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ABSTRACTS FROM AGS99


Transantarctic Mountains Deformation Monitoring Network (TAMDEF)\
South Victoria Land - Initial Results

Larry Hothem, Jerry Mullins and Robert Glover
U.S. Geological Survey, Reston, VA
and
Ian Whillins, Terry Wilson, and Mike Willis
Byrd Polar Research Center, The Ohio State University, Columbus, OH

TAMDEF is a collaborative GPS campaign initiated in 1996 by Ohio State University scientists in cooperation with the U.S. Geological Survey and sponsored by the National Science Foundation to measure horizontal and vertical deformation in the McMurdo Sound region.

An array of 28 GPS stations spans an area approximately 375 km north-south and 300 km east-west with the goal of measuring and attempting to differentiate between causes for the rock motions. The expected signals are: (1) crustal rebound - uplift is predicted for the north end of the study area (from considerations of glacial geology) with more uplift predicted at the south end (based on glaciological theory) due to formerly thicker ice in McMurdo Sound region of the Ross Sea; and, either an eastward or westward tilting depending on whether the ice-age glaciers in East Antarctica or West Antarctica thinned or thickened the most. (2) tectonic - there is evidence for active ‘normal’ fault motion in specific zones in the mountain front and active spreading is predicted across the Terror Rift. (3) volcanic - subsidence is possibly due to the weight of the volcanic material from the Ross Island volcanoes; and, Mt. Erebus is currently active and there may be episodic inflation or deflation.

In this region of Antarctica, model predictions for crustal rebound toward isostasy reach vertical motion rates of 3 to 20 mm per year. The directions and patterns of these predicted motions are mostly distinct. The design of the deformation monitoring network and the GPS observing campaign strategy was designed to discriminate among them.

The GPS surveys form geometrical elements at three spatial scales: (1) long baselines (100 km) that span the features most expected to show motion according to the hypotheses above - simultaneous tracking time is at least 2 days, often 7 days, (2) Short baseline (10 km) arrays crossing suspected fault zones with inferred neotectonic motions - simultaneous tracking time about 24 hours, and (3) Very short baselines (0.1-0.2 km) at each site to test for local motion due to such processes as frost action -simultaneous tracking time is 0.5-1.0 hours.

All monuments are special stainless steel pins set in the rock that stand about 0.05 m above the rock. Between November 1996 and January 2000, the station arrays were established and repeat measurements completed using dual-frequency late model GPS instruments in combination with choke-ring antennas. Analysis of the measurements from 3 observing campaigns are yielding repeat values in any coordinate ranging generally between 0 and 3 mm for the very short-baseline 'microfootprint' arrays and 2 to 5 mm for the short and long baseline arrays.

Scheduled for the 1999-2000 field season is the last of four independent observing campaigns in this phase of the TAMDEF project for the South Victoria Land region.


RECENT RESULTS OF GPS NETWORKS FOR CRUSTAL DEFORMATION CONTROL ON TERRA NOVA BAY AREA (Antarctica)

A.Capra, S.Gandolfi, P.Sarti, F.Mancini, L.Vittuari
DISTART- University of Bologna

The Italian geodetic network, located around Terra Nova Bay, Italian base in Antarctica, was monumented in 1990-91 as reference frame for scientific activities (photogrammetry, cartography, geology) and with geodynamics purposes. The network was completely surveyed two times in 1990-91, 1993-94 and it was surveyed in December 1998. A geodetic GPS network was also established in 1990-91 for the study of deformation control of Mount Melbourne volcano. The network has been surveyed four time: 1990-91, 1993-94,1995 and 1997-98. The coordinates variation resulted quite small after the fourth repetition, in comparison with method precision.

The results obtained with two different software (Geotracer v. 2.25 and Bernese v.4.0) and different approach to GPS data solutions (Lc,L1,L3) were significantly different. It is probably due to the different algorythms and to the modelisation of ionospheric effects.So a new data processing have been made with a third software, Gipsy, presenting a different approach . The results of the Gipsy application and the comparison with the other solutions, are presented. A deformation analysis has been made integrating geodetic measurements with geophysical observations.

Moreover the analysis of the data acquired from TNB GPS permanent station and the results of measurements of for very long occupation and obtained at very far away stations ( about 1000 km each other): TNB1 (Italian base), Dome C station (during Dome C Strain Net surveying in January 1999) and Mc Murdo (USA bas eare also presented.


GPS NETWORKS FOR THE OBSERVATION OF ICE SURFACE DEFORMATION IN DOME C AND TALOS DOME AREAS

G. Bitelli, A. Capra, S. Gandolfi, F. Mancini, L. Vittuari, M. Frezotti
DISTART - University of Bologna

Accurate topographical surface, surface ice deformation, bedrock topography and internal layering are important physical parameters to modelling the age of ice versus depth. In the framework of EPICA (European Project for Ice Coring in Antarctica), GPS kinematic profiles and a geodetic strain network of 37 stations were carried out at Dome C in 1995 during the 11th Italian Expedition in Antarctica. In order to determine the ice surface deformation, geodetic strain network were re-measured a second time in January 1999.

During 1996 ITASE Italian expedition a snow/firn core of 90 m has been drilled on the topographic top of Talos Dome. In the same area was established and surveyed a GPS strain network of 9 stations for the determination of ice deformation around the drilling site. GPS measurements were repeated in December 1998.

Results of Dome C and Talos Dome strain networks that was made in 1998-99 Italian expedition and the analysis of ice surface deformations are presented.


ABSOLUTE GRAVITY MEASUREMENT AT ABOA:
EFFECTS OF CLOSE-RANGE ICE AND SNOW COVER

Jaakko Mäkinen
Finnish Geodetic Institute
P.O.Box 15
FIN-02431 Masala
Finland
Ph: +358 9 295 55 317
Fax: +358 9 295 55 200
E-mail: Jaakko.Makinen@fgi.fi

In January 1994 the Finnish Geodetic Institute made a determination of absolute gravity at the base Aboa (73°03’S, 13°25’W) in Western Queen Maud Land. The JILAg-5 absolute gravimeter was used. The work was a part of the Finnish scientific Antarctic expedition FINNARP-93. I give a brief description of the results. A repeat measurement is planned in coming years, to detect a possible variation in gravity due to vertical motion and large-scale mass transfer.

The site is on a small mountain of basaltic rocks with a large solid angle to the surrounding glacier and to the snowy slopes descending towards it. I discuss the gravity effects of mass variations in this near field.


ACTIVITY OF POLISH SURVEYORS IN SPITSBERGEN

Leszek Kolondra
Silesian University
Chair of Geomorphology
Faculty of Earth Sciences
ul.Będzińska 60
41-200 SOSNOWIEC
email: lkolondra@geodezja.katowice.pl

The beginning of Polish geodetic works in Spitsbergen took place exactly 65 years ago. During the first Polish expedition in 1934 some of the last white spot existing on the Spitsbergen map were measured. Among the seven members of this expedition were couple surveyors. Triangulation network was established and the area of 260 km2 (Amundsenisen area of Wedel Jarlsberg Land) in the scale 1:50 000 was measured by means of terrophotogrammetric method. From this time, contemporary Norwegian maps (sheet B12, C12) contain many of Polish names, for example: Kopernikusfjellet, Polakkbreen, Curie-Sklodowskafjellet and many, many others.

Next period activity of Polish surveyors in Spitsbergen was the period 1957-59 - our contribution in the III International Geophysical Year and to the International Geophysical Co-operation (1959-60). In this time the buildings of Polish Scientific Polar Station was erected in Hornsund Fiord on Spitsbergen. Also at that time the astronomical point was established and terrophotogrammetric surveys were initiated (changes of the front position glaciers Hans, Werenskiold and another topographic works - in result of which was elaboration two maps of glaciers: Werenskiold 1: 5 000 (3 sheets, 42.3 km2) and Penck 1: 2 000 (2 sheets, 5 km2).

Unfortunately, Polish surveyor works (and scientific expeditions) to Spitsbergen were interrupted after ‘60 our century for a period of dozen years. Thanks to activity and pertinacity scientists of Wrocław University next scientific expedition took place. The photogrammetric works was not main aim of this search, however some terrophotogrammetric photos were used to determinate the changes of front position of glaciers Hans and Werenskiold.

The most important and fruitful period of our activity started in 1978, when Polish Scientific Polar Station on Spitsbergen was reactivated (and is working permanently up to now). The Institute of Geophysics of Polish Academy of Sciences guides the Station. Many scientific programmes are realised also by other regional academic centres not only in environs of Polish Polar Station.

The geodetic works are done mainly for specialists other sciences, especially for glaciology. The main topics are:

- Registration of changes of the front positions ,
- Determination of surfaces movement of the Hans Glacier,
- Topographic elaboration (maps of glaciers and them surroundings),
- DTM of glacier with radar and radio sounding of bedrock,
- Analysis geometry changes of glaciers (longitudinal profiling by means of GPS techniques and Airborne laser altimetry method,
- Mapping of a macro and mezo cryokarst form on glaciers surface.

The main geodetic and cartographic results (printed) of this works are:

- Topographic map 1: 5000 surroundings of Polish Polar Station,
- Map 1: 500 of Polish Polar Station,
- Map 1: 5 000 of frontal part Werenskiold Glacier (6 edition from different periods),
- Thematic map 1: 75 000 Geomorphology (Hornsund Fiord area),
- Thematic map 1: 75 000 Geology (Hornsund Fiord area),
- Topographic maps 1: 25 000 (10 sheets) Hornsund area,
- Topographic map 1: 25 Hans Glacier,
- Topographic map 1: 25 Amundsenisen,
- (In elaboration topographic map 1: 25 000 Werenskiold Glacier and surroundings in numeric form after digital elaboration of aerial photos).

From 1982 year we have permanent informations about changes of front position of Hans Glacier (over 100 cycles in different periods) and his surface movement (one week, one day period even - over 30 cycles). We are using the permanent photogrammetric station (autocentering iron ring) to registration cyclic observation.

In 1991 together with colleagues from Norsk Polarinstitutt - Oslo and Institute of Geography of Academy of Sciences - Moscov we participated in international programme survey of large glacier area. The longitudinal profiles of Amundsenisen Plateau, Lomonosovfonna and Kongsvegen - Svea Glacier were measured by means GPS method.

Thanks co-operation with NASA we have got data of airborne laser altimetry survey over glaciers situated near Polish Polar Station. Some data were elaborated (Paierl, Műlbacher and Amundsenisen) – the great reduction in heights of surface glaciers were observed.

The other results ours geodetic works are published in permanent publications and are presented on scientific conferences, symposiums and workshops in Poland and out borders.