBI present in any of the samples, averaged 1.2±0.7 and 2.1±0.7 pg cell−1, respectively. These were slightly lower than the HBI concentrations at 25 to 35 per mil (2.8±0.5 pg cell−1). The data indicate that although salinity has an influence on HBI production in H. ostrearia, factors other than salinity are probably more important in controlling the large variations of HBI alkene concentrations and distributions found in sedimentary environments. 相似文献
98.
R Alexander R.I Kagi S.J Rowland P.N Sheppard T.V Chirila 《Geochimica et cosmochimica acta》1985,49(2):385-395
The distributions of di- and trimethylnaphthalenes in two sedimentary sequences from Western Australia have been examined by capillary gas chromatography and combined gas chromatography-mass spectrometry. A general decrease was observed in the relative proportions of αα-dimethylnaphthalenes and ααβ-trimethylnaphthalenes with increasing thermal maturity. Similar trends were also observed for six crude oils which have very different ratios of ethylcholestane epimers indicating very different thermal histories. These results suggest that changes in the relative abundances of certain methyl substituted naphthalenes may be useful indicators of thermal maturity of sedimentary organic matter, and the use of a number of isomer ratios is illustrated. 相似文献
99.
Aspects of the differences in the erodibility of the waste rock dump and natural surfaces, Ranger Uranium Mine, Northern Territory, Australia 总被引:3,自引:0,他引:3
Small-scale flume experiments on the waste rock dump of Ranger Uranium Mine, Northern Territory, Australia, show that the unmanaged surface of the dump is 10–100 times more erodible than adjacent natural hillslopes. Silt and clay are preferentially removed and their proportion of the total sediment load is enhanced over their content in surface sediment. There is strong evidence that a low threshold of erosion does not exist and that even the smallest of flows across the waste rock dump can erode and transport some surface material. The erodible dump surface and the preferential removal of silt-clay could degrade ecosystems both on the dump and off-site. Rehabilitation of the waste rock dump will require special attention to erosion and its management. 相似文献
100.
The concentrations and distributions of highly branched isoprenoid (HBI) hydrocarbons in the surficial sediments of an intertidal mudflat in the Tamar Estuary, UK, were examined at monthly intervals throughout 1990. C20 and C25 HBIs were present all the year round and their concentrations covaried, maximising at several times in the year, notably in April–June. Since C25 HBIs are known to be produced by a species of diatom (Haslea ostrearia) in culture, it seemed likely that the sedimentary maxima were also due to production from sediment diatoms. It was interesting therefore that the April–June HBI maximum did not coincide with the (August) maximum concentration of the common diatom hydrocarbon n-heneicosa-hexaene (HE), even though HE is also produced by the diatom species which produces C25 HBIs in culture. Diatoms isolated from the sediments in August produced abundant HE and only a small proportion of C25 HBIs. These results suggest that HBI and HE production maximise at different diatom growth stages, or that the major sources of HBIs in the sediments are as yet unidentified diatom species. The diatoms isolated from the sediment did not produce C20 HBIs and to date no organism has produced these in culture. Nonetheless, the δ13C values of the sedimentary C20 HBIs were consistent with an algal source. 相似文献