USGS/Cascades Volcano Observatory, Vancouver, Washington
REPORT:
Geodetic Studies in the Novarupta Area, Katmai National Park, Alaska, 1990 to 1995
-- Kleinman, Jack W., Iwatsubo, Eugene Y., Power, John A., and
Endo, Elliot T., 1997,
Geodetic Studies in the Novarupta Area, Katmai National Park, Alaska,
1990 to 1995:
IN:
Dumoulin, Julie A., and Gray, John E., (eds.), 1997,
Geologic Studies in Alaska by the U.S. Geological Survey, 1995:
U.S. Geological Survey Professional Paper 1574, 328p.
Abstract
A five-station electronic distance meter (EDM) network centered around the
Novarupta dome in Katmai National park, Alaska, was established in 1990 and
resurveyed in 1993 and 1995. Both EDM and Global Positions System (GPS)
measurements were made in 1993. The 1995 survey was restricted to the more
accurate GPS surveying method. Analysis of EDM data in 1993 suggested an
average increase of 22.5 millimeters
in slope distances between stations from 1990 to
1993. Those changes were about 2-3 times the expected error for lines of this
length (1.5 to 4.7 kilometers) and suggested that ground deformation was taking
place in the Novarupta area. Loss of data from one of five GPS receivers in
1993 precluded complete comparison of GPS data with EDM results. In July 1995,
the network was occupied with five P-code GPS receivers. Two 12-15 hour
observations were made simultaneously at all five stations, which were located
relative to a reference GPS station in Fairbanks. For final L1-only solutions
and EDM line lengths between stations, one station was held fixed using these
new coordinates. The 1995 GPS results, when compared with recomputed EDM line
lengths for 1990 and 1993 and available 1993 GPS line lengths, indicate that the
Novarupta site moved about 15-20 millimeters to the west and the Mainstreet
station moved a similar distance to the northwest during the interval from 1990
to 1993. There is a suggestion that the Mainstreet stations also moved from
1993 to 1995. The movement at both stations is thought to be a result of a
deformation source to the southeast outside the network or associated with the
stability of the sites. The movement is not a result of volcano deformation
centered at Novarupta. To further evaluate ground deformation in the Katmai
area, extension of the network with GPS observations beyond the immediate
vicinity of Novarupta is recommended.
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03/03/98, Lyn Topinka