Secondary Plumes Research Articles

The effects of sewage discharge on water quality and phytoplankton of Hawai'ian coastal waters

The effects of sewage discharge on algal populations and the quality of Hawai'ian coastal waters were investigated. Two outfalls were studied. One discharges primary treated sewage and the other discharges secondary treated sewage but are otherwise similar. This enabled comparisons of the effects of these different levels of treatment on the water quality and algal productivity of receiving waters. Plumes were followed and repeatedly sampled in a time-series manner. Rhodamine dye was used as a conservative tracer to compare the dilution behavior of the plume constituents MRP, NO 3+NO 2, NH 4, Silicate, TDP, TDN, total bacteria, PC, and PN. Rates of initial dilution ranged from two to almost three orders of magnitude, and were in reasonable agreement with engineering model predictions. Dilution of plume constituents approximated that of Rhodamine until background concentrations were reached, typically within 10 min of discharge. Chl a concentrations did not increase through time in the primary sewage plume but did increase up to 30% in the secondary sewage plume. However, rates of far-field dilution were so rapid that the increase could not have been due to algal growth. The increase was attributed to the plume mixing with a water mass whose relative chl a concentrations were greater. Rates of secondary dilution ranged from 2 to 3 orders of magnitude resulting in total dilutions of 10 5–10 6 within 3 h of discharge. These rates of secondary dilution were much greater than model predictions. From a nutrient standpoint, secondary treatment exhibited no advantages over primary treatment because dilutions were so rapid.

Io’s Volcanos: Latest Results from Galileo and from the Earth

AbstractThree recent close flybys of Io by the Galileo spacecraft, and new observations from the Hubble Space Telescope and ground-based telescopes, have greatly advanced our understanding of Jupiter’s volcanic moon Io. Io’s volcanos are much hotter than previously suspected, perhaps requiring exotic silicate magma compositions. Despite much new data, Io’s largest volcano, Loki, is still poorly understood. New data on Io’s plumes suggest the existence of two types of plumes: primary plumes, relatively rich in S2 gas, which are emitted where magma first reaches the surface, and secondary plumes, more SO2 rich, which result from interaction of lava flows with a volatile-rich substrate.

Carbonate dispersal trains, secondary till plumes, and ice streams in the west Foxe Sector, Laurentide Ice Sheet

Regional carbonate dispersal trains cross Melville Peninsula in the northeastern Canadian Arctic. These trains are 50–125 km across and 100–300 km long. The northern dispersal train crosses upland and lowland areas, while the Rae Isthmus train follows the lowlands. The distribution of carbonate in boulder, pebble and matrix till fractions indicates long‐distance glacial transport of limestone, a low rate of dilution, and comminution from pebble to silt sizes. Dispersal patterns and geotechnical properties of the till suggest deforming bed and basal gliding mechanisms of ice flow associated with ice‐streaming. Regional ice streams may have been ‘normative’ in carbonate terrain during the main Foxe (Wisconsin) Glaciation. Till plumes within regional dispersal trains, showing little dilution of carbonate down‐ice from bedrock sources, are oriented towards lowlands. These features, sharp‐edged and 300 mwide, mark zones of augmented flow. They are late‐glacial features that formed after calving bays developed in Committee Bay. The dimensions of the dispersal trains, and ice‐flow styles and mechanisms, are similar to those of modern Antarctic ice streams. The sharp edges of till plumes may delineate flow boundaries marked by lateral crevasse zones in the late‐glacial ice sheet. Secondary streams‐within‐ice streams have not been reported previously in the literature.

Carbonate dispersal trains, secondary till plumes, and ice streams in the west Foxe Sector, Laurentide Ice Sheet

Carbonate dispersal trains, secondary till plumes, and ice streams in the west Foxe Sector, Laurentide Ice Sheet

Blob instability in rotating compositional convection

The onset and structure of compositional convection in a rotating system are investigated experimentally. A vertically oriented cylindrical annulus filled with NH4Cl‐H2O solution is cooled from the bottom and can be rotated about its axis at rates ranging up to 10.5 rad s−1, corresponding to Ekman numbers down to 7.5 × 10−6. The Coriolis force has a strong effect on the structure of plumes above the mush‐liquid interface. Helical motion of the conduit, which is weakly developed in the non‐rotating case, is amplified by Coriolis forces that twist the plume conduits to lie nearly horizontally. This results in secondary plumes (or blobs) that rise from the sub‐horizontal primary plume conduits. This new instability could be an efficient mechanism for producing small‐scale flow in the form of buoyant blobs that ascend through the polar regions of the outer core.

Mesoscale structures in the transition zone: Dynamical consequences of boundary layer activities

Recent geophysical evidence from seismology, mineral physics, viscosity inversion shows that the mantle between 400 and 1000 km is extremely complicated, with intermediate scale structures present regionally as seismic reflectors under the 660 km discontinuity and bent plume-like structures under the transition zone. We have studied the dynamics of the transition zone with two models, an axisymmetric spherical-shell (2-D) model with a horizontally averaged temperature- and pressure-dependent viscosity and a 3-D Cartesian model with a depth-dependent viscosity. Two mantle phase transitions have been employed in both models. Results of the 2-D axisymmetric model show that the interaction of the lower mantle plumes with the transition zone can result in a horizontal channel flow right underneath the 660 km and in the birth of secondary plume some distance away from the lower mantle plume. The strength of the secondary plume increases in strength with larger viscosity contrast across the 660 km discontinuity. In the 3-D model we have found that with the presence of a second low viscosity zone somewhere between 660 and 1000 km, many secondary instabilities are developed in the second asthenosphere and the mesoscale thermal structure developed can become quite complex. Many small-scale plumes can emanate from the transition zone. Occasionally a very large plume burst, with a near-surface radius exceeding 1000 km, can develop from the hot lower-mantle material trapped in the second asthenosphere. Both the viscosity and the phase transition structure between 660 km and 1000 km can exert a significant influence on the plume distribution and cause singular plume eruption events in the upper mantle. Plume instabilities originating below the 660 km discontinuity in the western Pacific might have launched a large hot upwelling into the upper mantle, thus precipitating the massive flood basalt volcanism in the Ontong-Java region.

Dynamical effects of a temperature- and pressure-dependent lower-mantle rheology on the interaction of upwellings with the transition zone

We have examined the consequences of a temperature- and pressure-dependent lower-mantle viscosity on the interaction of upwellings with the two major phase transitions. The viscosity used is only temperature-dependent in the upper-mantle but assumes both temperature- and pressure dependences in the lower-mantle. The activation enthalpy increases with depth dependence scaled after experimental melting curves of lower-mantle components. We have employed a two-dimensional cartesian box with an aspect-ratio of five and a mantle layer thickness of 2900 km, using an extended Boussinesq model with a depth-dependent thermal expansivity. Latent heat release and viscous dissipation have been included in the temperature equation. We have considered models both without and with a viscosity jump (a factor of 8) across the 660 km boundary. The range of averaged Rayleigh numbers (Ra) considered lies between 2 × 10 6 and 10 7. A major effect of this temperature- and pressure-dependent rheology is the stabilization of the upwelling plumes and the increase of viscous heating in the bottom portion of these plumes. The impingement of these heated plumes at the endothermic phase boundary causes the development of secondary plumes to rise into the upper-mantle. Shear-heating together with the latent heat release produces large temperature increases in the plumes passing through the transition zone, which may cause melting in the deep upper-mantle. Although the average Rayleigh number in the case of temperature- and pressure-dependent viscosity is around a factor of 5 lower than in a case with purely temperature-dependent viscosity, the resulting flow is only slightly less layered, which is contrary to the earlier finding of Christensen and Yuen (1985). The tendencies for the development of secondary plumes and high temperatures inside the upwellings are enhanced by the viscosity jump at the 660 km boundary. In this situation few nearly steady, vigorous upwellings exist in the lower mantle, while in the upper mantle vigorous time-dependent convection takes place. For an averaged Rayleigh number of 10 7, the system becomes layered with many thin plumes appearing in the lower mantle.

Bombay gravity high and eruption of Deccan flood basalts (India) from a shallow secondary plume

The western margin of India, especially the area surrounding the gravity high of Bombay, is covered by a thick pile of Deccan flood basalts. The massive eruption is one of the largest continental volcanic events at the Cretaceous/Tertiary biological mass extinction boundary ( ∼ 65 Ma ago). The area is characterized by several hidden tectonic features, and their origin and evolution have remained controversial. In the search for magma source structure, attention was focused on an unusual oval-shaped positive gravity anomaly over the Bombay coastal zone. The gravity analysis indicates the presence of two subsurface structures at depths of 4.5 ± 0.5 km and 18 ± 2 km. These depths correspond to the top of the crustal basaltic layer and an upwarped Moho discontinuity, respectively. The positive gravity anomaly in three-dimensional analysis reveals a possible magma conduit structure and the near absence of the granitic layer. The unusually shallow Moho layer coincides with the region of a broad high heat flow anomaly (average heat flow more than 80 mW/m 2). The geophysical signatures from the neighborhood show that the asthenosphere has welled up considerably and is located at a depth of about 40 km. High heat flow and asthenospheric depth estimates suggest melting conditions at very shallow depths. It is suggested that the highly differentiated magma associated with the major eruptive phase of Deccan Traps did not originate at the D′' layer. It is hypothesized that magma was brought to the surface by a major secondary plume at a much shallower depth within the lithosphere and possibly at the crust-mantle boundary, as a consequence of subcrustal erosion and secondary melting caused by the extreme velocity of India during the late Cretaceous and early Tertiary. Substantial melting of the base of the lithosphere due to frictional heating might have resulted in the accumulation of a large quantity of magma below the thinned lithosphere at the pre-existing fracture zone near the continental margin. The presence of a magmatic conduit structure above the Moho, derived from the inversion of gravity data and other tectonic conditions, suggests a possible triggering of the magma reservoir by a large bolide impact ( ∼ 10 km diameter) at the Cretaceous/Tertiary boundary near Bombay.

Tectonic regime and major processes governing the chemistry of water and gas discharges from the rotorua geothermal field, New Zealand

The chemical composition of water and gas discharges clearly shows that the Rotorua geothermal system produces several types of fluids having travelled distinctly different paths. A plume of high Cl ( >1400 mg/kg ), high temperature ( >250°C) waters feeds a discharge area, possibly partly submerged in Lake Rotorua, in the east and centre of the field. A closely related secondary plume of slightly altered such waters supplies the Whakarewarewa thermal area. A third plume of lower temperature (≈ 220°C) and lower Cl (≈ 500 mg/kg) , but high HCO 3 waters, likely to have travelled underground more slowly or over longer distances, supplies the northern and western parts of the system. Cl, B, CO 2, N 2, Ar and He contents in the fluids encountered over the northern and western parts of the field resemble closely those produced from other geothermal systems along the western half of the Taupo Volcanic Zone, systems thought to be associated with extensional tectonics. Of all these “rift”-type discharges from the TVZ, those from the southern and eastern parts of the Rotorua geothermal field appear to represent fluids most directly derived from an environment dominated by basaltic magmatism.

Enhancement of fine-scale turbulence for improving fuel-rich plume combustion

A passive method to enhance fine-scale mixing was developed and studied in cold flows. Its effect on the combustion intensity and flame stability was then studied in reacting flows. Hot-wire anemometry was used to map the mean and turbulent flowfields of the nonreacting flows. Reacting flows were studied in a free flame and ducted gas-generator fuel-rich plume using planar laser-induced fluorescence imaging, a rake of thermocouples , and high-speed photography. A modified circular nozzle having several downstream-facing steps upstream of its exit was used to introduce numerous inflection points in the initial mean velocity profiles, thus producing multiple corresponding sources of fine-scale turbulence generators and reducing the strain rates in the initial region. Cold flow tests showed turbulence increases of up to six times the initial turbulence level relative to a circular nozzle and a substantial decrease of the mean velocity gradient. The flame of this nozzle was more intense with a homogeneous heat release in the free-flame experiments and ducted-plume combustion experiments, even when the gas-generator exhaust velocity was supersonic. Secondary plume ignition was obtained under conditions that prevented sustained afterburning using the circular nozzle.

The Effects of Biochemical Reactions on Investigations and Remediations

Bacteria and biological methods are having a large impact on the soils and groundwater areas. To truly understand a contaminated ground water, and the methods that must be used to clean it up, we must understand the environment in which the contamination occurs. Contaminants do not move through the soil and aquifer at the same rate that the water moves through the contaminated areas. Natural bacteria will degrade the organic compounds found in the soils and aquifer. Due to limitations caused by the lack of nutrients and oxygen, the reaction rate of this natural degradation is slow. The bacteria are present along with the organics in the contamination zone. The main design criteria is movement of the water to the zone, and control of the water after it passes through the zone so that it does not create a secondary plume. Bacteria have also been applied to remediation in aboveground reactors.

Changjiang river plume and suspended sediment transport in Hangzhou Bay

Hangzhou Bay is situated immediately south of the mouth of Changjiang, the fourth largest river in the world in both water and sediment discharge. Synoptic and anchor-station observations of hydrography and suspended sediment during July 1981, December 1982, and December 1983 have been used to describe the water and sediment discharge from Changjiang into Hangzhou Bay. A secondary Changjiang river plume is found to play an important role in both the circulation and sediment transport inside the bay. The plume front serves as a guide for sediment transport and it may be related to the rapid accretion at the south shore of Hangzhou Bay.

A point source of heat in a stable salinity gradient

When a salinity gradient is heated at a single point, a hot plume is formed with a series of layers around and above it in a ‘Christmas-tree’ flow pattern. Qualitative visual observations of the development of this system are reported. Three kinds of layers are observed: the first kind is formed above the basic plume from a hierarchy of secondary plumes on top of the basic one, the second develops around the upper part of the basic plume, and is driven by the same mechanism as the layers in sidewall-heating experiments, and the third, forming around the lower part of the basic plume, is of the same nature as the second type but also has something in common with double-diffusive intrusions. A characteristic feature for all the three kinds of layers is the existence of systematic shearing motions and vortices. Quantitative estimates for the plume height and the thickness of the layers are obtained.

Equatorial plasma bubbles: Vertically elongated wedges from the bottomside F layer

We address the question regarding the two‐dimensional shape of equatorial plasma bubbles in the plane transverse to the geomagnetic field. By comparing the east‐west spatial relationship of ion‐density depletions measured in‐situ by the Atmospheric Explorer E (AE‐E) satellite to backscatter plumes measured by the ALTAIR radar, we show that plasma bubbles are vertically elongated depletions that extend upward from the bottom side of the F layer, in the form of tilted wedges, rather than more isotropically shaped but isolated structures. The shape of plasma bubbles is inferred from (1) ion density depletions that exceeded 99% in the ‘neck’ regions of plumes and (2) the eastward drift velocities of the plumes. The expected electrodynamics of vertically elongated plasma bubbles are consistent with the observations of large eastward drift velocities of plumes that are comparable to F region plasma drift measurements made at Jicamarca and to F region neutral wind measurements made at Kwajalein. The results also reveal that the west wall of large‐scale altitude modulations of the bottomside F layer that produces the primary plumes and bubbles becomes structured, and evolves with the generation of secondary plumes and bubbles.