Mt. Discovery Minna Bluff MA 80 MB 69 Diatom 021 GE 036-2 041-I 045-A 42 46 47 Actnocyc/us e//ipticus (early-mid. Miocene) 1 A. inqens s. s (undulated) (mid-late Miocene) Coscinad,scus lentiginosus (early Pliocene-Recent) • C. len/iqinosus I obovatus (mid. Plio.-early Pleisto.) Race//a viqi/ans (late Oligocene) • Synedrajouseana (late Miocene) Tbaloss,osira tarokina (late Miocene-early Plio.) S • S S - rrinacria ventricosa (late Eocene) S Microplankton 5 ______S

Figure 2. Selected diatom taxa in samples from Mount Discovery and Minna Bluff, southern McMurdo Sound.

References Leckie, R. M., P. N. Webb. 1979. Scallop Hill formation and associated Pliocene marine deposits of southern McMurdo Sound. Antarctic Journal of the U.S., 14(5), 54-56. Barrett, P. J. and B. C. McKelvey. 1981. Cenozoic glacial and tectonic McIntyre, D. J., and G. J. Wilson. 1966. Preliminary palynology of some history of the Transantarctic Mountains in the McMurdo Sound re- Antarctic Tertiary erratics. New Zealand Journal of Botany, 4(3), 315-321. gion: Recent progress from drilling and related studies. Polar Record, Webb, P. N. 1972. Wright Fjord, Pliocene marine transgression of an 20(129), 543-548. Antarctic dry valley. Antarctic Journal of the U.S., 7(6), 225-232. Davey, F J., D. J. Bennett, and R. E. Houtz. 1982. Sedimentary basins of Wilson, C. L. 1967. Some new species of Lower Tertiary dinoflagellates the Ross Sea, Antarctica. New Zealand Journal Geology and Geophysics, from McMurdo Sound, Antarctica. New Zealand Journal of Botany, 5(1), 25, 245-255. 57-83.

Seismic observations by the telemetry network. This is the main Geophysical studies on Mount Erebus program of IMESS. The telemetry network with five seismic stations has been operated by the American party on the sum- mit and flank of Mount Erebus since 1980. The Japanese party TAKESI NAGATA installed the recording systems for the seismic telemetry net- work at Scott Base, and the wintering members in Scott Base National Institute of Polar Research have maintained the recording system during the winter sea- ltahashi, Tokyo, Japan son. The Japanese party has supplied magnetic tapes and charts for the recording systems every year and has had the respon- sibility of playing back the magnetic tapes. Three Japanese scientists visited McMurdo Station for the Japanese scientists played back the magnetic tapes which international Mount Erebus seismic studies (IMESs) during the have been recorded since September 1982. The daily number of 1982-1983 field season. The Japanese participants were K. Ka- volcanic earthquakes occurring in and around Mount Erebus minuma of National Institute of Polar Research, S. Ueki of from 14 September to 24 December 1982 is shown in figure 1. An Tohoku University, and E. Koyama of Earthquake Research average of 102 earthquakes had been recorded each day from 14 Institute, University of Tokyo. They conducted the following September to 6 October, 82 earthquakes from 11 to 31 October, research programs while staying at McMurdo Station from 4 and 71 earthquakes from I to 7 November. Data were not avail- November 1982 to 13 January 1983. able because of some trouble of the transmitting system during

38 ANTARCTIC JOURNAL

rkII V kIIIIiflD ( ADrur%IIAvQ

N 200

150

100

50

15 20 25 30 5 10 15 20 25 30 5 10 15 20 25 30 5 10 15 20 SEP. OCT. NOV. DEC.

Figure 1. Daily number of earthquakes recorded at Abbott Peak from 14 September to 24 December 1982.

HOURLY NUMBER OF EARTHQUAKES AND DURATION OF TREMOR October 7 - 9, 1982 EXTREME TREMOR---)L 4? N VOLCANIC TREMOR 150 r INTERMITTENTLY

ID The biggest earthquake

50

0 6 18 0 6 12 18 0 6 12 OCT. 07 OCT. 08 OCT. 09

Figure 2. Hourly number of earthquakes and the activity of volcanic tremors on 7-9 October 1982.

1983 REVIEW 39

8 to 15 November. An average of 99 earthquakes per day had Observations by temporary seismic network. Nine temporary been recorded from 16 to 30 November and 33 earthquakes seismic stations were established on the flank of Mount Erebus from 1 to 24 December. to determine with high accuracy earthquake locations from 15 An extreme earthquake swarm with more than 680 earth- November 1982 to 4 January 1983. Because the magnetic tapes quakes and extreme volcanic tremors were recorded during 8 and batteries at two stations were not changed due to bad and 9 October. (The variations of the earthquakes and the trem- weather in mid-December, data for the latter half of the observa- or activities are shown in figure 2.) One hour after the swarm tion period were obtained at seven stations rather than nine. occurred the tremors also began to occur. Because the exact The earthquake locations will be calculated with high accuracy number of earthquakes could not be counted during the ex- using data from both the temporary and telemetry seismic treme tremors, the hourly number of earthquakes might be networks. actually greater than shown in figure 2. Hypocenters of 60 Gravity measurements. Gravity measurements by the LaCoste- earthquakes were obtained using Ohmoris constant (k =3) and Romberg gravimeter (model G) were carried out at the nine the P-S times (the time differences between P and S wave arriv- temporary seismic stations. Twenty additional gravity stations als) of three stations (Abbott Peak, Hoopers Shoulder, and were established around the summit crater when two Japanese Bomb Peak); unfortunately the important station, the Summit, scientists stayed at the summit hut with the American and New has not worked since the winter season in 1982. Epicenters were Zealand participants for repairing the summit telemetry located in the northwestern flank of Mount Erebus as shown in station. figure 3. Most earthquakes occurred at the depth of 1 to 6 These three research programs have been supported by the kilometers below sea level. Only 5-10 earthquakes per month National Science Foundation (United States), the Antarctic Divi- were recorded in the swarm area during the last two summer sion of the Department of Scientific and Industrial Research seasons [Shibuya et al. in press; Takanami et al. in press (a), in (New Zealand), and the National Institute of Polar Research press (b)]. (Japan). During the visual observation at the summit in mid-De- cember, scientists did not see any evidence (such as lava flows or a large volume of ejecta in the summit crater) of a big eruption; References however, earthquakes in this area might be caused by primary magma coming up from the lower part of the crust to the Shibuya, K., M. Baba, M. J . Kienle, R. R. Dibble, and P. R. Kyle. In magma reservoir which is estimated to be located at the depth of press. A study on the volcanic and seismic activities of Mount Erebus, 1-5 kilometers under the summit. Antarctica 1981-1982. Proceedings of the third symposium on antarctic

OCTOBER 8, 1982 (Ohmoris constant K = 3.0)

0

ABB D 0 cP 0 00 0 0 1 2 K 0 I I 0 00 0 0 0 080 00 0 0 00 c 0000 0 b00 000 0

BOM 0 0

Lava lake

3000 m HOO 0

Summit Crater

Figure 3. Epicenter locations of earthquakes on 8 October 1982. ("km" denotes kilometer; "rn denotes meter.)

40 ANTARCTIC JOURNAL geosciences 1982. (Memoirs of NIPR, Tokyo, Japan, October 1982.) Takanami, T., J. Kienle, P. R. Kyle, R. R. Dibble, K. Kaminuma, and K. Takanami, T., K. Kaminuma, K. Terai, and N. Osada. In press (a). Shibuya. In press. Seismological observation on Mt. Erebus, Seismological observation on Mt. Erebus, Ross Island, Antarctica, 1980-1981. In J. B. Jago and R. L. Oliver (Eds.), Antarctic earth sciences. 1980-1981. Proceedings of the third symposium on antarctic geosciences Proceedings of the Fourth International Symposium on Antarctic 1982. (Memoirs of NIPR, Tokyo, Japan, October 1982.) Earth Sciences, Adelaide, Australia, August 1982.

tion of photographs suggests that this is relatively minor, but Volcanic activity and seismicity of exactly how much lower the lake surface is not known. Sim- Mount Erebus, 1982-1983 ilarly, no major deformation has been observed using precise surveying methods (Kyle and Otway 1982). The lava lake represents the top of a magma column which is JUERGEN KIENLE and connected at depth to a magma chamber. Preliminary calcula- DIANNE L. MARSHALL tions based on knowing the present rate of degassing of sulfur dioxide, knowing the initial and present-day sulfur content of Geophysical Institute the magma, and assuming about 80 years of activity, suggest the University of Alaska magma chamber beneath the lava lake is about 1 cubic Fairbanks, Alaska 99701 kilometer. As in previous years, small strombolian explosions continued PHIL Il R. KYLE to occur at rates of two to six per day. Volcanic bombs ejected onto the crater rim were collected for the study of the petrologic Department of Geoscience and geochemical evolution of the lava lake. To date no change New Mexico Institute of Mining and Technology has been observed in the degree of crystallization or chemical Socorro, New Mexico 87801 composition of the magma. This past field season, 1983, marked the third year of con- KATSUTADA KAMINUMA and tinued operation of a permanent, radio-telemetered, short- KAZUO SHIBUYA period seismic array designed to monitor the long-term seis- micity associated with the volcanic activity at Mount Erebus (see National Institute of Polar Research also Kienle et al. 1982). The program, the international Mount Tokyo 173, Japan Erebus seismic study, involves scientists from the U.S., Japan, and New Zealand. An original tripartite array of short-period RAY R. DIBBLE seismic stations was installed in December 1980. During the 1981-1982 field season, this array was expanded by two sta- Department of Geology tions. All stations have single-component, vertical seis- Victoria University mometers. The summit station also transmits acoustic data to Wellington, New Zealand monitor explosive gas discharge from the lava lake. Another data channel is used to monitor electromagnetic signals induc- ed by the eruption of conducting magma in the static field of the Surveillance of the activity associated with the anorthoclase Earth in a wire loop laid around the summit crater. The current phonolite lava lake at Mount Erebus continued during the network of five stations was serviced and upgraded during the 1982-1983 austral field season. All authors participated in the 1982-1983 field season. Most of the microearthquakes recorded field study. The summit crater was visited by U.S., New Zea- over the past 3 years occurred beneath Mount Erebus proper. land, and Japanese scientists on several occasions between Figure 1 shows as an example the hypocenters of 75 events that November 1982 and February 1983. The lava lake was still pres- were located between 23 December 1981 and 18 January 1982. ent and the pattern of activity was similar to that observed over All but one of these events were positively correlated with the past 6 years. The lake continued to show simple convection, acoustic and sometimes electromagnetic signals. We interpret with magma welling up from two sources about a third of the these events to be explosion earthquakes associated with strom- way from each end of the lake and welling down around its bolian eruptions from the lava lake. edges and along a zone running across the middle of the lake. A more detailed analysis of 162 earthquakes selected from a First discovered in December 1972 (Giggenbach, Kyle, and catalog of 1,000 events recorded during the 1981-1982 season Lyon 1973), the lava lake gradually increased in size over a 4- showed two principal distributions of hypocenters which year period and eventually formed a semicircular lake about 100 Shibuya et al. (in press) called type 1 and type 2 events. Type 1 meters long by December 1976 (Kyle et al. 1982). Since 1976, the events were located centrally beneath the summit crater of lake area has stayed fairly constant. Mount Erebus and had a vertical, pipe-like, hypocenter dis- Observations of the lake level are always obscured by the tribution extending from sea level to the 3,974 meter high sum- gases emitted from the lake. Although a slight lowering of the mit, similar to the hypocentral distribution shown in figure 1. lake surface has been reported over the last 4 years, an examina- Type 1 events are positively correlated with acoustic signals and

1983 REVIEW 41