MULTIPLE ERUPTIVE PHASES OF THE BLUE DRAGON LAVA FLOW, CRATERS OF THE MOON NATIONAL MONUMENT, IDAHO

Craters of the Moon National Monument in the eastern Snake River Plain of southern Idaho encompasses the largest Holocene lava field in the conterminous U.S., with about 60 eruptive events in the past 15,000 years, many produced by fissure eruptions from the Great Rift, a dike-fed central rift zone. The largest (280 km²) and one of the youngest (2076 ± 45 years) flows is the Blue Dragon flow, which has a hawaiite composition and is characterized by unique coloration that ranges from a typical dark gray to a vibrant blue, thought to be caused by clusters of microscopic titanium magnetite crystals in the surface glass. The intensity of this color and morphological characteristics vary across the surface of the flow in high-resolution multispectral remote sensing imagery, and field observations show color boundaries correspond to previously undocumented flow boundaries and stratigraphic offsets, evidence for multiple eruptive phases. Rock samples taken from each eruptive phase were analyzed for a suite of major and trace elements using X-Ray Fluorescence (XRF), and the results show distinct geochemical differences and a clear fractional crystallization trend from the oldest to youngest mapped phase. These geochemical data were combined with estimated volumes for each mapped phase and the cooling history of the source dike system and time between each eruptive phase were constrained.