ABSTRACT
A unique high-temperature apparatus was developed to trigger chaotic mixing at high-temperature (up to 1800 °C). This new apparatus, which we term Chaotic Magma Mixing Apparatus (COMMA), is designed to carry out experiments with high-temperature and high-viscosity (up to 10(6) Pa s) natural silicate melts. This instrument allows us to follow in time and space the evolution of the mixing process and the associated modulation of chemical composition. This is essential to understand the dynamics of magma mixing and related chemical exchanges. The COMMA device is tested by mixing natural melts from Aeolian Islands (Italy). The experiment was performed at 1180 °C using shoshonite and rhyolite melts, resulting in a viscosity ratio of more than three orders of magnitude. This viscosity ratio is close to the maximum possible ratio of viscosity between high-temperature natural silicate melts. Results indicate that the generated mixing structures are topologically identical to those observed in natural volcanic rocks highlighting the enormous potential of the COMMA to replicate, as a first approximation, the same mixing patterns observed in the natural environment. COMMA can be used to investigate in detail the space and time development of magma mixing providing information about this fundamental petrological and volcanological process that would be impossible to investigate by direct observations. Among the potentials of this new experimental device is the construction of empirical relationships relating the mixing time, obtained through experimental time series, and chemical exchanges between the melts to constrain the mixing-to-eruption time of volcanic systems, a fundamental topic in volcanic hazard assessment.
ABSTRACT
Upper gastrointestinal hemorrhage secondary to gastric varices still has a high death rate. Fourteen patients were admitted to our unit with bleeding gastric varices from November 1989 to August 1991. Endoscopic injection sclerotherapy obtained control of the bleeding in 92.3%; however, recurrences occurred in 33% of these cases in the first 24-48 hours, with a death rate of 50% during the second stage of the upper gastrointestinal hemorrhage. Total mortality rate was 21.4%. Of the fourteen patients, nine exhibited junctional varices, while five hand fundic varices. In ten of the fourteen patients, gastric varices developed during esophageal sclerotherapy. While hospitalized, it was observed that patients with gastric varices in the fundus had more recurrences and mortality, than those located next to the cardio-esophageal junction. Sclerosis of the varices only obtained temporary control of the bleeding with greater frequency of recurrences and mortality.
