From: joe@montebello.soest.hawaii.edu (Joe Dellinger)
Subject: HVO report
Reply-To: joe@montebello.soest.hawaii.edu
Organization: School of Ocean and Earth Science Technology
Date: Sun, 30 Aug 1992 02:47:33 GMT

[edited from the Volcano Watch column, Hilo Tribune-Herald, 
8/23/92, p. 8]

HOW ARE LAVA MEASUREMENTS MADE?

Kilauea's ongoing eruption from the episode 51 vents resumed 
on Aug. 15 after a four-day pause in the activity and 
reoccupied the tube system down to the southern edge of the 
lava shield.  Pahoehoe flows are advancing from the end of 
the tube to the southeast and southwest.  The flows are 
confined to the area of earlier episode 51 flows and extend 
about 1.2 miles from the vent.  Almost no activity is visible at 
the vents, because the lava is fed directly into the tube.  The 
lava pond next to the 51 vents is empty, as it has been since 
early July.  The lava pond within the Pu'u 'O'o Crater is about 
200 feet below the rim.

The eruption updates that appear regularly in this column are 
primarily the result of weekly trips to the eruptions site by 
geologists from the Hawaiian Volcano Observatory.  The 
geologists who monitor the ongoing eruption assess the 
potential hazards to life and property and conduct research 
that will increase our understanding of how the volcano works.  
This research enables us to make more accurate predictions of 
future activity.  In addition to disseminating information to the 
public, the media, and other government agencies, we report 
the results of our research in scientific journals.

On a typical trip to the eruption site, a crew of three geologists 
reaches the rim of the Pu'u 'O'o Crater after a three-and-a-half 
hour hike.  At Pu'u 'O'o, we measure the depth to the surface of 
the lava pond, using a distance range-finder and inclinometer.  
We change the film in a time-lapse movie camera, perched on 
the rim, that exposes a frame every three minutes and 
gives us a continuous record of the pond's activity and changes 
in its level.  From the crater's rim, the crew walks around the 
cone to the 51 vents [on the base of Pu'u 'O'o's western slope].  
Aside from noting any changes at the vents, our main aim is to 
collect a molten sample of lava, either spatter or lava dipped 
from flows, as close to the vent as possible.  When the 51 lava 
pond was still active, we could collect a sample on a hammer 
head thrown into the pond on the end of a length of steel cable.  
Currently, we must walk to the south across the new lava flows 
until we find an active flow to sample by the same means.

The samples are analyzed in a laboratory to determine the 
chemical composition of the lava and the temperature at which 
it erupted.  Thin sections of the samples are prepared for 
microscopic study of the minerals, glass, and gas bubbles that 
make up the lava.  These samples contribute to our long-term 
record of the changing conditions within the magma plumbing 
system of Kilauea.  Since 1986, the lava chemistry has 
remained relatively constant, and the eruptive temperature of 
the magma has slowly decreased.  This tells us that the 
eruption is still tapping a single batch of magma that is slowly 
cooling.  A sudden change in chemistry or increase in 
temperature would indicate that a new batch of magma was 
supplying the eruption, with the possible consequence of 
prolonging the eruption.

HVO geophysi[ci]sts make direct measurements of the volume 
of erupted lava at the 51 vents, using magnetic and electrical 
instruments that detect the lava as it flows through lava tubes.  
[One technique takes advantage of the change in resitivity of 
flowing magma when a very long frequency wave passes 
through it (VLF).  These surficial techniques are not sensitive 
enough, however, to detect the deeper magmatic plumbing 
system of the East Rift Zone.]  Monitoring eruptive volume is 
another means of gaining insight into the workings of the 
volcano.  We were able to accurately predict the demise of the 
Kupaianaha vent in February 1992 by measuring its steadily 
declining output.  [In fact, the VLF technique helped us 
document the steadily decreasing cross-section of that lava 
tube as its output decreased and the sides cooled.]  During 
periods when lava flows are threatening inhabited areas, 
monitoring lava volume in the tube near the vent can help us 
to make short-term predictions of the activity at the flow front.

About once a month, we hire a commercial helicopter so that 
we can map and photograph the flows from the air and do 
surveying work that requires heavy instruments.  The maps 
we make from the overflights are preliminary.  For more 
precise maps, we work from vertical aerial photos, taken from 
an airplane flying at approximately 20,000 feet above the 
ground.  Recently, we have begun using portable GPS (Global 
Positioning System) receivers to map the active lava flows as 
we walk around the margin of the flow field.
 
At present, no residential areas are immediately threatened by 
the eruption.  The main concern now is for archeological sites 
within the National Park and for the native forest, which is 
vulnerable to forest fires set by the flows.  We exchange 
information with the National Park Service on flow advance 
and keep Civil Defense informed.  On days when we are not in 
the field, we rely on information that commercial helicopter 
pilots provide us on the location of the lava flows.  [As of 
Saturday, 8/22, commercial helicopter pilots were reporting 
that flows had entered the forest on the southern side of the 51 
vents.]
 
Volcano Watch is a weekly feature provided by the scientists at 
Hawaiian Volcano Observatory.
 
Aloha+73 de Greg wh6dt@wh6af.hi.usa.oc

     /\    /\    /\/\/\/\/\/\/\.-.-.-.-.......___________
    /  \  /  \  /Hawaii Institute of Geophysics, Honolulu\/\/\.-.-....__
___/    \/    \/Joe Dellinger, Internet: joe@montebello.soest.hawaii.edu\/\.-.__
Newsgroups: sci.geo.geology