Izu Peninsula

Japanese: 伊豆半島 - いずはんとう

A peninsula jutting out into the Pacific Ocean in the eastern part of Shizuoka Prefecture, it separates Sagami Bay from Suruga Bay. It stretches 50km from north to south, 35km wide at its widest point from east to west, and has an area of about 1,500km2. The base of the peninsula is the passage point of the Tanna Tunnel, which connects Atami City and Kannami Town. Formerly part of Izu Province, it borders Sagami to the east along the ridges of the Hakone and Yugawara volcanoes, and Suruga to the west along the old Oba River course that runs through Mishima City and the Sakai River. Administratively, it includes the seven cities of Atami, Ito, Numazu, Mishima, Shimoda, Izu, and Izu no Kuni, as well as Kannami Town in Tagata County and five towns in Kamo County. The Izu Islands were transferred to Tokyo Prefecture in 1878 (Meiji 11), and Kimisawa County in the northwest of the Izu Peninsula was merged with Tagata County in 1896.

[Kitagawa Mitsuo]

Nature

Located in the center of Honshu, it is the junction of the Northeast Japan Arc, Southwest Japan Arc, and Izu-Ogasawara Arc. Geologically, it is an uplifted zone of marine strata deposited in the Fossa Magna geosyncline, and belongs to the Green Tuff tectonic zone. The topography and geology are complex due to volcanic activity from the Pliocene to the Holocene (Alluvial Epoch), with the Yugashima Formation and Shirahama Formation of the Miocene of the Neogene Period as its base. As it is a tectonic zone, crustal movement is intense, and active fault movement and abnormal uplift continue, making it an unstable area with earthquakes such as the North Izu Earthquake, the Izu Peninsula Offshore Earthquake, and the Izu Oshima Offshore Earthquake. The line from Kawazu on the east coast to Toi on the west coast is the approximate border, and in the southwest, a mountain range made of andesite and pyroclastic rocks on the basement approaches the sea. In the north, the Kano River is separated by the Daruma, Tanaba, and Nekoko volcanoes to the west, and the Yugawara, Taga, Usami, Omuro, and Amagi volcanoes to the east, making it an extension of the Fuji volcanic belt. There are many types of volcanic landforms, such as the cone-shaped volcano of Omuroyama, the Sakibara lava plateau, the crater of Haccho Pond, the dammed Lake Ippeki, and the crater and lava flows of Kawagodaira. In addition to the Kano River, which originates near the Amagi Pass in the center of the peninsula and flows north, there are small and medium-sized rivers such as the Kawazu, Aono, Inouzawa, Nishina, and Naka Rivers, and they have developed alluvial plains at their mouths, but there are few terraces or flat land. The Amagi Mountains upstream of the Kano River are highly undulating, with many collapsed areas due to the quality of the rocks and severe erosion. The river course has a gorge, and Jorennotaki Falls, caused by lava flows, is a popular tourist destination. The North Izu Plain downstream is a large plain that includes the low-humid Tagata Plain and the alluvial fan of the Kise River. The area has suffered many floods, including those caused by the Kano River typhoon, and the Kano River Floodway was completed in 1965 (Showa 40). Looking at the coast, the winding rocky shoreline has sea cliffs eroded by waves, sea caves, and oddly shaped rocks, creating a unique landscape, and Nishikigaura, Jogasaki, Irozaki, Hagachizaki, and Koganezaki are scenic spots. There are sandy beaches such as Shirahama, Imaihama, and Yumigahama, and the coastline is diverse with developed gravel bars at Heda and Osezaki.

[Kitagawa Mitsuo]

industry

Agricultural production is restricted due to the lack of flat land, but the area has a warm climate, which is known for the plum orchards in Atami and the early flowering of daffodils at Tsumekizaki. Flower cultivation in Minamiizu and forced outdoor cultivation of vegetables are possible thanks to the long hours of sunshine and high temperatures, such as an average January temperature of 6°C at Irozaki. Carnations in Toi and Kawazu, and margarets and snow peas in Minamiizu are specialty products that are shipped in winter. Strawberries in the North Izu Plain, mandarin oranges from Nishiura in Numazu City to Toi, and sweet summer mandarins in Higashiizu are also famous, and tourism-oriented agriculture is also progressing. Wasabi is widely produced in the Amagi mountain area, and the streams and spring waters of the Kano River, Omi River, and upstream Kawazu River are used. Dairy farming in Tanna, Kannami Town, is a unique area with a long history.

Izu is surrounded by the sea, so the fishing industry is thriving, and fishing villages have been established in the lowlands at the back of the bay, and fishing ports have opened up. In southern Izu, which has many rocky beaches and reefs, the main activities are harvesting seaweed such as Tengusa, and fish and shellfish such as abalone, turban shells, and spiny lobsters. Shirahama, Susaki, and Kumomi were once major Tengusa production areas, but these have been converted into guesthouse villages, and in Kumomi, hot spring guesthouses can be found, thanks to the hot springs that gush out. The east coast is dominated by coastal fishing using fixed nets and pole-receiving nets. On the west coast, due to the influence of winter westerly winds and the undersea topography, offshore fishing and deep-sea fishing are the norm, and Toda, Tago, Iwaji, and Shimoda are bases for deep-sea fishing. In the inner bays of Nishiura and Shizuura in Numazu City, marine aquaculture of yellowtail, horse mackerel, sea bream, and other fish is thriving.

Izu receives a lot of rainfall, with annual rainfall exceeding 3,000 mm on Mt. Amagi, which provides ideal conditions for forest growth and is blessed with abundant forest resources and a large area of national forest. Mt. Amagi was once written as Amagi, and the Edo Shogunate established a system of controlled trees to protect the forests, which prohibited the felling of six species of trees - cedar, pine, cypress, zelkova, camphor, and sawara - but later oak, fir, and hemlock were added, and the area was called the Nine Amagi Trees. Trees were cut down and transported, but they were sent down the river on rafts, and so the place names "Ikadaba" (rafting sites) remain along the Kawazu River and Omi River. The area was once a producer of charcoal as a forest product, but this declined and shiitake mushroom cultivation took hold. As for natural vegetation, the Amagi Mountains are home to virgin forests of beech, fir, and Japanese andromeda, as well as beautiful blooming colonies of Amagi azalea and Azuma rhododendron, and a large area has been designated as an academic reference protected forest. The coastal areas also have unique vegetation landscapes, such as the juniper forest at Osezaki (a nationally designated natural monument) and the dogwood colony at Toda Mihamazaki. The Izu Peninsula is also blessed with many mineral deposits associated with volcanic activity and is rich in mineral resources. Okubo Nagayasu began development of the Izu gold mines during the Tensho era (1573-1592), and mining progressed in Toi, Yugashima, Nawaji, and Uryuno, reaching its peak during the Keicho era (1596-1615), when Nawaji had the largest production volume. Most of the mines are now abandoned, and gold and silver mining and refining took place in Seigoshi and Mochikoshi in Izu City, but Mochikoshi is currently engaged in a project to recycle gold and silver from industrial waste containing gold and silver. A special type of mining is the Izu Silica Mine in Ugusu, Nishiizu Town. Silica is formed when andesite is altered by volcanic sulfuric action and turned into silica, which is extracted as a raw material for glass and as aggregate for lightweight concrete, but it has destroyed mountainous areas and is a problem in terms of disaster prevention.

[Kitagawa Mitsuo]

Transportation and Tourism

The beauty of the mountains, the coastline, the abundance of hot springs, and other natural diversity, as well as the historical and literary background, have increased Izu's value as a tourist resource, and the designated area of the Fuji-Hakone-Izu National Park is also large. It is said that the name Izu comes from "Yuzu" (hot water), and there are more than 30 hot springs. Atami, Ito, Izunagaoka, and other hot springs have large amounts of water, Atagawa, Mine, and Shimogamo have high-temperature boiling springs, and Yugashima and Yugano are mainly natural springs. The spring quality is mostly simple hot springs and chloride springs, and Ajiro (Minami Atami) and Shimogamo are chloride springs. Rendaiji, Ohito, and Toi have springs that well up from within mines. Dogashima, Matsuzaki, and Kumomi are new hot springs that have emerged from drilling, while Imaihama and Shimoda are pumped water. The development of tourist destinations is closely related to the improvement of transportation conditions. The opening of the National Railways Atami Line (currently the JR Tokaido Main Line between Kozu and Atami) in 1925 (Taisho 14), the National Railways (currently JR) Ito Line in 1938 (Showa 13), and the Izu Kyuko Line in 1961 (Showa 36) brought a rapid increase in tourists and promoted the development of eastern Izu, and Atami and Ito grew into international tourist hot spring cultural cities. The opening of the Izu-Hakone Railway Sunzu Main Line in 1924 and the Tokaido Shinkansen Mishima Station in 1969 brought about a transformation of the areas along Shimoda Kaido in central Izu and the west coast. The construction of National Routes 135 and 136, and the construction of tourist roads such as the Izu Skyline, Nishi Izu Skyline, and Minami Izu Road (Margaret Line), not only attracted tourists but also expanded golf courses, villa areas, and leisure facilities, raising issues regarding the conservation of the natural environment. In addition, the Kawazu Nanadaru Loop Bridge on National Route 414, which was constructed in Nashimoto, Kawazu Town as part of disaster recovery efforts, has been designated a new tourist attraction.The area from Amagi Pass in the center of the Izu Peninsula to Haccho Pond, known as a habitat for the Japanese green tree frog, has been designated the Showa no Mori Amagi Natural Recreational Forest for its forests, valleys, and wild birds, and is being developed in many ways, including the establishment of a forest museum and the Izu Modern Literature Museum, and the establishment of the Odoriko Course at the old Amagi Pass.

In addition to its natural tourist resources, Izu is known as the setting for literary works by authors such as Kawabata Yasunari and Inoue Yasushi, and is known for its literary walking trails. Historically, Izu also offers a variety of sightseeing tours of famous places and historical sites, such as Shuzenji, which has ties to the Genji clan, Hirugakojima, and the Shimoda area, which is associated with the Black Ships and the opening of the port to Japan.

[Kitagawa Mitsuo]

Seismic activity

Over the long geological period, crustal movements and volcanic activity have been repeated frequently, and most of the peninsula consists of plateau-like volcanoes such as Taga, Omuro, Amagi, Tanaba, and Daruma in the Fuji volcanic belt, and most of the coast is rocky beaches. Seismic activity is also active, and in 1930 (Showa 5), the North Izu earthquake (M 7.3, 272 deaths) occurred six months after the Ito earthquake swarm. In recent years, destructive earthquakes have moved northward, such as the 1974 (Showa 49) Izu Peninsula Offshore Earthquake (M 6.9, 29 deaths), the 1978 Izu Oshima Near Sea Earthquake (M 7.0, 25 deaths), and the 1978-1980 intermittent earthquake swarm off the east coast of the Izu Peninsula. Combined with the ground uplift in the central and eastern part of the peninsula, the outcome is attracting attention. Earthquake swarms have continued to occur intermittently since then, and crustal activity is constantly monitored by the Earthquake Research Institute of the University of Tokyo and other institutions. According to plate tectonics (ocean-floor spreading theory), the Izu Peninsula is moving north on the Philippine Sea Plate, colliding with the Japanese archipelago, which sits on the Asian continental plate, and is being pushed against it.

[Akira Suwa]

"Izu Peninsula, edited by Hoshino Michihira et al. (1972, Tokai University Press)" ▽ "Local History of the Izu Peninsula, edited by the Japanese Association of Historical Geographers (1978, Rekishi Toshosha)"

Kawazu Seven Waterfalls
A group of waterfalls on the Kawazu River, south of Amagi Pass. From upstream, there are seven waterfalls: Kama Falls, Ebi Falls, Hebi Falls, Shokage Falls, Kani Falls, Deai Falls, and Otaki Falls. The photo shows Shokage Falls, which has a drop of about 10m and a width of about 7m. A statue of "The Dancer and I" stands on the riverside. Part of Fuji-Hakone-Izu National Park. Kawazu Town, Kamo District, Shizuoka Prefecture © Shizuoka Prefecture Tourism Association ">

Kawazu Seven Waterfalls

Joren Falls
A waterfall in the upper reaches of the Kano River in the Amagi Mountains. 25m high and 7m wide. With an abundant amount of water, it is one of Izu's most famous waterfalls. It is surrounded by a colony of Haikomochi Fern, a prefectural natural monument. It is part of the Fuji-Hakone-Izu National Park. Izu City, Shizuoka Prefecture © Shizuoka Prefecture Tourism Association ">

Joren Falls

Cape Irozaki
The southernmost cape on the Izu Peninsula. Its coves are sawtooth-shaped, and the landscape is rich in variety, with sea cliffs and oddly shaped rocks. The area is part of the Fuji-Hakone-Izu National Park, and is also part of the "Southwest Izu Coast," a nationally designated scenic spot. The photo shows the Iro Gongen Festival, a festival at Iro Shrine, which is held to pray for safety at sea and a good catch. Irozaki Lighthouse can be seen on the cliff, and Iro Shrine in the middle. Minamiizu Town, Kamo District, Shizuoka Prefecture © Minamiizu Town Tourism Association ">

Cape Irozaki

Golden Cape
A scenic spot on the west coast of the Izu Peninsula. Known as a famous sunset spot. When the setting sun hits the yellow-brown andesite cliffs, the rock surface shines golden. It is part of the Fuji-Hakone-Izu National Park and has a walking trail, a grassy plaza, an observation deck, and more. Nishiizu Town, Kamo District, Shizuoka Prefecture © Shizuoka Prefecture Tourism Association ">

Golden Cape

Shirahama
The coast of the southern Izu Peninsula. The white sand beach made of white limestone is the origin of the place's name. It is part of the Fuji-Hakone-Izu National Park, and in the summer it is crowded with families swimming and playing on the rocks. The photo shows Shirahama Central Beach. Shimoda City, Shizuoka Prefecture © Shimoda City ">

Shirahama

Cape Mihama
A 750m long sandbar that separates Suruga Bay (in the back of the photo) from Toda Port. There are Mihama Misaki Park and the Shipbuilding Local History Museum, and the sandy beach facing the port is a swimming beach. It is part of the Fuji-Hakone-Izu National Park. Numazu City, Shizuoka Prefecture © Shizuoka Prefecture Tourism Association ">

Cape Mihama

Osezaki (Numazu City)
A cape that juts out about 1 km into Suruga Bay at the northwestern tip of the Izu Peninsula. It is also called Biwa Island. It is part of the Fuji-Hakone-Izu National Park, and its juniper forest, a nationally designated natural monument, is the northernmost natural forest in Honshu. Numazu City, Shizuoka Prefecture © Izu Peninsula Geopark Promotion Council ">

Osezaki (Numazu City)

Senganmon Gate
A sea cave located south of Cape Asama in Kumomi, Matsuzaki Town. The cave is about 15m high and 10m wide and carved into a huge rock on the sea, allowing pleasure boats and tourist boats to pass through. It is part of the Fuji-Hakone-Izu National Park and is also part of the nationally designated scenic spot "Southwest Izu Coast." Matsuzaki Town, Kamo District, Shizuoka Prefecture © Izu Peninsula Geopark Promotion Council ">

Senganmon Gate

Atami Plum Garden
This plum grove is known for being the first to bloom in the country. Over 700 plum trees are planted here, and they bloom one after the other, starting early, then mid-season, then late. The annual Atami Plum Garden Plum Festival is held every year from January to March, attracting many tourists from all over the country. Atami City, Shizuoka Prefecture ©Shogakukan ">

Atami Plum Garden

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

静岡県東部、太平洋に突出し、相模灘(さがみなだ)と駿河湾(するがわん)とを分ける半島。南北約50キロメートル、東西の最大幅は35キロメートルに達し、面積約1500平方キロメートル。半島の基部は、熱海(あたみ)市と函南(かんなみ)町とを結ぶ丹那(たんな)トンネルの通過点にあたる。かつては伊豆国をなし、東の相模とは箱根や湯河原火山の稜線(りょうせん)で接し、西の駿河とは三島市を流れる旧大場川流路と境川がその境界であった。行政的には熱海、伊東、沼津、三島、下田(しもだ)、伊豆、伊豆の国の7市と、田方(たがた)郡函南町、賀茂(かも)郡5町が含まれる。なお、伊豆諸島は1878年（明治11）に東京府に移管され、伊豆半島北西部の君沢郡は1896年に田方郡と合併した。

［北川光雄］

自然

本州中央部に位置し、東北日本弧、西南日本弧、伊豆‐小笠原(おがさわら)弧などが接する会合部にあたる。地質的にはフォッサマグナ地向斜に堆積(たいせき)した海成層の隆起帯であり、グリーンタフ変動地帯に属する。そして、新第三紀中新世の湯ヶ島層、白浜層を基盤にして、鮮新世から完新世（沖積世）に至る各時代の火山活動によって地形と地質は、複雑に構成されている。変動帯であるため地殻運動も激しく活断層の運動、異常隆起も継続し、北伊豆地震や伊豆半島沖地震、伊豆大島近海地震など不安定地帯となる。東海岸の河津(かわづ)から西海岸の土肥(とい)に至る線をほぼ境にして、その南西部は基盤の安山岩や火山砕屑岩(さいせつがん)からなる山地が海に迫る。北部は狩野(かの)川を挟んで西側に達磨(だるま)、棚場(たなば)、猫越(ねっこ)火山、東側に湯河原、多賀(たが)、宇佐美(うさみ)、大室(おおむろ)、天城(あまぎ)火山が続き、富士火山帯の延長にあたる。大室山の円錐(えんすい)形火山や、先原(さきばら)溶岩台地、噴火口の八丁(はっちょう)池、堰(せ)き止めによる一碧(いっぺき)湖、カワゴ平の噴火口と溶岩流など火山地形の種類も多い。半島中央部の天城峠付近を源流とし北流する狩野川のほか、河川は河津、青野、稲生沢(いのうざわ)、仁科(にしな)、那賀川などの中小河川で、河口部には沖積地を発達させるが、段丘や平地は乏しい。狩野川上流の天城山地は起伏量も大きく、岩質に起因する崩壊地も多く侵食も激しい。流路は峡谷をもち、溶岩流の影響による浄蓮(じょうれん)ノ滝は観光地となっている。下流の北伊豆平野は低湿な田方平野と、黄瀬(きせ)川の扇状地も含めて大きな平野となる。狩野川台風の洪水をはじめ、水害の被害も多く、1965年（昭和40）狩野川放水路が完成した。海岸をみると屈曲した磯浜(いそはま)は波食による海食崖(がい)、海食洞、奇岩が特殊な風景をつくり、錦(にしき)ヶ浦、城ヶ崎(じょうがさき)、石廊崎(いろうざき)、波勝(はがち)崎、黄金(こがね)崎などは景勝地となる。白浜、今井浜、弓ヶ浜などの砂浜もみられ、戸田(へだ)や大瀬(おせ)崎には砂礫州(されきす)が発達して海岸も多様である。

［北川光雄］

産業

平坦地(へいたんち)に恵まれず農業生産は制約されるが、熱海の梅園や、爪木(つめき)崎のスイセンの開花期の早いことで知られるように温暖な気候による農業の特色がある。南伊豆の花卉(かき)栽培や、野菜の促成露地栽培は長い日照時間と、石廊崎の1月平均気温6℃といった気温の高さによる。土肥や河津のカーネーション、南伊豆のマーガレットやキヌサヤエンドウは特産となり、冬季出荷されている。北伊豆平野のイチゴ、沼津市西浦から土肥にかけてのミカン、東伊豆の甘夏ミカンなども有名で、観光農業化も進んでいる。天城山間地ではワサビの生産が多く、狩野川、大見川、河津川上流の渓流や湧水(ゆうすい)を利用している。特殊なものとして函南町丹那の酪農の歴史は古い。

　伊豆は海に囲まれているので水産業が盛んで湾奥部の低地には、漁村が立地し漁港が開けてきた。磯浜や岩礁の多い南伊豆ではテングサなどの海草類、アワビ、サザエ、イセエビなどの魚貝類の採取がおもで、白浜、須崎、雲見(くもみ)などはテングサの主産地であったが、民宿村に転換し、温泉の湧出による温泉民宿が雲見でみられる。東海岸は定置網、棒受(ぼううけ)網などによる沿岸漁業が中心である。西海岸は冬季の西風や海底地形の影響で沿岸より沖合漁業や、遠洋漁業がおもで、戸田、田子(たご)、岩地、下田などは遠洋漁業の基地である。また、沼津市西浦や静浦の内湾ではハマチ、アジ、タイなどの海面養殖が盛んである。

　伊豆は降水量が多く、天城山では年降水量3000ミリメートルを超え、森林の生育条件に適し、林産資源に恵まれ国有林面積も広い。天城山はかつて甘木とも書かれ、江戸幕府は森林保護のために御制木という制度を設け、スギ、マツ、ヒノキ、ケヤキ、クス、サワラの6種が禁伐であったが、のちにカシ、モミ、ツガが加えられて天城九木とよばれた。伐木により搬出も行われたが、筏(いかだ)で送流したため、河津川や大見川沿いには筏場(いかだば)の地名が残っている。林産物としてかつては木炭の生産地であったが衰退し、シイタケの栽培が伸びた。自然の植生として天城連山にはブナ、モミ、アセビなどの原生林があり、アマギツツジやアズマシャクナゲの群落も美しい花を咲かせ、学術参考保護林に指定された範囲も広い。なお、海岸部でも大瀬崎のビャクシン樹林（国指定天然記念物）、戸田御浜(みはま)崎のイヌマキの群落は独特な植相景観をもつ。伊豆半島は火成作用に伴う鉱床も多く鉱産資源にも恵まれている。伊豆の金山は天正(てんしょう)年間（1573～1592）から大久保長安(ながやす)がその開発を始め、土肥、湯ヶ島、縄地(なわじ)、瓜生野(うりゅうの)などで採鉱が進み、慶長(けいちょう)年間（1596～1615）が最盛期であり、縄地は生産量が最大であった。現在ではほとんど廃鉱となり、伊豆市清越(せいごし)、持越(もちこし)などで金銀鉱の採掘と精錬がみられたが、現在、持越では含金銀工業用産業廃棄物から金・銀の再生事業を行っている。特殊な鉱業として西伊豆町宇久須(うぐす)の伊豆珪石(けいせき)鉱山がある。安山岩が火山性硫気作用で変質し、珪石に変わったもので、ガラス原料鉱石として、また軽量コンクリート用骨材として採取されているが、山地を破壊し、防災上問題となっている。

［北川光雄］

交通・観光

山岳美、海岸美、温泉の豊かさなど自然の多様性、歴史的文学的背景は観光資源としての伊豆の価値を高め、富士箱根伊豆国立公園の指定区域も広い。伊豆の名前は「湯出(ゆず)」によるといわれるように30を超える温泉地がある。熱海、伊東、伊豆長岡などは湧出量が多く、熱川(あたがわ)、峰、下賀茂などは泉温の高い沸騰泉、湯ヶ島、湯ヶ野は自然湧出を主とするなど温泉ごとに特性をもつ。泉質は単純温泉、塩化物泉が多く、網代(あじろ)（南熱海）、下賀茂は塩化物泉である。蓮台寺(れんだいじ)、大仁(おおひと)、土肥などは鉱山の鉱内湧出が泉源である。堂ヶ島(どうがしま)、松崎、雲見などは掘削により湧出した新しい温泉地であり、今井浜、下田などは引き湯による。観光地の発展には交通条件の整備との関係が深く、古くは1925年（大正14）の国鉄熱海線（現、JR東海道本線国府津―熱海間）、1938年（昭和13）の国鉄（現、JR）伊東線、1961年（昭和36）の伊豆急行線の開通は、観光客の急増をもたらし東伊豆の開発を進め、熱海、伊東は国際観光温泉文化都市に成長した。1924年の伊豆箱根鉄道駿豆(すんず)本線、1969年の東海道新幹線三島駅開業は、下田街道に沿う中伊豆、西海岸方面の地域変容をもたらした。国道135号、136号の整備、伊豆スカイライン、西伊豆スカイライン、南伊豆道路（マーガレットライン）など観光道路の建設は、観光客とともにゴルフ場、別荘地、レジャー施設を拡張し、自然環境保全が問題となった。また、河津町梨本(なしもと)に災害復旧として建設された国道414号の河津七滝(ななだる)ループ橋は、道路自体が新名所とされている。また、伊豆半島中央部の天城峠からモリアオガエルの生息で知られる八丁池にかけては、森林、渓谷、野鳥をもとに昭和の森天城自然休養林に指定され、森林博物館、伊豆近代文学館なども併設され、旧天城峠は踊子コースが設けられるなど多面的に整備が進んでいる。

　自然的な観光資源に加えて川端康成(かわばたやすなり)や井上靖(やすし)などの文学作品の舞台としての伊豆には、文学散歩コースが知られるし、歴史的にも源氏ゆかりの修善寺、蛭ヶ小島(ひるがこじま)、黒船と開港にちなむ下田周辺など名所旧跡巡りも多彩である。

［北川光雄］

地震活動

長い地質時代にわたって、地殻変動や火山活動が盛んに繰り返されてきており、半島の大部分が富士火山帯の多賀、大室、天城、棚場、達磨などの高原状の諸火山からなり、海岸はほとんどが磯浜海岸である。地震活動も盛んで、1930年（昭和5）には伊東群発地震の半年後に北伊豆地震（M7.3、死者272人）が発生。近年も1974年（昭和49）伊豆半島沖地震（M6.9、死者29人）、1978年伊豆大島近海地震（M7.0、死者25人）、1978～1980年断続的な伊豆半島東方沖の群発地震と、破壊地震が北上し、半島中東部での地盤隆起などと相まって、成り行きが注目されている。群発地震はその後も断続的に発生しており、東京大学地震研究所などで地殻活動の常時監視が行われている。プレートテクトニクス（海洋底拡大説）によれば、伊豆半島はフィリピン海プレートにのって北上し、アジア大陸プレートにのっている日本列島とぶつかり、押し合っているという。

［諏訪　彰］

『星野通平他編『伊豆半島』（1972・東海大学出版会）』▽『日本歴史地理学会編『郷土史話伊豆半島』（1978・歴史図書社）』

[参照項目] | 天城山 | 伊豆国 | 狩野川 | 北伊豆地震 | 富士火山帯 | 富士箱根伊豆国立公園

河津七滝
天城峠の南方、河津川にある滝群。上流から釜滝、エビ滝、蛇滝、初景滝、カニ滝、出合滝、大滝の七つの滝がかかる。写真は落差約10m、幅約7mの初景滝。河畔には「踊り子と私」の像が建つ。富士箱根伊豆国立公園の一部。静岡県賀茂郡河津町©静岡県観光協会">

河津七滝

浄蓮ノ滝

石廊崎
伊豆半島最南端の岬。入り江が鋸歯状に入り組み、海食崖や奇岩など、変化に富んだ景観を呈する。一帯は富士箱根伊豆国立公園に含まれ、国指定名勝「伊豆西南海岸」の一部でもある。写真は海上安全や大漁を祈願する石室神社の祭礼、石廊権現祭のようす。断崖上に石廊埼灯台、なかほどに石室神社がみえる。静岡県賀茂郡南伊豆町©南伊豆町観光協会">

石廊崎

黄金崎
伊豆半島西海岸の景勝地。夕陽の名所として知られる。黄褐色に変質した安山岩の断崖に夕陽が当たると、岩肌が黄金色に輝く。富士箱根伊豆国立公園に含まれ、遊歩道、芝生の広場、展望台などが整備されている。静岡県賀茂郡西伊豆町©静岡県観光協会">

黄金崎

白浜

御浜岬

大瀬崎〈沼津市〉

千貫門
松崎町雲見の浅間崎の南にある海食洞門。海上の巨岩にうがたれた高さ約15m、幅約10mの洞門で、遊覧船や観光船がくぐり抜けることができる。富士箱根伊豆国立公園に含まれ、国指定名勝「伊豆西南海岸」の一部でもある。静岡県賀茂郡松崎町©伊豆半島ジオパーク推進協議会">

千貫門

熱海梅園
全国一の早咲きで知られる梅林。700本を超えるウメが植栽され、早咲きから中咲き、遅咲きと、時期をずらしながら次々に開花する。毎年1月から3月にかけて恒例の「熱海梅園梅まつり」が開催され、全国から多くの観光客が訪れる。静岡県熱海市©Shogakukan">

熱海梅園

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