Title

Geomorphological development of coastal ridges during the Holocene and recent
beach erosion : case studies of the coastal lowlands along Suruga bay andAmanohashidate along Miyazu bay
Sub Title
完新世の砂州地形発達と現代の海岸侵食 :駿河湾沿岸低地および宮津湾沿岸天橋立を例にしてAuthor松原, 彰子(Matsubara, Akiko)Publisher
慶應義塾大学日吉紀要刊行委員会
Publication year 2015
Jtitle慶應義塾大学日吉紀要. 社会科学 (The Hiyoshi review of the socialsciences). No.26 (2015. ) ,p.1- 16
JaLC DOI
Abstract
Notes
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Genre
Departmental Bulletin PaperURL
https://koara.lib.keio.ac.jp/xoonips/modules/xoonips/detail.php?koara_id=AN10425
830-20160331-0001
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Geomorphological Development of Coastal Ridges during the Holocene and Recent Beach Erosion

Geomorphological Development of Coastal Ridges
during the Holocene and Recent Beach Erosion:
Case Studies of the Coastal Lowlands along Suruga Bay andAmanohashidate along Miyazu BayAkiko Matsubara

I. Introduction
Considering the geomorphological development of coastal ridges, studies on barrier
complexes worldwide have shown that the rise in sea level during the Holocene was amajor factor affecting the development of coastal barriers. Generally, barriers developedand transgressed landward when the sea level was rapidly rising. In contrast, the barriersbegan to grow seaward when sedimentation rate exceeded the rate of sea level rise.
Following this, beach ridges also began to develop in a seaward direction.
A common trend in the relative sea level change around Japan during the Holocene isthat the sea rose above the present level as a result of hydroisostatic movements. During
the Holocene transgression, the relative sea level generally reached its maximum (3 to 5m higher than at present) around 7,000 cal BP. As such, the geomorphological evolutionof the coastal lowlands was deeply influenced by these Holocene sea level changes.
Matsubara (1988, 2000, 2002, 2005, 2015) reconstructed the palaeoenvironmentalchanges in the coastal ridges developed in the coastal lowlands, on the basis of an analysis
of fossil foraminiferal assemblages in bore-hole cores, and used these to describe thegeomorphological development of the coastal ridges during the Holocene. These casestudies served to indicate the processes involved in the development of coastal barriers―1―while the sea level was rising during the early to mid-Holocene, in addition to those
involved in the development of beach ridges when the sea level stabilized or slightly
lowered during the late Holocene.
On the modern coast of the lowlands, coastal erosion caused by a decrease in sedimentsupply from rivers, has become a serious problem since the period of economic growth
after WWII in Japan.
In this paper, the geomorphological development of coastal ridges during the Holocene
in three areas: Inner part of Suruga Bay (Coast of the Ukishimagahara lowland), Westernpart of Suruga Bay (Miho Spit in the Shimizu Lowland), and Inner part of MIyazu Bay(Amanohashidate), is summarized. Furthermore, beach erosion in those coastal ridges
will be discussed (Fig. 1).

II. Inner part of Suruga Bay: Coast of the Ukishimagahara lowland
The coast along the inner part of Suruga Bay is situated between the mouths of theKano River to the east and the Fuji River to the west (Fig. 2). The Ukishimagahara
lowland along the coast is recognized as a barrier-backmarsh system. The present-day
coastal ridges consist of sand and gravel, supplied mainly from the Fuji River flowing
along Fossa Magna, the plate boundary between the North American and Eurasian Plates
in the central part of the Japanese Islands (Fig.1). Furthermore, sand and gravel aresourced from the volcanic rocks distributed in the Kano River basin. Suruga Bay issituated at the plate boundary at which the Philippine Sea Plate subducts beneath theEurasian Plate along the Suruga Trough (Fig. 1). The Suruga Trough is considered to be
one of the hypocentral regions of massive earthquakes. Therefore, tsunamis are predicted
to significantly influence the coast. Additionally, the coast of the inner part of Suruga Bay
often suffers from the damaging influences of high waves and high tides in typhoons,because high waves can reach the inner bay through the bay’s wide mouth, which is open
to the Pacific Ocean.
The Ukishimagahara lowland, representing sand and gravel ridge-backmarsh
complexes, is located in the west of the Kano River delta, and adjoins the alluvial fans of―2―

Geomorphological Development of Coastal Ridges during the Holocene and Recent Beach Erosion

145°E

140°

Sea of Okhotsk

N45°

135°

40°

Sea of Japan

a130°

3e35°

2 1c

Paciﬁc Oceanbd30°

0100

200 300 km

Fig. 1 Distribution of coastal ridges and plate boundaries in Japan
1. Inner part of Suruga Bay (Ukishimagahara Lowland)
2. Western part of Suruga Bay (Miho Spit in Shimizu Lowland)
3. Inner part of Miyazu Bay (Amanohashidate)a. Japan Trench b. Izu-Ogasawara Trench c. Sagami Troughd. Suruga-Nankai Trough e. Fossa Magna

―

3―N

Mt. Ashitaka▲●Mt. Hakone

M83

Ukishimagahara
R. KiseR. Fuji

Suruga Bay
K1

R. Kanomountains

alluvial fanscoastal ridges

natural leveesdeltasbackmarshes

abandonedchannels

0

K1：boring site after Matsubara (1984)

12●Mts. Shizuurakm

M83：boring site after Yonekura et al. (1985)

Fig. 2 Geomorphological map of Ukishimagahara Lowland along inner part of Suruga Bay

the Fuji River to the west (Figs. 2; 3). The lowland extends approximately 20 km in lengthfrom east to west. The coastal ridges in this region comprise sand and gravel. In thebackmarsh area, peaty clay with scoria (ObS) is underlain by marine sand and gravel. The
surface height of the marine sand and gravel deposits, including the buried barrier(coastal ridge I) deposits, becomes deeper towards the northwest (both towards theSuruga Trough and landward). Coastal ridge II, which is buried behind the present-daycoastal ridge III, had prograded seaward from coastal ridge I in the eastern and central
parts of the Ukishimagahara lowland, whereas in the western portion of the lowland, theridge developed upward. This is likely caused by local differences in the subsidence rate.
The geomorphological development of the Ukishimagahara lowland during theHolocene, on the basis of an analysis of fossil foraminiferal assemblages in bore-holecores may be summarized as follows (Fig. 4).
Sea water that invaded the region began to form a bay around 10,000 cal BP. Although
the influence of sea water from outside the bay increased between 9,000 and 8,000 cal BP,open sea water had not yet directly influenced the environment of the bay at this time.
Around 8,000 to 7,400 cal BP, the bay began to be enclosed by a coastal barrier and wastransformed into a lagoon. This lagoon then turned into a marsh since after ca. 6,800 cal―4―

Geomorphological Development of Coastal Ridges during the Holocene and Recent Beach Erosion

Fig. 3 Ukishimagahara Lowland at the southern foot of Mt. Fuji

BP. As marine sand and gravel had been already deposited between 9,000 and 8,000 cal
BP, coastal ridge I must have begun to form before ca. 8,000 cal BP, emerging between
8,000 and 7,400 cal BP and completely enclosing the lagoon by ca. 6,800 cal BP. This is
supported by the results after Fujiwara et al. (2008), based on the analyses of sedimentary
facies, fossil ostracodes and molluscan assemblages of the Holocene deposits behind
coastal ridge I. The peat behind coastal ridge II, which developed seaward from coastal
ridge I, began to accumulate around 5,000 cal BP; consequently, coastal ridge II isconsidered to have enclosed the backmarsh around this time. Furthermore, the presentday coastal ridge III is considered to have been constructed before 2,000 cal BP, because
historic relics found both on the ridge and in the backmarsh date from the Yayoi period,
around 2,000 cal BP.
Coastal erosion, caused by a decrease in sediment supply from rivers, has become aserious problem since the 1960’s. As a result, breakwaters have been constructed against
coastal high waves and tsunamis. Additionally, the construction of offshore breakwaters
and concrete armours has taken place, and beach nourishment has been implemented as―

5―8,000 ～ 7,000 cal BPSuruga Bay2km

ca. 5,000 cal BP

2km

ca. 2,000 cal BP△△△△△△△△△△△△

2km△

mountainslava

alluvial fanscoastal ridges

marshessealagoonpresent coast line

sandy deposits

Fig. 4 Palaeogeographical changes in Ukishimagahara Lowland―

6―△

Geomorphological Development of Coastal Ridges during the Holocene and Recent Beach Erosion

Fig. 5 Shingle beach along the coast of inner part of Suruga Baya form of damage control against coastal erosion (Shibayama and Kayane, eds., 2013)(Fig. 5).

III. Western part of Suruga Bay: Miho Spit in the Shimizu lowland
The Miho spit is located in the eastern part of the Shimizu lowland, and developed fromthe southeastern part of Udo hill towards the northeast (Figs. 6; 7). The sediments of thecoastal ridges in the Shimizu lowland, including the Miho spit, are considered to havebeen supplied from both the Abe River, which flows in the west of the lowland, and thesea cliffs in the south and southeastern part of Udo hill during the Holocenetransgression. The Abe River had also supplied much sediment to develop the alluvial fanat the mouth of the river. The Abe River has been the main source of recent sediments.
The Shimizu lowland faces the western part of the Suruga Bay, and is surrounded by
Neogene mountains to the north and the Pleistocene Udo hills to the south. Within the―

7―

N

▲

mountains and hills
alluvial fans

S95 ●

III

Miho SpitIII

coastal ridges
natural levees
backmarshes

R. Tomoe

abandoned channelsOrido●S85seaUdo Hill

I ～ III : coastal ridges
S85, S95：boring sites
after Matsubara (2000)

Suruga Bay
012km

Fig. 6 Geomorphological map of Shimizu Lowland along the coast of western part of Suruga Baylowland, the Tomoe River runs eastward and flows into Suruga Bay. Three coastal ridges,
numbered I to III in a seaward direction, are remarkably developed in a north to south
direction. Coastal ridges I and II may be recognized as Holocene marine terraces in frontof the former sea cliffs to the east of Udo hill, which developed on the abrasion platforms.
Furthermore, the Miho spit comprising sand and gravel, is developed from thesoutheastern part of Udo hill towards the northeast.
The 14C date of a shell in the uppermost marine deposits of coastal ridge I at the easternfoot of Udo hill is around 6,600 cal BP (Matsushima, 1984). This suggests that theinnermost coastal ridge at the eastern foot of the Udo hill had already developed aroundthe time of the culmination of the Holocene transgression. The Orido inlet exists between
the coastal ridges and the Miho spit (Fig. 6), and a valley was formed on the surface of
the Udo hill sediments beneath the Orido inlet, extending southward to a submarine―8―

Geomorphological Development of Coastal Ridges during the Holocene and Recent Beach Erosion

Fig. 7 Miho Spitcanyon in Suruga Bay. Simultaneously, the Miho spit developed on a ridge on the surfaceof the Udo hill sediments.
The development of the coastal ridges in the Shimizu lowland, on the basis of ananalysis of fossil foraminiferal assemblages in bore-hole cores can be summarized asfollows (Fig. 8).
Sea water had already invaded the region by around 8,500 cal BP, and had also flowed
through the narrow pass between Udo hill and the Miho spit. The innermost coastal ridge
I had been constructed before at least ca. 6,600 cal BP, and the coastal ridge II began todevelop seaward from ridge I and emerged to completely enclose the bay around 4,200
cal BP. Furthermore, the Miho spit developed and began to connect with Udo hill around
6,400 cal BP. Finally, the outermost coastal ridge III began to develop after 1,800 cal BP.
A large amount of gravel was dug from the riverbed for construction materials in theperiod of economic growth after WWII in Japan; therefore, the sediments supplied to theMiho spit decreased rapidly, and severe coastal erosion began to occur along the spit.
After gravel digging was prohibited in the late 1960’s, sediment supply again increased in―9―

ca.7,000 cal BP

Udo Hill

Suruga Bay

2km

5,000～4,000 cal BP

Miho Spit

2km

―

10 ―

Geomorphological Development of Coastal Ridges during the Holocene and Recent Beach Erosion

ca. 2,000 cal BP

2kmmountains・hills

alluvial fanscoastal ridges

sealagoonpresent coast line

marshesFig. 8 Palaeogeographical changes in Shimizu Lowland

some parts of the coast. Later, offshore breakwaters were constructed and beachnourishment has been implemented to guard against coastal erosion (Uda, 2010) (Fig. 9).

IV. Inner part of Miyazu Bay: Amanohashidate
Amanohashidate is one of the most famous coastal barriers in Japan; it is situated in thesoutheastern part of the Tango Peninsula in Kyoto Prefecture, facing the Sea of Japan(Fig. 1). Amanohahsidate developed north to south, approximately 3 km in length (Figs.
10; 11). It encloses Miyazu Bay, which is one of the inlets along Wakasa Bay. The lagoon―11 ―Fig. 9 Offshore breakwaters of Miho Coastbehind the coastal barrier is called Aso-Kai (Lake Aso). According to the bathymetric mapof Lake Aso, the deepest area around －13 m is situated just behind the barrier (Fig. 10).
The lake deposits are mainly composed of muddy sediment (Hirai, 1995). The Noda Riverflows into Lake Aso at the western (innermost) part of the lake. Coastal ridges develop on
the delta around the mouth of the Noda River.
According to Uemura (2010), the Holocene marine deposits along the Noda River arerecognized in the area about 1.5 km inland from the river mouth. This suggests that aformer bay expanded around Lake Aso during the Holocene transgression. Matsubaraand Shiomi (2010) analyzed the fossil molluscan assembalges in the Holocene marine
deposits obtained in the Noda River delta. The fossil molluscan assembalges mainly
consist of Ringicula doliaris and Papiha undulate belonging to a typical assemblage foundin the middle part of the bay with muddy bottoms. Consequently, it is inferred that thepalaeoenvironment of the inner part of Lake Aso had not been influenced by the open seawater.
Concerning Amanohashidate, coastal erosion was recognized in this area during the―12 ―Geomorphological Development of Coastal Ridges during the Holocene and Recent Beach Erosion
Tango Pen.

N▲

51012.5←

Amanohashidate

Aso-Kai (L. Aso)
Miyazu Bay

105
2.5

12.5

7.5

mountains

R. Nodacoastal ridges
deltasbackmarshes
sea and lake
100

Fig. 10 Geomorphological map of Amanohashidate

Fig. 11 Amanohashidate from the northern mountains
Miyazu Bay (left side), Lake Aso (right side)―13 ―bathymetric lines (m)1km

abFig. 12 Coastal changes in Amanohashidate from the southern mountains
a. 1987 AD b. 2014 AD
Lake Aso (left side), Miyazu Bay (right side)―14 ―Geomorphological Development of Coastal Ridges during the Holocene and Recent Beach Erosion

Showa period after the sediment supply into Miyazu Bay for this coastal barrier from therivers decreased because of river improvements such as the construction of sand-trap
dams. Furthermore, two ports constructed to the north of the barrier have prevented
sand supply from upcoast. Coastal dikes were constructed to protect against beacherosion after WWII. Particularly, since 1971, the larger dikes 30 m long at intervals of 200
m began to be constructed. However, the decrease in sand supply could not be improved,and smooth coastlines along Miyazu Bay changed into serrated ones (Hirai, 1995). In an
attempt to rectify this, sand bypass and recycling have been conducted since 1979, whichhave been effective means of beach nourishment (Shibayama and Kayane, eds., 2013)(Fig. 12).

V. Conclusions
The processes of the geomorphological development of the coastal ridges in threeareas are clarified in relation to the relative sea level changes during the Holocene.
Furthermore, beach erosion in each area since 20th century is discussed. Coastal erosion
has become a serious problem because of a decrease in sediment supply from rivers
caused by a large amount of sand and gravel digging, or by a construction of sand-trap
dams. As a form of damage control against coastal erosion, the construction of offshore
breakwaters has taken place, and beach nourishment also has been implemented.
The formation and evolution of coastal ridges during the Holocene have been mainlyinfluenced by the Postglacial Marine Transgression, whereas the landforms of the coastal
ridges at the coastline have been changed by human activities for several decades.
It is predicted that the coastal landforms in the future will be changed not only by thesea level rise caused by global warming, but also by human activities around the coast.

References
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environmental changes in the Ukishima-ga-hara lowland, along the Suruga Bay, central Japan.
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Hirai, Y. 1995: Lake Environment of the Coastal Lagoons in Japan. Kokon-Shoin. 186p. ( J)Matsubara, A. 1984: Geomorhpic development of the alluvial plain facing the inner Suruga Bay.
Geogr. Rev., Japan, 57, 37–56. ( J+E)
Matsubara, A. 1988: Geomorphic development of barriers in the coastal lowlands during theHolocene —A case study of the coastal lowlands along the Suruga Bay, Central Japan— Bull.
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Matsubara, A. 2000: Holocene geomorphic development of coastal barriers in Japan. Geogr. Rev.,
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Matsubara, A. 2015 : Holocene Geomorphic Development of Coastal Ridges in Japan. Keio UniversityPress, 169p.
Matsubara, H. and Shiomi, R. 2010: Fossil molluscan assemblages of the Iwataki bore hore coreand palaeoenvironment of the Aso-Kai. In Uemura, Y. (ed.) Palaeoenvironment and geomorphic
development of the Kumihama Bay —in comparison with the Aso-Kai and Amanohashidate(Kyotango City Board of Education), 105–110. ( J)Matsushima Y. 1984: Neotectonics deduced from Holocene marine terraces along the coast ofSagami Bay, Central Japan. The Quat. Res., 23, 165–174. ( J+E)
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Uda, T. 2010: Japan’s Beach Erosion —Reality and Future Measure. Advanced Series on OceanEngineering —Vol.31, (World Scientific), 418p.
Uemura, Y. 2010: Outlines of the research of boring around the Aso-Kai. In Uemura, Y. (ed.)
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Yonekura, N., Ikeda, Y., Kashima, K. and Matsubara, A. 1985: Boring of alluvial deposits in thecoastal lowlands around Suruga Bay, Central Japan. In Sakaguchi, Y. (ed.) Environmental
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Note: ( J): in Japanese, ( J+E): in Japanese with English abstract.

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