ACUTE LATERAL HAZARDS OF LAVA FLOWS: EXAMPLES FROM KĪLAUEA, HAWAIʻI (Invited Presentation)

The advancing front of a lava flow is usually considered the main hazard for forecasting purposes. While this is true during the primary phases of many effusive eruptions, secondary lateral hazards become important during long-lived events. Lateral hazards include surge-controlled overflows of channels, ooze-outs along margins from ephemeral feeder networks, flow branching, or a combination of these mechanisms. These processes were responsible for a 37% increase to the Ahuʻailāʻau (Fissure 8) flow field area during the 2018 lower East Rift Zone (LERZ) eruption of Kīlauea (HI), resulting in 20% of the building destruction. Currently, forecasting tools do not sufficiently address the potential for secondary flow widening and therefore further investigation is required. For this study, we examine the processes and precursors of major secondary flow field growth by the formation and failure of perched levee features and ooze-outs from the Pu‘u‘ō‘ō and LERZ eruptions of Kīlauea. A combination of lidar point clouds, thermal and webcam imagery, geophysical monitoring, and detailed field observations collected through time are used to track and identify the precursors, dynamics, and impacts of these events in unprecedented detail. We find that large oscillations in effusion rate influence down-channel rheology, causing channel back-ups which then produce overflows. These overflows rapidly increase the height of the levees, and once the levee height exceeds 15-20 m, the levees become prone to failure. The constructional history of levees also plays a role, as pre-existing structural weaknesses inherited from the initial flow emplacement can be exploited by intrusions into the walls (seeps). Seeps are a result of density contrast, which is driven by the increasing channel depth as the levee grows. We find overpressures >5 bars can result in seep-driven levee failure and eventual collapse. Additionally, gently sloping terrain enhances perched and ponded flow development, and overthickening can drive rapid inundation and overcome low drainage divides to expand and more readily re-route lava channel networks. Our results identify precursory activity and features that should be monitored during effusive eruptions to potentially forecast and model these secondary failure-induced branching and flow widening events.