Submarine lava deltas of the 2018 eruption of Kīlauea volcano

Abstract

Hawaiian and other ocean island lava flows that reach the coastline can deposit significant volumes of lava in submarine deltas. The catastrophic collapse of these deltas represents one of the most significant, but least predictable, volcanic hazards at ocean islands. The volume of lava deposited below sea level in delta-forming eruptions and the mechanisms of delta construction and destruction are rarely documented. 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. Bathymetric differencing reveals that the 2018 deltas contain more than half of the total volume of lava erupted. 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. We attribute this difference to less efficient fragmentation of the 2018 ‘a‘ā flows leading to fragmentation by collapse rather than hydrovolcanic explosion. 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. This difference, if validated for other lava deltas, would provide a means to assess potential delta stability in future eruptions.

Submarine and Subaerial Morphological Changes Associated with the 2014 Eruption at Stromboli Island

“…A more realistic estimate of the mobilized volume can be obtained by taking into account the A4 seafloor accretion area (Figures 4b, 5 and 10a), interpreted as the landslide deposits recognizable at the base of the scar and accounting for approximately +6 × 10 5 m 3 (Table 2). The low runout of the mobilized material is likely due to a rapid dissipation of pore pressures during the slide, similarly to what was reported for small submarine slope failures affecting the 2018 'a'ā lava delta off Hawaii [38]. Again, this figure is likely underestimated because (a) the mapping of the landslide deposits is limited down to 500 mwd (Figure 5), and (b) the distal part of the moving landslide could be evolved downslope as sedimentary gravity flow, due to the steep gradients characterizing the SdF slope.…”

“…More generally, the results of this study are important to better understand the behavior and morphological evolution of lava flows penetrating into the sea, mainly in relation to the paucity of bathymetric monitoring of coastal areas during eruptive crisis [25,38], with observations mainly limited to the subaerial part of lava deltas [27,39,40] or scuba dives at water depth less than 50 m [41,42]. This is a very important issue considering the possible hazard associated with these events in active insular and coastal volcanoes.…”

The petrologic and degassing behavior of sulfur and other magmatic volatiles from the 2018 eruption of Kīlauea, Hawaiʻi: melt concentrations, magma storage depths, and magma recycling

“…No samples from phase 2 of the LERZ eruption were analyzed. (Gansecki et al 2019) but do not include the substantial submarine deposits (Soule et al 2021). A total of 24 eruptive fissures opened during the eruption, including fissure 9 (F9) and the en-échelon fissure 17 (F17).…”

“…Applying the "petrologic method" to estimate erupted lava volumes (e.g., Rose 1977;Devine et al 1984;Thordarson et al 1996;Sharma et al 2004;Harris et al 2007), Kern et al (2020) use the cumulative SO 2 emissions and an estimated melt SCSS T concentration (1250 ppm S) to calculate DRE erupted lava volumes of ~ 1.7 ± 0.6 km 3 (1σ). This sulfur-based estimation of erupted lava volume is valuable for understanding the scale of the 2018 LERZ eruption because substantial offshore lava emplacement (Soule et al 2021) leaves volume estimates imperfectly constrained.…”

“…Symbol colors are maintained throughout all figures. Subaerial lava flows are colored by eruption phase(Gansecki et al 2019) but do not include the substantial submarine deposits(Soule et al 2021). A total of 24 eruptive fissures…”