Ground-based video of the spillway was
used to quantify flow behavior and effusion
rates. During a representative 20-min period
in mid-July, two pulsing cycles were recorded,
with velocities of 4 to 5 m s−^1 during low lava
levels and 12 to 15 m s−^1 during high lava levels
(Fig.2DandmovieS4).Weobservedacorrela-
tion (R= 0.92) between the height of the lava in
the spillway and the velocity in that area (Fig.
2E). On the basis of these velocity and lava
depth results and the measured channel width
at this location (30 m), we estimated that bulk
effusion rates decreased to ~350 m^3 s−^1 in the
troughs of the pulses and reached ~1700 m^3 s−^1
at the peaks (Fig. 2F) [see Eq. 1 in ( 30 )].
We used the relationship between lava level
and velocity (Fig. 2E) to convert 4 hours of
time-lapse images of lava level from July 14
(Fig. 3B) to bulk effusion rates (Fig. 5A). The
effusion rate estimates had a general inverse
relationship with RSAM, decreasing almost
exponentially with higher RSAM values. In-
frasound energy was also correlated inver-
sely with bulk effusion rate during pulsing
(Fig. 5B).Surges: long-term fluctuations
Field crews reported that fissure 8 fountaining
and flow in the spillway seemed to increase in
vigor (“surge”) after summit collapse events,
which occurred with recurrence intervals of 25
to 50 hours. These visual observations were
supported by changes in ground tilt, RSAM,
andinfrasoundatLERZstationsthatoccurred
within minutes of the summit collapse events.
For instance, during July, LERZ tremor and
infrasound energy exhibited conspicuous peaks
that began within minutes of the summit col-
lapse events (Fig. 6) ( 30 ). These RSAM and in-
frasound peaks suggested that eruptive vigorincreased in the LERZ immediately after the
summit collapses.
Lava-level changes in the spillway confirmed
for us that there was a major increase in ef-
fusion rate at fissure 8 after summit collapse
events. For example, on July 31, the lava level
inthespillwaywasrelativelylowandsteadyin
the 2 hours before the summit collapse event
(Fig. 7 and movie S5). Within minutes, a clear
rise in RSAM began, reaching a broad peak 2
to 3 hours after the event. The lava level in the
area of the channel used for effusion rate mea-
surements did not register a clear rise for
~30 min, but another, more sensitive, portion
of the channel showed a rise in lava level that
beganwithin~13minofthesummitcollapse
(fig. S13). Lava levels peaked ~3 hours after the
summit collapse event. Using ground-based
video to convert the lava level in the time-lapse
images to effusion rate, the estimated bulkPatricket al.,Science 366 , eaay9070 (2019) 6 December 2019 3of10
0 200 400 600 800 1000 120045674567Lava thickness in channel, m0 200 400 600 800 1000 12000500100015002000A Non-pulsing regimeB Pulsing regime (trough)C Pulsing regime (peak)10 mTime, sTime, s051015Velocity, m/sLava thickness in channel, mVelocity, m/s(^051015)
Bulk effusion rate, m
3 s
-1
Q
bulk
=250 m
/s^3
500 1000
1500
R=0.92
trough peak trough
D
E
F
Fig. 2. Short-term cycles in effusion rate (pulses).(A) Typical lava level in
the channel during nonpulsing eruptive behavior on 14 July 2018. (B) During
the low levels (troughs) of pulsing, the level dropped several meters lower
than normal, steady level. (C) During the high levels (peaks) of pulsing, the lava
level rose several meters higher than the normal level. (D)Resultsfrom
ground-based video of the lava channel spillway during pulsing regime on
19 July 2018. Velocity and lava level fluctuate in concert. (E) Correlation
between velocity and lava level. (F) Time series of bulk effusion rates (i.e.,
not corrected for volume of bubbles) during pulsing. Gray area shows
the uncertainty in effusion rate estimates based on ±1 m uncertainty in lava
level in the channel. Panels (D) to (F) cover the time period of 8:10:06 to
8:29:52 HST on 19 July 2018.
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