Fan Zone Research Articles

Morphology and facies of the alluvial-fan sedimentation in the Kangra Valley, Himachal Himalaya

A number of alluvial fans, having an average width (E-W) of 10–15 km and length (N-S) of 8–15 km, have been mapped using the LANDSAT TM imageries on 1:250,000 scale in the Kangra Valley of Himachal Himalaya. This important geomorphic zone of alluvial fans is confined between the foot of the Dhauladhar Range and the Siwalik ridges. These fans are gently sloping from north to south and are slightly dissected having distinct horizons of glacial, glacio-fluvial, fluvial, lacustrine and loessic sediments derived from the Dhauladhar granitic complex, Dharamsala and Siwalik Formations during the glacial and interglacial climatic stages of the Quaternary period. The vertical lithological profiles of these fans show a dominance of gravelly (nearly 60%) facies along with other lithofacies associations representing a braided-river depositional environment. In general, the thickness of fan sediments ranges between 90 and 120 m. The vertical facies are subdivided into three main facies, i.e. lower-, middle- and upper-fan facies, showing distinct sediment characteristics. The presence of glacial moraines and clay-rich debris-flow deposits is significant in the upper-fan facies. The middle-fan facies is gravel-dominated along with some interbedded sandy channel-fill deposits, whereas the lower-fan facies is composed of sand, silt and mud. The genesis of these three fan facies is closely related with the uplift of the source area and climatic changes during the Pleistocene period.

Aeolian morpho_logy preserved by lava cover, the Precambrian Mussartut Member, Eriksfjord Formation, South Greenland

Investigations of sedimentary deposits in elastic interval 5 of the Mussartilt Member have revealed the occurrence of aeolian sandstones. The aeolian deposits rest on pebbly sandstones and conglomerates of fluvial origin, and the are sharply overlain by a c. 70 m thick lava flow. The aeolian sandstones comprise up to 10 m thick and 200 m wide dome-shaped bodies that are initiated by thin and patchily preserved aeolian sand sheet deposits. The bulk of the aeolian sandstone bodies constitute low-medium-angle, dipping lee-side deposits of dome-shaped dunes. The dome-shaped dunes migrated towards a zone of distal alluvial fans perhaps during the influence of prevailing NE trade winds. Superimposed smaller-scale dunes formed during periodic strong winds from the E. Erosion of the dunes at the base of the lava flow was insignificant and most of the original dome-shape form of the dunes seems to have been preserved. The dome-shaped dunes may represent part of a migrating erg system, but continued dune migration was stopped by extrusion of the lava flow.

Ductile-to-brittle transition of rubber-modified polypropylene

The deformation behaviour of blends of polypropylene (PP) with ethylene-propylene rubber was studied as a function of temperature and composition under tension. The damage ahead of the deliberately introduced defect was traced quantitatively as a function of external load with the aid of intensity analysis. In unmodified PP or in rubber-modified blends, no stable crack growth was obtained up to 99% of the maximum stress. However, a hierarchy of failure events was observed. First, there was a gradual occurrence of a fan-shaped damage zone. Then an intense damage zone initiated. Finally, a slow tearing mode of crack growth occurred at the maximum stress and the sample failed. The size and shape of the damage zone were influenced by temperature, composition and the artificially introduced stress-raiser. Voids were dominant in the fan zone with some crazes close to the intense damage zone. In the intense damage zone, the crazes coalesced to form a network of deformation bands. The description of the fan zone was achieved by a non-linear or elastoplastic failure approach, analogous to the Hilton-Hutchinson formalism, and the analysis of the intense zone by a critical stress instability criterion. There was also a fair correlation with the Dugdale model for the growth of a wedge-like intense damage zone in the specific case of unmodified PP at −40° C.

Distribution and mobility of selenium and other trace elements in shallow groundwater of the western San Joaquin Valley, California

Samples of shallow groundwater that underlies much of the irrigated area in the western San Joaquin Valley of California were analyzed for various major ions and trace elements, including selenium. Concentrations of the major ions generally were similar for groundwater collected in the two primary geologic zones - the alluvial fan and basin trough. Most of the variance in concentrations of major ions, as determined by principal components analysis, was associated with groundwater salinity and the dominant ions - magnesium, sodium, sulfate, and chloride. Most of the variance in trace elements was associated with concentrations of boron, molybdenum, selenium, and vanadium, which are present as mobile oxyanions. The concentrations of oxyanions trace elements were significantly correlated with groundwater salinity, but the correlations between selenium and salinity and molybdenum and salinity were significantly difference in the alluvial fan geologic zone compared with the basin-trough geologic zone. In addition, selenium concentrations are significant higher in the groundwater of the alluvial fan zone than in the basin-trough zone. The Evidence suggests that the main factors influencing selenium concentrations in the shallow groundwater are the degree of groundwater salinity and geologic source of the alluvial soil material. 31 refs., 5 figs., 3 tabs.

Frost protection in orchards using air from the temperature inversion layer

A new type of wind machine comprising a 21-ft. diameter, low-speed, vertical-axis fan is described, and its efficacy in raising the air temperature in orchards and in protecting citrus and deciduous trees from frost damage is discussed. The fan was shown to be effective in raising the temperature in the orchard, the amount being governed by the strength of temperature inversion. The actual range of effect of the fan was found to be inversely related to the rise in temperature at the centre of the fan's zone of influence. The extent of a rise in temperature equivalent to 25 per cent. of that under the fan varied from 1 to 1½ acres in citrus and from 2 to 8 acres in almonds, depending on the strength of the inversion. The range in citrus was considerably increased by skirting the trees. It was shown that under exceptionally severe frost conditions the area in which actual frost damage to the fruit and trees was reduced by the fan was very small, and because of this the fan in its present form is not considered an economic means of frost protection. The theoretical basis for the formation of temperature inversion is considered and data showing the types of temperature inversion recorded at Griffith, N.S.W., are presented and discussed.