Rose, W.I., R.L. Chuan, and P.R. Kyle. 1985. Rate of sulphur emission Symonds, R.B., P.R. Kyle, and W.I. Rose. 1985. S021 emission rates and from Erebus volcano, Antarctica. Nature, 310, 710 - 712. the 1984 activity at Mt. Erebus, Antarctica. EOS, (Transactions of the Ross, J. 1847. Voyage to the southern seas (Vol. 1). London: John Murray, 216-220. American Geophysical Union), 66(18), 417 (abstract). Scott, B., and P. Otway. 1985. Volcanic deformation studies—Mt. Woollard, G.P. 1962. Crustal structure in Antarctica. In H. Wexler, M.J. Erebus. New Zealand Antarctic Record, 6(2), 20 - 23. Robin, and J.E. Caskey, Jr. (Eds.), Antarctic Research. (Geophysical Smithson, S. B. 1972. Gravity interpretation in the Transantarctic Moun- tains near McMurdo Sound. Geological Society of America Bulletin, 83, Monograph No. 7.) Washington, D.C.: American Geophysical 3437-3442. Union.
Geophysical studies on Mount Erebus fl------D&ily ,,o,,b& 01 earthquakes counted at Hooper Shoulder
5 0 ------Doily ,oe,be, 01 large eruptions ,000,d.d at Hoopeoo Shoulder ,ed/o, Scott Base K. KAMINUMA and K. SHIBUYA
National Institute of Polar Research Itabashi, Tokyo, Japan
K. NuDA
Faculty of Science, Hokkaido University Kita-ku, Sapporo, Japan
Continuous seismic observations have been carried out since September October November December 1980 by a cooperative International Mount Erebus 1964 Seismic Study (IMEss) which includes Japan, the United States, Figure 1. Daily number of earthquakes counted at the Hoopers and New Zealand (Takanami et al. 1983; Kienle et al. 1982). We Shoulder station (shown with columns) and daily number of large three Japanese scientists participating in the IMESS visited eruptions recorded at the Hoopers Shoulder station and/or Scott McMurdo Station during the 1984 - 1985 austral summer. We Base. conducted a series of scientific research programs during our tenure at McMurdo Station from 11 November 1984 to 15 Janu- Seismicity. The seismic activity observed on and around ary 1985. Mount Erebus is summarized from the IMESS observation rec- Earthquakes and eruptions. New volcanic activities of Mount ords in 1980 - 1984 as follows: (1) volcanic earthquakes were Erebus commenced on 13 September 1984 (Kienle et al., Ant- detected at a rate of 20 to 160 events per day; (2) the earthquakes arctic Journal, this issue). A number of large explosions were were distributed over a wide area around Mount Erebus; and recorded by the IMESS network seismic stations on Ross Island. (3) some earthquake swarms with more than several hundred The numbers of earthquakes recorded daily at Hoopers Shoul- events per day occurred on the flanks of Mount Erebus and der station and the numbers of large eruptions counted daily at continued for several days after initiation. Hoopers Shoulder and/or Scott Base are shown in figure 1. The epicentral distribution of earthquakes is shown in the In the middle of September, the seismic stations were not upper part of figure 2, and the focal depth distributions are transmitting seismic signals to Scott Base continuously because projected onto a vertical northeast-southwest section across there was not enough sunlight to the solar panels during the Ross Island in the lower part of figure 2. These results cover a 2- austral winter to charge the batteries, therefore we estimated year IMESS observation period from 16 February 1982 to 11 Feb- the number of earthquakes per day in September from partial ruary 1984. About 230 earthquakes are depicted in figure 2; the observations. The exact number of earthquakes for the days epicenter locations for these earthquakes were determined with indicated with an arrow at the top of the column was probably horizontal and vertical errors less than 3 kilometers. An greater numbers than those shown in figure 1. aseismic zone located in the southwest area of the summit The number of earthquakes per day decreased very rapidly (figure 2) is apparent as a zone of very few earthquakes. This by the end of September. From 50 to 100 events per day were aseismic zone has also been reported by Shibuya et al. (1983), recorded in October and November. Ueki et al. (1984), and Kaminuma et al. (in press). The aseismic From 5 to 19 large explosions were clearly recorded at Scott zone might be associated with the existence of a magma reser- Base each day from 13 to 24 September. The explosions in- voir supplying fresh magma to the lava lake at the Erebus creased from 25 to 29 September (12 to 31 per day). About 20 summit. explosions per day on average occurred in October and 15 per Explosion seismic measurements. To reveal the structure of the day in November. A new type of eruption which can be suitably Erebus volcano, especially to confirm the existence of the mag- called a gas-jetting eruption, commenced on 3 December, and ma reservoir, explosion seismic measurements were carried out the large eruptions began to cease at the same time. in December 1984. In addition to the 10 telemetry seismic sta-
28 ANTARCTIC JOURNAL
tions, seven temporary seismic stations were established on The gravity measurements were carried out at the seven Mount Erebus (figure 3, section A). Three stations out of seven temporary seismic stations and five telemetry stations to obtain were installed at the summit area at elevations of 3,000 to 3,200 gravity values with higher accuracy than the data measured in meters, and the other four stations were located on the flanks of the last season. Mount Erebus.
1984 - 1985 SEISMIC NETWORK
168E 166E
• ----- Telemetory Station 0----- Temporary station ----- Explosion points
McMurdo 0 10 20 30 Station Scott Base
BAR - x •viJ------
H00 -
TSC--
ABB - :-: ..- ---- NE TRU ------SW-:pi LFA
BOM .------
SBA - Ie.--.--.-o------10 • - CLA ------, -
TER - - - - l5Lkm
Figure 2. Hypocentral distributions of earthquakes in the period 09h56m00s Dec. 10, 1984 57m00s from 16 February 1982 toll February 1984. Top: epicenter locations. Bottom: focal depth distributions projected onto vertical cross- section oriented northeast-southwest. Solid circles denote an Figure 3. A. Seismic stations for explosion seismic experiments and earthquake and open squares denote radio-telemetered stations. the location of explosion points. B. Seismograms of the explosion ("km" denotes "kilometer." See figure 3 caption for station name earthquake experiment (at 09 hours 56 minutes 00 seconds) 10 abbreviates.) December 1984. Stations: BAR (Cape Barns), HOO (Hoopers Shoul- der), TSC (Three Sisters Cone), ABB (Abbott Peak), TRU (Truncated Cone), LFA (Lower Fang Ridge), BOM (Bomb), SBA (Scott Base), CLA (Clush Site), and TEA (Summit of Mount Terror).
All seven explosions listed in the table produced excellent records. The shot points were located at Cape Barns, Lower List of seismic explosion experiments Fang, Three Sisters Cone, and Bomb. An example of the seis- mogram for one of the Cape Barns shot point experiments is Remarks Shown in figure 3, section B. The arrow on the Cape Barns Date (1984) Time Location ecord (figure 3, section B top) indicates the explosion time of origin. 4 December 02 11 Lower Fang Ridge Test - First arrival times at the station closest to the shot point are 03 08 Lower Fang Ridge Test clearly indicated. At all stations first arrivals could be identified 04 14 Lower Fang Ridge except for Scott Base where much background noise was pres- 7 December 02 05 Three Sisters Cone Test ent. The epicentral distance from the Mount Terror Station to 10 December 09 56 Cape Barns the Cape Barns shot point was 40 kilometers, hence the dimin- 19 December 01 39 Three Sisters Cone ished energy. 20 December 03 08 Bomb Gravity. Five new gravity stations were established on Ross Island during the 1984 - 1985 austral summer. a In hours and minutes.
1985 REVIEW 29 Geological survey. To enhance the study of the structure of the Cole, J.W., P.R. Kyle, and V.E. Neal!. 1971. Contributions to Quaternary McMurdo volcanoes using both geophysical and geological geology of Cape Crozier, White Island and Hut Point Peninsula, methods, a geological survey was also carried out during the McMurdo Sound region, Antarctica. New Zealand Journal of Geology 1984 - 1985 austral summer. Late Cenozoic volcanic rocks of the and Geophysics, 14(3), 528 - 546. McMurdo Volcanic Group are widespread in and around Ross Frobs, R.B. 1983. Ultrabasic inclusions from the basalts of the Hut Point Island. It has been well known that the volcanic rocks carry a area, Ross Island, Bulletin Volcanologique, 16, 13 - 21. Kaminuma, K., M. Baba, K. Shibuya, and R.R. Dibble. In press. Explo- large number of ultramafic to mafic xenoliths; lherzolites in sion earthquakes of Mount Erebus, Antarctica. Memoir of National basanite from Cinder Hill, Cape Bird (Cole and Ewart 1968), Institute of Polar Research, Special issue. dunites and lherzolites in basanites from Cape Crozier (Cole, Kienle, J. , D.L. Marshall, S.A. Estes, R.R. Dibble, K. Shibuya, and P.R. Kyle, and Neal! 1971), various types of xenoliths in basanites Kyle. 1982. Seismicity of Mount Erebus, 1981 - 1982. Antarctic Journal from Hut Point Peninsula (e.g., Frobes 1963; Cole et al. 1971), of the U.S., 17(5), 29 - 31. and !herzo!ites in basanites from Mount Nubian, Black Island Kienle, J. , C.A. Rowe, P.R. Kyle, W.C. McIntosh, R.R. Dibble, K. (Cole and Ewart 1968). Kaminuma, and K. Shibuya. 1985. Eruption of Mount Erebus and During the 1984 - 1985 austral summer, field studies were Ross Island seismicity, 1984-1985. Antarctic Journal of the U.S., 20(5). made on the volcanic rocks and the xenoliths of Cape Bird, Cape Crozier, Hut Point Peninsula, and Black Island. The purpose of the geological field work at these volcanic sites was to study and Shibuya, K., M. Baba, J. Kienle, R.R. Dibble, and P.R. Kyle. 1983. A collect xenoliths. study of the seismic and volcanic activity of Mount Erebus, Ant- arctica, 1981-1982. Memoir of National institute of Polar Research, Special Issue, 28, 54 - 66. Takanami, T., K. Kaminuma, K. Terai, and N. Osada. 1983. Seis- References mological observations on Mount Erebus, Ross Island, Antarctica, 1980— 1981. Memoir of National Institute of Polar Research, Special Issue, Cole, J.W., and A. Ewart. 1968. Contributions to the volcanic geology of 28, 46-53. the Black Island, Brown Peninsula and Cape Bird area, McMurdo Ueki, S., K. Kaminuma, M. Baba, E. Koyama, and J. Kienle. 1984. Sound, Antarctica. New Zealand Journal of Geology and Geophysics, Seismic activity of Mount Erebus, Antarctica in 1982-1983. Memoir of 11(4), 793 - 828. National institute of Polar Research, Special issue, 33, 29 - 40.
Mineral chemistry of the Kirkpatrick the chemistry of the minerals and use the data for modelling possible paths of evolution within the low-titanium rocks and Basalt, northern Victoria Land between the low- and high-titanium rocks. The plagioclase compositions are illustrated in figure 1. The most notable feature of these plagioclase grains is the high M.A. HABAN and D.H. ELLIoT anorthite (An) content which in some cases is more than An. Individual samples show a range in values of about 10 percent Institute of Polar Studies and cluster either in the calcic anorthite (An) or sodic and anorthite (An7080) range. The high-titanium lavas have more Department of Geology and Mineralogy albitic plagioclase (An 70). The more calcic anorthite composi- Ohio State University tions (greater than An) are among the most calcic plagioclases Columbus, Ohio 43210 ever recorded from continental flood basalt fields; equivalent compositions have been reported only from East Greenland (Upton, Emeleus, and Beckinsale 1984) and certain Deccan Tholeiitic lavas of the Kirkpatrick Basalt and sills of the Ferrar lavas (Krishnamurthy and Cox 1977). Dolerite crop out in an area about 60 x 100 kilometers in the Mesa Range region (73 11 S 162°55 E) of northern Victoria Land The pyroxene data are plotted in figure 2. The calcium-rich (Elliot et al. 1982, 1983). In the Mesa Range itself, the strat- pyroxenes in the low-titanium rocks are, in general, high mag- igraphic thickness of the basaltic lavas attains a maximum of nesium/iron augites with a scattering of more iron-rich augites about 780 meters and consists of up to 40 flows ranging in and subcalcic augites. The calcium-poor pyroxenes include both thickness from less than 1 meter to more than 80 meters. The orthopyroxene and pigeonite. The former have compositions lavas and sills appear to fall into two distinct compositional similar to orthopyroxenes from other flood basalts. The types, designated the low-titanium and high-titanium magma pigeonites, however, include some of the most magnesian re- types (Siders and Elliot 1985). The high-titanium type has been corded from any geologic setting. Among the continental flood found only as the capping unit in the Mesa Range and Sculpture basalts, comparable pigeonites have been reported by Upton et Mountain, and has a thickness of more than 70 meters. All other al. (1984) for a single tholeiite flow, which, like the Mesa Range analyzed flows and sills belong to the low-titanium type. flows, is also high in silica (approximately 54 percent). The high- Electron microprobe data have been obtained for plagioclase, titanium rocks contain only clinopyroxene, and both the augite pyroxene and opaque grains, and volcanic glass in these and pigeonite compositions are like those of the most iron-rich tholeiitic rocks (Haban 1984). The objective was to investigate clinopyroxenes from the low-titanium rocks.
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