Eruption Report

From: Aoki Masahiro
Date: Fri, 8 Mar 1996 09:12:55 MST

Subaqueous eruption from the caldera of
Akademii Nauk volcano on January 2-3, 1996.

Karpov G.A., Muravyev Ya.D., Shuvalov R.A., Fazlullin S.M. and Chebrov V.N.

Institute of Volcanology
Far East Division
Russian Academy of Sciences
Petropavlovsk-Kamchatsky 683006 Russia

On January 2nd,1996, at about 0800 local time, an eruption began from the Karymsky volcano in Kamchatka. The eruption was preceded by upsurge in seismic activity, which began in april 1995. volcanologists have made a forecast that the eruption will probably occur. On december 31,1995, at 1926 LT, an earthquake of M=5.8 occurred in the Kronotsky gulf, 50-60 km north-east of volcano. On January 1, at 2057 LT, an earthquake of M=5.2 was recorded immediately in the Karymsky volcano region and then, at 2157 LT, an earthquake of M=6.9 occerred at distance of about 25 km south of volcano. During the next day, more than 10 events of M >/=5.0 took place in the epicentral zone of the earthquake of M=6.9. On January 2, at 1540 LT, a group of volcanologists from the Institute of Volcanology has arrived in the eruption area by helicopter. Flying in the vicinity of the volcano, two eruptive centers have been marked: one, near the summit of Karymsky and another, 5-6 km south of the volcano, in the Karymsky Lake (d~4 km, max. depth - 115m), which fills the caldera of the Akademii Nauk volcano. The eruption from Karymsky volcano began with the formation of vent with a diameter of 20 - 30 m, which was located 50 m below the summit of the volcano. Very violent impulsive emmissions of gas jets higly loaded with ash, rising to one kilometer above the eruption vent, took place on the south-west slope. Steam - gas jets, occasionally with noticeable black-colored matter, were ejected by pushes to several hundred meters from beneath the water of the Karymsky Lake. The presumed eruptive center was located 100 - 200 m from the shore in north-west sector of the lake. Turbulent steam - gas uprushes rose to 5 -6 km above the water surface, which can be outlined as a circle 200 m in diameter. Ice covering the lake has entirely melted. On January 3 and 4 the eruption of the Karymsky volcano increased. On January 3, the near-summit crater increased in size, reaching 50 m in diameter. Two eruptive vents have already been acting: one, in the summit crater and another, on the south-west slope. One could see pure gas and steam ejections (gas blasts) to be alternated and enchanced by explosions with ash ejections, the both vents being active simultaneously. Most frequently, ash was ejected from the upper eruptive vent, whereas white-colored gas was commonly ejected from the lower vent. Ash ejection lasted 2 - 3 minutes, then gas blasts occurred during 1.5 - 2 minutes. An ash and gas eruptive column rose to some 1 - 1.2 km above the eruptive vents and then drifted by the wind to the east and south-east, oceanward. The surface of the Karymsky Lake steamed intensely. Clouds of steam rose to 800 - 1000 m above the lake. Water areas of green color were visible through rents in the clouds. A newly-formed beach zone of black color was distinctly seen. In the northen and north-easten sector of the lake a narrow spit, beginning from the source of the Karymsky river and extending for 250 - 300 m to the center of the lake, has formed.The level of the water table in the lake reduced by a few meers. The upper reaches of the river has dried up, but as volcanologists reported, on January 2, waves from the subwater eruption (up to 10 m high or maybe higher) had overflowed the north shore of the lake, and the huge mass water flooded a wide valley of the river 1.5 km below the source. During a surveillance flight over the eruption area on January 4, large areas of the valley at this place were seen to be covered by mud of black color. Within the formed beach zone of the lake 70 - 100 m wide, three fumarole vents are well seen. They seem to follow the fault zone of north-eastern strike. Immediately in the area of the Karymsky river source, in a radius 500-800 m, the surraunding hills are covered with snow, in which thousands of funnels with a diamrter ranging from 10 cm to 1.5 - 2 m are seen. These are tracks of intense lithic materiale jections from lakeside. The area buried by ash from the Karymsky volcano was preliminarily estimated to be 150 - 200 km2. Ash of ligth gray color is dacite in composition. At a distance of 8 km from the volcano fractions ranging from 0.16 to 0.06 mm dominant. Accoding to estimates, made by Prof. S.A.Fedotov, on January 2 and 3 the ash ejection rate from the summit crater reached 3 - 4 t/s. High gas abundance in the air was felt in the vicinity of the volcano.

Results of air inspections show great changes in the configuration of the shore zone of the lake. The level of water continues to fall becouse ot its intense evaporation. The temperature of water in the lake probably increased very abruptly and all fish in the lake seem to die. We suppose that a volcanic cone forms st the lake bottom (or probably an extrusive dome forms or an exposure of sill occurs). It is not excluded that its sammit will emerge above the water surface. In the subwater part of the eruption the formation of pillow lava flows is possible and after the active phase of the eruption ceases, fumarolles will be very active and we have every reason to suppose the appearance of "smokers" (subwater smokers), i.e. the zones of ore material deposition.

Routine observations carried out from January 2 through February 11, 1996, have shown that a climactic phase of the subaqueous eruption continued for no more than 12-15 hours. Actually, it was a series of frequent explosions probably of phreato-magmatic genesis, during which vapor-gaseous mixture with cinder-bomb material was ejected to the surface. In the northern sector at the shore of the lake west of the Karymsky river-head, barked trees were noticed which are an evidence of two eruptive sources located at 500-600 m distance from each other. In this zone, the main concentration of bomb material ejected from the lake is observed. Besides, a portion of the shoreline (150-200 m long and 5-15 m wide) east of the river-head sank into the lake to several meters.

The eruption centre is supposed to be at 500 m distance from the lake shore. Also smaller peripheral eruptive centres were observed. As a result of the eruption, in the NNW sector of the lake near the shore, a beach zone formed in the form of a wide cape 0.4 km2 in area, the narrow spit of which is followed to SE to 620 km distance from the old shore. The length of the new shoreline is 2.4 km. Large shoal is observed around the new peninsula and, according to the preliminary estimations, the ejected material deposits in the lake are at least 1 km2 in area and 5-10 mln. m3 in volume.

Thermal springs of Akademii Nauk volcano that discharge at the southern shore of the lake, 3 km from the eruption centre, ejected the material which filled their gryphons as a result of this eruption, the gryphon edifices were destroyed and several new mud pots were formed. Chemical composition of the solutions (sample 11.02/1), Table 1) was not changed.

Near the central part of the newly-formed beach composed of sand-gravel and bomb material, a chain of five explosive vents with diameters from 1.5 to 30 m is observed in the submeridional direction. In the north, the chain is bounded by a round thermal site with a diameter of about 50 m. This site vapors intensively. It is covered by sublimates and one can feel a hydrogen sulphide odour. A dry funnel with a diameter of about 3 m, high gas emission and temperature of 97 C is in the central part of this site.

The other explosion funnels have water at a depth of 1.2-1.5 m with a temperature from 33 to 70 C, level of which depends on the water level in the lake. In three closest to the lake shore funnels and in the opposite shore zone, gas emissions with a temperature of 97-98 C are observed.

The chemical analyses (Table 1, sample 22.01/5) show that hot water seeps at this beach, has chiefly bicarbonate-chloride-sulphate- sodium composition which is similar to that of the Karymsky springs with the total mineralization reaching 1.5 g/l. But water composition in the lake is different. These are mainly sulphate- sodium-calcium solutions with rather high concentrations of F, Fe and Mn. Ni and Cu are also abundant (Table 1, samples 22.01/1, 22.01/2, 11.02/3). Note low pH of the lake water and high alkalinity of the Karymsky river water (sample 04.01/5, Table 1).

Sample 04.01/5 was taken from the river 6 km below the river-stream on January 4, 1996 when run-off from the lake ceased owing to the damming of an effluent by the ejected material. Melt water (leaching ashes) from the neighbouring creeks and solutions from the discharge zone of the Karymsky thermal springs are supposed to be in the river. It is really similar to the Karymsky springs in saline composition, but has much higher pH and higher Ca and Mg concentrations. Obviously, that the composition of the Karymsky river waters, pH of which is similar to the solutions of the Akademii Nauk springs, cannot be explained only by simple mixture of waters from the Karymsky springs and melt waters.

Taking into account chemical composition and pH of water extracts from the Karymsky volcano ash (Table 2), we can suppose that the water composition of the lake is affected by gas components of fluids which discharge in the eruptive zones and by water-soluble part of magmatic material lying at the lake bottom. A possibility is not excluded of both the breakthrough of vapor-gaseous reservoir which feeds the Akademii Nauk springs and participation of thermal waters of the Karymsky springs in the discharge.

If somebody would like to join for study of this phenomenon, pleas contact with Sergei Fazlullin by e-mail:

Table 1

                                  No of sample
Component mg/l
                04.01/5   22.01/1  22.01/2  11.02/3   22.01/5  11.02/1

  H+             0.00      0.60      0.08     0.69      0.00     0.00

  NH4+           0.1       0.1       0.1      0.2       0.1      0.1

  Na+            61.1      56.6      85.1     75.0      341.7   255.0

  K+             4.8       8.5       9.8      7.3        43.2    13.9

  Ca2+           40.1      66.1      126.3    66.0      50.1      5.6

  Mg2+           46.2      19.5      53.5     14.4      30.4     <0.2

  Fe2+            -        <0.3      <0.3     <0.3      <0.3      0.0

  Fe3+            0.1      24.0      5.25     <0.3      <0.3      0.0

  Mn              1.40     2.00      3.30       -        0.5       -

  Zn*             0.02     0.04       -         -        0.04      -

  Cu*             0.008    0.05       -         -        0.0003    -

  Cd*             0.02     0.001      -         -        0.003     -

  Ni*             0.002    0.019      -         -        0.003     -

  Cl-             49.7     49.0       67.5     35.5     224.4    303.0

  F-              1.36     2.06       2.51      1.8      0.43     1.7

  SO42-           172.9    405.8      730.1    379.0    691.6    86.5

  HCO3-           200.1     0.0        0.0      0.0      70.8    42.7

  CO32-            0.0      0.0        0.0      0.0      0.0     23.4

  H3BO3             -      <0.7       <0.7      <0.7     14.8    32.6

  H4SiO4 dissolv.  108      210        279        -      193      -

  H4SiO4 coll.      0        0          0         -      209      -

  pH               8.10     3.22       4.10     3.16     6.75     9.35

  To C              10       22        26-28     19       56       98

Date of sampling 04.01.96 22.01.96  22.01.96 11.02.96 22.01.96 11.02.96

04.01/5  - Karymsky river; 22.01/1, 22.01.2 -  Karymsky lake at
shore; 11.02/3 - Karymsky lake, central part; 22.01/5  - explosive
funnel N3, 11.02/1 - Akademii Nauk springs.
Analyses were made at the Institute of Volcanology. * - Data by
S.M.Fazlullin, "-" - not detected.

Table 2

                                  No of sample
Component, mg/l
                   3.01/Ovs.        3.01/Budn.         4.01/Fazl.

H+                 0.00275          0.4208             0.5616

Na+                27.85            133.4              115.9

K+                 3.72             23.52              <14.2

Ca2+               38.82            872                304.3

Mg2+               7.57             54.4               25.4

Fe2+               20.14            14.4               <10.9

Fe3+               0.61              9.6               <10.9

Cl-                42.74            163.5               257

F-                 4.86             12.64                8.3

SO42-              181.4            2643                1112

HCO3-              0.0              0.0                  0.0

CO32-              0.0              0.0                  0.0

H4SiO4 dissolv.    4.5               78                   -

H4SiO4 coll.       0.0               0.0                  -

pH                 5.26              3.07                2.95
3.01/Ovs. - sample collected at 800 m distance from Karymsky lake.
3.01/Budn. - sample collected at a hut at Dvor volcano.
4.01/Fazl. - sample collected at 8 km distance from Karymsky volcano
             and at the same distance from Karymsky lake.
Masahiro AOKI