Accumulation Terraces Research Articles

後期更新世における宮崎平野の地形発達

The Miyazaki Plain has the best-developed late Quaternary terraces and deposits in Kyushu. But the landform evolution of this plain has not been investigated in detail in previous works. This study tephrochronologically describes the landform evolution in late Pleistocene.Thick weathered tephra layers overlying the terrace surfaces are subdivided into an older and a younger groups. The younger tephra group, which has been deposited in the last ca. 100, 000 years, contains many marker tephra layers, in ascending order, Ata, K-Tz, FkP and Aso4 of 90, 000-70, 000y.B.P., ; AyP, IwtP, IwP, AwS, HnS II and OtP of 60, 000-30, 000y.B.P.; OsP, ItoPfl, AT and KbP of 22, 000-15, 000y.B.P.; and Ah of 6, 000y.B.P.The older tephra group covers the higher terrace group of middle Pleistocene. The younger group covers the following lower terrace surfaces, in descending order: the Sanzaibaru surface, the Karasebaru surface, the Nyutabaru I, II, III surfaces, the Saitobaru I, II surfaces, the Toyobaru I, II surfaces, the Oyodo surface, the Kunitomi I, II surfaces, the Mikazukibaru I, II surfaces, and the Holocene terrace surface group.Of many terrace surfaces in the Miyazaki Plain, the Sanzaibaru surface is the most extensive one. It is mostly of marine origin, composed of thick transgressive deposits called the Sanzaibaru Formation and lithologically subdivided into three members. The lower member is fluvial gravelous deposit in the regressive stage. The middle member consists of alternating beds of sand and silt with fossils of mollusccs that lived in the embayment of a warm sea in the transgressive stage. The upper member is sandy deposit of deltaic and beach conditions in the maximum stage of the transgression. On the Sanzaibaru surface, the upper member forms sand ridges which are inferred to have been bars, barriers and dunes.The oldest marker tephra layer on the Sanzaibaru surface is the Ata ash which erupted from the Ata caldera ca. 90, 000-80, 000y.B.P.. The Sanzaibaru surface underlying the Ata ash is thought to have emerged ca. 100, 000y.B.P., in the Last Interglacial Stage. It is estimated by subtracting the height of the base of the Sanzaibaru Formation from the height of the shoreline of the surface that sea level rose more than 100m in the Sanzaibaru stage.The Nyutabaru I, II, III surfaces are characterized by gentle gradients and wide distribution. They are of fluvial origin, although the Nyutabaru II and probably III surfaces are partly of marine origin in the northern part of the plain. The Nyutabaru III surface is an accumulation terrace formed during the little transgression. These surfaces are thought to have emerged ca. 90, 000-60, 000y.B.P., when a relatively high sea level was maintained because regression was slow and debris supply from the Kyushu Mountains increased or discharge in rivers decreased.The Saitobaru I and II, Oyodo, and Kunitomi I and II surfaces, which are characterized by steeper and more linear longitudinal profiles, are erosional terraces and are mostly of fluvial origin. Their surfaces came out ca. 50, 000-10, 000y.B.P., in the Last Glacial Stage, when rapid regression occurred and sea level stayed relatively lower. The discharge of the rivers tended to increase gradually.The Karasebaru, Toyobaru I and II and Mikazukibaru I and II surfaces in the northern part of the plain are fluvial fans. They were formed in three regressional stages: the late Last Interglacial Stage, the early Last Glacial Stage and the late last glacial stage. These fans were formed under conditions in which the river bed gradient was steeper than that of the continental shelf when the sea level went down.

Spatial Variation in the Structure and Litterfall of a Sumatran Rain Forest

In this paper an explanation for the spatial variation in the structure of a Sumatran rain forest is suggested. The forest area consisted of a series of topographical units (terraces, mountain slopes) of increasing age and decreasing pH and fertility. With increasing soil age the production of leaf litter and fruit decreased whereas the proportion of mature-phase forest increased and gap cover decreased. There is variation in the growth strategies of trees depending on soil fertility; this results in higher tree longevity on poor soils, and hence in forest with fewer gaps and with more large trees, than on rich soils. Thus, Janzen's (1974) hypothesis of the effect of soil fertility on the prevalence of anti-herbivore defenses and fruiting periodicity is extended to include aspects of forest structure. THERE IS LONG-STANDING EVIDENCE of spatial variation in the floristic composition of the Malesian rain forests (van Steenis 1935; Richards 1952; Ashton 1964, 1982; Whitten 1982). More recently, much attention has been given to the temporal variation in floristic composition in both the Malesian (Poore 1968) and the neotropical (e.g., Hartshorn 1980) regions. The interest in forest dynamics has led to a number of studies in which structure and productivity are linked with secondary successional processes (e.g., Odum et al. 1970). For forests in the wet and moist tropical life zone it is established that leaf area index and leaf biomass are restored within a few years of the start of secondary succession (Golley 1978, Snedaker 1980) and that the rate of increase in total biomass and litter production slows down after some 20 years (Brown and Lugo 1982). In the mature phase, however, net primary production and perhaps litterfall tend to increase again (Whitmore 1975). There are no such dear patterns of spatial variation in structure and productivity of the forests for the wet and moist tropical life zone. The general concensus is that soil factors affect neither litter production (Tanner 1980, Leigh and Windsor 1982, Proctor et al. 1983b) nor structure and biomass (Proctor et al. 1983a). The aim of the present study is to compare the structure, dynamics, and litter production of a number of habitat types within one small area of tropical rain forest containing soils of various ages and fertilities. The results suggest that variation in soil fertility may be responsible for the observed spatial variation in structure and productivity. STUDY AREA The upper half of the course of the Alas river lies in the Semangko Rift zone, a graben running the full length of Sumatra and flanked by the Barisan mountain range (Verstappen 1973). The Ketambe field station (3041'N, 97?39'E) lies just below the confluence of the fast-flowing and rocky Alas and Ketambe rivers (Fig. 1) at an altitude of about 3 50 m. The graben is only a few km broad here and contains a number of accumulation terraces (van Beek 1982). The study area (about 200 ha) includes these terraces and the lower slopes of the mountain range (see fig. 16 of Rijksen (1978) for altitudes) which consists mainly of crystalline metamorphic schists, alternating in places with hard limestones of late Paleozoic origin (van Beek 1982). When the Toba volcano erupted some 75,000 years ago (Francis 1983) the exit from the rift valley was blocked by inflowing volcanic material. As a result the valley filled with ignimibrites and became a lake. The erosion base has since been lowered discontinuously by tectonic activity and, due to variation in the weathering resistance of the layered sediments, resulting in a series of terraces. It is estimated that the highest of these terraces became dry about 10,000 yr ago (van Beek, pers. comm.). The area is considered sacred by the local inhabitants of the Alas valley and, with the possible exception of one small part of the lowest terrace near the field station, has not been disturbed by human activities other than the collection of forest produce. Some people say that this part of the lower terrace was prepared for cultivation of rice around 1940 but was abandoned after an outbreak I Received 5 December 1983, revision accepted 14 June 1984. 196 BIOTROPICA 17(3): 196-205 1985 This content downloaded from 157.55.39.255 on Sat, 16 Apr 2016 04:28:25 UTC All use subject to http://about.jstor.org/terms

GLACIAL LANDFORMS AND ACCUMULATION TERRACES AROUND MT. CHOGATAKE, THE NORTHERN JAPANESE ALPS, CENTRAL JAPAN

The Pleistocene glacial landforms in the Northern Japanese Alps have been studied by many researchers, and the existence of several glacial stades, ranging from 60, 000 to 10, 000 years B. P., has been proposed by Kobayashi (1958), Iozawa (1962, 1972), Koaze et al. (1974), Fukai (1975) and Ono (1980). The glacial extent and the valley filling before 60, 000 years B. P. have been little recognized. This paper describes the glacial landforms and the accumulation terraces before 60, 000 years B. P., located along the River Karasu, at the eastern part of Mt. Chogatake in the Northern Japanese Alps. At Chogatake Cirque, a rather dissected old cirque at the eastern side of Mt. Chogatake (2, 664 m), the cirque bottom, situated about 2, 000 m in altitude, is partly eroded away by the dissection of the River Chozawa. In this area, the present writer found out two sets of terminal moraines: the Honzawa and the Mameuchi Moraines (Fig. 5). The former, located 1, 600 m high, indicates the Pleistocene maximum glacial extension along the Hon-zawa Valley, and the latter, located at a height of 1, 900 m on the frontal edge of the Chogatake Cirque, shows a recessional feature. Along the downstream of the River Karasu, five accumulation terraces develop which are classified into Terraces I to V in this paper (Fig. 8). Terrace II which extends to the Honzawa Moraine on the terrace profile (Fig. 9), consists of fluvioglacial deposits judging from the sedimentary facies. The pumice fall deposits of Tateyama Volcano (DPm) are intercalated in the periglacial deposits covering the gravel of Terrace II. The pumice fall deposits of the EPm or OPm are intercalated in the periglacial deposits cover-ing Terrace III (Fig. 7). In view of the presumed age of the DPm fall, a stage of glacial extension and accumu-lation terracing (Tarrace II) in this area should be one of the cold periods before 100, 000 years B. P.. This glacial stage is named here the Chogatake Glacial, which can be divided into two stades, judging from the existence and location of the two terminal moraines. After the Chogatake Glacial, a periglacial environment seems to have governed this area during the period between 60, 000 and 35, 000 years B. P., on the basis of the presumed age of the EPm and OPm. Almost no glaciation occurred around the Chogatake Cirque, although the existence of a glacial stade of this period is widely recognized in other parts of the Northern Japanese Alps by many researchers (Fig. 10).

Terrace landforms and quaternary deposit arounf Pokhara Valley, central Nepal

The Pokhara Valley, a typical intramontane basin in the Nepal Himalayas, is spread around the midstream of the Seti Khola. It is filled with a large volume of gravelly deposits brought mostly from the Annapurna Himal, and splendid river terraces are present. Thus the Pokhara Valley is endowed with excellent conditions for the Quaternary chronological study of the Himalayas.
 Quaternary deposits in the valley are divided into nine stratigraphic units. Among them, the Ghachok and Pokhara Formations are most prominent, forming conspicuous accumulation terraces named the Pokhara and Ghachok Terraces. So far these accumulations were cosidered to have taken place during the glacial ages. In this study, however, the Pokhara Formation was dated by radiocarbon method to prove that the accumulation occurred in the late Holocene.
 Hagen (1969) considered that the Pokhara Valley, as well as the Kathmandu Valley, was once occupied by a single huge lake, and his hypothesis has many followers in spite of Gurung (1970)'s refutation. According to the present study, however only marginal lakes were formed due to damming of tributaries, and the possibility of the existance of a single huge lake in the Pokhara Valley is ruled out.

Distribution Change of Sand and Gravel during the Holocene, in the Abe River Plain, Shizuoka Prefectere, Central Japan

In order to estimate sediment yield change during the Holocene, the author investigated distribution change of sand and gravel on the basis of analysis of a large number of bore-hole logs in an area supplied with a great deal of sand and gravel. In such areas the change of Holocene deposits distribution is expected to be influenced by environmental change in catchment areas.The Abe River Plain, extending about 12km from north to south and 7km from east to west, is located in the central part of the Honshu Island and is known as a typical torrential river. The upper parts of this river dissect rugged mountains, the Akaishi Mountains, forming steep mountain slopes where landslides have frequently occurred. And the accumulation terraces, which were attributed to the rapid erotion, are distributed along the river (Machida, 1959).Most of the plain is occupied with alluvial fans formed by the Abe River and other small rivers, and the alluvial formations of the plain are dominated by sand and gravel. But the seaward front of sand and gravel dominated area varies in several levels in the alluvial formation. Figs. 11-a, b, c, d, e, f represent the distribution of sand and gravel at intervals of 5m from the level of -20m (which means 20m below the present sea-level) to 0m, and +3m (which means 3m above the present sea-level), which provides the lowest surface on the plain.The results obtained from these 6 figures are as follows;(1) From the level of -20m to that of -10m and from that of -5m to that of +3m, the sand and gravel deposition area is reduced. On the other hand it is expanded from the level of -10m to that of -5m.(2) The area of sand and gravel is the largest on the level of -5m and on that of +3m the smallest.(3) The above trend of progression and retrogression of seaward front of sand and gravel dominated area does not correspond to the general trend of sea-level change during the Holocene.These results suggest the increase of sand and gravel supply of the Abe River around the age represented by the level of -5m. It calls for the reexamination of the assumption that the rate of deposition has kept constant rate during the Holocene in the Honshu Island.

Accumulation Terraces of the Quaternary Ice Age in the Mountains of Central Japan

Accumulation Terraces of the Quaternary Ice Age in the Mountains of Central Japan

14C-Age of an Accumulation terrace at Mitsumata, San'nai-mura, Akita Prefecture in the backborn range of Northeast Japan

¹⁴C-Age of an Accumulation terrace at Mitsumata, San'nai-mura, Akita Prefecture in the backborn range of Northeast Japan

Terrace Topography in the Nozawa Basin and its Vicinity

The accumulation terraces consisting of pumiceous materials from the Tadami Valley are distributed in the valley along the upper course of the Aagano River, making a noticeable feature of the valley. The author tried to make clear the following facts on the relations between the accumulation terraces and terraces of other origin from his survey.(1) In this region the terraces are classified into three groups; the higher, the middle and the lower terraces. The surfaces of the middle terraces are subdivided into four groups; P, P', M and M' Surfaces. P and P' Surfaces are the surfaces of the accumulation terraces consiting of pumiceous materials ejected from Numazawa Volcano. The accumulation of the pumiceous materials in the different parts of the previous valley floor occurred separately, making the narrow gorges its temporary base-levels. Consequently the longitudinal profile of the P Surface is discontinuous at the gorges and intersects the profile of the M Surfaces.(2) The structures of the terraces can be devided into four types (Fig. 3). The surfaces of the lower terraces at A and B types reappear at the previous valley bottom. The surfaces of the lower terraces are lower than the bottom of the valley at the C type.(3) Through the structural study of the terraces the author considers that the tectonic movement influenced the construction of the terraces in this region.

ON THE ACCUMULATION TERRACE IN THE UPPER REACHES OF THE RIVER ABE

In the upper reaches of the River Abe, a typical torrential river in Central Japan, there stretches the accumulation terrace which was attributed to the rapid erosion. The writer has investigated the forming process of the terrace by the exact observation on its topography and deposits, and estimated the velocity of downcutting by correlating these physical aspects with the records of catastrophes described in literature. The results obtained are as follows:— 1) The accumulation terrace was produced by the surges of erosion on the waste-filled valley which had been formed by recurred debris flows derived from the upper part of Oya River Basin (Oya-kuzure)(Fig. 2 is the topographic map which the writer made by the method of transit-stadia surveying.) 2) The terraces are divided into two groups (as shown in Fig. 3); the higher terrace and the lower one. The former, having the fan-shaped surface, is the depositional surface of debris flow, and the latter is “non-cyclic terrace” which was formed by continued downcutting accompanied by slight lateral erosion. (Cross sections of the valley are shown in Fig. 4) 3) The debris flows repeatedly dammed the tributaries of the River Abe, forming the lakes and ponds Judging from the records in the old manuscripts, the newest damming ocurred in 1702 The higher terrace surface, therefore, seems to have been formed at that time. 4) The longitudinal profiles of the terrace surfaces and the present stream (illustrated in Fig. 5) suggest the amount of downcutting and the mode of revival. The downcutting attains the maximum relief of 70m below the knick point, “Akamizu-fall”. 5) The fall, localized on resistant ledges of sand stone, was produced after the formation of the lower terrace-2 at about the end of the 19th century. This lower terrace-2 is distinguished by the characteristic veneer deposits which contain the exotic gravels derived from the adjacent river basin after the destruction of the dammed lakes. 6) Rejuvenation may have been caused chiefly because of decrease in load.

River Terraces of Takkiri River, Formosa (2)

In almost all the rivers of Formosa, we see numerous terraces (Fig. 17). The writer studied the terraces of the Takkiri River. Lying in the northeastern part of Formosa, it is about 45 km in length. It rises in the high mountains of Nankotaizan (3797m) and Gokanzan (3416m), and flows into the Pacific Ocean. The, terraces along the Takkiri are distributed as shown in Fig 1, the high ones of which have a relative height of 100m in its lower course and over 3003m above sea level in its upper course. The low terraces have relative heights of less than 100m. The larger ones along the Takkiri are mostly those formed by changes in the river course. There were two depositions; first, the high terraces were formed, followed by the low ones (Fig 7). The writer obtained a fossil (Celtis sp.) near the base of a high terrace and also striated gravels from that deposit (Fig 7) . The main terraces along the. Takkiri are as follows: Name Above sea level (m) Relative height (m) Remarks Rotien. 155 120 Fig 3 Browan 392 192 Fig 5 Doyon 750 380 Fig 7 440 70 Daoras 710 230 Profile resembles Fig 7 Kumoheru 980 300 Fig 8 Siipau 980 380 Fig 9 Umezono 1100 380 Fig 10 Tausai 1420 430 Fig 11 Fig 13, 14, 15 show the Takkiri terraces projected over the profile of that river. From the projection, the writer believes tat deposition took place as shown in Fig 16. It is possible to conceive that depo-sition Occurred, resulting in two groups of terraces, high and low, in all the other rivers of Formosa. There seems to be no special reason for the development of the Takkiri terraces. The main accu-mulation terraces in Formosa with large relative height are as follows Name of rivers Name of terraces Above sea level (m) Relative height (m) Girandaktisui Menotan 1300 220 Daidakusni Piy ahaw 1060 200 Takkiri Tausai 1420 480 Tansui Teirikk 800 200 Taian Tengu 900 200 Taiko Sikayo 1650 100 Taito Makanaji 1200 100 Dakusui Trock 1520 180 Muso 1820 Sobun Tappo 980 140 Simotansui Magatun 909 150 Takkuf akura 1030 242 Regardless of the direction, rivers that take their rise in high moun-tain ranges have large deposition, and the development of terraces begin upstream. In those mentioned above, the cause of depostion may be either the subsidence of the whole of Formosa or climatic changes. As to the latter, it is reported that there are eirges at Nankotaizan and glacial relic flora and fauna in the high mountains of Formosa. To explain the depostion, climatic change is highly pro-bable. The cause of the revival of erosion may be also both crustalup he aval and climatic changes.