SOFTWARE REVIEWS

Electromap World Atlas , Version 1.1. Interactive Population Statistical System , Version 1.0. Jerry W. Wicks and Jose Luiz Pereira de Almeida MATHCAD , Version 2.5. Memory Mate. Micro DEM +, Version 5.21. Peter Guth NCSS – Number Cruncher Statistical System , Version 5.02. Dr. Jerry L. Hintze     

Spatial Statistics Of Windflow And Blowing-Snow Fluxes Over Complex Topography

A linear theory is used to model windflow over a tundra landscape, taken as an example of complex topography. The autocorrelation between gradients at different points in this landscape has an exponential dependence on separation, characterized by a correlation length. Areal variances of simulated windspeeds are proportional to the variance of the topographic gradient. Simulations with synthetic topographies having the same correlation structure show that the constants of proportionality in these relationships depend on the correlation length. Statistics of snow sublimation and transport calculated using simulated windspeed distributions in a distributed blowing-snow model are found to be in good agreement for real and synthetic topographies.     

Effective elastic thickness of island arc lithosphere under Japan

Abstract Using topography and observed gravity anomalies, we have estimated the effective elastic thickness as a measure of strength of Japanese island arc lithosphere. The thickness is found to range from about 3 km to >20 km. The thickness seems to be controlled primarily by the thermal state of the lithosphere. The higher the heat flow, the thinner is the elastic plate. However, several areas show significant deviations. The smaller effective elastic thickness in the northern Ryukyu arc than that inferred from heat flow may be attributed to the stress regime. In Japan, extensional tectonics are going on only in the Ryukyu arc region. Shallow subducting slab under the south-western Japan frontal arc probably increases the effective thickness by several kilometers. The determined effective elastic thickness suggests that when we consider vertical movements in the volcanic arc, we should take account of topographic and subsurface loading over a few hundred kilometers. However, if the dip of the slab is shallow, the flexural responses of the underlying slab, not only that of the island arc lithosphere, should be taken into account for the compensation, as is the case of the south-western Japan frontal arc.     

Constraints on the dynamics of mantle plumes from uplift of the Hawaiian Islands

The ∼0.2 mm/yr uplift of Hawaiian islands Lanai and Molokai and Hawaiian swell topography pose important constraints on the structure and dynamics of mantle plumes. We have formulated 3-D models of mantle convection to investigate the effects of plume-plate interactions on surface vertical motions and swell topography. In our models, the controlling parameters are plume radius, excess plume temperature, and upper mantle viscosity. We have found that swell height and swell width constraints limit the radius of the Hawaiian plume to be smaller than 70 km. The additional constraint from the uplift at Lanai requires excess plume temperature to be greater than 400 K. If excess plume temperature is 400 K, models with plume radius between 50 and 70 km and upper mantle viscosity between 10²⁰ and 3×10²⁰ Pa s satisfy all the constraints. Our results indicate that mantle plume in the upper mantle may be significantly hotter than previously suggested. This has important implications for mantle convection and mantle melting. In addition to constraining plume dynamics, our models also provide a mechanism to produce the observed uplift at Lanai and Molokai that has never been satisfactorily explained before.