The volcanic island chain of southwest Japan and British-Satsuma contacts

南西諸島火山と薩英交流

T. Bouquet1, T.Fukuzumi2 & K.Kinoshita3

ブーケ トーマス 1 ・ 福澄孝博 2 ・ 木下紀正 3

1鹿児島大学理学部，2十島村歴史民俗資料館，3鹿児島大学多島圏研究センター

鹿大多島圏研究センター・関西大東西学術研究所合同研究集会, 2008.12.22

Contents

• Tectonic setting of Nansei Shoto island volcanoes

• “Volcano tour” moving north to south• Satsuma-Iojima to Iwo-Torishima (Okinawa)

• gas / volcano plume observation

• geology and volcanic activity

• Geographical context of the Anglo-Satsuma War, 1863

• Tokara Nakanoshima astronomical observatory

• Landing of British ship at Takarajima, 1824

南西諸島火山：トカラ列島

(map from USGS – based on Simkin & Siebert, 1994)

• Volcanic island chain extending about 800 km from Sakurajima (north) to Iriomotejima (south)

• At least 13 “activevolcanoes” – classified as having erupted at least once in the last 10,000 years

• Tokara island volcanoes: Kuchinoshima to Yakoatejima

• Unknown outside of Japan (although discussed by John Milne, 1886)

• Japan is at the tectonic boundary of at least three tectonic plates –the northwest quadrant of the “Pacific Ring of Fire”

• Subduction of the Philippine plate under the Eurasian plate > Ryukyu Arc

Tectonic setting

(from USGS)

Ryukyu Arc

Complex tectonic activity

Okinawa trench

Okinawa trough

(map from Wikipedia Commons)

Tectonic setting

(diagram by R.J. Stern)

南西諸島火山鹿児島県本土-奄美にかけてのSiPSE-3D画像

海洋情報研究センター海底地形データ・国土地理院数値標高データ・JAXA地球観測センター受信ランドサットデータを用い鹿児島大学SiPSEグループ作成

SO2 degassing observed at Japanese volcanoes using an ultraviolet imaging camera

日本の火山におけるSO2ガス放出の紫外線カメラ観測

T. Bouquet, K. Kinoshita, M. Watson日本火山学会秋季大会、岩手大学、2008年10月13日

Sulphur dioxide gas emissions

0 1200600300 900

SO2 column concentration (ppm.m)

0 0.60.3 0.450.15SO2 absorbance

Sakurajima plume observation (Volcanic Cloud Research Group, Kagoshima University)

薩英戦争 1863年8月: “The bombardment of Kagoshima”

Illustrated London News, 7 November 1863

尚古集成館

生麦事件 (Namamugi incident; Richardson affair)

生麦事件参考館

横浜開港資料館

Geographical situation in Kagoshima Bay, 1863

Coast extended due to 1914 Taisho lava

Now reclaimed land

Sir Ernest Satow (1843-1929)

(map from Illustrated London News, 1863)

SiPSE image: extension of coastline since 1863

薩摩硫黄島 (from GSJ)

Kikai Caldera: formed in catastrophic eruption ~7,300 yrBP. Largest eruption on Earth in the last 10,000 years.

硫黄岳稲村岳Caldera rim

SO2 degassing and plume observation

• Digital camera observation

• Network camera linked to Kagoshima University by broadband internet

• Also for other volcanoes including Suwanosejima and Mayon (Philippines)

SO2 degassing and plume observation

Summit gas sampling with GSJ

Low temperature fumarole field

SO2 degassing and plume observation

UV camera imaging

0 500250125 475SO2 column concentration (ppm.m)

0 0.150.08 0.110.04SO2 absorbance

口永良部島

• Group of young stratovolcanoes, 15km west of Yakushima

• Aligned N to S according to the island chain; the youngest is Shindake

• All historical eruptions recorded at Shindake, including 1933 (village destroyed, 8 people killed)

Shindake (photo by JMA)

~3km

口之島

• At least 10 andesitic lava domes

• Last magmatic eruption more than 1000 years ago

• Phreatic (steam) eruption from Moetake possibly occurred in the 19th

century (Geshi & Nakano, 2007)

~3km

トカラ 中之島

• Old dissected volcano to the south; active andesite cone, Otake (御岳; 979m), to the north

• Summit crater fills with water in rainy season, but last eruption was in 1914 (small mud eruption)

~3km

Photograph:

Near-Infrared image:

九州では最大級のカセグレン式60センチ反射望遠鏡です。一度にたくさんの人が星を見ることができるモニターを装備。

60cm reflecting-type telescope: constructed in 1991 and was the second largest telescope in Kyushu at that time – now 7-8th largest.

TOKARA中之島天文台

Solar eclipse: 2009年7月22日 ~10.56時 (±3分)

鹿児島県天文協会提供

Akusekijima (悪石島)

諏訪之瀬島: Japan’s most active volcano?

諏訪之瀬島

• Andesitic stratovolcano with two historically active craters

• Largest historical eruption was in 1813-1814: thick scoria deposits, lava flows to the west. At the end of the eruption the summit crater Otake collapsed forming a large debris avalanche and the horseshoe-shaped Sakuchicaldera. Island remained uninhabited for 70 years afterwards.

• Lava flows to the east coast in 1884.

Sakuchi caldera

Photograph:

Near-Infrared image:

自然色 近赤外 近赤外３Ｄ （南の空から）

• 最近数年間では日本で最も激しい噴火活動

• 鹿児島大噴煙研究グループ：インターネット接続の噴煙自動観測システムを諏訪之瀬島北東25kmの中之島に設置し02年8月－07年7月まで可視, 近赤外観測

• 気象庁福岡管区気象台: 2003年3月から中之島小中学校に可視高感度カメラと専用回線による監視

• モヤや大陸からの汚染気塊のため映像が不鮮明な場合が多い

Volcanic plume observation

諏訪之瀬島の新観測体制 2008.8-鹿大噴煙研究グループ, 学術情報基盤センター, 平島小中学校諏訪之瀬島分校

分校体育館 2階から可視, 近赤外観測、ブロードバンド接続

2008.10.8_18:00

中之島から気象庁

島内の体育館から可視, 近赤外

2008.11.3_11:25-12:43 Visible

Fieldwork: 27-28 May, 2008

• UV camera observation

• However, no gas was detected! (Wind direction blew gas plume behind mountain)

Takarajima (宝島): the British again…

• Contact between islanders and British whaling ship in 1824

• Incident reinforced the policy of Uchi-harai-rei by the Tokugawa bakufu

やっぱり、イギリス人ですね・・・ （＾＿＾；）

文政7（1824）年7月，イギリスの捕鯨船が宝島（現・鹿児島郡十島村）に来着した。在番官らが出て応対したが，言葉が通じなかった。異国人は牛を欲しがったが在番官は拒否し

た。しかし，異国人は銃を乱射して，牛を奪取した。このとき，別の用途で宝島にいた横目・吉村九兵衛が鹿児島へ報告したものであ る。この事件を契機に幕府は，翌年異国船打払令を公布して，鎖国体制を強化した。

A legend about William Kidd, one of the most notorious pirates in history.

The legend says that the pirates attacked Takarajima and requested food and cattle from the inhabitants of the island. Their offer was refused and so 23 of the pirates landed and burned the inhabitants alive in a lime cave. Afterwards, Kidd hid his treasure in one of the caves, never coming back for it due to his execution in England.

キャプテン･キッドの財宝伝説も残る隆起サンゴ礁の島、宝島。そして、そこはイギリスの小説「宝島」のモデルになった島

“Treasure Island”

William “Captain” Kidd, Scottish pirate 1645-1701

(source unknown)

イギリス坂: English Slope

• Iō-Torishima (also known as Okinawa-Torishima) is a complex volcano

• Historical eruptions dating back to 1664 have been mild-moderate

• Part of Ryukyu Kingdom and sulphur was exported to China (Great Ming)

• Eruption in 1967 forced islanders to evacuate, and has been uninhabited ever since

硫黄鳥島

横当島 (Yakoatejima)• Most southern island of the Tokara chain

• Post caldera andesite cones

• Not well known, but historical documents suggest ash plumes during late Edo period

小林先生 （鹿児島大理学部）

硫黄鳥島の火山地質 （日本火山学会、2008年10月）

‘硫黄岳’

Lava dome. Most recent deposits and crater lake

‘グスク火山’

Wide crater with smaller crater in the centre. In the very centre is a lava dome with fumaroles

‘前岳火山’

Very old…

ありがとうございました

硫黄鳥島・与路島学術調査http://cpi.kagoshima-u.ac.jp/project-iwotori.html