Cataclysmic Late pleistocene flooding from glacial Lake Missoula: A review

Late Wisconsin floods from glacial Lake Missoula occurred between approximately 16 and 12 ka BP. Many floods occurred; some were demonstrably cataclysmic. Early studies of Missoula flooding centered on the anomalous physiography of the Channeled Scabland, which J. Harlen Bretz hypothesized in 1923 to have developed during a debacle that he named ‘The Spokane Flood’. Among the ironies in the controversy over this hypothesis was a mistaken view of uniformitarianism held by Bretz's adversaries. After resolution of the scabland's origin by cataclysmic outburst flooding from glacial Lake Missoula, research since 1960 emphasized details of flood magnitudes, frequency, routing and number.Studies of flood hydraulics and other physical parameters need to utilize modern computerized procedures for flow modeling, lake-burst simulation, and sediment-transport analysis. Preliminary simulation models indicate the probability of multiple Late Wisconsin jökulhlaups from Lake Missoula, although these models predict a wide range of flood magnitudes.Major advances have been made in the study of low-energy, rhythmically bedded sediments that accumulated in flood slack-water areas. The ‘forty floods’ hypothesis postulates that each rhythmite represents the deposition in such slack-water areas of separate, distinct cataclysmic floods that can be traced from Lake Missoula to the vicinity of Portland, Oregon. However, the hypothesis has numerous unsubstantiated implications concerning flood magnitudes, sources, routing and sedimentation dynamics.There were multiple great Late Wisconsin floods in the Columbia River system of the northwestern United States. Studies of high-energy, high altitude flood deposits are necessary to evaluate the magnitudes of these floods. Improved geochronologic studies throughout the immense region impacted by the flooding will be required to properly evaluate flood frequency. The cataclysmic flood concept championed by J. Harlen Bretz continues to stimulate exciting and controversial research.     

Earthshine: not just for romantics

Peter Thejll, Chris Flynn, Hans Gleisner and Andrew Mattingly explain how classic astronomical techniques, married to the latest technology, can be used to observe earthshine, and learn about Earth's climate, among many other things.     

The lepton asymmetry: the last chance for a critical-density cosmology?

We use a wide range of observations to constrain cosmological models possessing a significant asymmetry in the lepton sector, which offer perhaps the best chance of reconciling a critical-density Universe with current observations. The simplest case, with massless neutrinos, fails to fit many experimental data and does not lead to an acceptable model. If the neutrinos have mass of order 1 eV (which is favoured by some neutrino observations), then models can be implemented which prove a good fit to the microwave anisotropies and large-scale structure data. However, taking into account the latest microwave anisotropy results, especially those from BOOMERANG, we show that the model can no longer accommodate the observed baryon fraction in clusters. Together with the observed acceleration of the present Universe, this puts considerable pressure on such critical-density models.     

Hydrodynamical simulations of the Sunyaev–Zel'dovich effect: the kinetic effect

We use hydrodynamical N -body simulations to study the kinetic Sunyaev–Zel'dovich effect. We construct sets of maps, one square degree in size, in three different cosmological models. We confirm earlier calculations that on the scales studied the kinetic effect is much smaller than the thermal (except close to the thermal null point), with an rms dispersion smaller by about a factor of 5 in the Rayleigh–Jeans region. We study the redshift dependence of the rms distortion and the pixel distribution at the present epoch. We compute the angular power spectra of the maps, including their redshift dependence, and compare them with the thermal Sunyaev–Zel'dovich effect and with the expected cosmic microwave background anisotropy spectrum as well as with determinations by other authors. We correlate the kinetic effect with the thermal effect both pixel-by-pixel and for identified thermal sources in the maps to assess the extent to which the kinetic effect is enhanced in locations of strong thermal signal.     

Can Jupiters be found by monitoring Galactic bulge microlensing events from northern sites?

In 1998 the EXPORT team monitored microlensing event light curves using a charge-coupled device (CCD) camera on the IAC 0.8-m telescope on Tenerife to evaluate the prospect of using northern telescopes to find microlens anomalies that reveal planets orbiting the lens stars. The high airmass and more limited time available for observations of Galactic bulge sources make a northern site less favourable for microlensing planet searches. However, there are potentially a large number of northern 1-m class telescopes that could devote a few hours per night to monitor ongoing microlensing events. Our IAC observations indicate that accuracies sufficient to detect planets can be achieved despite the higher airmass.