Science - 06.12.2019

lava lake level, lasting hours to days, were
driven by magma reservoir pressure ( 34 , 42 ),
again, like the fissure 8 vent.
This shared pattern of pressure- and gas-
driven behavior at Halema‘uma‘uandfissure
8 is noteworthy given the very different erup-
tion styles and might suggest a general start-
ing point for interpreting and forecasting
fluctuations at open-vent basaltic volcanoes—
short-term (minutes to hours) variations in
eruptivebehaviorarelikelytobedrivenbyshal-
low outgassing fluctuations, whereas longer-
term (hours to days) changes are likely related
to lava supply rates and reservoir pressure.

Insights into caldera collapse and the
magmatic system

Eruption rate variations on Kīlauea’sLERZin
2018 provided us with broader insights into

the volcano’s magmatic system and, more gen-

erally, into rift-summit interactions during

basaltic caldera-forming eruptions. Summit

collapse–driven surges in lava supply to the

LERZ vent bear relevance to two concepts on

caldera collapse that have developed in recent

decades. First, studies show that there can be

a complex interplay between flank eruptions

and their parental summit magma reservoirs

( 27 , 43 , 44 ). Summit reservoirs supply pres-

surized magma to the flank vents, but the

flank conduits regulate the rate of summit

reservoir draining, producing a two-way

interaction. Second, most of the caldera col-

lapses monitored with modern instrumen-

tation, including those atMiyakejima(Japan),

Fernandina (Galapagos), Piton de la Fournaise

(Reunion Island), Bárðarbunga (Iceland), and

now Kīlauea, have exhibited episodic, and qua-

siperiodic, progression ( 8 , 43 , 45 ). Our results

confirmed and extend these two concepts to

show that the episodic rhythm of summit

caldera collapse sequences may be imparted

on the accompanying flank eruption, and

this episodic flank effusion can have direct

implications for hazard.

ThepostcollapsesurgesatKīlauea offered

clear evidence of an efficient hydraulic con-

nection between the summit and ERZ (Fig. 1A).

A sustained magmatic link between the sum-

mit and ERZ was illustrated during the 35-

year-long Pu‘u‘Ō‘ōeruption, and repeated

observations showed that transient pressure

increases in the summit magma reservoir pro-

duced higher eruption rates at the Pu‘u‘Ō‘ō

vents 20 km from the summit ( 42 , 46 ). The

postcollapse surges in 2018 demonstrated that

transmission of pressure changes by a sub-

horizontal magmatic conduit can be sustained

over twice that distance, at >40 km. Although

previous work has shown that lateral magma

transfer can occur at distances of 40+ km ( 43 ),

our results build upon this to show that pres-

sure communication between the summit

and flank vent over these distances can occur

over time scales as short as minutes. Quantita-

tive estimates of time-variable eruption rates

during fissure 8 surges will be a vital compo-

nent in future efforts to model the magma

flow from the summit to the vent and could be

used to constrain the properties of the ERZ

conduit and the summit reservoir during the

collapse events ( 47 , 48 ).

Tremor as a tool for monitoring eruption rates

Seismic tremor has been correlated with erupt-

ion intensity at several volcanoes and across

different eruption styles ( 49 – 52 ). Reliably link-

ing tremor amplitude with the volumetric

eruption rate is a valuable objective for opera-

tional monitoring and hazard assessment be-

cause tracking tremor is much easier than

estimating real-time effusion rates. However,

robust comparison datasets are rare. Compli-

cating the relationship is that tremor asso-

ciated with basaltic volcanism is often strongly

tied to near-surface outgassing ( 41 , 53 , 54 ),

which may not be indicative of deeper magma

supply rates.

If we disregard short-term gas-driven changes

(pulses) in RSAM and focus on long-term

surges, we find a correlation (R=0.80)be-

tween RSAM and effusion rate (Fig. 5C). This

trend suggests that, insome circumstances,

tremor can be used to gauge lava supply rates

during basaltic eruptions. We note the caveat

that outgassing-driven fluctuations must be

identified and disregarded.

Infrasonic tremor has also been explored as a

tool for monitoring volumetric eruption rates,

primarily at explosive volcanoes ( 52 , 55 , 56 ).

For the Kīlauea eruption, both infrasonic and

seismic tremor had a direct scaling with lava

Patricket al.,Science 366 , eaay9070 (2019) 6 December 2019 7of10

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100

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26 27 28 29 30 31 01 02 03 04 05

0

2

4

1 minute RSAM

30 minute median

30 minute median

1 minute energy

UWD tilt, μrad

(summit)

RSAM, counts

(LERZ)

Infrasound energy, Pa

2 s

(LERZ)

POO tilt, μrad(middle ERZ)

JKA tilt, μrad

(LERZ)

July August

A

B

C

D

E

Distance from summit collapse

2 km

20 km

41 km

42 km

32 km

summit

collapse

events

end of major

LERZ effusion

Fig. 6. Ten days of tilt, RSAM, and infrasound spanning five summit collapse events.Summit
collapses were registered sharply at summit tilt stations [(A), UWD station]. Tilt offsets were also
registered tens of kilometers away in the middle ERZ [(B), POO station] and LERZ [(C), JKA station].
During this period, the summit collapse events were followed by an increase in tremor (shown by
peaks in RSAM) in the LERZ [(D), from station KLUD; Fig. 1B], suggesting an increase in LERZ
eruption vigor. (E) Infrasound energy showing peaks after the summit collapses, another indicator
of eruption escalation on the LERZ.

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