August 2009 Addendum to UW Coastal Geology team tephra report — Lobtsova Locality,
northern Kunashir — J. Bourgeois and Jesse Einhorn
Note: Some results of these analyses were presented following the 2006 field season. Bourgeois
has attempted to compile all the raw data and to support the correlation made by Jesse Einhorn in
his senior thesis project 2006-2007. These data are relevant to paleotsunami analyses.
On 25 July 2006, a coastal geology team measured one profile and described four excavations
[and one beach outcrop] on the Pacific coast of northern Kunashir [Figures 1 and 2] — we called
this locality “Lobtsova”. The field team was J. Bourgeois, B. MacInnes, M.E. Martin, J. Einhorn,
and M. Nikula-Olsen.
1994 tsunami
deposit
Tephra from
Tyatya 1973 eruption
9-10
1m
1990 + 25
2100 + 35
Ta-c
23
Soil volc anic lastic bac kground
[prim arily Tyatya c inders and ash]
Tephra, ac idic
Sand, undifferentiated
48
Analyzed sam ples
50 m
48
45
10 m
Tsunami deposit
45
beach
outcrop
off
profile
23
9-10
Figure 1. Summary diagram of Lobtsova profile and excavations, including radiocarbon
analyses of samples [black dots], and highlighting acid tephra [red dots] chosen for Einhorn’s
microprobe analysis. Tsunami deposits are shown in darker green. Ligher green sands may also
be tsunami deposits, but we are less certain. Excavation 48 and the original sketch of the
excavation are shown in Figure 2. See appendix for original profile and sketches.
Figure 2. Left: Photograph of Excavation 48 on Lobtsova profile [see Figure 1]. Right: Fieldseason sketches of excavations 48 [left] and 45 [right], with some correlations and interpretations
superimposed. Red dots on sketches indicate samples taken for potential tephra analyses, black
dots for radiocarbon, and green dots for [tsunami] sand samples. All samples are archived at the
University of Washington. The two samples where glass geochemistry has been analyzed are the
“non-local tephra” in excavation 48 [called “Lobtsova 48”], and the orange-colored tephra at the
base of excavation 45 [right] [called “Lobtsova 45”].
General background and description
The soil-pyroclastic cover exposed in excavations is composed primarily of tephra from
nearby Tyatya volcano, capped by a thick sequence of medium-gray ash from the 1973 eruption.
Tyatya Volcano, situated in Kunashir Island at the southwestern end of Kuril Islands, is a large composite
stratovolcano and one of the most active volcanoes in the Kuril arc [Nakagawa et al., 2002]. Tyatya tephra
are basic [relatively low silica, 50-60%, medium-dark gray in color] in composition [Nakagawa
et al., 2002]. Previously from closer to Tyatya’s flank, Nakagawa et al. [2002] reported several
sicilic tephras and correlated them geochemically with Baitushan B-Tm tephra [A.D. 969, from
mainland China] and younger tephras from Hokkaido, from Mashu, Tarumai and Komagatake
volcanoes [Figure 3].
Figure 3. [caption is copied from Nakagawa et al., 2002]. Distributions of widespread tephras
(<ca 1 Ka) from volcanoes in Hokkaido and from Baitoushan Volcano (inset). Localities
identifying each tephra are shown in the figure from Tokui (1989), Machida (1996), Furukawa et
al. (1997), Wada et al. (2001) and M. Nakagawa et al. (unpubl. data, 2002). Data from W Hirose
(unpubl. data, 2000) and H Honma (unpubl. data, 2000) are also included. Distribution of B-Tm
from Baitoushan is after Machida and Arai (1983). B-Tm (ca AD 969 •} 20) from Baitoushan–
Tomakomai Volcano; Ko-c1 (AD 1856) and Ko-c2 (AD 1694) from Hokkaido–Komagatake
Volcano; Ma-b (ca 1 Ka) from Mashu Volcano; and Ta-a (AD 1739) from Tarumai Volcano.
At the Lobtsova site, in older excavations [48 and 45] toward the back of the coastal
plain/beach-ridge complex [Figure 1], there are two thick silicic [aka acidic, light-colored]
tephras relatively low in the sections. One tephra occurs in both sections [labeled “non-local
tephra” on Figure 2], and the other occurs at the base of Excavation 45. For sake of shorthand,
we will refer to these two tephra as “Lobtsova 48” and “Lobtsova 45,” because the analyzed
samples were from those excavations, respectively. Lobtsova 45 is older than Lobtsova 48.
Neither of these tephra occur in shoreward excavations 23 and 9-10, indicating that the land
surface at these shoreward points is younger than the two silicic tephras of interest. We started
an excavation in the low area between points 23 and 45, but ran out of time to complete and
describe it.
The general trend in excavations from shore to land [Figure 1 and Appendix] is for the
proportion of sand and number of sand layers to decrease and the number and maximum age of
tephra to increase. The sand is derived from the shoreline and may be deposited by tsunamis
across the plain and by storms close to the shore. Tephra, deposited by airfall, should be more
blanket-like, but the proximity to Tyatya, the main tephra source, means that tephra are more
variable from excavation to excavation [e.g., see the Tyatya 1973 example, Figure 1,2 and
Appendix]. Although excavations 48 and 45 are relatively close to one another, their detailed
stratigraphy varies, but for the reasons already mentioned, and also likely because they are close
to a steeper slope, where some material may have washed down onto the surface of those
localities.
The most easily correlated part of the excavations [in addition to Tyatya 1973] is a lightcolored tephra overlain by a black, organic-rich muck. Even so, the thickness and character of
the light-colored tephra varies, and the space between the light-colored tephra and the black
muck also varies. We are confident in our correlation of this tephra, which we refer to herein as
“Lobtsova 48.” The other obviously silicic tephra in the sequence occurs only in Lobtsova 45,
at the base.
[need physical description of samples from Jesse, or redo]
Geochemical analyses and correlation
[need protocol Jesse used on JEOL microprobe at UW]
Multiple glass particles were analyzed in March 2007, for major element composition on the
JEOL microprobe in the Department of Earth & Space Sciences at the University of Washington.
Results of those analyses are provided in Appendix Tables and summarized in plots Figure 4, 5
and 6 and 7. Results of microprobed glass of Lobtsova 48 are consistent [Appendix Table 1],
whereas Lobtsova 45 showed some outliers in analyses [Appendix Table 2]. In both sets of
analyses, titanium-oxide results are quite variable [see Figures 5,6].
Lobtsova 48 has a glass composition [Appendix Table 1] very similar to tephra from Tarumai
volcano on Hokkaido [summarized in Nakagawa, 2002 with earlier references; also see
Furukawa et al., 2006; Furukawa and Nanayama, 2006; Nanayama et al., 2007] [Figures 4-7].
Based on this chemistry, and also on the overlying radiocarbon dates of 1990 + 25 and 2100 + 35,
we correlate this tephra to Tarumai Ta-c, age given in Nanayama et al. [2007] as 2500-2700 B. P.
Lobtsova 45 lies below Lobtsova 48 and has no additional age control from radiocarbon or
otherwise. Its glass geochemistry [Appendix Table 2] is similar to a Pleistocene tephra A-Tn
from Aira volcano on South Kyushu island, used as a standard in glass geochemical analyses in
Japan [Figure 5-7]. The age of this tephra A-Tn is reported to be 26-29 ka, and it is highly
unlikely that Lobtsova 45 is that old — it is likely no older than 5 ka, and probably younger.
Thus this tephra Lobtsova 45 remains uncorrelated with a known marker tephra.
Oxide Wei ht Percent
g
100.00
Major Element Composition
10.00
1.00
0.10
Kunashir tephra
0.01
Si
O2
Ti
O2
Al
2O
3
Fe
O
= Tarumai c. 2500 BP
M
nO
M
gO
Ca
O
Na
2
O
K2
O
Figure 4. [from Jesse Einhorn’s powerpoint]. Major element composition of Lobtsova 48
compared to typical Tarumai tephra composition [Jesse, where is the Tarumai plot from?].
Based on stratigraphic position and radiocarbon ages [Figure 2], M. Nakagawa [e-mail
communication] agrees that this tephra is likely Tarumai Ta-c, with a reported age of 2500-2700
ybp [also see Nanayama et al., 2007].
4.00
3.50
Lobtsova48
3.00
K2O
Lobtsova48b
2.50
Lobtsova45
Lobtsova45b
2.00
Tarumai Ta-a
A-Tn
1.50
1.00
0.50
0
0.2
0.4
0.6
0.8
1
1.2
TiO2
Figure 5. Plot of TiO2 vs. K20 for analyzed Lobtsova tephras and selected marker tephras from
Japan, Tarumai Ta-a [Nakagawa et al. 2002] and Aira A-Tn [Machida, 1999? Jesse, which refs?].
TiO2 vs. K20 is a common plot for correlating tephras from Japan [Figure 7; also see Nakagawa
et al., KPB reports], but analyses of the Lobtsova tephras produce high variability in TiO2. Note
that although we point out the similarity between Lobtsova 45 and A-Tn, we do not suggest a
correlation, because A-Tn is Pleistocene, and we are quite sure that Lobtsova 45 is Holocene.
We correlate Lobtsova 48 with Ta-c [Furukawa et al., 2006; Furukawa and Nanayama, 2006; no
analyses plotted, but similar to Ta-a, which is much younger]. Geochemical data for plotted
Lobtsova points are in Appendix Tables 1 and 2.
4
Lobtsova45
3.5
A-Tn
K2O
3
Lobtsova48
Tarumai Ta-a
2.5
2
1.5
1
0.5
55
60
65
70
75
80
SiO2
Figure 6. Plot of SiO2 vs. K20 for Lobtsova tephras compared to Tarumai Ta-a and A-Tn [see
Figure 5 for references]. Note that although we point out the similarity between Lobtsova 45 and
A-Tn, we do not suggest a correlation, as A-Tn is Pleistocene, and we are quite sure that
Lobtsova 45 is Holocene. Geochemical
data for plotted Lobtsova points are in Appendix Tables
points 45 & 48 plotted on Nanayama fig 6, showing
1 and 2.
widespread Holocene tephras of northern Japan
Potassium oxide (weight percent)
5
4
point 48
point 48 average
3
point 45
point 45 average
2
1
0
0
0.2
0.4
0.6
Titanium oxide (weight percent)
Figure 7. [provided by Jesse Einhorn]. Plots of geochemical analyses of glass from Lobtsova
48 and 45 on Figure 6 from Nanayama et al. (2007), showing range of compositions of
widespread Holcene marker tephra in northern Japan. The unlabeled gray zone is the reference
composition of Aira tephra A-Tn
Implications and further work
The positive correlation of Lobtsova 48 [and the same tephra physically correlated in the
adjacent excavation] extends the known distribution and isopach map of Tarumai Ta-c [Figure 8].
This marker should be very useful on the island of Kunashir, and its occurrence should extend
onto Iturup to the north. The age of this tephra [c. 2500 BP, or 2500-2700] makes it useful for
paleotsunami, archaeological and other studies. Our radiocarbon ages are limiting minima; their
proximity above Ta-c may be useful in establishing the age of this tephra, in that we would
suggest that the age may be closer to 2500 than 2700.
The unknown correlation of Lobtsova 45 tephra, older than Lobtsova 48, has no implications
in the short term, but clearly a correlation and mapping of this tephra would be useful,
particularly if it has an age, e.g., of 3500 years, which could aid in future stratigraphic work in
the region.
No other obvious silicic tephra were identified in our excavations, albeit we worked quickly.
Moreover the sections are very rich in Tyatya tephra, which may obscure thin silicic layers.
Thus although we did not find Baitoushan B-Tm or other younger Holocene tephras expected on
Kunashir [see Figure 3], they may well be present and identifiable in other and in expanded
sections on northern Kunashir.
The study at Lobtsova was done in one day, and clearly more work could be useful. Even on
this profile, additional excavations and more time for careful description and sampling would
benefit the study. However, the amount accomplished in this one day is enough to make a new
correlation and also to contribute to the paleotsunami history of northern Kunashir, previously
unreported [see paleotsunami report].
8 cm
TARUMAI ~2500
Figure 8. [Figure modified from Einhorn powerpoint, map from Google Earth]. The correlation
of a thick silicic tephra at the Lobtsova site on northern Kunashir [red dot, 8 cm thick] with
Tarumai Ta-c [about 2500 years old] [see Figure 3 for other relevant marker tephra].
References
114December 2002
368
Tyatya Volcano
M. Nakagawa
et al.
10.1046/j.1038-4871.2002.00368.x
Research
Furukawa R., Nakagawa M., Furukata C., Yoshimoto M. (2006a) Pre-historic activities of
Tarumai volcano, Hokkaido, North Japan. Chikyu Monthly, 28, 302-307. [in Japanese, reference
provided by M. Nakagawa]
Furukawa R., Nanayama F. (2006b) Holocene pyroclastic fall deposits along the Pacific coastal
region of Eastern Hokkaido. Bull. Volcanol. Soc. Japan, 51, 351-371. [in Japanese, reference
provided by M. Nakagawa]
Machida, H., 1996. Tephras in Marshland at Kucharo Caldera, Biruwa (HK-10). Inventory of
Quaternary Outcrops-Tephras in Japan. Japan Association for Quaternary Research, Tokyo. 109
pp. (In Japanese).
Machida H. & Arai F. 1983. Extensive ash falls in and around the Sea of Japan from large late
Quaternary eruptions. Journal of Volcanology and Geothermal Research 18, 151–64.
Machida H. & Arai F. 1992. [Atlas of Tephra in and Around Japan]. University of Tokyo Press,
Tokyo (in Japanese).
Nakagawa, Mitsuhiro, Yoshihiro Shizuka, Takashi Kudo, Mitsuhiro Yoshimoto, Wataru Hirose,
Yasuo Ishizaki, Nobuo Gouchi, Yoshio Katsui, Alexander W. Solovyow, Genrikh S. Steinberg,
and Arslan I. Abdurakhmanov, 2002. Tyatya Volcano, southwestern Kuril arc: Recent eruptive
activity inferred from widespread tephra: The Island Arc, v. 11, p. 236-254.
Nanayama, Futoshi, Ryuta Furukawa, Kiyoyuki Shigeno, Akito Makino, Yuji Soeda, and Yaeko
Igarashi, 2007. Nine unusually large tsunami deposits from the past 4000 years at Kiritappu
marsh along the southern Kuril Trench: Sedimentary Geology, v. 200, p. 275–294
Appendix — Field and geochemical data
Appendix Figure 1. Field-season sketches of excavations at Lobtsova.
Lobtsova Point
Elevation (m)
28
24
20
16
12
8
4
0
-4
-20 -40
Distance from shore (m)
500 480 460 440 420 400 380 360 340 320 300 280 260 240 220 200 180 160 140 120 100 80 60
40 20
0
Appendix Figure 2. Lobtsova Profile, pink points are, from left to right, points 48, 45 and 23.
The fourth excavation, between points 9 and 10, is in the low spot between 40 and 50 m from the
shoreline. O on this profile is high tide mark at the back beach.
Appendix Table 1: Microprobe analyses of glass from tephra at Lobtsova Point 48, depth of
122-130 cm [analyses by Jesse Einhorn, 2007 at University of Washington].
Oxide Weight Percent (5 March):
Pt#
Label
25
2
6
5
21
30
24
22
26
28
point 48
pt48tephra12
pt48tephra1
pt48tephra3
pt48tephra2
pt48tephra8b
pt48tephra16
pt48tephra11
pt48tephra9
pt48tephra13
pt48tephra14b
SiO2
78.75
76.77
76.53
76.31
76.2
75.92
75.91
74.93
74.36
73.94
TiO2
0.0921
0.5983
0
0.3223
0.2763
0.5985
0.1844
0.2759
0.3217
0
Al2O3
13.24
12.57
11.69
12.65
12.24
13.58
13.29
14.87
13.96
13.67
FeO
1.9927
1.9734
1.8832
2.1202
1.956
1.8639
1.4995
2.6834
2.9751
2.2465
MnO
0.0694
0.1561
0
0.0694
0.0174
0.0694
0.0347
0
0
0.052
MgO
0.1952
0.3673
0.3144
0.4323
0.0868
0.1963
0.2415
0.2844
0.4852
0.3866
CaO
1.9528
2.136
1.9311
2.1236
1.8223
2.0078
2.0099
2.8372
2.7573
2.5689
Na2O
2.5926
3.61
3.94
2.4865
3.31
3.33
3.77
3.5
3.04
3.67
K2O
2.3995
2.1473
2.3111
2.221
2.3346
2.4119
2.1905
2.1269
2.007
2.5289
Total
101.28
100.33
98.59
98.74
98.25
99.98
99.14
101.51
99.91
99.06
Average:
75.9620
0.2670
13.1760
2.1194
0.0468
0.2990
2.2147
3.3249
2.2679
99.6790
1.7375
2.2
1.6652
1.9252
2.0697
1.7666
1.8094
2.0693
1.5355
1.9107
1.911
2.0986
2.3012
2.1564
1.9251
1.6941
1.867
1.983
1.9827
2.1268
2.5307
2.0409
2.0409
1.8963
2.214
2.3432
2.3287
2.3574
0.1522
0.0169
0.0169
0.2029
0
0
0.0338
0.0338
0.0508
0.0507
0
0.0338
0
0
0
0.0338
0.1352
0.1352
0.0169
0.0338
0.0507
0.0169
0
0
0
0
0
0.0676
0.181
0.276
0.2909
0.2081
0.3069
0.1662
0.2461
0.2612
0.3079
0.2838
0.3292
0.2996
0.4086
0.2612
0.201
0.2119
0.2157
0.3788
0.2921
0.2848
0.3649
0.447
0.447
0.341
0.4135
0.4294
0.3722
0.4066
1.9546
2.187
1.8009
1.9834
1.7056
2.1074
2.07
2.213
2.0574
2.1074
2.1783
1.9026
2.0556
1.99
2.1996
2.042
1.9099
2.0268
2.3526
1.8792
2.5454
1.8592
1.8593
2.317
2.4617
2.3065
2.6336
2.5914
2.9788
3.06
3.34
3.34
3.45
3.12
3.66
3.16
2.6305
3.36
3.33
3.57
3.04
3.18
3.39
3.69
3.28
3.5
3.61
3.42
3.46
3.58
3.58
3.53
3.6
3.6
3.48
3.51
2.2164
2.183
2.1923
2.1442
2.2158
2.1756
2.1828
2.0052
2.0414
2.3745
1.8632
2.1755
2.1034
2.2548
2.1571
2.0883
2.3983
2.0639
2.093
2.4204
1.8117
2.1042
2.1043
2.046
1.846
1.8844
1.931
2.1546
99.14
99.6
99.14
99.08
98.92
98.08
99.66
99.64
97.94
98.76
98.51
98.39
98
98.31
98.11
98.42
98.5
97.97
98.95
98.17
99.99
98.08
98.06
98.18
98.44
98.03
98.4
98.24
Oxide Weight Percent (7 March):
34
2
3
32
12
15
31
38
39
37
41
6
16
13
14
29
28
27
10
7
35
25
24
18
22
23
20
36
122-130 cm
pt48tephra30c
pt48tephra18b
pt48tephra18c
pt48tephra30
pt48tephra23
pt48tephra24
pt48tephra29
pt48tephra32b
pt48tephra32c
pt48tephra32
pt48tephra33b
pt48tephra20
pt48tephra24b
pt48tephra23b
pt48tephra23c
pt48tephra28b
pt48tephra28
pt48tephra27c
pt48tephra22b
pt48tephra20b
pt48tephra31
pt48tephra27
pt48tephra27
pt48tephra25
pt48tephra26b
pt48tephra26c
pt48tephra25c
pt48tephra31b
Average (7 Mar):
point 48 averages
point 48
76.86
76.84
76.57
76.57
76.38
76.12
76.02
76.02
75.93
75.83
75.82
75.81
75.76
75.75
75.59
75.56
75.5
75.32
75.24
75.23
75.18
75.13
75.13
74.98
74.51
73.58
73.42
73.41
0.2704
0.1352
0.5859
0.0451
0.4954
0.4057
0.3605
0.7655
0.2255
0.2253
0.4506
0.2252
0.1351
0.3153
0.7659
0.1352
0.4505
0
0.4505
0.8103
0.4949
0.0901
0.0901
0.3605
0.045
0.495
0.4501
0.2251
122-130 cm
12.79
12.71
12.67
12.66
12.3
12.22
13.28
13.12
13.16
12.62
12.63
12.27
12.2
12.4
11.89
12.97
12.75
12.56
12.92
11.97
13.56
12.8
12.8
12.7
13.36
13.39
13.78
13.52
75.50214 0.339425 12.78571 2.017396 0.038639 0.308307 2.117764 3.373189 2.115404 98.59679
75.6232
0.3478
0.208562
12.8884
2.0442
0.0408
0.3059
2.1433
3.3605
2.1430
0.159573
98.8816
Appendix Table 2: Microprobe analyses of glass from tephra at Lobtsova Point 45, depth of
164-178 cm [analyses by Jesse Einhorn, 2007 at University of Washington].
Oxide Weight Percent: 10 March
Noraml Analyses:
Pt# labels
1 pt45tephra3
2 pt45tephra3b
3 pt45tephra3c
6 pt45tephra5
7 pt45tephra5b
8 pt45tephra6
11 pt45tephra8b
12 pt45tephra9
14 pt45tephra9c
19 pt45tephra11b
averages:
combined average
std dev
point 45
164-178 cm
SiO2
78.05
78.91
78.1
77.29
78.3
76.62
77.57
76.81
76.75
77.95
TiO2
0
0
0
0.1391
0
0
0.1391
0.1391
0.2318
0
Al2O3
12.15
12.55
12.26
12.41
12.11
12.25
12.21
12.21
12.13
12.4
FeO
0.8467
1.2472
1.1584
1.0246
1.1285
0.8911
1.0839
0.98
1.0839
0.9654
MnO
0.1951
0.1596
0.0887
0.1241
0.1773
0.1951
0.195
0.1419
0.0887
0.1241
MgO
0.1215
0.2275
0.1254
0.1636
0.1448
0.2509
0.2317
0.1942
0.2093
0.2056
CaO
0.9195
1.1691
1.0366
1.2568
1.1247
1.191
1.1614
1.2937
1.0806
1.1468
Na2O
3.65
3.11
3.48
3.71
3.85
3.71
3.33
3.8
3.62
3.99
K2O
3.44
3.53
3.18
3.35
3.35
3.27
3.46
3.47
3.52
3.2
Total
99.37
100.9
99.43
99.47
100.19
98.37
99.39
99.04
98.72
99.98
77.64
0.06
0.08
0.093492
12.27
1.04
0.15
0.19
1.14
3.63
3.38
3.38
0.111128
99.49
Al2O3
12.3
12.29
13.31
12.46
FeO
1.306
1.2623
1.0985
1.1433
MnO
0.3899
0.1064
0.195
0.0887
MgO
0.2784
0.1056
0.1634
0.1293
CaO
1.1238
1.3526
1.0288
1.2057
Na2O
3.77
2.0897
3.5
3.5
K2O
3.31
3.41
3.44
3.45
Total
100.65
98.89
100.03
98.33
These anaylses have anomalous points
Pt# labels
SiO2
TiO2
10 pt45tephra8
78.17
0
13 pt45tephra9b 78.04
0.2319
18 pt45tephra11
77.1
0.1854
20 pt45tephra12
76.3
0.0464