ON IO THE LITHOSPHERE EVOLVES OVER SHORT TIME SCALES. I PROPOSE TO USE THE SPACING OF VOLCANIC EDIFICES TO PROVIDE NEW CONSTRAINTS ON THE THERMAL AND MECHANICAL STRUCTURE OF THE IONIAN LITHOSPHERE. IT HAS BEEN SHOWN THAT HOT SPOTS NEAR THE EQUATORIAL REGIONS OF IO ARE NOT RANDOMLY DISTRIBUTED BUT ARE BEING ACTIVELY REPELLED FROM EACH OTHER (HAMILTON ET AL. 2013). I PROPOSE THAT THIS NON-RANDOM SPACING IS DUE TO THE BEHAVIOR OF MELT RISING THROUGH THE LITHOSPHERE. AS MELT TRAVELS UPWARDS THROUGH THE LITHOSPHERE IT MAY GENERATE A PERMEABILITY BARRIER OF CRYSTALLIZED MAGMA. A HORIZON OF MELT OR DECOMPACTION CHANNEL SHOULD FORM UNDER THE PERMEABILITY BARRIER. I WILL MODEL THE FORMATION OF PERMEABILITY BARRIERS AND DECOMPACTION CHANNELS DETERMINE UNDER WHAT CONDITIONS THE CHANNEL MAY BECOME UNSTABLE AND PRODUCE SURFACE VOLCANOES WITH A CERTAIN SPACING. I WILL THEN USE THE OBSERVED DISTRIBUTION OF VOLCANOES ON IO TO CONSTRAIN THE THERMAL STRUCTURE OF THE IONIAN LITHOSPHERE AT THE DEPTH OF THE PERMEABILITY BARRIER. WHEN MAGMA PRODUCED FROM DEPTH RISES INTO THE COOLER LITHOSPHERE IT BEGINS TO CRYSTALLIZE. THE CRYSTALLIZATION PRODUCTS MAY CLOG THE POROUS NETWORK IN THE LITHOSPHERE THROUGH WHICH MELTS RISE FORMING A PERMEABILITY BARRIER (SPARKS AND PARMENTIER 1991). MELT THEN CANNOT RISE PAST THE BARRIER AND ACCUMULATES INSTEAD IN A DECOMPACTION CHANNEL IMMEDIATELY BELOW THE BARRIER. I WILL DETERMINE THE DEPTHS IN THE IONIAN LITHOSPHERE WHERE PERMEABILITY BARRIERS MAY OCCUR USING THE MELTS THERMODYNAMIC CALCULATOR (GHIORSO AND SACK 1995; ASIMOW ET AL. 2004). THE MELTS SOFTWARE IS FREE TO USE AND ACCEPTED IN THE PETROLOGICAL COMMUNITY. I WILL SIMULATE MELT RISING THROUGH A PRESSURE AND TEMPERATURE MODEL OF THE LITHOSPHERE SIMILAR TO THE METHOD USED IN HEBERT AND MONT SI (2010) AND SCHOOLS AND MONT SI (2016). THE PERMEABILITY BARRIER MAY BECOME UNSTABLE DUE TO THE FEEDBACK BETWEEN HEAT RELEASED BY THE CRYSTALLIZATION OF MAGMAS WHICH THERMALLY ERODES THE BARRIER AND THE FOCUSING OF MELT INTO THE THERMALLY ERODED PORTIONS OF THE PERMEABILITY BARRIER WHICH BRINGS ADDITIONAL HEAT. THIS PROCESS WILL CONTINUE UNSTABLY BUT THE LENGTH SCALE OF THE INSTABILITY IS LIMITED BY THE SUPPLY RATE OF MELT FROM BELOW. THE SIZE OF THE THERMALLY ERODED REGIONS WILL BE REFLECTED BY THE PATTERN OF VOLCANOES ON THE SURFACE. I WILL START BY CONDUCTING AN ANALYTICAL PERTURBATION ANALYSIS OF THE PERMEABILITY BARRIER LOCATION. I WILL MODEL NUMERICALLY INSTABILITY DEVELOPMENT IN TWO DIMENSIONS USING A CONSTANT THERMAL GRADIENT TO VERIFY THE RELEVANCE OF THE ANALYTICAL PERTURBATION ANALYSIS AND PROBE ITS BEHAVIOR AT FINITE AMPLITUDE. THE NUMERICAL MODELING TASKS WILL BE PERFORMED USING THE DEAL.II SOFTWARE PACKAGE. DEAL.II IS A FLEXIBLE OPEN SOURCE FINITE ELEMENT LIBRARY THAT SOLVES SETS OF PARTIAL DIFFERENTIAL EQUATIONS AND IS USER-ORIENTED BY DESIGN (BANGERTH ET AL. 2007). DANNBERG AND HEISTER (2015) IMPLEMENTED THE TWO-PHASE FLOW EQUATIONS NEEDED HERE IN DEAL.II THIS WORK WILL FOLLOWS THE PLANETARY SCIENCE DIVISIONS ADVISED RESEARCH ACTIVITY TO ADVANCE THE UNDERSTANDING OF HOW CHEMICAL AND PHYSICAL PROCESSES IN OUR SOLAR SYSTEM OPERATE. PREVIOUSLY UNSTUDIED PORTIONS OF THE STRUCTURE AND DYNAMICS OF INTERIOR OF IO WILL BE CHARACTERIZED BY OUR RESEARCH. I WILL CONSTRAIN THE DEPTH OF MAGMA ACCUMULATION AND THE THERMAL STRUCTURE AT THAT DEPTH IN THE IONIAN LITHOSPHERE BY MATCHING THE SPACING OF HOTSPOTS AND CALDERA. MY RESEARCH WILL CONSTRAIN THE EVOLUTION OF IGNEOUS PROCESSES ON IO. I WILL MODEL DIRECTLY THE EVOLUTION OF MELT ACCUMULATING IN THE LITHOSPHERE OF IO AND WILL ANALYZE THE PETROLOGY OF THE RESULTING MAGMAS AS THEY ASCEND. ANY NEW CONSTRAINTS ON THE STRUCTURE OF THE IONIAN LITHOSPHERE WILL BE ABLE TO GUIDE INTERPRETATIONS OF RESULTS FROM THE JUNO INFRARED CAMERA AND POTENTIALLY IO OBSERVATIONS OF THE FUTURE EUROPA CLIPPER MISSION.