The rapid emplacement of the 1823 CE Keaīwa lava flow from the Great Crack in the Southwest Rift Zone of Kīlauea volcano
Date
2024
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Abstract
The 1823 CE Keaīwa lava flow in the Southwest Rift Zone (SWRZ) of Kīlauea volcano is uniquefor its expansive pāhoehoe sheet flow morphology and lack of constructive vent topography,
despite having a similar tholeiitic basalt composition to other lavas erupted from Kīlauea. This
lava flow issued from a ~10 km-long continuous fissure known as the Great Crack, and has an
unusually thin sheet flow-like morphology with margin thicknesses of ~15–110 cm (average of 42
cm). Based on field observations of the lava flow at its fissure vent (e.g., drain-back features), we
propose that the Great Crack formed, or at least significantly widened, syn-eruptively during the
1823 CE eruption. The absence of pyroclastic or scoria cones indicates that the eruption consisted
of a rapid outpouring of relatively degassed lava as the fissure unzipped. This rapidly moving lava
flow overtopped pre-existing tumuli and scoria cones (e.g., Lava Plastered Cones) up to ~10 m
tall. Glass and whole-rock chemistry yield homogeneous compositions for the lavas erupted from
the Great Crack, with glass compositions of 6.40 ± 0.10 wt. % and whole-rock compositions of
7.39 ± 0.07 wt. % MgO. A shorter western fissure system is richer in mafic minerals (e.g., olivine
and clinopyroxene), and therefore the lavas from this fissure are slightly more MgO-rich (7.79 ±
0.05 wt. %). MgO-in-glass thermometry was used to calculate eruption temperatures of 1153±
13°C from spatter from the Great Crack fissure. These temperatures are typical of Kīlauea lavas,
thus the extensive sheet-like lava flow morphology is not a direct consequence of unusual
magmatic or rheological conditions (i.e. low viscosity). Instead the flow morphology is associated
with high effusion rates caused by sudden drainage of uprift magma through the Great Crack. Lava
flow modeling using VolcFlow on a 2 m DEM indicates that a minimum bulk effusion rate of
~11,200 m3/s (~6,700 m3/s dense rock equivalent, assuming ~40 % vesicularity) and a minimum
flow velocity of ~11 m/s are required for the lava to overcome the Lava Plastered Cones. These
effusion rates are amongst the highest inferred for eruptions in Hawai’i. This study sheds light on
an anomalous eruption style that occurred from the unique fissure that is the Great Crack and the
dynamics involved in its lava flow emplacement; providing new insights into potential risks and
hazards during basaltic eruptions from Kīlauea and possibly Mauna Loa. An eruption similar to
1823 CE with a time frame shorter than an hour, high effusion rates, and rapid flow front velocities
would not easily allow for evacuation.
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Geology, Geochemistry, effusion rate, fissure, lava flow, modeling, SWRZ
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42 pages
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