The PI has devised a method to determine atmospheric pressure based on vesicle size distributions in basaltic lava flows. The size and space distributions of vesicles is dependent on migration and coalescence processes which can be modelled, as well as flow thickness and atmospheric pressure. The atmospheric pressure dependence arises from the sensitivity of the size distribution to decompressive expansion during bubble rise through the fluid lava. The objective of the research is to refine and implement the method on modern basalts emplaced at high and low elevations, thereby calibrating the sensitivity of the technique. During phase II, the analysis will be applied to ancient low elevation baslts to measure paleo-atmospheric pressure. This work will provide the first data on paleo- atmospheric pressure, thus shedding light on planetary degassing and evolution of the atmosphere. Once sea level pressure is known, the technique can be used to obtain paleo-elevation of mountain ranges, with implications in paleogeography and atmospheric circulation. In addition, the bubble size distribution as a function of stratigraphic position in a flow can be used as a measure of lava viscosity, and should yeild more accurate results than previous estimates. In order to accomplish the goals of the project, the numerical model already developec (Sahagian, 1985; in press) will be refined to provide greater accuracy and sensitivity of vesicle size distribution to atmospheric pressure. Modern field samples will be collected to calibrate the sensitivity of th model and laboratory technique. In Phase II, ancient samples will be collected to provide the first paleo-atmospheric pressure data.
