December 27, 1996
A weekly feature provided by scientists at the Hawaiian Volcano
Observatory.
HVO: 1996 in review
As 1996 draws to a close, we can look back and reflect on the
tumultuous year that the U.S. Geological Survey's Hawaiian Volcano
Observatory experienced. The year started with the Federal government
in a partial shutdown, and HVO operated with a reduced staff for three
weeks. Even with such an ominous start, there were many highlights
throughout the year. The shutdown ended in time for our seismic staff
to participate in a month-long experiment involving 25 visiting
international seismologists.
The principal goal of the experiment was to record volcanic tremor
and volcanic earthquakes with a dense, 116-station array of portable
seismographs in the Kilauea Volcano summit region. On the morning of
February 1, a swarm of small, shallow earthquakes and rapid inflation
of the caldera floor heralded the possibility of a summit eruption.
After four hours of inflation, the summit started to subside,
coincident with a three-fold increase of lava output from the Pu`u `O`o
vent. This surge in lava production lasted late into the night and led
to the first of four pauses in activity during 1996.
Kilauea was chosen as the site of the experiment because of the
complementary modern seismic network operated by HVO and because of
the high incidence of earthquakes. Since January 1, 1996, a total of
43,302 earthquakes were recorded by the 54-station HVO seismic network
on the island of Hawai'i. Of this total, 4,950 earthquakes were large
enough to be located, and 59 were reported felt.
The largest earthquakes in 1996 occurred in July during the Lo`ihi
Volcano earthquake swarm. A magnitude of 4.9 was registered by three of
the 4,519 earthquakes recorded from Lo`ihi. A total of 96 earthquakes
from Lo`ihi had magnitudes 4.0 or larger. Scientists from the
University of Hawaii discovered a new pit crater in the summit of
Lo`ihi.
HVO hosted a week-long geodesy conference involving forty
participants who discussed various techniques in monitoring surface
deformation and presented innovative methods of modeling and analyzing
geodetic data. The HVO surface deformation group collaborated with
investigators from the University of Hawaii and Stanford University in
establishing an array of thirteen permanent Global Positioning System
(GPS) stations on the south flank of the Big Island. The annual
measurement of Mauna Loa Volcano revealed a retardation in the rate of
inflation.
The geochemistry group deployed a network of continuous gas
monitoring instruments developed at HVO to measure the flux of carbon
dioxide and sulfur dioxide gases at fumaroles around Kilauea. Changes
in gas volumes and ratios are caused by changes in the magma body from
which these gases emanate. The February 1 event caused a major increase
in carbon dioxide emissions in the summit region.
The geophysics group continued to monitor the volume of lava flowing
through the tube system from Pu'u 'O'o to the coast. The average output
of lava is about 400,000 cubic meters per day, but there was no net
change in the size of the island.
The static size of the island is the result of frequent collapses of
the coastal lava delta (bench). Mapping by the geology group
determined that a 25-acre block slumped beneath the waves on December
2. This was the largest bench-collapse in the 14 years of the
eruption. Fortunately, National Park officials, on the advice of HVO,
restricted visitor access to this hazardous area and no one was killed
or injured.
The monitoring groups are supported by electronics, computer,
library, and administrative staff, who keep the programs running. The
staff and associates of the U.S. Geological Survey's Hawaiian Volcano
Observatory wish a 'Happy New Year' to all of the faithful readers of
this column. Your interest in keeping abreast of volcanic and seismic
events and in being informed of geologic hazards and ways to mitigate
those hazards has sustained our efforts in producing this column. We
appreciate your support and will continue our mission of providing
unbiased Earth science information to the public.
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