Microgravity Changes and Ground Deformation at Rabaul Caldera, 1973–1985
A progressive gravity decrease of more than 410 µgal took place at Rabaul Caldera, Papua New Guinea, between August 1973 and July 1985. The gravity change correlates with ground deformation at the caldera, particularly with uplift of more than 1.8 m. The patterns of gravity, elevation, horizontal distance and tilt changes indicate a principal source of inflationary deformation beneath the east-central part of the caldera. These phenomena, together with increases in seismicity, are expressions of a new phase of caldera unrest which commenced in 1971 and intensified markedly during late 1983 and 1984.
The observed relationship between gravity and uplift is about -216 µgal m−l. This relationship is consistent with an increase of sub-surface mass, presumed to be a magmatic intrusion. A simple model which accounts for the observed gravity and elevation changes is a “point” source at a depth of 1.8 km. The depth of the source remained constant suggesting that it is a well-established feature capable of accommodating the inferred physical change without becoming unstable, and/or that further ascent of magma was prevented by an overlying body of unyielding rock.
The scale of the monitored geophysical changes is generally indicative of a relatively small-scale intrusion. Calculations based on the gravity changes indicate a mass increase of 1.0 × 108 t. The magnitude of this intrusive event is well within the range of magnitudes of previous eruptions at the post-caldera vents.
KeywordsGround Deformation Crisis Period Elevation Change Gravity Change Gravity Measurement
Unable to display preview. Download preview PDF.
- Anderson EM (1936) The dynamics of the formation of cone sheets, ring-dikes and cauldron subsidences. R Soc Edinburgh Proc 56: 128–163Google Scholar
- Brooks JA (1971) Investigations of crustal structure in the New Britain/New Ireland Region, 1969. Part 1: Geophysical and geological data. Aust Bur Min Res, Record 71/131 (unpublished)Google Scholar
- Brown G (1878) Journal of the Rev. G. Brown, 1860–1902, (11 volumes) (unpublished). Mitchell Library, Sydney AustGoogle Scholar
- Cifali G, d’Addario GW, Polak EJ, Wiebenga WA (1969) Rabaul preliminary crustal seismic test, New Britain 1966. Aust Bur Min Res, Record 69/125 (unpublished)Google Scholar
- Cooke RJS (1977) Rabaul Volcanological Observatory and geophysical surveillance of the Rabaul Volcano. Aust Phys 1977: 27–30Google Scholar
- Crick IH (1975) Investigation into a change in topography at Rabaul Golf Course. Geol Surv Papua New Guinea Report 75/6 (unpublished)Google Scholar
- Fisher NH (1939) Geology and vulcanology of Blanche Bay, and the surrounding area, New Britain. Territory of New Guinea Geol Bull 1: 1–68Google Scholar
- Fisher NH (1976) 1941–42 Eruption of Tavurvur Volcano, Rabaul, Papua New Guinea. In: Johnson RW (ed) Volcanism in Australasia. Elsevier, Amsterdam, pp 201–210Google Scholar
- Groten E (1983) Report on high precision gravimetry Volume II. International Association of Goedesy Special Study Group 3. 37. Verlag des Institutes für Angewandte Geodäsie. Frankfurt A.M. 103 pGoogle Scholar
- Iida K, Hayakawa M, Katayose K (1952) Gravity survey of Mihara Volcano, Oosima Island, and changes in gravity caused by eruption. Geol Surv Jpn Rep 152: 1–28Google Scholar
- Kushiro I (1978) Density and viscosity of hydrous calc-alkalic andesite magma at high pressures. Carnegie Inst, Washington, Year Book, 77: 675–677Google Scholar
- Mogi K (1958) Relations between the eruptions of various volcanoes and the deformations of the ground surface around them. Bull Earthq Res Inst 36: 94–134Google Scholar
- Nairn IA, Talai B, Wood CP, McKee CO (1988) Geology of Rabaul Caldera (in preparation)Google Scholar
- Sapper K (1910) Beiträge zur Kenntnis Neupommerns und des Kaiser-Wilhelmsland. Petermanns Mitt 56:189–193, 255–256 (in German)Google Scholar
- Schleinitz GEG (1889) Die Forschungsreise S.M.S. “Gazelle” in den Jahren 1874 bis 1876 unter Kommando des Kapitän zur See Freiherrn von Schleinitz. Herausgegeben von dem Hydrographischen Amt des Reichs-Marine-Amts. I. Teil des Reiseberichts. Mittler, Berlin (in German)Google Scholar
- Scott BJ (1982) Tiltmeter recordings at Rabaul Caldera Papua New Guinea: 1963–1979. Geol Surv Papua New Guinea Report 80/13: 1–12 (unpublished)Google Scholar
- Simpson CH (1873) Hydrographical extract from a six months cruise among the South Sea Islands. Report to the Admiralty, 11 December 1872, Great Britain, Parliamentary Accounts and Papers, Session 6 February–5 August 1873, Colonies and British Possessions, pp 1–50Google Scholar
- Smith RL (1979) Ash-flow magmatism. In: Chapin CE, Elston WE (eds) Ash-flow Tuffs. Geol Soc Am Spec Paper 180: 5–27Google Scholar
- Speith MA, Stuart WD, Kinoshita WT (1975) Time-dependent gravity and elevation changes on Kilauea Volcano. EOS Trans Am Geophys Union 56: 1071Google Scholar
- Walker GPL, Heming RF, Sprod TJ, Walker HR (1981) Latest major eruptions of Rabaul Volcano. In: Johnson RW (ed) Cooke- Ravian Volume of Volcanological Papers, Geol Surv Papua New Guinea Mem 10: 181–193Google Scholar