Sub-theme
5. Tsunami boulders within and around historical tsunami trace points
5.1 Ishigaki Island
1) Ryukyu limestones in the Miyara Bay, southern Ishigaki Island: Fig. 5-1
In the vicinity of the airport in southern Ishigaki Island, Ryukyu, limestone thought to be tsunami boulders is scattered in the Miyara Bay. At that point the 1771 Yaeyama/Meiwa tsunami has reported 30 m tsunami traces.
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（GSI Web Map used）
Fig. 5-1 Ryukyu limestones in the Miyara bay, southern Ishigaki Island.
(Aerial photo taken by T. Ohsumi on January 25, 2019)
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2) Tsunami Fuuishi (Ohama Elementary School): Fig.5-2 to 5-4
"Tsunami Fuuishi" at the Sakihara Park at Ohhama, which is said to have been moved by the tsunami, has a maximum diameter of ~11.5 m, a depth of ~ 9.6 m, and a height of ~ 6 m. It is estimated that it was launched by the Skishima Great Tsunami about 2000 years ago from the dating result of the corals adhering to the surface.
The height of "Tsunami Ufuishi" is of 10.0 m elevation (data source: DEM 5 B), and it is ~150 m distance from the coast of the Miyara Bay.
（GSI Web Map used）
Fig. 5-2 "Tsunami Ufuishi" at the Sakihara Park of Ohhama.
Fig. 5-3 Close up of "Tsunami Ufuishi". There are fossil of corals.
(photo taken by T. Ohsumi on January 22, 2019)
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Fig. 5-4 Natural Monument (Nationally Designated).
Information Plate;
The name "Tsunami Ufuishi" (Tsunami boulder) was applied by the late local history researcher Mr. Kiyoshi Makino. Originally, Makino seemed to believe that it was the tsunami boulder in the 1771 Great Yaeyama/Miwa Tsunami which caused great damage mainly in Ishigaki Island in 1771. However, from the results of the carbon dating of the corals adhering to the surface, it became clear that it was launched to its present place by the Sakishima tsunami about 2,000 years ago. Also, in a study that specializes in paleomagnetism, although this stone did not move greatly at the time of the 1771 Great Yaeyama/Miwa Tsunami, the possibility that the terrestrial magnetism was moved due to rotation by the power of the wave has been pointed out.
In this way, as a result of repeated scientific verifications, there is no doubt that it is a tsunami boulder, and there is also a moral element that the devastating tsunami hit the area before the 1771 Great Yaeyama/Miwa Tsunami. I understood that it was a tsunami boulder.
In addition to this "Tsunami Ufuishi", "Takakoruseishi" (Ohhama), which is said to have been launched by a tsunami or located in the eastern cast of Isjgaki Island, Amataria-Suuari (Touri), Yasura-Ufu-Kane (Hirakubo) and Bari-Stone (Ibaruma) are listed as the "eastern cast of Isjgaki Island's tsunami boulders".
It is specified as a Natural Monument (Nationally Designated).
The four megaliths other than "Tsunami Ufuishi" were tsunami boulders from the 1771 Great Yaeyama Tsunami, according to the historical description “Ohnaminotoki-Kakumurano-Nariyukisyo” and the results of scientific inspections by carbon dating and so on.
June 2016, Ishigaki City Board of Education Cultural assets section.
169 3) Coast of Miyara Bay: Fig. 5-5
In coast of Miyara Bay, Ryukyu limestone which seems to be tsunami boulders is scattered in Miyara Bay. These tsunami boulders are shown by aerial photograph.
（GSI Web Map used）
Fig. 5-5a Ryukyu limestone in Miyara Bay.
Fig. 5-5b Ryukyu limestone in Miyara Bay.
Fig. 5-5c Ryukyu limestone in Miyara Bay.
(photo taken by T. Ohsumi on January 24, 2019)
170 4) Taka Koruseishi: Fig. 5-6
"Taka Koruseishi" at Aza Ohham in Ishigaki City, Okinawa Prefecture, is also a Natural Monument (Nationally Designated) the same as "Tsunami Ufuishi". The height of "Taka Koruseishi" is 2.4 m (data source: DEM 5 B), and it is at a distance of ~ 100 m from the coastline.
It is thought that the stone, which was carried to "Koruse Utaki" by the Sakishima Great Tsunami 2,000 years ago moved to the north again ~ 600 m in the 1771 Yaeyama Tsunami.
（GSI Web Map used）
Fig. 5-6 "Taka Koruseishi " in Ohham in Ishigaki City height: 2.4 m elevation (data source: DEM 5 B)
(photo taken by T. Ohsumi on January 22, 2019) 5) Matsumuto-House: Ryukyu Limestone: Fig. 5-7
Matsumuto-House is located in "Matsumuto-House" at Tonoshiro, inland 615 m from Yashimacho port facility, where the 1771 Yaeyama/Miwa tsunami's tsunami boulder is placed. The height is 7.7 m elevation (data source: DEM 5 B).
171
（GSI Web Map used）
a
b
Fig. 5-7 Tsunami boulder at "Matsutou-House" height: 7.7 m elevation (data source: DEM 5 B).
Information plate: a
In the 1771 Yaeyama earthquake the boulders in the sea were launched onto the land by the great tsunami of the Miwaji era. At the moment, it is this tsunami boulder at "Matsutou-House".
172 Information plate: b
Ishigaki Island and Miyako Island are related to the Yaeyama Earthquake which occurred in south-southeast of Ishigaki Island around 8 am on April 24, 1771. It was a devastating tsunami with about 12,000 deaths, and more than 2,000 houses swept away by overwhelming large waves.
In Ishigaki Island near the epicenter, the tsunami landed from the southeast of the island, and moved immediately along the river into the deep part of the island, instantly flooding the fields, houses and livestock towards Nagura Bay.
According to the historical documents, Miyara, in the village tsunami runup height reached as much as 85 m.
With this tsunami, coastal rocks were lifted up onto the land, and in remote islands such as Kuroshima and Shinjyo Island, the aftermath of the tsunami swept away the whole island.
In Yaeyama, of the total population of 28,992 people, 9,313 died, that is 32% of the total population was lost.
There was a total collapse of the eight villages of Maesato, Ohhama, Miyara, Shiraho, Nakayumi, Ibaruma, Yasura and Yarabu. Partial collapse took the seven villages of Arakawa, Ishigaki, Ohkawa, Tonoshiro, Hirae, Kuroshimaand Shinjyo. Especially great was the damage to Shiraho Village, 98% of the village population of 1,574 people were exposed to the wave. On the other hand, Miyaki Island was a bit far from epicenter, but still 12 villages were damaged and there were 2,548 victims. In addition, deaths due to crop damage, famine, pestilence, and other events that followed the tsunami continued, and the population of Yaeyama Islands dramatically declined. For this reason, forcibly relocated from the village where damage was little to village which was destroyed, village rebuilding was done. However, deaths due to starvation and infectious diseases continued after that, and the population of Yaeyama sharply declined. For this reason, in the village which has been destroyed, the village was forcibly resettled to the village with little damage, and the village is being rebuilt. However, the deaths due to starvation and infectious diseases, etc. continued afterwards, and in the Meiji period about 100 years later, the population of Yaeyama Islands has decreased to one-third before the earthquake. The severe head tax by the Shuri Kingdom also had a big influence on this.
Regarding the Meiwa Yaeyama Tsunami, it is summarized in detail in the report of the warehouse overseer
"Kuramoto", the shogunate government's branch office.
(photo taken by T. Ohsumi on January 22, 2019)
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6) Meiwa-Ohtsunami Victim Memorial Monument: Fig.5-8 to 5-15
Located in Ishigaki Cityi Aza Miyara, according to Hatori (1988) [19] it was said to be 30 m high at the 1771 Yaeyama Tsunami. This point is ~1 km from the Miyaragawa River and the height of this point is a 63.2 m elevation (data source: DEM5 B). According to "Ohnaminotoki - Kakumurano - Nariyukisyo", the tsunami run-up was 84.8 m high at Ishigaki Island. The tsunami hit with three waves and the second wave was said to have been the biggest.
（GSI Web Map used）
(photo taken by T. Ohsumi on January 23, 2019)
Fig.5-10 Contents of Inscription panels are shown below;
Fig.5-8 Meiwa-Ohtsunami Victim Memorial Monument.
Fig.5-9 Distance from the Monument to the Miyaragawa River ~1 km, from the coastline 1.2 km and altitude: 63.2 m elevation (data source: DEM5 B).
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Fig. 5-11 Inscription：According to the "Ohnaminotoki - Kakumurano - Nariyukisyo", (April 24, 1771)
Information plate
Yaeyama, there was the Great Earthquake in Yaeyama Islands around 8 o'clock in the morning.
When the earthquake had settled, a thunder-like sound roared in the eastern area of Ishigaki Island, soon the tide ebbed to the outer shores. The sea tides drifted soon toward northeast and southeast.
Large waves from the ocean struck the streets like black clouds and also the town island of Shimamura village. Immediately, the wave was out of the Straits. A big wave struck like a black cloud from the northeastern and southeastern seas, and a storm covered the whole village. The waves repeatedly hit three times. This is the historically famous Meiwa-Ohtsunami of Yaeyama.
The devastating tsunami fiercely struck the eastern and southern coast of Ishigaki Island. The total number of collapsed villages were 13. 2 villages that were half collapsed were on Kuroshima Island and Aragusuku Island. The number of deaths climbed up to over 933. Thus, Ishigaki Island, the political, economic and cultural center of the archipelago, was hit by a devastating tsunami.
There was also hunger, disease and death due to subsequent harvest, epidemic diseases and so on. The population decreased year by year. Following this, the "Jinto" taxable trading of the Yaeyama society became more difficult, and its influence was truly difficult to measure.
Even after 212 years, there is still an overwhelming sense of grief when this study think of the people who suffered this disaster. This monument was built in memory of the people who died on all of the islands. This study hope that the history of this unprecedented disaster is handed down for generations. This monument was built with the cooperation of Ishigaki City, Taketomi Cho, Yonakuni Cho, organizations, and organizations from inside as well as outside of the island.
April 24, 1983 Meiwa - Ohtsunami Victim Memorial Monument Proposer
碑 文八重山の古記禄大波之時各村之形行書によれば、乾隆三十六年（日本年号明和八年）三月十日（一七七一年四月二十四日）午前八時ごろ大地震があり、それが止むと石垣島の東方に雷鳴のような音がとどろき、間もなく外の瀬まで潮が干き、東北・東南海上に大波が黒雲のようにひるがえり立ちたちまち島島村村を襲った。波は三度もくりかえした。史上有名な八重山の明和大津波である。津波は石垣島東岸と南岸で激甚をきわめ、全半潰あわせて十三村、ほかに黒島、新城二村が半潰し、遭難死亡者は九三一三人に達した。こうして群島の政治・経済・文化の中心地石垣島は潰壊滅的打撃をうけ、加えてその後の凶作、飢餓、伝染病などによる飢餓者、病死者も続発出して、人口は年年減少の一途をたどり、人頭税制下の八重山社会の歩みを一層困難なものとし、その影響はまことに計り難いものがあった。この天災から二一二年、狂瀾怒涛のなかで落命した人人を思うとき、いまなお断腸の念を禁ずることができない。このたび有志相謀り、群島全遭難死亡者のみたまを合祀してその冥福を祈り、あわせてこの未曾有の災害の歴史が永く後世に語りつがれていくことを念願し、島内外各面の浄財と石垣市、竹富町、与那国町並びに諸機関、団体の御協力を仰いでここにこの塔を建立した。 一九八三年（昭和五八）四月二四日明和大津波遭難者慰霊碑建立期成会
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Fig. 5-12 Excerpts from records on the Meiwa Great Tsunami disaster Information plate
According to Tokyo astronomical observations, science chronology edited, “The Yaeyama Tsunami Jishinn”
with a magnitude of 7.4, the epicenter was at the north latitude 124.3 and east longitude of 24. The epicenter was Ishigaki Island Shiraho Saki south southeast 40 km.
According to "Ohnaminotoki - Kakumurano - Nariyukisyo", the tsunami situation occurring at Ishigaki Island tsunami run-up was 84.8 m, 60.6 m, 75.7 - 78.7 m, 6 - 7 m, offshore stones were launched, the stones on the land and the roots of big trees were blown away.
Totally collapsed villages: Maesato on Ishigaki Island, Ohhama Miyara, Shiraho Nakayomi, Ibaruma, Yasura, and Tarumachi on Yarabu
Partially collapsed villages: Seven villages of Kuroshima Island, Aragusuku Island of Ohkawa, Ishigaki, Arakawa, Tonoshiro, and Hirae, remote island of Ishigaki Island the condition of being overtaxed as “Jintouzei”.
With a total of 9,313 (which is equivalent to 32.22% of the archipelago population), Ishigaki Island suffered 8,815 deaths (94.7%), 299 deaths (3.1%) for Kuroshima Island, 205 deaths (2.2%) for Aragusuku Island.
Housing totally collapse, total 2,176 houses, inundation of 1,003 units, farmland swept away: 1,626 hectare, crop damage 1,777 hectarea, the public building of warehouse overseer "Kuramoto", 13 village guard stations at "Murabansyo", 4 meeting places at "Kaisyo", 14 shrines at "Utaki", bridge 6 shoe, the Tourinji temple and 2 statues of Nio Guardians of the same temple, Gongen, tribute rice and so on, were damaged.
明和大津波災害関係諸記録抜粋地震の規模と位置（東京天文台編理科年表による）(マグニチュード)七・四震源地東経一二四・三度北緯二四度「八重山地震津波」と記録（石垣島白保崎南南東四〇キロメートルと測定される）津波の状況（大波之時各村之形行書による）石垣島で「潮揚高弐拾八丈（八四・八メートル）、或弐拾丈（六０・六メートル）或弐拾五・六丈（七五．七～七八・七メートル）或弐、参丈（六～九メートル）、沖ノ石陸へ寄揚、陸ノ石並大木根乍被引流」とある災害の状況（大波之時各村之形行書御手形寫御問合控等による）全潰した村石垣島の真栄里大浜宮良白保仲与銘伊原間安良屋良部の計八村、半潰した村、石垣島の大川、石垣、新川、登野城、平得、離島の黒島、新城の計七村遭難死亡者総計九三一三人（群島人口の三二・二二％に当る）内、石垣島八八一五人（九四・七％、在番、頭職等の公職者八八人及び蔵元の公用で離島からきて遭難死亡した三七六人を含む）、黒島二九三人（三・一％）、新城島二０五人（二・二％）住家の全潰、総計二一七六戸、浸水一００三戸、田畑の流失、総計一六四二町四反五畝一二歩、作物被害、田畑総計一七九五町二反六畝一０歩、その他の流潰流失、蔵元庁舎、村番所一三棟、会所四棟、御嶽一四棟、橋梁六座、桃林寺及び同寺の仁王像二、権現堂、貢納米等
M
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There is a Tacolasser Stone on the north side of this area. "Takorasa stone" means a high dark coast stone. "Takorasa Stone" has a legend that those surviving persons the 1771 Meiwa era Yaeyama Tsunami gathered to rely on torchlight. This stone after the tsunami and had burned a torch after the sunset, survivors gathered to rely on that lighting, as they rescued survivors and procured foods.
Fig.5-13 Tacolasser Stones located on the north side of this area. This stones which was supposed to have gathered people who survived the Yaeyama/Meiwa Tsunami. A legend has it that "Survivors of the 1771 Meiwa era Yaeyama/Meiwa Tsunami gathered to rely on torchlight.
(photo taken by T. Ohsumi on January 23, 2019)
According to Goto and Shimabukuro (2012) [22], the description of the 85 m tsunami run up described in the Inscription says that the description of the survey result needs to be evaluated taking the error into consideration. Actually, the height value is not so high at the point set at 85 m. As the result of numerical calculation does not arrive at 85 m, it seems that the Tredecesor of the ancient document contains something that is overestimated significantly.
The flow path of the tsunami that went from Miyara Bay to Nagura Bay listed in the ancient document is indicated by the data source: DEM 5 B, the height is at most ~ 30 m elevation. Also, from the description of survivor's rescue and procurement of food in front of the ~ 60 m high or more Tacolasser the 85 m record of tsunami run up is of low reliability. For the tsunami run-up, 30
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m of tsunami run-up height indicated by Hatori (1988) [21] is reliable.
According to Banzai (2015) [23], as to talk with the local people, the tsunami rushed to Panna Dake, crossed the small mountain in the north side and came to the sea on the side of Nakura Bay, when the stone crossed the mountain. Fig.5-15 shows a full view of Nagura Bay and the low land from the north side of Mt. Panna.
Fig.5-14 The 1771 Yaeyama/Meiwa tsunami's historical tsunami trace and run-up route in the Ishigaki Island (after Goto and Shimabukuro (2012) [22]) （GSI Web Map used）
Fig.5-15 A full view of Nagura Bay and the north side of Mt. Panna.
(photo taken by T. Ohsumi on January 25, 2019)
Nagura Bay
Mt. Panna
Tsunami run-up Tsunami run-up
178 7) Amataria-Suari: Fig.5-16 to 5-17
“Amatariya-Suari” is inland of 160 m from the coastline, and the altitude is 6.2 m elevation (data source: DEM 5 B). It is described in historical documents that Lime stone which was on the beach
“Amateriya” was launched inland. Coral fossils are scattered around.
（GSI Web Map used）
Fig.5-16 View of “Amatariya-Suari ”.
Fig.5-17 Coral fossils are scattered around in this point.
(photo taken by T. Ohsumi on January 23, 2019)
179 8) Other historical tsunami trace points: Fig.5-18
Other historical tsunami trace points and current picture shows Fig.5-18. Okinawa limestones are scattered, but it is unknown whether these are washed away by the tsunamis or the storm waves.
However, it seems that the events that were shown by the tsunami are repeated. Goto et al. (2010) [24] classified the tsunamis or the storm waves. Storm wave boulders are distributed on the flat reef within 300 m landward of the reef edge in the Ryukyu Islands. However, tsunami boulders on the Ryukyu Islands are deposited far landward of this limit.
Fig.5-18 Other historical tsunami trace points and current pictures.
(photo taken by T. Ohsumi on January 22-24, 2019)