converting the bulk effusion rates to DRE ef-
fusion rates using the vesicularities that we
observed from lava samples collected from the
spillway (figs. S10 and S12) ( 30 ). The measured
vesicularity range of 50% (gas-poor lava during
pulsing troughs) to 82% (gas-rich lava during
pulsing peaks) reduces the wide span of ob-
served bulk effusion rates (350 to 1700 m^3 s−^1 )
(Fig. 2F) during pulsing to a narrower DRE
effusion range (175 to 306 m^3 s−^1 ). Although
the average DRE values of peak and trough
stages remain offset, the uncertainty in the
bulk effusion rate values (~15%) ( 30 )(Fig.2F),
combined with the likelihood that the lava
samples may not capture the whole range of
vesicularity of lava flowing in the channel,
precludes confidence of a lava supply rate
change. The exercise demonstrates that much
of the bulk effusion rate difference could be
accounted for by vesicularity changes from the
variable degassing that we observed in the
UAS video.
Origin of long-term fluctuations (surges)
The short delay (minutes) between the sum-
mit collapse events and the onset of increased
effusion rates at fissure 8 (Figs. 7 and 8 and
figs. S13 and S14) and the 40-km span from
the summit to the LERZ eruption site (Fig. 1A)
informed us about the process behind the
surges. We inferred that the surges were driven
by a pressure pulse transmitted down the ERZ
conduit, not by the transport of a batch of new
magma. The pressure transient would move
alongthe40-km-longconduitatseismicveloc-
ities, whereas migration of the magma itself
would require much longer time scales (hours
or longer) ( 35 ). Although bubbles in the magma
would reduce the seismic velocity compared
withdenserock,thetraveltimeinthispressure-
driven scenario would nevertheless be tens of
seconds ( 36 – 38 ).
Although effusion rates began to increase
within minutes of summit collapses, surge-
driven effusion rates took ~2 to 4 hours topeak(Figs.7Fand8,D,H,andL).Thisdelayis
an important constraint on the process driving
surges and might be explained by pressure
buffering by an intermediate magma storage
zone or zones along the ERZ conduit ( 39 ).
Pressure buffering in a shallow reservoir was
used to explain pressure transients that peaked
at Pu‘u‘Ō‘ōseveral hours after their onset at
the summit, 20 km away, during the recent
years of the Pu‘u‘Ō‘ōeruption ( 39 ).
Unlike the short-term pulses, our geophysi-
cal and downflow observations offer evidence
that the increase in bulk effusion rate asso-
ciated with surges was reflective of a major
increase in lava supply rate. The direct scal-
ing among seismic tremor, infrasound, and
bulk effusion rate (Fig. 5, C and D) suggested
that an increase in fountain vigor at the vent
(the likely driver of much of the tremor and
infrasound) accompanied the increase in bulk
effusion rate. This relationship was opposite to
that of the pulses (Fig. 5, A and B), demon-
strating a concurrent increase in fountain and
flow activity. Downflow, the increased bulk ef-
fusion rate associated with the surges, pro-
duced overflows in the distal portion of the
flow (movie S6), suggesting a large increase
in DRE effusion rate that was sufficient to
cause changes kilometers down the channel.
The pulses, on the other hand, had no medial
or distal effects, consistent with any change in
bubble content in the near-vent channel being
lost to outgassing rapidly with distance ( 17 , 40 ).
If we assume that the gas content of lava
did not change greatly during the surges, then
we can use a constant vesicularity to convert
the observed bulk effusion rates to DREs. The
main profile of samples from the spillway chan-
nel walls has a mean vesicularity of 72% (SD
4%) and we assumed this value. Applying this
value to the bulk effusion rates during pe-
riods before surges (mean: 548 ± 126 m^3 s−^1 ),
we estimated DRE effusion rates of 153
(±35) m^3 s−^1 for typical rates before the surges.
Peak surge levels of bulk effusion rate were
1400 to 1700 m^3 s−^1 ,or~400to500m^3 s−^1 for
DRE effusion rate. These DRE values during the
surge peaks are ~100 times greater than recent
effusion rates at Pu‘u‘Ō‘ō( 24 , 25 )butsimilar
to common Mauna Loa effusion rates ( 17 ).Gas- and pressure-driven fluctuations
The pressure- and gas-driven dichotomy for
the fissure 8 channel bears similarity to the
behavior of the lava lake in Halema‘uma‘u
during Kīlauea’s2008–2018 summit eruption
( 34 ). In the Halema‘uma‘u lava lake, short-term
(minutes to hours) fluctuations in the height
of the lava surface weredriven by shallow out-
gassing, specifically gas pistoning ( 34 , 41 ).
These short-term level variations had an in-
verse relationship with outgassing rates, RSAM,
and infrasound, like the fissure 8 vent (Fig. 3C).
Longer-term variations in the Halema‘uma‘uPatricket al.,Science 366 , eaay9070 (2019) 6 December 2019 6of10
50 100 150 200 250
KLUD RSAM0500100015002000250030003500050010001500200025003000350080 100 120
KLUD RSAM05001000150020000500100015002000024 6 8
Infrasound energy, Pa^2 sInfrasound energy, Pa^2 s12 3 4 5July 29
July 31
August 2Short-term pulsations (5-10 min cycles): outgassing drivenLong-term surges (25-50 hr cycles): pressure drivenBulk effusion rate, m3 s-1Bulk effusion rate, m3 s-1Bulk effusion rate, m3 s-1Bulk effusion rate, m3 s-1A BCDFig. 5. Relationship of RSAM and bulk effusion rates for two types of cycles.(A) Bulk effusion rate
showing an inverse correlation with RSAM during short-term pulsations. (B) Relationship between bulk
effusion rate and infrasound energy during short-term pulsing. (C) Bulk effusion rate showing a linear
correspondence with RSAM during the longer-term surges. (D) Bulk effusion rate showing a correlation with
infrasound energy during the longer-term surges.
RESEARCH | RESEARCH ARTICLE
on December 12, 2019^http://science.sciencemag.org/Downloaded from