http://www.solid-earth.net/Solid Earth Latest Articlesenhttp://www.solid-earth.net/1/71/2010/<b>Candidates for multiple impact craters?: Popigai and Chicxulub as seen by the global high resolution gravitational field model EGM2008</b><br /><br />Solid Earth, 1, 71-83, 2010<br /><br />Author(s): J. Klokočník, J. Kostelecký, I. Pešek, P. Novák, C. A. Wagner, and J. Sebera<br /><br />In 2008 the new Earth Gravitational Model (EGM2008) was released. It contains a complete set of spherical harmonic coefficients of the Earth's gravitational potential (Stokes parameters) to degree 2190 and order 2159 and selected orders to degree 2190, that can be used for evaluation of various potential quantities with both the unprecedented accuracy and high spatial resolution. Two such quantities, the gravity anomaly and second-order radial derivative of the disturbing potential, were computed over selected areas with known impact craters. The displays of these derivatives for two such sites clearly show not only the strong circular-like features known to be associated with them but also other symmetrical structures which appear to make them multiple impact sites. At Popigai, Siberia, the series of circular features fall in a line from the "primary crater" in the southeast (SE) direction. At Chicxulub, Yucatán, there appears to be one more crater close to the "primary" in the northeast (NE) direction, as well as possibly others in the vicinity of the main crater (SW). Gravity information alone is not, however, proof of impact craters but it is useful in identifying <i>candidate sites</i> for further study, for examination by geologists and geophysicists. In the case of Chicxulub, a very recent single seismic profile suggests that a more likely explanation for the observed circular like gravity signal from EGM2008 NE of the "primary" is a pre-impact basin.Wed, 21 Jul 2010 00:00:00 +0200http://www.solid-earth.net/1/61/2010/<b>Rheological control on the dynamics of explosive activity in the 2000 summit eruption of Mt. Etna</b><br /><br />Solid Earth, 1, 61-69, 2010<br /><br />Author(s): D. Giordano, M. Polacci, P. Papale, and L. Caricchi<br /><br />In the period from January to June 2000 Mt. Etna exhibited an exceptional explosive activity characterized by a succession of 64 Strombolian and fire-fountaining episodes from the summit South-East Crater. Textural analysis of the eruptive products reveals that the magma associated with the Strombolian phases had a much larger crystal content (&gt;55 vol%) with respect to the magma discharged during the fire-fountain phases (~35 vol%). Rheological modelling shows that the crystal-rich magma falls in a region beyond a critical crystal content where small addition of solid particles causes an exponential increase of the effective magma viscosity. When implemented into the modeling of steady magma ascent dynamics (as assumed for the fire-fountain activity), a large crystal content as the one found for products of Strombolian eruption phases results in a one order of magnitude decrease of mass flow-rate, and in the onset of conditions where small heterogeneities in the solid fraction carried by the magma translate into highly unsteady eruption dynamics. We argue that crystallization on top of the magmatic column during the intermediate phases when magma was not discharged favoured conditions corresponding to Strombolian activity, with fire-fountain activity resuming after removal of the highly crystalline top. The numerical simulations also provide a consistent interpretation of the association between fire-fountain activity and emergence of lava flows from the crater flanks.Thu, 01 Jul 2010 00:00:00 +0200http://www.solid-earth.net/1/49/2010/<b>The stochastic quantization method and its application to the numerical simulation of volcanic conduit dynamics under random conditions</b><br /><br />Solid Earth, 1, 49-59, 2010<br /><br />Author(s): E. Peruzzo, M. Barsanti, F. Flandoli, and P. Papale<br /><br />Stochastic Quantization (SQ) is a method for the approximation of a continuous probability distribution with a discrete one. The proposal made in this paper is to apply this technique to reduce the number of numerical simulations for systems with uncertain inputs, when estimates of the output distribution are needed. This question is relevant in volcanology, where realistic simulations are very expensive and uncertainty is always present. We show the results of a benchmark test based on a one-dimensional steady model of magma flow in a volcanic conduit.Tue, 22 Jun 2010 00:00:00 +0200http://www.solid-earth.net/1/25/2010/<b>Particle size distributions by laser diffraction: sensitivity of granular matter strength to analytical operating procedures</b><br /><br />Solid Earth, 1, 25-48, 2010<br /><br />Author(s): F. Storti and F. Balsamo<br /><br />We tested laser diffraction particle size analysis in poorly coherent carbonate platform cataclastic breccias and unfaulted quartz-rich eolian sands, representing low- and high-strength granular materials, respectively. We used two different instruments with different sample dispersion and pumping systems and several wet analytical procedures that included different pump speeds, measurement precision tests with and without sample ultrasonication, and different dispersant liquids. Results of our work indicate that high strength material is not strongly affected by analytical operating procedures, whereas low strength materials are very sensitive to the pump speed, ultrasonication intensity, and measurement run time. To reduce such a data variability, we propose a workflow of analytical tests preliminary to the set up of the most appropriate SOP.Mon, 19 Apr 2010 00:00:00 +0200http://www.solid-earth.net/1/5/2010/<b>Earth's surface heat flux</b><br /><br />Solid Earth, 1, 5-24, 2010<br /><br />Author(s): J. H. Davies and D. R. Davies<br /><br />We present a revised estimate of Earth's surface heat flux that is based upon a heat flow data-set with 38 347 measurements, which is 55% more than used in previous estimates. Our methodology, like others, accounts for hydrothermal circulation in young oceanic crust by utilising a half-space cooling approximation. For the rest of Earth's surface, we estimate the average heat flow for different geologic domains as defined by global digital geology maps; and then produce the global estimate by multiplying it by the total global area of that geologic domain. The averaging is done on a polygon set which results from an intersection of a 1 degree equal area grid with the original geology polygons; this minimises the adverse influence of clustering. These operations and estimates are derived accurately using methodologies from Geographical Information Science. We consider the virtually un-sampled Antarctica separately and also make a small correction for hot-spots in young oceanic lithosphere. A range of analyses is presented. These, combined with statistical estimates of the error, provide a measure of robustness. Our final preferred estimate is 47&plusmn;2 TW, which is greater than previous estimates.Mon, 22 Feb 2010 00:00:00 +0100http://www.solid-earth.net/1/1/2010/<b>The Eons of Chaos and Hades</b><br /><br />Solid Earth, 1, 1-3, 2010<br /><br />Author(s): C. Goldblatt, K. J. Zahnle, N. H. Sleep, and E. G. Nisbet<br /><br />We propose the <i>Chaotian Eon</i> to demarcate geologic time from the origin of the Solar System to the Moon-forming impact on Earth. This separates the solar system wide processes of planet formation from the subsequent divergent evolution of the inner planets. We further propose the division of the Hadean Eon into eras and periods and naming the proto-Earth <i>Tellus</i>.Tue, 02 Feb 2010 00:00:00 +0100