Science - 06.12.2019

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

-50

0

50

80

100

120

140

1

2

3

4

5

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

0

500

1000

1500

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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