INTRODUCTION: SPATTER BLOBS OF LAVA THROWN INTO THE AIR DURING AN ERUPTION BUILDS FEATURES LIKE CONES AND WALLS (RAMPARTS) AROUND MILDLY-EXPLOSIVE VOLCANOES. THE PRODUCTION OF SPATTER HAS BEEN HYPOTHESIZED TO PRESENT IN PLACES SUCH AS THE NEPHENTES/AMENTHES REGION OF THE IMPACT BASIN UTOPIA (BROZ AND HAUBER 2013) AND CERBERUS PLAINS (LANAGAN ET AL. 2001. SPATTER FEATURES GROWTH RATE IS LIMITED BY THERMAL AND ERUPTIVE CONDITIONS TOO FAST AND MATERIAL COALESCES AND FLOWS AWAY TOO SLOW AND MATERIAL HARDENS INTO SCORIA CREATING A DIFFERENT TYPE OF VOLCANIC DEPOSIT. IDENTIFYING THIS GROWTH (ACCUMULATION) RATE WOULD ALLOW FOR US TO CONSTRAIN ERUPTION DURATION FOR ANCIENT ERUPTIONS ON MARS AND LINK ACCUMULATION RATE TO MORPHOLOGICAL FEATURES SEEN IN SPATTER DEPOSITS ON EARTH. WE HAVE THUS FAR CHARACTERIZED SPATTER MORPHOLOGY ON EARTH (RADER ET AL. IN PRESS) AND EXPERIMENTALLY LINKED SPATTER ACCUMULATION RATES WITH MORPHOLOGICAL CHANGES (RADER ET AL. IN PREP) HOWEVER WE HAVE NOT HAD THE OPPORTUNITY TO MEASURE ERUPTING SPATTER ACCUMULATION RATES AND GROUND-TRUTH OUR EXPERIMENTS UNTIL THIS TARGET OF OPPORTUNITY OF THE LEILANI ESTATES ERUPTION COMMENCED ON MAY 4TH 2018. THE RAPID DEPLOYMENT OF OUR TEAM WOULD ALLOW FOR IN-SITU MEASUREMENTS OF ACCUMULATION RATES AND THERMAL RADIANCE OF THIS TYPICALLY HARD TO SAFELY ACCESS AND DIFFICULT TO ISOLATE VOLCANIC PROCESS. GOALS AND OBJECTIVES: WE PROPOSE TO DOCUMENT ERUPTIVE CONDITIONS (ACCUMULATION RATE AND TEMPERATURE) OF THE LEILANI ESTATE ERUPTIVE FISSURE DURING THE OPENING PHASE OF A MODERATELY EXPLOSIVE BASALTIC ERUPTION. THIS TIMELY DATA WOULD PROVIDE CONSTRAINTS ON ERUPTION DURATION AND TEMPERATURE FOR ANCIENT ERUPTIONS MARS AND ON EARTH AND BUILD UPON PREVIOUS WORK LINKING ERUPTION CONDITIONS TO SPATTER DEPOSIT MORPHOLOGY. METHODOLOGY: THE RELATIVE EASY AND SAFE ACCESS TO THIS BRAND-NEW FISSURE ALLOWS FOR THE FIRST TEMPORALLY AND THERMALLY-LINKED STUDY OF SPATTER ACCUMULATION RATES FOLLOWED BY MORPHOLOGICAL STUDIES CONNECTED TO THOSE EXACT ERUPTION CONDITIONS. WE PROPOSE TO TRAVEL TO THE LEILANI FISSURE AND MEASURE THE HEIGHT OF THE SPATTER RAMPART AT 3-10 LOCATIONS ALONG ITS LENGTH EVERY TWO DAYS WITH A LASER ALTIMETER/ RANGE FINDER TO CALCULATE SPATTER ACCUMULATION RATES AND LINK THESE OBSERVATIONS WITH THERMAL MEASUREMENTS USING A HANDHELD FLIR CAMERA. LOCATIONS WOULD BE SELECTED BASED ON SAFETY (PROXIMAL ENOUGH TO MAKE MEASUREMENTS BUT DISTANT ENOUGH TO AVOID SPATTER IMPACTS) EASE OF OBSERVATION AND TO TARGET DIFFERENT ERUPTIVE CONDITIONS (MAXIMUM AND MINIMUM SPATTER ACCUMULATION RATES). AT EAST SITE ONCE EVERY OTHER DAY HEIGHT OF THE SPATTER FEATURE AND SURFACE TEMPERATURE OF THE FEATURE AND THE DEPOSITED CLASTS WOULD BE MEASURED. THESE LOCATIONS WOULD BE VISITED AGAIN AT THE END OF THE FUNDING PERIOD WHEN VOLCANIC ACTIVITY HAD STOPPED TO MEASURE THE MORPHOLOGY OF THE RESULTING COOLED DEPOSIT. CLAST SIZE SHAPE AND VESICULARITY CHEMICAL COMPOSITION (PORTABLE XRF) AND THE VOID SPACE AND AMOUNT OF FUSION BETWEEN THE CLASTS. IF THE ERUPTION HAD NOT CEASED AND OLD SITES HAD BEEN PREVIOUSLY COVERED BY NEW MATERIAL NEW SITES WOULD BE MEASURED AND MONITORED AS THE ERUPTION PROGRESSED UNTIL MORPHOLOGICAL MEASUREMENTS COULD BE OBTAINED ONCE THE ACTIVITY WANED. IF THE ERUPTION HAS CEASED COMPLETELY THEN WE WILL FOCUS ON MEASURING CLASTS AT VENTS THAT ALREADY HAVE DOCUMENTED DURATIONS (PLUS OR MINUS A FEW HOURS) FROM THE HAWAIIAN VOLCANO OBSERVATORY REPORTS. THESE FISSURES WILL PROVIDE US WITH THE MINIMUM BUT NOT MAXIMUM ACCUMULATION RATES OF SPATTER DEPOSITS AND WILL STILL BE VERY USEFUL AS A GROUND TRUTH FOR OUR PREVIOUSLY RUN EXPERIMENTS.