２０１７年ネパール通信７
ランタンの旅をまとめ、ポカラへ
３月末から４月初めにかけてのランタンの調査を終え、４月１１日と１２日のSOHAM会議の後に、カトマンズ大学の講義がはじまり半月たった。その間にランタン調査の原稿（下記）を締め切りに間にあわせて投稿したら、時すでに5月を迎えようとしている。歳のせいだろうか、最近は、時のたつのがとくに速いのを感じる。
５月初めには、１年ぶりにポカラに行き、国際山岳博物館の展示の更新をする。その他にポカラでは、懸案の大森さんの大型写真の更新にも目処をたてるとともに、ランタン村でのヒマラヤ災害情報センター構想の実現をめざす活動について国際山岳博物館のネパール側関係者とも相談することに加えて、昨年末に亡くなった友人の米道裕彌さんの石碑＊を、すでに祀ってあり、ヒマラヤの神々の座に見守られている友人・先輩たちに仲間入りしてもらおうと思っている。
＊ 友人の米道裕彌さんの石碑
ネパールでは今年２月後半の余震の後、この２ヶ月間は全く余震のない状態が続いている。その間、地震エネルギーが地下に蓄積されていることを考えると、余震がないことは地下が安定しているのではなく、近い将来の大きな地震発生の兆候だとも解釈できるので、安心はできないだろう。
ポカラへは４月３０日にカトマンズをたち、５月７日にもどる、いつものバスの旅になる。
それでは、みなさまもご自愛ください。ナマステ！
（カッコウの歌声が聞こえるカトマンズ大学にて記す）
記
The
avalanche sediments of Langtang village and the terminal change of Khimshun
glacier－A preliminary report from Langtang excursion for the first time in
20 years－
Hiroji
Fushimi
Kathmandu
University
Preface
From 27 March to 5 April 2017, I made a short excursion to Langtang
village (Fig. 1) suffered from a huge avalanche that occurred at 11:56 on 25
April, 2015, at the time of the Gorkha earthquake and it was my Langtang
trekking for the first time in 20 years. Also, I visited Kyanjin (Fig. 1) for
measuring the Khimshun glacier that I had once been to the area in 1975. Here,
I would like to present a preliminary report of the avalanche sediments of
Langtang village and the terminal change of Khimshun glacier, and the related impression
on landslide disasters in Langtang valley.
Fig. 1 Google Earth map of Langtang valley
with GPS trail.
Fig. 2 The avalanche sediments are seen
from Chamki.
1) Avalanche sediments of
Langtang village
When I saw firstly the avalanche sediments of Langtang village from
Chamki, I was very much surprised to have seen that the avalanche sediments
were divided by Langtang river into 5 parts; the main body (AS0) in the right
bank and another 4 bodies (AS1-4) in the left bank of Langtang river (Fig. 2-3),
and also, each body has ice layers; A and B (Fig. 4).
Right after the Gorkha earthquake 2015, the avalanche sediments
covered almost all parts of Langtang village located in the right bank of
Langtang river, and also reached to the left bank of the river blocking the
river course. The original surface of the avalanche sediments (B0) is detected
from the boundary between the grass flank and the debris one along the left
bank of the river (Fig. 3 and 8) and the height difference between B0 and the
surface of the present B layer is approximately 10m showing the amount of the surface
melting during these two years since the occurrence of the Gorkha earthquake,
consequently the annual melting rate of the B layer surface is about 5m. So, since
the terminal sediment thickness will reach to almost 50m in the middle part of
the avalanche sediments observed along Langtang river, the ice layers under the
avalanche sediments will be preserved for at least ten years,
Fig. 3 Ther are four ice bodies (AS1-4)
left at the left bank of Langtang river.
Fig. 4 There are two ice layers A and B
observed in the both sides of Langtang river.
The lower ice layer A was formed at the time of the first avalanche
occurred on 25 April 2015 when the Gorkha earthquake happened. However I don’t
know when the upper ice layer B was formed, since Ito Y, et. al. (2016)
reported that it occurred on 12 May 2015 at the time of a large after-shock
with magnitude 6.8, but local people denied that nothing happened on 12 May and
the second avalanche occurred on 2 May 2015. According to National Seismological Centre, there were a
after-shock with magnitude 5.1 reported, so it might be a trigger to cause the
second avalanche that formed the lower ice layer B on 2
May 2015.
Fig. 5 Field map of Langtang avalanche
sediments with GPS trail.
Fig. 6 Panoramic views of avalanche
sediments (the upper photos is taken from E, the middle from D and the lower
from B points in Fig. 5 and 7).
As local people said that the avalanche
sediments itself was now stable and no more rock falls were seen from the huge
cliff above Langtang village, so I made a field observation of the avalanche
sediments (Fig. 5) and I found that a really vast avalanche sediments cover the
entire parts of the past Langtang village (Fig. 6). There are even ponds and
river seen on the surface of the sediments (Fig. 7).
Fig. 7 The field map of Langtang avalanche
sediments compiled on the air photo taken by Prof. Yagi K. of Yamagata Univ, on
3 June 2015.
Fig. 8 There is a stratigraphic boundary
between A and B ice layer in the ice body (AS4) shown by arrows.
There is a stratigraphic boundary between A and B ice layer in the
ice body (AS4) observed at the downstream part of the avalanche sediments in
the left bank of Langtang river and it is shown by arrows(Fig. 8), and the B
ice layer observed in the ice body AS1 also contains boulders and debris within
ice body (Fig. 9).
Fig. 9 The B ice layer in the ice body AS1
contains boulders and debris within ice body.
Fig. 10 The recent Langtang village is
still under construction of new houses and hotels built very close to the
avalanche area.
Though the Langtang people is now eager to construct their houses
and hotels in the dangerous area very close to the avalanche sediments (Fig.
10), there are hanging glaciers and steep cliffs in the area of Mt. LangtangⅡ(6596m) and Mt. Langtang Ri (7205m) from where the 2015 avalanche originated
and attacked the Langtang village shown by the red arrow in Fig. 11. When a
glacial lake will be formed in the 16th century moraine (the upper
left photo in Fig. 11), there is a possibility that the so-called GLOF (Glacial
Lake Outburst Flood) will occur and attack Langtang village. So, it will be
important to monitor a formation of the glacial lake in the 16th
century moraine near the hanging galciers.
Fig. 11 The 16th Century moraine
with hanging glaciers is seen above Langtang village.
Fig. 12 The present terminal area of
Khimshun glacier.
2) Terminal change of Khimshun
glacier.
I
re-visited the Khimshun glacier in the north of Khanjin on 1 April, 2017 and I
found the glacial retreat (Fig. 12). Fig. 13 is the 1975 terminal area of
Khimshun glacier with the recent terminal shape shown by red dotted lines.
Fig.13 indicates that nearly 100m retreat at the left side and 50m at the
central part, but no significant changes observed at the right side.
As
far as the terminal changes of the cirque glaciers in Khumbu region such as
Gyajo glacier (Fig. 14), the climate warming accelerate glacial retreat with a
formation of glacial lakes and a glacier becomes a perennial snow patches
showing no glacial flow any more. As the Khimshun glacier is a kind of a
hanging glacier having an ice-fall feature, the characteristics of terminal
changes may be different from the cirque glacier and also the Gorkha earthquake
2015 might has an effect on the terminal glacier flow.
Fig.13 The 1975 terminal area of Khimshun
glacier with present terminal shape shown by red dotted line.
Fig. 14 The Gyajo glacier in Khumbu region
changes into a perennial snow patch in 40 years.
3) Landslide disasters in
Langtang valley
The
Langtang valley close to the capital, Kathmandu, is a center of the sightseeing
tourism with beautiful scenery (Fig. 15), however Langtang area has a steep
topography of U shaped valley with many talus topography causing frequent rock
falls (Fig. 16). Vanessa
Banks et.al. (2015) reported that Satellite images north of the Tibet – Nepal
border at Nyalam show extensive areas of landsliding and avalanching. At the time of the Gorkha earthquake 2015, many houses were destroyed
by rock falls (Fig. 17). There is a high risk of talus rock-falls observed at
hotel area of Bamboo showing dangerous topographic situations to stay safely (Fig.
18). The following four pictures show how Langtang villages have been suffered
from avalanches and rock falls due to the steep topography and how dangerous
valley it is for us to stay safely, We must find out safer places and facilities
to stay at the time of Langtang trekking.
Fig. 15 New Langtang village constructed
close to the 2015 avalanche area.
Fig. 16 Newly built hotel in Ghodatabela
with talus rock falls behind.
Fig. 17 Local house in Rimche was destroyed
by talus rock falls at the 2015 Gorkha.
Fig. 18 Dangerous Bamboo hotels influenced
by risks of talus rock falls.
References
Ito Y, et. al. (2016) A relationship
between the 2015 Nepal earthquake disaster and the depth of snow cover (in
Japanese).
National
Seismological Centre, Department of Mines and Geology, Recent Earthquakes
http://www.seismonepal.gov.np/index.php?action=earthquakes&show=recent
Vanessa
Banks et.al. (2015) Gorkha earthquake in Nepal: a landslide map and update on
the landslide hazard.
Acknowledgements
I am very much thankful for Ms. Sadakane A.
and Langtang people such as Mrs. Temba Lama, Nima Lama, Dawa Nurpu and Son
Nurpu to have informed me about the occurrences of the avalanche sediments when
I visited the Langtang valley. Also, I must pay hearty tribute to Drs. Rijam B.
Kayastha, Shiraiwa T., Fujita K., Yagi K. and Mr. Sato H. for giving me various
kinds of important information in terms of the Langtang avalanches including
air photos taken before and after the disaster occurrence.
Supplementation
There was a mountaineering party to Mt. Langtang Ri (7205m), located
in the west of Mt. Langtang Lirung (Fig.19), from Osaka City University in
April 2015 and one of the member, Mr. Sato H. took valuable pictures of the
collapsed summit of Mt. Langtang Ri (7205m) from where the huge avalanche
originated and finally attacked Langtang village on 25 April, 2015 right after
the Gorkha earthquake (Fig. 20 and 21). This first avalanche must has formed
the A ice layer composed of the lower part of the Langtang avalanche sediments
already discussed in the chapter 1).
Fig. 19 Air photo shows Mt. Lagtang Lirung,
Mt. Langtang Ri and Langtang.
Before Gorkha earthquake, there was a triangular shape of the summit
seen from Base Camp for Mt. Langtang Ri (Fig.20), but the summit shape changed
largely from a triangular shape to a rugged summit collapsed was seen after the
earthquake (Fig.21).
Fig. 20 Triangular summit of Mt. Langtang
Ri was seen before the earthquake (This processed photo was taken by Mr. Sato H.).
Fig. 21 Rugged summit of Mt. Langtang Ri
collapsed was seen after the earthquake (This processed photo was taken by Mr. Sato H.).
