Lichenometry

Field studies in 1992/93 showed that the crustose lichen Rhizocarpon geographicum (sensu lato) could be used as an age indicator. It occurs widely on young deposits of differing genesis, including glacial and volcanic rocks. Maximum diameters of all the largest lichens were measured on moraine and lava-flow surfaces. For elliptical lichens, the major and minor axes were measured, and the arithmetical means calculated. If the variance for a sub-set of the five maximum dimensions did not exceed a few millimetres, the greatest diameter was taken as the surface-age index. If the maximum diameter was significantly greater than the other four measurements of the sub-set, it was eliminated and the sixth largest lichen was added to the sub-set. To make rough estimates of lichen-growth rate, lava flows of known age (Fig. 2) were explored: Plosky Tolbachik (1941), Yubileiny (1945), Apakhonchich (1946), Vernadsky (Klyuchevskaya volcano) (1956) and the Kozelsky glacier moraine (1976). Since no lichens have yet appeared on the young Kozelsky glacier moraine, the lichen measurements on the lava flows alone were used. Because diameters of 8–13 mm were attained by lichens on the lava flows of the 1940s to 1950s, the approximate rate of Rhizocarpon geographicum growth at its first stage of development is estimated as 0.25 mm a⁻¹.

Fig. 2.

The growth curve of Rhizocarpon geographicum (sensu lato) for the Kamchatka mountains (see text).

Tephrochronology

As a result of tephrochronological studies by the Institute of Volcanic Geology and Geochemistry, Petropavlosk-Kamchatskiy, a generalized soil–pyroclastic section was constructed for the Avachinsky volcano. Pyroclastic layers associated with its eruptions in 1945, 1855, 1779 and 1737 were detected in the upper part (Reference Melekestsev, Braytseva., Dvigalo and Bazanova.Melekestsev and others, 1993). Individual moraines from the stratigraphie sequence were correlated with these tephra horizons. Sections of the overlapping soil–pyroclastic sequence at the surface of moraines were studied and then compared to the generalized sections.

Kozelsky glacier, Avachinsky Group

Direct observations of the dynamics of Kozelskv glacier show that it retreated from the late 1940s to the earl} 1960s, then settled into a steady slate, advanced from 1971 to 1976, and then returned to a steady state (Reference Vinogradov and Murav’yev.Vinogradov and Muravyev, 1992).

The first moraine (Fig. 3; No. 1), bordering the glacier terminus, formed as a result of glacier displacement in the 1970s. Morphologically it is a series of ice cliffs and ridges covered with a thin cinder layer also containing large boulders. It grades into the stagnant ice surface formed since the glacier’s retreat from 1940 to 1960 (Fig. 3; No. 2). Here, the first patterns of lichens (Rhizocarpon geographicum) were found, the maximum diameter of individual lichens being 8 mm. A new “rung” begins 50 m lower along the chute, where more coarse, fragmented material is seen and some vascular plants appear. This moraine rampart is better-defined, having more distinct outlines and a steep outer slope, and is clearly expressed in aerial photographs (Fig. 3; No. 3).

Fig. 3.

Moraine complex of Kozelsky glacier. A, Tongue of glacier; B, topography contours in m; C, moraines of different ages (numbers explained in the text); D, limits of moraine complex: E, site of meteorological observations.

Below, at about 820 m, lies a new belt of moraines containing two distinct ramparts (Fig. 3; Nos. 4 and 5), chiefly composed of large fragments of grey andesites produced by the Kozelsky volcano. The size of the lichens and rough assessments of the growth rate (0.25 mm a⁻¹) suggest that these moraines formed in the 19th century. This is corroborated by the soil–pyroclastic sequence on the older outer moraine rampart Fig. 3; No. 6). A 50 cm thick sequence that contains two tephra layers is associated with the 1945 Avachinsky eruption and the 1907 Ksudach eruption (Fig. 4a). The lower ash layer is underlain by a thin layer of talus deposits which overlies the moraine. Tephra from the 1855 Avachinsky eruption was not observed here, so the moraine must have formed between 1855 and 1907.

Fig. 4.

Soil–pyroclastic sequence on moraines of Kozelsky glacier. (a) moraine of the second half of the 19th century; (b) moraine of the end of the 17th century. AV, ash from Avachinsky eruptions (1945, 1855, 1779 and 1737); KS, ash from Ksudach eruption (1907).

On the outside, a complex of young; unsodded moraines (Fig. 3; Nos. 1–6) lies adjacent to the older, sodded moraine which is covered with elfin-wood cedar (Fig. 3; No. 7). This moraine has smooth outlines and the ridge itself apparently lacks an ice core; the base of the moraine lies at 715 m. The morphological difference between these two generations of moraines is so great that despite their close proximity the corresponding stages of glacier advance would normally be expected to be separated by a significant time interval. Yet, licheno-metric and tephrochronological studies of the older, sodded moraine (Fig. 3; No. 7) imply quite a different interpretation. From the observed maximum lichen diameter of only 76 mm, and using a lichen growth rate of 0.25 mm a⁻¹, the age of the moraine is roughly 300years, i.e. within the LIA. A soil–pyroclastic sequence on it is about 60 cm thick and contains live pyroclastic layers (Fig. 4b) from top to bottom as follows: cinder lapilli from the 1945 Avachinsky eruption; a layer of transition ash from the 1907 Ksudach eruption; and tephra from the Avachinsky eruptions of 1855, 1779 and 1737. The other, older ash layers are missing. Thus, the moraine predates 1737 and is at least 255 years old. The lower pyroclastic layer is underlain by a 12 cm layer of sandy loam which grades into the moraine deposits, indicating that the moraine was formed a few decades earlier than the upper age limit (1737). The lower age limit is 320–340 BP, as determined by radiocarbon dating (Geological Institute, Moscow, sample 6983). This value was obtained on the upper part of the buried soil layer (16 cm thick) underlying the tephra of 1737. Thus, two additional points used as time markers were obtained for constructing the lichen-growth curve (Fig. 2). The relationship between substratum age and maximum lichen diameter is nearly linear, and may be described by the equation, y = 5.5 + 3.8x, where y is the age of the surface (years BP), and x is the maximum lichen diameter (mm). This curve was the basis for dating the moraines formed by other glaciers in the region.

Novograblenov Glacier, Avachinsky Group

Novograblenov is a surging glacier with a northwestern orientation, and terminates at 850 m. Much of the snout, broken up by crevasses into individual blocks, is covered with a cinder layer. No terminal moraines occur below the tongue. The lateral moraines appear as a long rampart approximately 1.5 m high and 20 m wide extending along the left flank, and as two ramparts of somewhat poorer preservation along the right flank. The left lateral moraine (Fig. 5a; No. 1) formed simultaneously with the englacial moraine on the right (Fig. 5a; No. 2), after an advance at the beginning of the 20th century. The older moraine rampart probably dates from the second half of the 19th century. Movograblenov glacier is larger now than at the beginning of the 20th century, since the left lateral moraine is overlapped by the modern terminus of the glacier. No lichens were found on this moraine.

Fig. 5.

Scheme showing the dated moraines of some glaciers at Avachinsky volcano: (a) Novograblenov, (b) Larinshchikov, (c) Elizovsky and (d) Kambalny glaciers. A, moraine ramparts; B, points of lichenometric studies; C, cliffs (i) and crests (ii); D, glaciers; E, nunataks; F, rocks; G, “dead ice”.

Lavinshchikov Glacier, Avachinsky Group

Lavinshchikov is a small foot glacier in the Elizovskaya river valley. It is segregated into two near-slope glaciers, which were united in August 1993 by a drifting snowpack that descended to the terminal moraine, outlining the contours of the glacier during the LIA. The upper moraine has no lichens, but lichens up to 23 mm in diameter occur on the lower moraine. The moraines on the left flank are preserved as several ramparts a few lens of metres long, with pointed ridges and steep slopes. The ages of three of them were estimated at roughly 50, 70 and 120 years (Fig. 5b; Nos. 1, 2 and 3, respectively). Two fragments of moraines (Fig. 5b; Nos. 4 and 5) have been identified on the right flank near the glacier front. Their ages correspond to those of moraines 2 and 3 (Fig. 5b), and they are better preserved, but lichens found here show their stages of advance to be somewhat older, about 75 and 140 years, respectively.

Elizovsky Glacier, Avachinsky Group

Elizovsky is a cirque glacier of southwest orientation, terminating at about 1300 m. It descends in the form of three “rungs” into a narrow valley. The only datable feature is the lateral moraines, which give an approximate upper age limit (Fig. 5c). Three or four “rungs” of lateral moraines were identified, but they are interrupted by eroded areas, and cannot be traced along the entire tongue. The lower moraine rampart, nearest the ice front, has no lichen growth and probably formed recently. The second generation (Fig. 5c; Nos. 2 and 4), which left traces on both sides of the valley, formed at least 50 years ago, but is probably older, given the sizes of the two largest lichens (19 and 17 mm). The higher level of marginal moraines (Fig. 5c; Nos. 1 and 3), deduced from the size of lichens, is attributed to activity in the mid- to late 19th century.

Kambalny Glacier, Avachinsky Group

Kambalny glacier terminates at 1180 m. near an exposure of rock on the right flank of the chute. Comparison with 1974 aerial photographs shows that over the last 20 years it has advanced about 250 m, corresponding to a drop of 100 m. Its from, a steep lobe of pure, till-free ice, suggests that the glacier was advancing in 1993, A small, roughly 10 m long, fresh moraine rampart was seen under the ice near the left side. No other moraines were found near its from.

A cliff promontory ‘Fig. 5d; No. 1) near the terminus has a fresh surface with traces of glacier polishing and scouring. No lichens were found on the lower part of the cliff, but 15–20 m above the chute floor Rhizocarpon geographicum of 25–27 mm diameter was observed. A low terrace (up to 3–5 m), eroded in some places by slope wash, borders the cliff (Fig. 5d; No. 2). It lies directly-adjacent to talus deposits, which probably supply part of the terrace’s surface material. The size of lichens indicates that the terrace formed in the mid-20th century, but the landform is partially rejuvenated by fragments from the slope, complicating the age determination. This terrace formation is linked to glacier retreat from a previous lower position, as supported by the half-eroded moraine line (Fig. 5d; No. 3) surrounding it. The age of these moraines is about 140 years. No consistent moraine line was found on the left side of the valley, but subtle traces of sediment-accumulation features exist at about the same level.

The other three glaciers studied lack any such moraine complexes from which a glacial history could be reconstructed.

Gheremonshny Glacier, Klyuchevskaya Group

Moraine-like features, most of them apparently created by volcanic activity, were discovered near Cheremonshny glacier. Only one moraine (~50 years old) could be dated by lichenometry, but this date is unreliable because of the lack of lichens.

Popkov glacier, Klyuchevskaya group

The Popkov glacier area (Bolshaya Zimina volcano) is covered by lava flows of different ages, so traces of glacial activity are partially obscured. However, lichens are abundant on the large boulders that comprise part of the mixed moraine debris, volcanic ash and recently formed soil covering the surface of the snout. Also, the maximum lichen size on the front is nearly consistent with that on the oldest moraine of Kozelsky glacier. This suggests that the maximum advance of Popkov glacier also occurred in the 17th century, but that its margins have not changed since. Probably, the surface gradually lowered during the last three centuries, and the englacial till melted out, building thicker moraine cover at the terminus.

Erman glacier, Klyuchevskaya group

A similar picture is evident from Erman glacier, the largest in Kamchatka. In spite of its unusual activity, viz. advance during the past 50 years, large masses of “dead ice” exist along its margins and are presently stationary. Preliminary data show that the maximum diameter of lichens on the “dead ice”, is 35 mm. A tephra layer from the 1854 Shiveluch volcanic eruption (Reference BelousovBelousov, 1985) was detected in a 60 cm thick layer of supraglacial moraine overlying the “dead ice” so the age of the “passive-ice” surface is near the mid-19th century.

Kronotsky glacier, Kronotsky volcano

An analogous preservation of superficial cover on Kronoisky glacier moraines was reported by Reference TsiurupaTsiurupa (1988). The glacier lobe. 100 m from the front, is covered by volcanic cinder supporting abundant vegetation: Oxitropis sp., Vacinum uliginosum L., Oxiris digina (L.) Hill., Saxifraga purpurasoens Kom. and two species of dwarf willow, Salix ovlifolia Trautv. and S. berbeifolia (?) Pall. ssp. Kamchatcia A. Skvort. The age of one of the species of Salix ovalifolia Trautv. was estimated at 151 BP.