Science - 06.12.2019

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supply rate (Fig. 5D) after excluding the gas-
driven pulses (Fig. 5B). Both were largely re-
cording activity at the vent that appears to
scale with effusion rate. This demonstrates
that infrasonic tremor may be a reliable tool
for tracking eruption rates in nonexplosive
eruptions.


Hazard implications


The short duration of the pulses in the 2018
LERZ eruption of Kīlauea resulted in their
hazard being limited to the proximal region of


the flow. Occasional overflows were a threat to
evacuated homes adjacent to the flow margin
along the first kilometer of the lava channel,
and pulsing regimes warranted greater cau-
tion in the proximal flow region. Surges, how-
ever, produced hazards with a farther reach,
asshownonAugust2.Then,theincreased
effusion rate caused lava to rise in the distal
channel and overflow the levees, triggering
new lobes extending out from the existing
flow margins and creating hazards for nearby
residents on Noni Farms Road and Papaya

Farms Road (Fig. 1B). The observation that
the summit collapse events preceded peaks in
effusion rate at fissure 8 allowed Hawaiian
Volcano Observatory geologists to anticipate
potentially hazardous conditions and warn
Hawai‘i County Civil Defense.
The link between effusion rate and hazard
of an advancing flow is well established, as ef-
fusion rate is a major control on the flow length
and advance rate ( 13 ). The fissure 8 flow quickly
advanced to the ocean and established a rela-
tively stable channel that persisted for 2 months.
Although the distal portions of the flow, nearest
the coast, changed frequently, the remainder
of the channel system sustained high effusion
rates with only occasional disruptions. Disrupt-
ions, such as channel overflows, coincided with
the effusion rate fluctuations driven by the
surges. Thus, whereas the absolute effusion
rate was important for gauging hazards dur-
ing initial flow advance, once a persistent
channel was established, the lateral hazards
were controlled by the variations in effusion
rate. Overflows trigger new lobes, generating
hazards along the flow margins; they may also
trigger levee breaches that reduce supply at
the flow front and lessen hazard there ( 17 ).

Conclusion
The 2018 LERZ eruption of Kīlauea presented
an excellent opportunity to study the dynam-
ics of high-effusion lava flows using modern
tools. The sustained nature of the fissure 8
flow allowed us to collect a robust, multi-
disciplinary dataset to examine the diverse
processes that drive fluctuations in flow vigor.
The two time scales of effusion rate fluctua-
tions corresponded to a shallow, near-vent
outgassing process and a deeper, pressure-
driven change originating from the episodic
caldera-collapse events at the summit, 40 km
distant. The hydraulic connection between the
summit magma reservoir and the flank erup-
tion allowed the episodic nature of summit
collapses to be rapidly expressed as changes
in eruption vigor on the flank. The integ-
rated dataset, coupled with frequent direct
observations, was essential for understand-
ing the nature and hazard implications of
these variations.

Materials and methods
U.S. Geological Survey (USGS) field crews
were on the ground 24/7 during the eruption
andmadefrequentdirectobservationsofthe
proximal fissure 8 channel. Lava flow effusion
rates were estimated using constraints on the
velocity and cross-sectional area of lava flow-
ing through the proximal channel from ground-
based video and time-lapse images. We followed
the technique described previously ( 13 )to
correct for the depth-averaged flow velocity.
Bulk effusion rates were converted to DRE
(bubble-free) values using the density of lava

Patricket al.,Science 366 , eaay9070 (2019) 6 December 2019 8of10


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03 04 05 06 07 08 09 10 11 12 13 14 15 16 17

0

500

1000

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B post-collapse (surge)


11:09 HST

A pre-collapse


06:12 HST

Tilt, μrad(summit)

RSAM
(Lower ERZ)

Bulk effusion

rate, m

3 s

-1

Infrasound energy,Pa

2 s (Lower ERZ)

Hours (HST), 31 July 2018

summit
collapse
event

C


D


E


F


1 min
RSAM

10 min
median

1 min
energy

10 min
median

Fig. 7. Example of a LERZ surge event after summit collapse on 31 July 2018.(AandB)Images
of the lava channel before and after the summit collapse event showing a major increase in flow vigor
after the event. (C) The summit collapse occurred at 08:00 HST, as shown by the tilt offset at the
summit. (D) RSAM increased within minutes of the summit collapse event, peaking 3to 4 hours after
the event. (E) Infrasound energy followed the trend in seismic tremor (RSAM). (F) Estimated bulk
effusion rate from the lava-level data showing an increase of a factor of 2 to 3 after the summit
collapse event. Gray area shows the uncertainty in effusion rate estimates based on ±1 m uncertainty
in lava level in the channel.


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