ᄢಽᄢቇᢎ⢒⑔␩⑼ቇㇱ⎇ⓥ♿ⷐ㧔Res. Bull. Fac. Educ.䋧Welf. Sci., Oita Univ.䋩ᄢಽ⋵⼾ᓟ㜞↰Ꮢ↰ᨴ⋆࿾ߩ࿾ᒻජ ↰  ᣹㧖‫ ⷐޣ‬ᣦ‫  ޤ‬࿖᧲ඨፉਛධㇱߩ↰ᨴ⨿ዊፒ࿾඙ߦߪ᫜↰߇ಽᏓߔࠆ‫ߩߘޕ‬᫜↰ߪ✭߿߆ߦ௑ߊᚸ⁁࿾ߦߺࠄࠇࠆ᫜↰ߢ޽ࠆ‫ޕ‬ᚸ⁁࿾㕙ߦߪ✭߿߆ߦᦛᵹߔࠆᴡ㆏〔߇ᄙߊᱷߐࠇߡ޿ࠆ‫ߩߘޕ‬ᴡ㆏〔ߪ᳓↰ߩᐔ㕙ᒻࠍⷙቯߒߡ޿ࠆ‫߃ࠁࠇߘޕ‬ᚸ⁁࿾㕙਄ߩᴡ㆏ᄌㆫ߇᳓↰ߩᓸᅱߥ㜞ૐᏅ߿ಽᏓᒻᘒࠍ૞ߞߡ޿ࠆ‫⚿ߩߘޕ‬ᨐߣߒߡ↰ᨴ⨿ዊፒ࿾඙ߩᄢㇱಽߩ᥊ⷰ߇૞ࠄࠇߚ‫ޕ‬᫜↰ߩἠṴࠪࠬ࠹ࡓߪ㜞޿᳓↰߆ࠄૐ޿᳓↰ߦ㗅ߦㅍࠄࠇࠆ㧘↰⿧ߒ࡮↰ㅢߒߢ޽ࠆ‫ߥ߁ࠃߩߎޕ‬᫜↰ߪਛ਎߆ࠄ⛯޿ߡ޿ࠆ߽ߩߢ㧘⥄ὼߣੱ㑆ᵴേߩ㑐ଥࠍ␜ߒߡ޿ࠆ‫ߩߎޕ‬㐳޿ᱧผࠍ฽ࠎߛᣣᧄߩࠝ࡝ࠫ࠽࡞ߩ᥊ⷰߪ㧘᳗ߊ଻ሽߐࠇߥߌࠇ߫ߥࠄߥ޿ߣ⠨߃ࠆ‫ޕ‬‫⼾  ޤ࠼࡯ࡢ࡯ࠠޣ‬ᓟ㜞↰Ꮢ㧘↰ᨴ⋆࿾㧘ዊፒ࿾඙㧘ᚸ⁁࿾㧘ᴡ㆏〔㧘᫜↰㧘ἠṴࠪࠬ࠹ࡓΣ ߪߓ߼ߦ ᄢಽ⋵⼾ᓟ㜞↰Ꮢධㇱߩ↰ᨴ⨿ߪ㧘࿖᧲ඨፉਛᄩㇱ߆ࠄᵹਅߒ⼾ᓟ㜞↰ߢ๟㒐ἥߦᵈߋ᩵Ꮉߩਛᵹㇱߦᐢ߇ࠆ↰ᨴ⋆࿾ࠍਛᔃߣߔࠆ࿾ၞߢ޽ࠆ㧔࿑ 1㧕‫ߩߘޕ‬ᡰᵹߩዊፒᎹߪ⷏ซጊߣ⪇ጪߩጊ࿾ࠍᵹၞߦ߽ߜ㧘᧲ᵹߩᓟ㧘ዊፒ㓸⪭߆ࠄർᵹߒጤ⣁ߔ߉ߢ᩵Ꮉߦวᵹߔࠆ‫ޕ‬ߎߩዊፒᎹߩਛᵹㇱߦ↰ᨴ⨿ዊፒ࿾඙߇૏⟎ߔࠆ‫ߩߎޕ‬࿾඙ߪ᳓↰ߩᢛ஻੐ᬺ߇ⴕࠊࠇߡ߅ࠄߕ㧘᫜↰ߩ᥊ⷰ߇ᐢ߇ߞߡ޿ࠆ‫ߒ߆ߒޕ‬ߘߩ᫜↰ߪጊ࿾ߦ߅ߌࠆߘࠇߢߪߥߊ㧘ዊ⋆࿾ߦ߅ߌࠆ✭߿߆ߥᚸ࿑ 1 ↰ᨴ⋆࿾ߩ૏⟎
ᐔᚑ 21 ᐕ 10 ᦬ 21 ᣣฃℂ㧖ߜߛ࡮ߩ߷ࠆ ᄢಽᄢቇᢎ⢒⑔␩⑼ቇㇱ࿾ℂቇᢎቶ

71

72

ජ  ↰⁁࿾ᕈߩ࿾ᒻࠍ␜ߔ࿾ၞߩ᫜↰ߢ޽ࠆ‫ߥ߁ࠃߩߎޕ‬࿾ᒻࠍ߽ߟ࿾ၞߩ᳓↰ߪ࿛႐ᢛ஻ߦࠃࠅᢛὼߣߒߚ඙↹ߩ᳓↰ߦᄌࠊߞߡ޿ࠆߪߕߢ޽ࠆ߇㧘ዊፒ࿾඙ߢߪ૑᳃ߩദജߦࠃࠅ᫜↰߇ᱷߐࠇߡ޿ࠆ‫ߢߎߘޕ‬ዊፒ࿾඙ߩ᳓↰߇✭߿߆ߥᚸ⁁࿾ࠍ␜ߔᐔ㊁࿾ᒻߣߤߩࠃ߁ߦ㑐ㅪߔࠆ߆㧘ฎ޿ᤨઍߩᣣᧄߢߪߤߎߢ߽⷗ࠆߎߣ߇ߢ߈㧘ੱ㑆ߣ⥄ὼߣ߇౒ሽߒߡᒻᚑߐࠇߚ᥊ⷰ߇ߤߩ
ࠃ߁ߥ߽ߩߢ޽ߞߚ߆ࠍ⍮ࠆߚ߼ߩ⎇ⓥࠍ⠨߃ߚ‫ᧄߜࠊߥߔޕ‬Ⓜߩ⋡⊛ߪ㧘ዊፒ࿾඙ߦ߅ߌࠆ↰ᨴ⨿ߣߒߡߩᢥൻ⊛ߥ᥊ⷰ߇㧘࿾ᒻ࡮࿾⾰ߣߤߩࠃ߁ߦ㑐ㅪߔࠆ߆㧘ߘߒߡㄭઍൻߩਛߢᄬࠊࠇߚㄘ᧛᥊ⷰߪߤߩࠃ߁ߥ߽ߩߢ޽ߞߚ߆ࠍ޽ࠄߚ߼ߡ⷗⋥ߔߎߣߦ޽ࠆ‫ޕ‬Τ ↰ᨴ⋆࿾ߩ᭎ⷰߣ࿾⾰࡮࿾ᒻ ᩵Ꮉਛᵹㇱߩ↰ᨴ⨿ਛᄩㇱߩ↰ᨴ⋆࿾ߪ㧘਄ᵹߪ↰ᨴ⡍㚍ߩጽ⼱ㇱ߆ࠄർ⷏㧙ධ᧲ᣇะߦ㐳ゲࠍ߽ߜ㧘ጤ⣁߆ࠄᷡṚߦ޿ߚࠆ⁜⓰ㇱ߹ߢߩ㧘㐳ߐ߅ࠃߘ 4.5km㧘᏷ 1.5km ⒟ᐲߩ⚦㐳޿⋆

࿑ 2 ↰ᨴ⋆࿾ߣߘߩ๟ㄝߩ࿾⾰᧻ᧄ߶߆㧔1984㧕㧘᧻ᧄ࡮ᚑ㊀㧔1985㧕ࠍ৻ㇱୃᱜᄢಽ⋵⼾ᓟ㜞↰Ꮢ↰ᨴ⋆࿾ߩ࿾ᒻ73

࿾ߢ㧘൨㈩ߪ 100 ಽߩ 0.7 ߩᐔမߥ࿾ᒻ߇ᐢ߇ࠆ‫ޕ‬࿾ᒻ⊛ߦߪ᳚Ửේ㧔⥄ὼႇ㒐Ꮺ㧕ߦ૏⟎ߒ㧘ᴡᎹߩᦛᵹߢ․ᓽߠߌࠄࠇࠆ‫ޕ‬

1 ࿾⾰
࿾⾰⊛ߦߪ㧘↰ᨴ⋆࿾ࠍਛᔃߣߔࠆ࿾ၞߪ㗔ኅᏪߩᄌᚑጤ㘃ߣߘࠇߦ⽾౉ߔࠆ⧎ፘጤ㘃ࠍၮ⋚ߣߒ㧘ߘߩ਄૏ߦߩࠆቝ૒ጀߩಽᏓ࿾ၞߢ޽ࠆ㧔᧻ᧄ࡮ᚑ㊀㧘1985㧕‫ޕ‬ቝ૒ጀߪᣂ╙ਃ♿ਛᣂ਎ߦ⡍㚍Ḻ࡮ቝ૒࿾ၞ߆ࠄ࿖᧲ඨፉߦ߆ߌߡᵴേߒߚἫጊᵴേߩྃ಴‛ߢ㧘ᄢㇱಽ߇ಝἯⷺ␕ጤߢ޽ࠆ߇㧘ㇱಽ⊛ߦߪ⷏ซጊ߿⪇ጪߥߤߢṁጤ߇ಽᏓߔࠆ౮⌀ 1 ⷏ซጊධ⷏㣽ߩቝ૒ጀ࡮㓁ᐔ቟ጊጤߩ㧔᧻ᧄ߶߆㧘1984㧕㧔࿑㧞㧕‫ޕ‬ಝἯⷺ␕ጤ߆ࠄߥࠆ⡍㚍ߩ㘑᥊↰ᨴ⋆࿾ౝߦߪᣂ╙ਃ♿㞲ᣂ਎߆ࠄ╙྾♿ᦝᣂ਎ߦ߆ߌߡߩḓᴧᕈၸⓍ‛ߢ޽ࠆୀ᳓ጀ߇ಽᏓߒ㧘᧲ᣇߢߪߘߩ਄૏ߦ╙྾♿ᦝᣂ਎ߩਔሶἫጊࠍ᭴ᚑߔࠆਔሶἫጊಝἯⷺ␕ጤ߇ಽᏓߔࠆ㧔᧻ᧄ࡮ᚑ㊀㧘1985㧧⍹Ⴆ߶߆㧘2005㧕‫ޕ‬ቝ૒ጀߪ㧘㚂⮮㧔1953a㧘-b㧘1962㧕ߩਛᣂ⛔࡮ቝ૒ጀ⟲ߣ㞲ᣂ⛔࡮⡍㚍Ḻጀࠍ৻᜝ߒߡ᧻
ᧄ࡮ᚑ㊀㧔1985㧕ߦࠃࠅฬߠߌࠄࠇߚ‫ޕ‬⍹Ⴆ߶߆㧔2005㧕ߪቝ૒ጀࠍቝ૒Ἣጊጤ㘃ߣߒ㧘ᚑጀἫጊߩᵴേߦࠃࠆྃ಴‛ߣ⠨߃ߚ‫ߡߒߘޕ‬ฎ޿ᣇ߆ࠄ⦁ㇱ቟ጊጤ㧘↰ේጊ቟ጊጤ㧘㓁ᐔ቟ጊጤ㧘↲የጊ࠺ࠗࠨࠗ࠻ߣࠃ߮㧘ߘࠇߙࠇ߇৻ߟ৻ߟߩἫጊߦ⋧ᒰߔࠆߣߒߚ‫ߜࠊߥߔޕ‬ቝ૒Ἣጊጤ㘃ߪቝ૒Ἣጊ⟲ࠍᗧ๧ߔࠆ‫↰ޕ‬ේጊ቟ጊጤߪ↰ේጊઃㄭߦಽᏓߒ㧘㓁ᐔ቟ጊጤߪ↰ේጊ቟ጊጤࠍⷒ߁ࠃ߁ߦಽᏓߒ㧘⪇ጪࠍᦨ㜞ὐߣߔࠆ㧔౮⌀㧝㧕‫ޕ‬K-Ar
ᐕઍ୯ߪ↰ේጊ቟ጊጤ߇
6.06Ma ߆ࠄ 10.0Ma㧘㓁ᐔ቟ጊጤ߇ 5.46Ma ߆ࠄ 6.13Maߩ୯ࠍ␜ߒߡ޿ࠆ‫ޕ‬ୀ᳓ጀߪᐔⴕጀℂࠍ߽ߟಝἯ⾰ࠪ࡞࠻ጀ㨪⍾ጀ߆ࠄߥࠆ‫ޕ‬⍹Ⴆ߶߆㧔2005㧕ߦࠃࠆߣ㧘ୀ᳓ጀ਄૏ߦ 1.47㨪1.2MaߩᑯಽἫ⎈ᵹၸⓍ‛߇ⷒߞߡ޿ࠆߎߣ߆ࠄ⏋ධጀ⟲㧔㚂⮮㧘
1953a㧕ߦኻᲧߐࠇߡ޿ࠆ‫ޕ‬౮⌀ 2 ↰ᨴዊፒߦ߅ߌࠆୀ᳓ጀୀ᳓ጀਛߩ⃯⮺ൻ⍹ߣߒߡ74ජ  ↰

Cyclotella comta㧘Melosira granulata㧘Cyclotella ocellata㧘Fragilalia breristriata ߇ႎ๔ߐࠇߡ޿ࠆ㧔᧻ᧄ࡮ᚑ㊀㧘1985㧕‫ߪࠇߎޕ‬᷷ᥦߥⅣႺਅߢߩࠕ࡞ࠞ࡝ḓ᳓ߢၸⓍߒߚ߽ߩߢ㧘
Cyclotella comta ߇ᄙ޿ߎߣ߆ࠄ⽺ᩕ㙃ߩḓ᳓ߣ⠨߃ࠄࠇߡ޿ࠆ‫ߜࠊߥߔޕ‬㧘ߎߩ࿾ၞߢߪᣂ╙ਃ♿ᧃ߆ࠄ╙྾♿ߦ߆ߌߡߩᤨᦼߦ⃻࿷ࠃࠅ߽ᐢ޿࿾ၞ߇⋆࿾ߦߥࠅ㧘ߘߎ߇ḓ᳓ൻߒ㧘ߘߩਛߦḓᚑၸⓍ‛ߣߒߡߩୀ᳓ጀ߇ၸⓍߒߚߎߣ߇ࠊ
߆ࠆ㧔౮⌀ 2㧕‫ߩߘޕ‬ᓟ㧘ਔሶἫጊߩᵴേߦࠃࠆಝἯⷺ
␕ጤߩၸⓍ߇޽ߞߚ߇㧘↰ᨴ⋆࿾࿾ၞߪ㧘ၮᧄ⊛ߦߪଚ㘩ၞߦ⟎߆ࠇ㧘᩵Ꮉ᳓♽ߩ⻉ᴡᎹ߇ዋߒߕߟ㐿ᨆߒ㧘⋆࿾ࠍᐢߍߡ߈ߚ‫ޕ‬
߅ࠃߘ 9 ਁᐕ೨ߦߪ㒙⯃ࠞ࡞࠺࡜ࠍᒻᚑߔࠆᦨᓟߩᵴേ߇޽ࠅ㧘ߘߩᤨߩἫ⎈ᵹߢ޽ࠆ㒙⯃ 4 Ἣ⎈ᵹ㧔ዊ㊁߶߆㧘1977㧕߇↰ᨴ⋆࿾ߦ߽ᵹ౉ߒ㧘߅ߘࠄߊ⋆࿾౮⌀ 3 㑆ᚭߦ߅ߌࠆ㒙⯃ 4 Ἣ⎈ᵹၸⓍ‛ోၞࠍၒⓍߒ㧘ᶏᛮ㜞ᐲ 100m ઃㄭߦἫ⎈ᵹบ࿾ࠍᒻᚑߒߚߣ⠨߃ࠄࠇࠆ㧔౮⌀ 3㧕‫ߩߎޕ‬࿾ၞߩ㒙⯃ 4 Ἣ⎈ᵹၸⓍ‛ߪἯ⊕⦡ߩ㕖ṁ⚿㨪ඨṁ⚿ࠟ࡜ࠬ⾰ἫጊἯࠍਥ૕ߣߒߡ⋥ᓘ 10cm એਅߩシ⍹ࠍ฽ࠎߢ޿ࠆ‫ߩߎޕ‬Ἣ⎈ᵹၸⓍ‛ߪ㧘᧻ᧄ࡮ᚑ㊀㧔1985㧕ߦࠃࠇ߫㒙⯃ 4B Ἣ⎈ᵹၸⓍ‛㧘⍹Ⴆ߶߆㧔2005㧕ߢߪ㒙⯃ 4A Ἣ⎈ᵹၸⓍ‛ߣߐࠇߡ޿ࠆ‫↰ޕ‬ᨴ⋆࿾ߢߺࠄࠇࠆ߽ߩߪᄢⷙᮨߦྃ಴ߐࠇߚ㒙⯃ 4A Ἣ⎈ᵹߣ⠨߃ࠄࠇࠆ‫ޕ‬㒙⯃ 4 Ἣ⎈ᵹ߆ࠄߥࠆบ࿾ߪ㧘ߘߩᓟߩᴡᎹߦࠃࠆଚ㘩ߢ㐿ᨆߐࠇࠆ߇㧘ߥ߅↰ᨴᮮᎨ㧘㑆ᚭ㧘↰ᨴ਄㊁ߥߤߦಽᏓߒߡ޿ࠆ‫ߩߘޕ‬ᓟߩଚ㘩ߩ
ㆊ⒟ߢ㧘ฎ޿ᴡ㆏߇ᴡጯᲑਐߣߒߡᒻᚑߐࠇࠆ߇㧘ߘߩ߶ߣࠎߤ߇஥ᣇଚ㘩ߢᶖᄬߒ㧘ᴒⓍጀ
ၸⓍߦࠃࠆᐔ㊁㕙߇ᐢߊಽᏓߔࠆ‫ޕ‬

2 ࿾ᒻ ↰ᨴ⋆࿾ߣߘߩ๟ㄝߩ࿾ᒻࠍ࿑ 2 ߦ␜ߒߚ‫ޕ‬ጊ࿾ߪਥߦቝ૒ጀߩಝἯⷺ␕ጤ߇ಽᏓߔࠆ࿾ၞߢ㧘ߘߎߢߪߣߊߦ⡍㚍ߩ࿾ᒻ߇ߺࠄࠇࠆ㧔ජ↰߶߆㧘2009㧕‫ޕ‬ᅏᗲቪ␠⢛ᓟߩፗ࿾ᒻ߿ᦺᣣጤደ㧘ᄕᣣጤደߥߤߪߎߩ⡍㚍ߩ࿾ᒻ߆ࠄߥࠆ᥊ⷰߢ޽ࠆ㧔౮⌀ 4㧕‫↰ߪࠄࠇߎޕ‬ᨴ⨿ዊፒ࿾඙౮⌀ 4 ᄕᣣጤደߩቝ૒ጀ࡮㓁ᐔ቟ጊጤߩ
ಝἯⷺ␕ጤၮ࿑ߪ⼾ᓟ㜞↰Ꮢ⊒ⴕ㧔㧕ߩ  ਁಽߩ  ࿾ᒻ࿑75࿑㧟 ↰ᨴ⋆࿾ߣߘߩ๟ㄝߩ࿾ᒻᄢಽ⋵⼾ᓟ㜞↰Ꮢ↰ᨴ⋆࿾ߩ࿾ᒻ ߩ᥊ⷰߦ߅޿ߡ㧘⢛ᓟߩ࿾ᒻߣߒߡ㊀ⷐߥⷐ⚛ࠍߥߒߡ޿ࠆ‫⷏ޕ‬ซጊߥߤߩጊ࿾㗂ㇱߦ✭ᢳ㕙߇ߺࠄࠇࠆ߇㧘ߎࠇࠄߪቝ૒ጀߩṁጤߩಽᏓߣ㊀ߥࠆ‫ޕ‬㒙⯃ 4 Ἣ⎈ᵹ߆ࠄߥࠆบ࿾ߪർㇱߩ↰ᨴᮮᎨ㧘ਛㇱߩ㑆ᚭ㧘↰ᨴ਄㊁ߦಽᏓߒ㧘ᐔမߥἫ⎈ᵹบ࿾ࠍዷ㐿ߔࠆ‫ߪࠇߎޕ‬ᶏᛮ 100m ⒟ᐲߩ㜞ᐲߦᐢ߇ࠆߎߣ߆ࠄ㧘㒙⯃ 4 Ἣ⎈ᵹߩᵹ౉ߦࠃࠅ⋆࿾ో૕߇߶߷ᶏᛮ 100m ߩ㜞ᐲ߹ߢ
ၒⓍߐࠇߚߎߣ㧘ߘࠇࠍ᩵Ꮉ᳓♽ߩ⻉ᴡᎹ߇ଚ㘩ߒߡ⃻࿷ߩ⋆࿾߇ᒻᚑߐࠇߚߎߣࠍ␜ߒߡ޿ࠆ‫ޕ‬ ↰ᨴ⋆࿾ߩᴒⓍ㕙ߦ․ᓽ⊛ߥ࿾ᒻߪ㧘᩵Ꮉߣߘߩᡰᵹߦߺࠄࠇࠆᣥᵹ〝ߩᴡ㆏〔ߢ޽ࠆ‫ޕ‬᩵

76

ජ  ↰

Ꮉฝጯߪഀว⋥✢⊛ߥᴡ㆏〔߇৻⥸⊛ߢ޽ࠆ߇㧘Ꮐጯ࿾ၞߪⶄ㔀ߥᴡᎹߩᦛᵹߩ〔߇ࠃߊᱷߞߡ޿ࠆ‫ߪࠇߎޕ‬᩵Ꮉᧄᵹߩ᡹᠄ᢳ㕙ߦ޽ߚࠆߎߣ߆ࠄ㧘஥ᣇଚ㘩ߦࠃࠅᐔ㊁ࠍ᜛ᄢߒߡ޿ࠆ᭽ሶࠍ␜ߒߡ޿ࠆ‫ࠄ߇ߥߒ߆ߒޕ‬㧘ߘࠇࠄߩᄢㇱಽߪ᳓↰ߩ࿛႐ᢛ஻ߦࠃࠅᶖṌߒߚ‫ޕ‬ዊፒᎹᵹၞߪߣߊߦᴡ㆏ߩᄌㆫ߇⪺ߒߊ㧘ᦛᵹߩ〔߇ᄙ޿‫ߪࠇߎޕ‬ዊፒᎹ߇᩵Ꮉߦวᵹߔࠆߚ߼ⶄ㔀ߦᵹ〝ࠍᄌᦝߒߚߎߣࠍ␜ߒߡ޿ࠆ‫ޕ‬Υ ↰ᨴ⨿ዊፒ࿾඙ߩૐ࿾ߩ࿾ᒻߣ᳓↰㧔౔ߩ 1㧘౔ߩ 2㧕㧘↪᳓㑐ଥߪᄢಽ⋵┙ቝ૒㘑࿯⸥ߩਐᱧผ᳃ଶ⾗ᢱ㙚㧔1987㧕ߦࠃࠆ‫ޕ‬

࿑ 4 ↰ᨴ⨿ዊፒ࿾඙ߩ࿾ᒻߣ↪᳓ߩᵹࠇၮ࿑ߪᄢಽ⋵┙ቝ૒㘑࿯⸥ߩਐᱧผ᳃ଶ⾗ᢱ㙚૞ᚑ㧔1987㧕ߩ 1000 ಽߩ 1 ࿾ᒻ࿑࡮Ꭸፒ࿾඙⹦⚦ᐔ㕙࿑ᄢಽ⋵⼾ᓟ㜞↰Ꮢ↰ᨴ⋆࿾ߩ࿾ᒻ77↰ᨴ⋆࿾ߩᴒⓍ㕙ߪ࿾ ᒻ ⊛ߦ ߪ  ಽߩ ߣ޿߁✭߿߆ߥ൨㈩ߩᐔ㊁ࠍߥߔ߇㧘ߘߩ਄ᵹၞࠍ᭴ᚑߔࠆᡰ
ᵹߩ 1 ߟߢ޽ࠆ↰ᨴ⨿ዊፒ࿾඙ߩዊፒᎹߪ ಽߩ  ߩ൨㈩ߢ௑ߊ㧘ో૕ߣߒߡ✭߿߆ߥዊፒᎹᚸ⁁࿾ࠍᒻᚑߒߡ޿ࠆ㧔࿑ 㧕‫ߎޕ‬ߩᚸ⁁࿾ߩ࿾ᒻ߇᫜↰ࠍߥߔዊፒ࿾඙ߩ࿾ᒻ⊛ߥ․ᓽߢ޽ࠆ‫ޕ‬ዊፒᎹᚸ⁁࿾ࠍᒻᚑߔࠆၸ
Ⓧ‛ߪ㧘㓏Ბ⁁ߩ᳓↰౮⌀ 5 ዊፒ࿾඙ߩ᳓↰ߦߺࠄࠇࠆ⇜ࠍߟߊࠆ␕ࠍ଻⼔ߔࠆߚ߼ߩ⇜ߩᠩოߦ૶ࠊࠇߡ޿ࠆᦨᄢᓘ 㨪EO ⒟ᐲߩ੝౞␕㨪੝ⷺ␕ߢ޽ࠆ㧔౮⌀ 5㧕‫ޕ‬ ߎߩᚸ⁁࿾␕ጀߣߒߡߩ␕ࠍขࠅ㒰߈᳓↰ൻߔࠆ૞ᬺ߇㧘ਛ਎ߩ⨿࿦ᒻᚑߦ߅ߌࠆᦨೋߩ઀੐ߢ޽ߞߚߣᕁࠊࠇࠆ‫ޕ‬ዊፒᎹᚸ⁁࿾ߪ௑ᢳ߇✭߿߆ߢ㧘ᚸ⁁࿾㕙ߦߺࠄࠇࠆᴡ㆏〔ߪ⋥✢⊛ߥᴡ㆏ߢߪߥߊ㧘߆ߥࠅᦛᵹࠍ␜ߔᴡ㆏ߣߒߡᱷߐࠇߡ޿ࠆ‫ޕ‬࿑ 4 ߦߪᣥᴡ㆏ߦࠃࠅᒻᚑߐࠇߚᲧセ⊛Ყ㜞ߩᄢ߈ߥፗࠍ␜ߒߡ޿ࠆ‫ޕ‬Ყ㜞߇ᦨ߽ᄢ߈޿ፗߪዊፒ࿾඙ർ᧲ㇱߩ 2.4m ߢ޽ࠆ߇㧘ߘࠇએᄖߪᢙ 10cm㨪1m ⒟ᐲߩፗߢ㧘ዊፒᎹ߇㗫❥ߦᵹ〝ࠍᄌ߃ߥ߇ࠄᚸ⁁࿾ࠍᒻᚑߒߚ
ߎߣࠍ␜ߒߡ޿ࠆ㧔౮⌀ 6㧕‫ޕ‬ᣥᴡ㆏ߩ〔ߪ᳓↰ߩᐔ㕙ᒻᘒߦᓇ㗀ߒ㧘߹ߐߦᚸ⁁࿾㕙਄ߩᴡ㆏ᄌㆫ߇᳓↰ߩᓸᅱߥ㜞ૐᏅ߿ಽᏓᒻᘒࠍ૞ࠅ㧘ߘߩ⚿ᨐߣߒߡ࿾ᒻࠍ೑↪ߒ㧘࿾ᒻߦㅒࠄࠊߥ޿᫜↰߇૞ࠄࠇߚߣ޿߃ࠆ‫ߚ߹ޕ‬㧘ߘࠇߪ᳓↰ߩ↪᳓ߩᵹࠇߦᓇ㗀ߒ㧘㜞޿᳓↰߆ࠄૐ޿᳓↰ߦ㗅ߦㅍࠄࠇࠆᒻᘒ㧘ߔߥࠊߜ↰⿧ߒ࡮↰ㅢߒߩἠṴࠪࠬ࠹ࡓࠍߥߒߡ޿ࠆ㧔౮⌀ 7㧕‫ޕ‬ᄢಽ⋵┙ቝ૒㘑࿯⸥ߩਐᱧผ᳃ଶ⾗ᢱ㙚㧔1987㧕ߩ⺞ᩏߦࠃࠆ↰ᨴ⨿ߩ᳓♽ߣ↪᳓ࡀ࠶࠻ࡢ࡯ࠢߩ⎇ⓥߢߪ㧘᳓↰ 1 ᨎᲤߩᮡ㜞߇⸥ߐࠇߡ߅ࠅ㧘᳓↰߳ߩ↪᳓ߩേ߈߇␜ߐࠇߡ޿ࠆ‫ޕ‬౮⌀ 6 ዊፒ࿾඙ߩᵹ〝ᄌㆫߦࠃࠆዊፗ

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ජ  ↰Φ ߅ࠊࠅߦ↰ᨴ⨿ዊፒ࿾඙ߩ᳓↰ߦߪਛ਎ߩ⨿࿦ߣߒߡߩ᳓↰ᒻᚑᤨએ㒠ߩ࿾ᒻ೑↪ߣ᳓↰ߩ㑐ଥ߇ᱷߐࠇߡ޿ࠆ‫ޕ‬⨿࿦ᒻᚑᦼߩੱ‫⥄߇ޘ‬ὼߦㅒࠄࠊߕ㧘⥄ὼࠍ೑↪ߒߡ᳓↰ࠍ૞ࠅ㧘Ⓑ૞ࠍⴕߞߡ޿ߚߎߣ㧘ߘߒߡ⥄ὼࠍήℂߥߊ㧘ή㚝ߥߊ೑↪ߒ㧘↢ᵴࠍ༡ࠎߢ߈ߚߎߣ߇ℂ⸃ߐࠇࠆ‫߁ࠃߩߎޕ‬ߥᓸ࿾ᒻ೑↪ߩᒻߪ㧘࿛႐ᢛ஻߇ⴕࠊࠇࠆߣోߊᄬࠊࠇߡߒ߹߁‫↰ޕ‬ᨴ⨿ዊፒ࿾඙ߩ᥊ⷰߪ㧘߆ߟߡߪᣣᧄߩ޿ߚࠆߣߎࠈߢ⷗ࠄࠇߚ᥊ⷰߢ޽ࠅ㧘ߘߩ᥊ⷰ߇⃻࿷߽ฃߌ⛮߇ࠇߡ޿ࠆߎߣ߇㧘⑳ߚߜߩᔃߩ቟ࠄ߉ߩ
᥊ⷰߣߒߡߩᗧ⟵ࠍ߽ߟ‫ߩߎޕ‬㐳޿ᱧผࠍ൮฽ߒߚᣣᧄߩේೋߩ᥊ⷰߪ㧘᳗ߊ଻ሽߐࠇࠆߴ߈߽ߩߢ޽ࠆߣ⠨߃ࠆ‫ޕ‬౮⌀ 7 ዊፒ࿾඙ߩᵹ〝ᄌㆫߦࠃࠆዊፗߣ↰⿧ߒ࡮↰ㅢߒߩἠṴࠪࠬ࠹ࡓ

ᢥ ₂
ජ↰ ᣹࡮Ꮉ㊁⵨Ꮢ࡮ᳰㄝ⾆዁㧔2009㧕㧦࿖᧲ඨፉ⋵┙⥄ὼ౏࿦ߩ࿾ᒻߣ࿾⾰㧚࿖᧲ඨፉ⋵┙⥄ὼ౏࿦⥄ὼⅣႺቇⴚ⺞ᩏႎ๔ᦠ㧘1-16㧚⍹Ⴆศᶈ㧦᳓㊁ᷡ⑲࡮᧻ᶆᶈਭ࡮ᤊ૑⧷ᄦ㧔2005㧕㧦⼾ᓟ᧶▽࿾ၞߩ࿾⾰㧚࿾⾰⺞ᩏ✚ว࠮ࡦ࠲࡯㧘83p㧚᧻ᧄᐈ㇢࡮᧛↰ᱜᢥ࡮੹ਛ໪༑㧔1984㧕㧦ᄢಽ⋵ർㇱߩ਄ㇱᣂ↢⇇ߩἫጊጀᐨΣ㧚ቝ૒࡮⡍㚍Ḻ࿾ၞ㧘ᾢᄢℂ♿ⷐ㧔࿾ቇ㧕㧘13㧘1-24㧚᧻ᧄᐈ㇢࡮ᚑ㊀᱄਽㧔1985㧕
㧦ᄢಽ⋵࿖᧲ඨፉߩἫጊ࿾⾰㧚ᾢᄢᢎ㙃♿ⷐ㧔⥄ὼ⑼ቇ㧕㧘20 ภ㧘61-76㧚ᄢಽ⋵┙ቝ૒㘑࿯⸥ߩਐᱧผ᳃ଶ⾗ᢱ㙚㧔1987㧕
㧦⼾ᓟ࿖↰ᨴ⨿ߩ⺞ᩏΤ㧔㒝࿑㧕㧚ᄢಽ⋵┙ቝ૒㘑࿯⸥ߩਐᱧผ᳃ଶ⾗ᢱ㙚ႎ๔ᦠ╙㧢㓸㧚
ዊ㊁ᤩม࡮᧻ᧄᓺᄦ࡮ችਭਃජᐕ࡮ኹጟᤃม࡮␹ᚭା๺㧔1977㧕㧦┻↰࿾ၞߩ࿾⾰㧚࿾⾰⺞ᩏᚲ㧘145p㧚㚂⮮ᰴ↵㧔1953a㧕㧦⼾Ꮊ⚥ጀ⟲ߩ࿾ผቇ⊛⎇ⓥ㧔Σ㧕㧚࿾⾰㔀㧘59㧘225-240㧚㚂⮮ᰴ↵㧔1953b㧕㧦⼾Ꮊ⚥ጀ⟲ߩ࿾ผቇ⊛⎇ⓥ㧔Τ㧕㧚࿾⾰㔀㧘59㧘372-384㧚㚂⮮ᰴ↵㧔1962㧕㧦਻Ꮊߩᦨᣂ⛔⻉ጀߩี๧㧙ኻᲧߩၮ␆㧔਻Ꮊߩᦨᣂ⛔ߩ࿾ผቇ⊛⎇ⓥ㧙Τ㧕㧚࿾
⾰㔀㧘68㧘301-312㧚ᄢಽ⋵⼾ᓟ㜞↰Ꮢ↰ᨴ⋆࿾ߩ࿾ᒻ

Geomorphology of Tashibu Basin, Bungotakada City,
Oita Prefecture, Northeast Kyushu, JapanCHIDA, Noboru

Abstract
Terraced paddy fields are distributed in Tashibu-no-sho Osaki districtin the central southern part of Kunisaki peninsula. These paddy fields areseen in alluvial fans which incline gradually. A number of gently
meandering older river channels have been left on the surface of thealluvial fans. These older river channels provide the plane of the paddy
fields. Therefore the river channels have precisely determined thedifference of elevation and the distribution form of the paddy fields. As aresult, terraced paddy fields have come to form most of the landscape ofTashibu-no-sho Osaki district.
The irrigation system of these terraced paddy fields is called"Tagoshi-Tadoshi", which means water sent sequentially from a higher
field to a lower one. Such terraced paddy fields have continued from themedieval period; therefore this shows the relationship between natureand human activity. It is considered that this original Japanese landscapewith its long history must be preserved.
䇼Key words‫  ޤ‬Bungotakada City, Tashibu basin, Osaki district, alluvial
fan, older river channel, terraced paddy field, irrigation system79