A review of solar type Ⅲ radio bursts

Solar type Ⅲ radio bursts are an important diagnostic tool in the understanding of solar accelerated electron beams. They are a signature of propagating beams of nonthermal electrons in the solar atmosphere and the solar system. Consequently, they provide information on electron acceleration and transport, and the conditions of the background ambient plasma they travel through. We review the observational properties of type Ⅲ bursts with an emphasis on recent results and how each property can help identify attributes of electron beams and the ambient background plasma. We also review some of the theoretical aspects of type Ⅲ radio bursts and cover a number of numerical efforts that simulate electron beam transport through the solar corona and the heliosphere.     

Debris-flow simulations on Cheekye River, British Columbia

Cheekye River fan is the best-studied fan complex in Canada. The desire to develop portions of the fan with urban housing triggered a series of studies to estimate debris-flow risk to future residents. A recent study (Jakob and Friele 2010) provided debris-flow frequency-volume and frequency-discharge data, spanning 20-year to 10,000-year return periods that form the basis for modeling of debris flows on Cheekye River. The numerical computer model FLO-2D was chosen as a modelling tool to predict likely flow paths and to estimate debris-flow intensities for a spectrum of debris-flow return periods. The model is calibrated with the so-called Garbage Dump debris flow that occurred some 900  years ago. Field evidence suggests that the Garbage Dump debris flow has a viscous flow phase that deposited a steep-sided debris plug high in organics in centre fan, which then deflected a low-viscosity afterflow that travelled to Squamish River with slowly diminishing flow depths. The realization of a two-phase flow led to a modelling approach in which the debris-flow hydrograph was split into a high viscosity and low viscosity phase that were modelled in chronologic sequence as two separate and independent modelling runs. A perfect simulation of the Garbage Dump debris flow with modelling is not possible because the exact topography at the time of the event is, to some degree, speculative. However, runout distance, debris deposition and deposit thickness are well known and serve as a good basis for calibration. Predictive analyses using the calibrated model parameters suggest that, under existing conditions, debris flows exceeding a 50-year return period are likely to avulse onto the southern fan sector, thereby damaging existing development and infrastructure. Debris flows of several thousand years return period would inundate large portions of the fan, sever Highway 99, CN Rail, and the Squamish Valley road and would impact existing housing development on the fan. These observations suggest a need for debris-flow mitigation for existing and future development alike.     

Relationships between mesoscale morphological units, stream hydraulics and Chinook salmon (Oncorhynchus tshawytscha) spawning habitat on the Lower Yuba River, California

An expert-based approach was used to identify 10 morphological unit types within a reach of the gravel bed, regulated Yuba River, California, that is heavily utilized by spawning Chinook salmon (Oncorhynchus tshawytscha). Analysis of these units was carried out using two-dimensional hydrodynamic modeling, field-based geomorphic assessment, and detailed spawning surveying. Differently classified morphological units tended to exhibit discrete hydraulic signatures. In most cases, the Froude number adequately differentiated morphological units, but joint depth–velocity distributions proved the most effective hydraulic classification approach. Spawning activity was statistically differentiated at the mesoscale of the morphological unit. Salmon preferred lateral bar, riffle, and riffle entrance units. These units had moderately high velocity (unit median > 0.45 m s^− 1) and low depth (unit median < 0.6 m), but each exhibited a unique joint depth–velocity distribution. A large proportion of redds (79%) were associated with conditions of convective flow acceleration at riffle and riffle entrance locations. In addition to reflecting microhabitat requirements of fish, it was proposed that the hydraulic segregation of preferred from avoided or tolerated morphological units was linked to the mutual association of specific hydraulic conditions with suitable caliber sediment that promotes the provision and maintenance of spawning habitat.     

A hydroclimatic threshold for landslide initiation on the North Shore Mountains of Vancouver, British Columbia

Landslides triggered by rainfall are the cause of thousands of deaths worldwide every year. One possible approach to limit the socioeconomic consequences of such events is the development of climatic thresholds for landslide initiation. In this paper, we propose a method that incorporates antecedent rainfall and streamflow data to develop a landslide initiation threshold for the North Shore Mountains of Vancouver, British Columbia. Hydroclimatic data were gathered for 18 storms that triggered landslides and 18 storms that did not. Discriminant function analysis separated the landslide-triggering storms from those storms that did not trigger landslides and selected the most meaningful variables that allow this separation. Discriminant functions were also developed for the landslide-triggering and nonlandslide-triggering storms. The difference of the discriminant scores, ΔCS, for both groups is a measure of landslide susceptibility during a storm. The variables identified that optimize the separation of the two storm groups are 4-week rainfall prior to a significant storm, 6-h rainfall during a storm, and the number of hours 1 m³/s discharge was exceeded at Mackay Creek during a storm. Three thresholds were identified. The Landslide Warning Threshold (LWT) is reached when ΔCS is −1. The Conditional Landslide Initiation Threshold (CTL_I) is reached when ΔCS is zero, and it implies that landslides are likely if 4 mm/h rainfall intensity is exceeded at which point the Imminent Landslide Initiation Threshold (ITL_I) is reached. The LWT allows time for the issuance of a landslide advisory and to move personnel out of hazardous areas. The methodology proposed in this paper can be transferred to other regions worldwide where type and quality of data are appropriate for this type of analysis.     

Photogrammetric and laser altimetric reconstruction of water levels for extreme flood event analysis

This paper assesses the feasibility of estimating water levels using digital photogrammetry. A common problem during an extreme flood event is that automated water level recorders do not record the highest water levels, as a result of instrument malfunctioning. This paper explores two possible solutions to this problem based upon data acquired using synoptic remote sensing methods. The first method requires: (a) high-resolution elevation data (for example, in the form of a digital elevation model for the floodplain); and (b) information on the planimetric position of the maximum flood extent, such as from debris lines (known as wrack lines) visible on aerial imagery flown after the event. The planimetric data can then be used to segment the topographic data in order to identify water level elevations. The second method uses a digitial photogrammetric approach and is suitable where no topographic data are available, but aerial imagery is available, flown after the event. Provided this imagery is of the right scale, digital photogrammetric analysis may be used to identify the elevations of wrack lines visible on the imagery. In this paper, the second of these options is compared with the first. The research shows that desktop photogrammetric methods, using 1:4500 scale imagery, can yield water level estimates that are precise to ±0·147 m, on the basis of check data obtained from lidar data. This is a worst possible estimate of the acquired precision given uncertainties in the lidar data. When compared with the first option, based upon segmenting lidar data using flood outlines, the photogrammetric approach was found to be preferable given both the quality of the lidar and uncertainties over how to segment it.     

Commingling and mixing of S-type peraluminous, ultrapotassic and basaltic magmas in the Cayconi volcanic field, Cordillera de Carabaya, SE Peru

The Cayconi district of the Cordillera de Carabaya, SE Peru, exposes a remnant of an upper Oligocene–Lower Miocene (22.2–24.4 Ma) volcanic field, comprising a diverse assemblage of S-type silicic and calc-alkaline basaltic to andesitic flows, members of the Picotani Group of the Central Andean Inner Arc. Basaltic flows containing olivine, plagioclase, clinopyroxene, ilmenite and glass, and glassy rhyolitic agglutinates with phenocrystic quartz, cordierite, plagioclase, sanidine, ilmenite and apatite, respectively exhibit mineralogical and geochemical features characteristic of medium-K mafic and Lachlan S-type silicic lavas. Cordierite-bearing dacitic agglomerates and lavas, however, are characterized by dispersed, melanocratic micro-enclaves and phenocrysts set in a fine-grained quartzo-feldspathic matrix. They contain a bimodal mica population, comprising phlogopite and biotite, as well as complexly zoned, sieve-textured plagioclase grains, sector-zoned cordierite, sanidine, quartz, irregular patches of replaced olivine, clinopyroxene and orthopyroxene and accessory phases including zircon, monazite, ilmenite and chromite. The coexistence of minerals not in mutual equilibrium and the growth/dissolution textures exhibited by plagioclase are features indicative of magmatic commingling and mixing. Trachytic-textured andesite flows interlayered with olivine+plagioclase–glomerophyric, calc-alkaline basalts have a phenocrystic assemblage of resorbed orthopyroxene and plagioclase and exhibit melanocratic groundmass patches of microphenocrystic phlogopite, Ca-rich sanidine, ilmenite and aluminous spinel. The mineralogical and mineral chemical relationships in both the dacites and the trachytic-textured andesites imply subvolcanic mixing between distinct ultrapotassic mafic melts, not represented by exposed rock types, and both the S-type silicic and calc-alkaline mafic magmas. Such mixing relationships are commonly observed in the Oligo-Miocene rocks of the Cordillera de Carabaya, suggesting that the S-type rocks in this area and, by extension, elsewhere derive their unusually high K₂O, Ba, Sr, Cr and Ni concentrations from commingling and mixing with diverse, mantle-derived potassic mafic magmas.     

Provenance of long‐travelled dust determined with ultra‐trace‐element composition: a pilot study with samples from New Zealand glaciers

We report high‐precision inductively coupled plasma mass spectrometric (ICP‐MS) compositional data for 39 trace elements in a variety of dust deposits, trapped sediments and surface samples from New Zealand and Australia. Dusts collected from the surface of alpine glaciers in the Southern Alps, New Zealand, believed to have undergone long‐distance atmospheric transport from Australia, are recognizable on account of their overabundances of Pb and Cu with respect to typical upper crustal values. Long‐travelled dust from Australia therefore scavenges these and other metals (e.g. Zn, Sb and Cd) from the atmosphere during transport and deposition. Hence, due to anthropogenic pollution, long‐travelled Australian dusts can be recognized by elevated metal contents. The relative abundance of 25 other elements that are not affected by atmospheric pollution, mineral sorting (Zr and Hf) and weathering[sol ]solubility (alkali and earth alkali elements) reflects the geochemistry of the dust source sediment. As a result, we are able to establish the provenance of dust using ultra‐trace‐element chemistry at regional scale. Comparison of long‐travelled dust chemistry with potential Australian sources shows that fits of variable quality are obtained. We propose that the best fitting potential source chemistry most likely represents the major dust source area. A binary mixing model is used to demonstrate that admixture of small quantities of local dust provides an even better fitting dust chemistry for the long‐travelled dusts. Copyright © 2005 John Wiley & Sons, Ltd.     

Identifying regional dust transport pathways: ­application of kinematic trajectory modelling to a trans‐Tasman case

A kinematic trajectory model is used to investigate potential pathways of dust transport from Australia to New Zealand. Historically, these have been assumed to follow rather direct west–east trajectories spanning 2 to 3 days, often resulting in red snow events in the Southern Alps of New Zealand. However, results from the present study which examined the route taken by air parcels originating in southern Australia during dust storms on 24 and 25 May 1994, indicate that trans‐Tasman dust transport trajectories are more diverse than previously thought, and display considerable variation during single events. These more divergent pathways tie in more closely with aeolian dust sedimentation patterns identified by ocean coring in the Tasman Sea, and may account for the deposition of Australian dust on sub‐Antarctic islands located well south of the Australian continent. Copyright © 2000 John Wiley & Sons, Ltd.     

Gardening at the edge: Documenting the limits of tropical Polynesian kumara horticulture in southern New Zealand

An Erratum has been published for this article in Geoarchaeology 19(6) 2004, 613. Kumara (Ipomoea batatus), a major food source for Maori, was brought to New Zealand from tropical Eastern Polynesia ∼700 years ago. Maori successfully adapted their cultivation techniques to grow kumara in New Zealand's cooler, seasonal climate, although most kumara cultivation was limited to the warmer North Island, with cultivation becoming more marginal southward. Banks Peninsula area is considered to be the southernmost limit for kumara gardening. The Okuora Farm archeological site on the southern side of Banks Peninsula has five pits that appear to be of the raised‐rim type used for over winter storage of kumara tubers. We conducted a preliminary investigation into the nature of the pits and surrounding 1 km² area using nondestructive techniques in accordance with Maori designation of food storage sites as tapu. Ground penetrating radar (GPR) investigation of two of the pits revealed subsurface disturbances consistent with postholes and drains, typical of raised rim kumara storage pits. Soil modification typical of kumara gardening was identified on a 1 ha area on a warm north‐northwest facing hillside. Several large borrow pits were identified as the likely source of the gravel added to the modified soil, possibly to retain heat and moisture. A plant phytolith study of soil samples identified several that appear to be from kumara. The combination of results strongly suggests this site was one of the southernmost Maori kumara gardening sites yet identified in New Zealand. © 2004 Wiley Periodicals, Inc.     

Interactions between aquatic vegetation,hydraulics and fine sediment: A case study in the Halswell River,New Zealand

This paper contributes a field study of suspended sediment transport through aquatic vegetation. The study was run over a 3 month period which was selected to coincide with scheduled weed cutting activities. This provided the opportunity to obtain data points with no vegetation cover, as well as to investigate the effects of weed cutting on Suspended Sediment Concentrations (SSC), particle size distributions and river hydraulics. Aquatic vegetation cover was quantified through remote sensing with Unmanned Aerial Vehicles and biomass estimated from ground truth sampling. SSC was highly dependent on aquatic vegetation abundance, and the distance upstream that had been cleared of aquatic vegetation. The data indicates that fine sediment was being trapped and stored by aquatic vegetation, then likely remobilised after vegetation removal. Investigation of suspended sediment spatial dynamics illustrated changes in particle size distribution due to preferential settling of coarse particles within aquatic vegetation, for example D50 decreased from 36.08 μm to 15.64 μm after suspended sediment travelled 304.2 m downstream and passed ~3700 kg of aquatic vegetation biomass. Hydraulic resistance in the study reach (parameterized by Manning's n) dropped by over 70% following vegetation cutting. Prior to cutting hydraulic resistance was discharge dependent (likely due to vegetation pronating at higher flows), while post cutting hydraulic resistance was approximately invariant of discharge. Aerial surveying captured interesting changes in aquatic vegetation cover prior to vegetation cutting, where some very dense regions of aquatic vegetation were naturally removed (without any high flow events) leaving behind unvegetated riverbed and fine sediment. The weed cutting boat had a lower impact on SSC than was originally expected, which indicates that it may offer a less damaging solution to aquatic vegetation removal in rivers than some other approaches such as mechanical excavation. This paper contributes valuable field data (which are generally scarce) on the research topic of flow-vegetation-sediment interactions, to supplement laboratory and numerical studies.