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Sunday, July 01,
2007

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As the Pu'u 'O'o
flow field quietly cools on June 21, this single
skylight on the Petunia lava tube is still
incandescent, but no lava is moving through the
tube. - U.S. Geological Survey Photos

Magma, magma, just who's got the
magma?

Sunday, July 1, 2007 8:34 AM
HST

Last week's Volcano Watch described
HVO's most recent and exciting challenge: to figure out
what might happen next with Kilauea's marked change in
eruptive activity. It is often through change that we
learn and grow in our understanding of life. The same
idea is certainly true for the study of volcanic
processes. Eruptive changes provide some of the best
opportunities to better understand how volcanoes
"live."

Philosophy aside, HVO staff members are
pretty jazzed right now about what's happening at
Kilauea. One of this week's big questions is a twofold
one: Where is the magma going and how might it
re-emerge?

To briefly recap the event, Kilauea's
24-year-old ongoing eruption was disrupted early on
Father's Day by a swarm of earthquakes in the upper east
rift zone, indicating that magma was intruding in a new
area near Kane Nui o Hamo, just east of Mauna Ulu.
Within several days, the rift zone in the intrusive area
spread apart nearly a meter (3 feet).

Lava broke
the surface, forming two small flows that covered an
area of about 0.8 hectares (2 acres) before stopping
abruptly. The intrusion and extrusion processes drained
a substantial amount of magma from Kilauea's summit
reservoir and appeared to have also nearly stopped the
supply to Pu'u 'O'o. The cone's crater floor collapsed,
leaving a gaping maw at least 100 meters (330 feet)
deep. Its lava tubes have drained, and flows are no
longer entering the ocean.

Overall, gas emissions
from the volcano have declined as well. Sulfur dioxide,
the gas principally responsible for the nearly
ubiquitous vog in Ka'u and Kona, has dropped by about 75
percent, and HVO has begun receiving phone calls of
appreciation for the improved air quality in these
districts.

One mystery right now, though, is the
disparity between how much magma we believe is still
entering the volcano from the mantle, and the fact that
no new lava and very little gas has been erupted at the
surface for over a week.

Several studies of
Kilauea's long-term behavior conclude that magma is
supplied to the volcano at a fairly consistent rate of
between 0.1 and 0.2 cubic kilometers (0.024 to 0.048
cubic miles) per year. This amount, as erupted lava,
could fill between 100 and 200 Olympic-sized swimming
pools (OSP) each day. For the past 24 years, Kilauea has
eschewed the Olympic pools, but instead, has favored
resurfacing nearly 120 square kilometers (46 square
miles) of the island, and has added an additional 202
hectares (500 acres) to Hawaii.

So if magma is
still being supplied at a rate of 100 OSPs per day,
where is it going, and what might happen next? The short
answer is that the intrusion and eruption of lava on the
upper east rift rapidly depleted Kilauea's summit
reservoir of the volume of magma required to produce the
intrusion and the small associated surface flow. Because
of this geologically "momentary" depletion, the
reservoir will take some time to refill.

We don't know yet precisely how much
magma is tied up in the new intrusion. Ground-based and
space-base measurements and modeling will help refine
estimates of this quantity. However, studying past
events like this one indicates that Kilauea has already
recovered roughly 25 percent of the deflation that
occurred in the summit area during the
event.

Still, the science of eruptive processes
is not always straightforward. Magma supply rate and
lava eruption rate are often not quite equal. And while
volcanologists studying Kilauea, mostly agree that magma
supply to the volcano has been steady in the long term
(tens to hundreds to thousands of years), shorter term
variations do occur.

Within the past several
years, for example, Kilauea showed signs -- increased
expansion and gas release -- that a short term magma
supply increase had occurred. With such supply rate
perturbations comes the interplay between getting magma
into the volcanic edifice and having it affect eruptive
processes. Time will tell what the very immediate
subsurface changes will actually bring in terms of
surface expression.

The eruptive changes
occurring now at Kilauea are unmistakably helping HVO
scientists better understand and appreciate the wonders
of this young volcano's life. In that same spirit, we at
HVO would like to wish two of our younger staff members,
Sara Abraham and Kevan Kamibayashi, our best wishes for
growth as they experience a change in their lives
together this week by becoming newlyweds. Aloha nui loa,
Sara and Kevan!

Activity update

Pu'u 'O'o
is no longer erupting, and there are no active surface
flows anywhere on the flow field or at the coast. This
is the first eruptive pause since Dec. 15, 2000. A small
pad of lava that was erupted on the northeast flank of
Kane Nui o Hamo shield early on June 19 was only active
for a few hours. There has been no continuation or
resumption of activity in this area. The output of steam
and fume from ground cracks near this new flow, and from
cracks west of the base of Kane Nui o Hamo shield, has
decreased and is now barely visible.

Only one
earthquake beneath Hawaii Island was reported felt
within the past week. A magnitude-2.9 earthquake
occurred at 6:15 p.m. on Wednesday, June 27, and was
located 15 km (9 miles) west northwest of Kawaihae at a
depth of 16 km (10 miles).

Mauna Loa is not
erupting. Two earthquakes were located beneath the
summit area in the past week.

Extension between
locations spanning the summit, indicating inflation,
continues at steady, slow rates which have slowed
further since May 2007.

Visit our Web site
(hvo.wr.usgs.gov) for daily Kilauea eruption updates and
nearly real-time Hawaii earthquake
information.

This article was written by
scientists at the U.S. Geological Survey's Hawaiian
Volcano Observatory.

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