Formation and failure of volcanic debris dams in the Chakachatna River valley associated with eruptions of the Spurr volcanic complex, Alaska

The formation of lahars and a debris avalanche during Holocene eruptions of the Spurr volcanic complex in south-central Alaska have led to the development of volcanic debris dams in the Chakachatna River valley. Debris dams composed of lahar and debris-avalanche deposits formed at least five times in the last 8000–10,000 years and most recently during eruptions of Crater Peak vent in 1953 and 1992. Water impounded by a large debris avalanche of early Holocene (?) age may have destabilized an upstream glacier-dammed lake causing a catastrophic flood on the Chakachatna River. A large alluvial fan just downstream of the debris-avalanche deposit is strewn with boulders and blocks and is probably the deposit generated by this flood. Application of a physically based dam-break model yields estimates of peak discharge (Q_p) attained during failure of the debris-avalanche dam in the range 10⁴<Q_p<10⁶ m³ s⁻¹ for plausible breach erosion rates of 10–100 m h⁻¹. Smaller, short-lived, lahar dams that formed during historical eruptions in 1953, and 1992, impounded smaller lakes in the upper Chakachatna River valley and peak flows attained during failure of these volcanic debris dams were in the range 10³<Q_p<10⁴ m³ s⁻¹ for plausible breach erosion rates.Volcanic debris dams have formed at other volcanoes in the Cook Inlet region, Aleutian arc, and Wrangell Mountains but apparently did not fail rapidly or result in large or catastrophic outflows. Steep valley topography and frequent eruptions at volcanoes in this region make for significant hazards associated with the formation and failure of volcanic debris dams.     

Martian rampart crater ejecta: Experiments and analysis of melt-water interaction

Viking images of Martian craters with rampart-bordered ejecta deposits reveal distinct impact ejecta morphology when compared to that associated with similar-sized craters on the Moon and Mercury. Topographic control of distribution, lobate and terraced margins, cross-cutting relationships, and multiple stratigraphic units are evidence for ejecta emplacement by surface flowage. It is suggested that target water explosively vaporized during impact alters initial ballistic trajectories of ejecta and produces surging flow emplacement. The dispersal of particulates during a series of controlled steam explosions generated by interaction of a thermite melt with water has been experimentally modeled. Preliminary results indicate that the mass ratio of water to melt and confining pressure control the degree of melt fragmentation (ejecta particle size) and the energy and mode of melt-ejecta dispersal. Study of terrestrial, lobate, volcanic ejecta produced by steam-blast explosions reveals that particle size and vapor to clast volume ratio are primary parameters characterizing the emplacement mechanism and deposit morphology. Martian crater ramparts are formed when ejecta surges lose fluidizing vapors and transported particles are deposited en masse. This deposition results from flow yield strength increasing above shear stress due to interparticle friction.     

The Spins of Astrophysical Systems and Extended Gravitational Theory

Recent data on the Tully–Fisher relation for spiral galaxies are compatible with the traditional correlation for astrophysical systems, where the angular momentum varies as the square of the mass. Such a correlation is consistent with standard gravitational theory, but is not explained by it. We here show that the noted relation follows from currently popular accounts of extended or higher-dimensional gravitational theory. The latter also predicts that the spins of spirals should decay as the universe expands, which can be tested by extending the Tully–Fisher data to higher redshifts.     

Artificial light at night: implications for early life stages development in four temperate freshwater fish species

Flora and fauna have both evolved under a natural cycle of light and dark. But especially in urban areas, the night is now increasingly disturbed by artificial light. Many traits and behaviours in fish are triggered by a circadian clock, for example hatching and swim bladder inflation, which predominantly take place at dusk or night. As lighting becomes brighter and extends farther into rural areas, the distinction between day and night becomes increasingly blurred. Therefore, the loss of diurnal trigger by artificial light at night was hypothesized having deleterious effects on these traits and impact fish reproduction. To assess these effects, eggs of four native freshwater fishes, Eurasian perch Perca fluviatilis, roach Rutilus rutilus, bleak Alburnus alburnus and chub Leuciscus cephalus, were incubated under two different light conditions: a photoperiod of 14 h light:10 h darkness (LD) and continuous illumination (LL). The time to hatch and swim bladder inflation was recorded. The species showed inconsistent reactions to the light treatments. In roach and bleak, the time to 50% hatch was longer in LL, whereas continuous lighting had an accelerating effect in chub. Incubation in LL elongated the hatching period in perch and roach and, in perch, the onset of darkness seemed to trigger hatching. The swim bladder inflation was significantly promoted by continuous light in chub and bleak but was not affected in roach. In conclusion, nocturnal artificial illumination could have an effect on hatching and initial swim bladder filling by masking the day–night-change and thereby diminish the trigger effect. However, the reactions were species specific and the increase in variation indicated a lack of diurnal triggering, whilst a general deleterious effect of artificial light at night has not been identified on early life stages.     

Meridional transport of sensible heat in contrasting monsoon activity: Spherical harmonic analysis

Spherical harmonic analysis is made of the grid point values of geopotential heights at 700 mb and 300 mb levels for the months April to August for the years 1967 and 1972. The year 1967 is a good monsoon year and 1972 is a bad monsoon year in India. Meridional transport of sensible heat is obtained in wave number domain using spherical harmonic coefficients at 500 mb level form=1 to 10 andn–m=0 to 10, wherem represents the wave number round the globe andn–m gives the numbers of zero points from north pole to south pole excluding the poles themselves.Large northward transports of sensible heat in the month of May and in the monsoon months at the subtropics are characteristic of bad monsoon. Wave 1 transports sensible heat southward (forn–m=0) and wave 2 transports sensible heat northward (forn–m=4). Strengthening of wave 1 is conducive to good monsoon year and strengthening of wave 2 is conducive to bad monsoon year. These are the same features obtained in Fourier analysis. The contrasting features exist in waves 1 and 2 both in good and in bad monsoon and are better defined in the present analysis than in the Fourier analysis of the earlier study. However, waves 1 and 2 reveal clearer contrast in the present analysis than in the Fourier analysis. Bad monsoon activity is associated with large divergence of heart at subtropics and large convergence of heat at extra tropics.     

土地利用变化空间模拟的进展--CLUE-S模型及其应用

土地利用变化的空间模拟是进行土地利用情景分析的重要基础。本文在介绍了国际上常用的细胞自控模型(CA)、土地利用变化及效应模型(CLUE)的基础上,重点分析了小尺度土地利用变化及效应模型(CLUE-S)的方法,并以邯郸地区为例进行了案例研究。认为CLUE-S模型采取经验模型的方法,通过建立土地利用空间分配和驱动因子之间的统计关系模拟近期土地利用变化的情景。同时也考虑了不同土地利用方式之间的竞争关系,因此可以较好地模拟小尺度地区的近期土地利用变化情景;考虑到短期或近期土地利用变化的因子主要与人类的社会经济活动有关,而社会经济因子的空间化尚存在一定难度。因此,突破这一瓶颈成为CLUE-S模型发展和应用的关键;CLUE-S模型主要解决的是不同空间尺度上的土地利用空间分配问题,在土地生产潜力评价、土地利用规划等方面具有广阔的应用前景。     

Measurements of radio noise at 0.700 mc and 2.200 mc from a high-altitude rocket probe

Radio noise observations at frequencies of 0·700 Mc and 2·200 Mc were made at altitudes between 3000 and 11,000 km from a Blue Scout Jr. high-altitude rocket probe on 30 July 1963. A steady background flux of (7·5₋₃⁺⁶) × 10⁻¹⁹ W m⁻²)(c/s)⁻¹ at 0·700 Mc and (1·8^+1.0_−0.5 × 10⁻¹⁹ W m⁻² (c/s)⁻¹ at 2·200 Mc was observed. Assuming a galactic origin of the observed fluxes at both frequencies, the averaged sky brightnesses are b(0·700 Mc) = (6₋₃⁺⁵) × 10⁻²⁰ W m⁻² (c/s)⁻¹ sr⁻¹b(2·200 Mc) = (1.4^+1.0_−0.5 × 10⁻²⁰ W m⁻² (c/s)⁻¹ sr⁻¹ The observed brightness at 2·200 Mc is in reasonable agreement with the results of other observers. The apparent brightness at 0·700 Mc is, however, greater than was expected from previous observations. An alternative source of the 0·700 Mc flux in the terrestrial exosphere, as well as characteristics of several noise bursts observed during the flight, is briefly discussed.