Krawczynski Michael J.

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Krawczynski
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Michael J.
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  • Article
    Constraints on the lake volume required for hydro-fracture through ice sheets
    (American Geophysical Union, 2009-05-16) Krawczynski, Michael J. ; Behn, Mark D. ; Das, Sarah B. ; Joughin, Ian
    Water-filled cracks are an effective mechanism to drive hydro-fractures through thick ice sheets. Crack geometry is therefore critical in assessing whether a supraglacial lake contains a sufficient volume of water to keep a crack water-filled until it reaches the bed. In this study, we investigate fracture propagation using a linear elastic fracture mechanics model to calculate the dimensions of water-filled cracks beneath supraglacial lakes. We find that the cross-sectional area of water-filled cracks increases non-linearly with ice sheet thickness. Using these results, we place volumetric constraints on the amount of water necessary to drive cracks through ∼1 km of sub-freezing ice. For ice sheet regions under little tension, lakes larger than 0.25–0.80 km in diameter contain sufficient water to rapidly drive hydro-fractures through 1–1.5 km of subfreezing ice. This represents ∼98% of the meltwater volume held in supraglacial lakes in the central western margin of the Greenland Ice Sheet.
  • Thesis
    Experimental studies of melting and crystallization processes in planetary interiors
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2011-09) Krawczynski, Michael J.
    Melting and crystallization processes on the Earth and Moon are explored in this thesis, and the topics of melt generation, transport, and crystallization are discussed in three distinct geologic environments: the Moon's mantle, the Greenland ice sheet, and the Earth's crust. Experiments have been conducted to determine the conditions of origin for two high-titanium magmas from the Moon. The lunar experiments (Chapter 2) were designed to explore the e ects of variable oxygen fugacity (fO2) on the high pressure and high temperature crystallization of olivine and orthopyroxene in high-Ti magmas. The results of these experiments showed that the source regions for the high-Ti lunar magmas are distributed both laterally and vertically within the lunar mantle, and that it is critical to estimate the pre-eruptive oxygen fugacity in order to determine true depth of origin for these magmas within the lunar mantle. Chapter 3 models the behavior of water ow through the Greenland ice sheet driven by hydrofracture of water through ice. The results show that melt water in the ablation zone of Greenland has almost immediate access to the base of the ice sheet in areas with up two kilometers of ice. Chapter 4 is an experimental study of two hydrous high-silica mantle melts from the Mt. Shasta, CA region. Crystallization is simulated at H2O saturated conditions at all crustal depths, and a new geobarometerhygrometer based on amphibole magnesium number is calibrated. In Chapter 5 I use the new barometer to study a suite of ma c enclaves from the Mt. Shasta region, and apply it to amphiboles in these enclaves. Evidence for pre-eruptive H2O contents of up to 14 wt% is presented, and bulk chemical analyses of the inclusions are used to show that extensive magma mixing has occurred at all crustal depths up to 35km beneath Mt. Shasta.