![]() The heating of seawater to steam can drive hydrovolcanic explosions that fragment the lava (e.g., Moore and Ault 1965 Mattox and Mangan 1997 Poland and Orr 2014). 1).Īs lava flows reach the coastline a variety of mechanisms lead to fragmentation. New bathymetric mapping conducted at the cessation of the eruption, seafloor observations from ROV, and observations from land provide a unique data set to examine the development of lava deltas during a high effusion rate Hawaiian eruption (Fig. The 2018 ocean entries, with lava delivered at high flux and as ‘a‘ā rather than pāhoehoe flows, present a useful contrast with ocean entries of the previous 35 years during the Pu‘u ‘Ō‘ō eruption. Lava flows from the 2018 eruption of Kīlauea Volcano reached the coastline and constructed over 3.5 km 2 of new land. This study examines lava deltas produced in the 2018 eruption of Kīlauea Volcano, compares them to those that formed at Pu‘u ‘Ō‘ō over decadal time scales, and provides new insight about delta formation and evolution. ![]() This is due, in part, to a limited understanding of the patterns of submarine lava transport and deposition, properties of delta material, mechanisms and modes of failure, and how these properties vary with lava flow type, flux, and composition. Unfortunately, there are limited means to predict the timing and size of bench/delta collapses. Landslides of delta material, that in some cases can extend to and include collapse of lava benches, can produce locally catastrophic results, including increased hydrovolcanic explosions (onshore and offshore), ejection of blocks, and generation of local tsunami waves (Mattox and Mangan 1997 Chiocci et al. Submarine lava deltas and subaerial lava benches pose a unique hazard on ocean island volcanoes. At the coastline, lava deltas are capped by lava benches, areas of flat-lying, subaerial lava flows that are built upon delta material. In this study, we consider lava deltas to be the submarine fan of clastic and intact material that is deposited (and in cases remobilized) below the waterline where lava flows enter the sea. In either case, lava that crosses the coastline is difficult to observe. In some instances, lava can pass quiescently across the waterline and continue as lava flows down shallow submarine slopes. The interaction of hot lava and cold seawater can drive hydrovolcanic explosions both at the coastline and slightly offshore that fragment the lava, which cascades down the submarine slopes (Mattox and Mangan 1997). This difference, if validated for other lava deltas, would provide a means to assess potential delta stability in future eruptions.Īt most volcanic islands, lava flows that traverse the volcano flanks often reach the coastline. ![]() We suggest a mechanistic model where the characteristic grain size influences the form and stability of the delta with fine grain size deltas (Pu‘u ‘Ō‘ō) experiencing larger landslides with greater run-out supported by increased pore pressure and with coarse grain size deltas (Kīlauea 2018) experiencing smaller landslides that quickly stop as the pore pressure rapidly dissipates. We attribute this difference to less efficient fragmentation of the 2018 ‘a‘ā flows leading to fragmentation by collapse rather than hydrovolcanic explosion. In addition, we find that the 2018 deltas are comprised largely of coarse-grained volcanic breccias and intact lava flows, which contrast with those at Pu‘u ‘Ō‘ō that contain a large fraction of fine-grained hyaloclastite. Bathymetric differencing reveals that the 2018 deltas contain more than half of the total volume of lava erupted. Here, we report on bathymetric surveys and ROV observations following the Kīlauea 2018 eruption that, along with a comparison to the deltas formed at Pu‘u ‘Ō‘ō over the past decade, provide new insight into delta formation. The volume of lava deposited below sea level in delta-forming eruptions and the mechanisms of delta construction and destruction are rarely documented. The catastrophic collapse of these deltas represents one of the most significant, but least predictable, volcanic hazards at ocean islands. Hawaiian and other ocean island lava flows that reach the coastline can deposit significant volumes of lava in submarine deltas.
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