Omuroyama (the light-brown hill at upper right of the photo) is one of the scoria cones of the Izu Tobu Volcano Group, which is an active terrestrial and submarine monogenetic volcano field located on and off the east Izu Peninsula. Omuroyama has a beautiful, pudding-like shape (1 km in diameter base, 300 m in height from the base) and a small (250 m in diameter) crater at the summit. We can easily enjoy the beautiful surrounding scenery from the summit of Omuroyama using a chairlift. The eruption of Omuroyama occurred about 4,000 years ago and its lava flows buried valleys and generated a lava plateau (Izu Kogen, a plateau at center to right center of the photo). Several lava flows reached Sagami Bay and formed a lava coast (Jogasaki Kaigan, a complicated coast at lower left to lower center of the photo). Along this coast we can see various lava structures, such as columnar joints and clinkers. (Photo: Motomaro SHIRAO, January 7, 2010; Explanation: Masato KOYAMA)
The importance of Holocene sea-level change has long been a central theme of Quaternary Science. Holocene sea-level records provide direct evidence of the progress of the melting of the ice sheet during the Holocene. Although the correlation between ice and ocean volumes is incontrovertible, casual links are commonly obscured. Some regional studies of coral-reef sites based on analyses of boring cores have been carried out from reef flat to reef slope at present-day reefs, demonstrating a long-term (1000-10000 years) and large-amplitude (10-100 m) melt-water history. However, short-term (< 100 years) and small-scale (< 1 m) sea-level changes that detail past sea-level records and play a major role in predicting sea-level fluctuations in the near future are not observed from reef cores. This paper is based principally on a re-examination of sea-level records from the literature and presents the following suggestions to reconstruct high-resolution Holocene sea-level records: (1) Identifying species from boring core samples is effective to reconstruct sea-level changes more precisely during the Holocene. (2) Relative abundance of data for each species is essential to determine position and course of sea-level curve within the envelope of their living depths. (3) The accuracy of reconstructing the sea-level record depends on the distribution pattern of corals; the vertical distribution in a present-day reef obtained from a site close to a given boring site is all that is required. The sea-level curve based on agreement with the above requirement is characterized by smaller fluctuations (±0.5 - ±2.5 m) during the Holocene, thus studies on the high-resolution sea-level record will provide predictions for research on the spatial and temporal histories of sea-level change to Holocene sciences and management of conservation of land in the near future.
Holocene environmental changes and vegetation history are constructed using phytolith and macroscopic-charcoal analyses of a 23-m-deep drilling core obtained at the Senchomuta marsh in Asodani Valley, northern part of Aso caldera, SW Japan. An intra-caldera lake existed in the Asodani Valley prior to approximately 9 cal ka (calibrated 14C age). Multiple large flood events occurred during the period 8.9-8.1 cal ka and emplaced thick sandy deposits in the valley basin. Thereafter, the center of the Asodani Valley (northern part of caldera floor) changed to swampy and fluvial environments. sasa (cool-temperature dwarf bamboo) grasslands and/or forests with understory sasa covered slopes of the Asodani Valley basin between 11 and 9 cal ka. sasa phytoliths significantly increased at ca. 7.3-6.5 cal ka, but thereafter decreased. Miscanthus (Japanese pampas grass) grasslands existed continuously on the slopes. Macroscopic-charcoal particles were abundant during the last 6000 years, and the peak (6.1 cal ka) amount of charcoal particles is consistent with that of Miscanthus phytoliths. This indicates that the existence of Miscanthus grassland might be related to fire events. Inside the Asodani Valley, Phragmites (reed) became established continuously along the shore of the intra-caldera lake (prior to ca. 9 cal ka) and in subsequent marshes. Gramineae phytoliths were detected predominately through all horizons of the drilling core, whereas a small amount of arboreal phytolith was observed at most horizons. We, therefore, believe that forests existed on steep slopes such as the caldera wall where human impacts were small, although sasa and Miscanthus grasslands were maintained by human activity outside Aso caldera.
This study attempts to estimate the source craters of the Yatsugatake-Kawakami Tephra Bed (Yt-Kw), one of the Yatsugatake Younger Tephra Beds (Yt-Kw, Yt-Pm1, Yt-Pm2, Yt-Pm3, and Yt-Pm4, in ascending order), using the refractive indices of orthopyroxene and plagioclase phenocrysts, for the purpose of constructing an eruptive history of the Yatsugatake Volcanic Chain in central Japan. Previous studies have already clarified that the source of the youngest Yt-Pm4 bed is located around the summit of Yokodake, north of the Yatsugatake Volcanic Chain, whereas the craters of the four other tephra beds have not been identified. Therefore, this study tries to find a correlation between distal tephras and proximal deposits, such as welded tuffs, to estimate the sources of the Yatsugatake Younger Tephra Beds. In addition, the lavas distributed in the proximal area are analyzed to examine whether they have any common refractive indices according to the area. Based on the results, the proximal deposits are classified into four groups: those from around Ioudake (group (1)), from around Tengudake (group (2)), from craters between Mugikusa Pass and Nakayama Pass (group (3)), and others. These results suggest that the Yt-Kw bed erupted from around Ioudake, and the Yt-Pm1, Yt-Pm2, and Yt-Pm3 beds from around Tengudake. Furthermore, the Yt-Kw bed is estimated to correlate with the Ioudake welded tuff because both pyroclastic products contain olivine phenocryst, and the refractive indices of the orthopyroxene and plagioclase phenocrysts are similar. The distribution pattern of the Yt-Kw bed also supports this correlation. Based on the similarity of refractive indices of phenocrysts, Mikaburiyama welded tuff may correlate with one of Yt-Pm1-3. These tephras may erupt in the near ages of Tengudake lower lava, Tengudake middle lava, and Tengudake upper lava.
To understand the submarine volcanism surrounding the Tokara Islands, a submarine topographic analysis and 67 dredge samplings were carried out. Prior to the submarine investigations, we reviewed comprehensively geological and geophysical data on this region and confirmed the complexity of both volcanic activity and tectonic setting of the Tokara Islands. In contrast to the homogeneous subaerial volcanic rocks comprising predominantly two-pyroxene andesite lava flows, the dredged samples vary from basaltic andesite to rhyolite in composition. Furthermore, we reveal that dacitic and rhyolitic pumices are abundant and broadly distributed throughout the submarine area. The recovered volcanic rocks were mainly subangular to angular cobble-boulder fragments of lava, scoria, and variably vesiculated pumice. Volcanic rocks with hornblende phenocrysts occur only north of the Tokara strike-slip fault, which is a major tectonic element of volcanism. The pumices can be classified into three categories based on the size and abundance of the phenocrysts: aphyric pumice, fine-grained porphyritic pumice, and coarse-grained porphyritic pumice. Occurrences, such as amount in a dredge, shape without extensive abrasion, large fragment size, and bulk rock chemical compositions of the major pumice fragments suggest that they are in situ, rather than originating as drifted pumice or air fall, exotic pyroclastic fragments derived from the four super-eruptions of Kyushu Island. Because dredged samples contained fresh volcanic glass in the groundmass, and are not covered by iron-manganese oxide crust, they appear to have originated from the Quaternary eruptions. Indeed volcanic islands have developed above the submarine erosional terraces (indicated as knick points at approximately 110 m in depth), which is assumed to have formed during the last glacial age. K-Ar age dating on the representative pumice samples resulted in ages of 0.60 ± 0.20 Ma and < 0.2 Ma, respectively. These newly obtained submarine data support that acidic volcanisms occurred around the submarine calderas during the Mid-Pleistocene age.
Food producers have increasing concerns about geographical brands as an efficient instrument for gaining market competitiveness. In the case of the Spanish wine industry, denominations of origin (DO) for wine have nearly trebled in number since the mid-1980s. DO is expected to allow producers to acquire market recognition not merely by specifying the places where products originate (origin appeal), but also by ensuring the unique quality associated with the place identified by a geographical term (quality appeal). These points of appeal, when combined, would generate added value for products and promote their sales in the market. However, the proliferation of DOs in recent years makes us reconsider if all of these DOs, with different features in terms of geographical scale or type of products, might assume equally their function of linking the origin and quality of a product. This article analyzes how DOs in the Spanish wine industry achieve product differentiation through a comparative study on three cases of DOs (DO Penedès, DO Cava, and DO Catalunya) overlaid on the Penedès Region in Catalonia. After examining the reason justifying the coexistence of the three DOs in the Penedès Region, the author analyzes in some detail how wine producers registered in different DOs make use of those geographical brands in their product strategies. An empirical study reveals that, although none of the three DOs in the Penedès region enjoy a reputation of prestigious geographical brand, they work efficiently for products as a distinctive sign in the market to be differentiated from generic products or other competing products made elsewhere.
Quantitatively estimating denudation is generally difficult because it essentially involves the removal and loss of materials in situ. The denudation rate of mountainous areas in Japan has commonly been studied from the volume of sediment in a basin or catchment. Nonetheless, the availability of these methods is constrained spatially by upstream area and temporally by depositional age. In the last few decades, thermochronometric methods that evaluate thermal history using radiometric-dating methods have been used to evaluate the denudation and tectonic history of orogenic belts around the world. The advantages of thermochronometric methods are that we can calculate the denudation rate at each sampling point and that combining multiple methods and/or target minerals enables us to calculate denudation rates in multiple periods. However, thermochronometric methods have been applied to areas with extraordinarily high denudation rates in island arc areas such as Japan. Thus, the effectiveness of thermochronometric methods for estimating denudation rates in island arc areas has not been demonstrated. We applied apatite and zircon fission-track thermochronometry to granitic rock samples collected from outcrops and a borehole to estimate the tectonic history of the Rokko area, southwest Japan. Previous studies suggested that the Rokko Mountains have been uplifted by active faulting along their northern and southern margins during the Rokko movements, a Quaternary tectonic movement in the Kinki district. However, the tectonic history of the Rokko area prior to 1 Ma has not been revealed due to a lack of prevalent geologic markers. We estimated average denudation rates in various periods based on apatite and zircon FT ages and previously reported radiometric ages. We obtained denudation rates at about 0.04-0.10 mm/yr after about 30 Ma, 0.05-0.7 mm/yr during 50-30 Ma, 0.7-4.0 mm/yr during 70-50 Ma. The denudation rate after the deposition of the Kobe Group (36.9-30.4 Ma) is estimated to be in the 0.01-0.1 mm/yr order, while bedrock uplift rate after about 1 Ma is estimated to be about 0.5 mm/yr. Thus, the tectonic activity of the Rokko Mountains area prior to 1 Ma has been relatively low.
The Eastern Marginal Fault of the Tokamachi Basin is located on the right bank of the Shinano River, the longest river in Japan, in the Niigata area, within the Neogene fold and thrust belt of central Japan. The activity of this fault is partly responsible for the formation of the Tokamachi tectonic basin. The fault zone is composed of several subparallel fault branches that strike N-S to NNW-SSE and deformed late Pleistocene to Holocene fluvial terraces. These fault branches are characterized by west-facing scarps with some subsidiary east-facing scarps to the east of the basin. Although the destructive 2004 and 2007 earthquakes occurred in the northern part of this fold and thrust belt, no historical rupture has been recorded in the Tokamachi Basin. To obtain paleoseismic records in this tectonically formed basin, we excavated four trenches across different fault branches. The Banba South, Banba North, and Shinmiya trenches are located across the west-facing scarps, and the Miyakuri trench is on an east-facing scarp. Fault exposures and deformed terrace deposits are present in these four trenches. These results confirm that these geomorphic scarps are indeed produced by faulting. At the Banba S trench, three fault traces that have nearly horizontal to very shallow dipping fault planes with upthrown side on the east are present, and show clear evidence of the latest event at ca. 3,500-3,100 yrs BP (BC 1,965-1,630 to BC 1,505-1,145). A penultimate event possibly occurred at after ca.11,000 yrs BP. (BC 11,810-9,800), although its exact timing is not determined. At the Banba N trench, the terrace deposits of ca. 5,300 yrs BP (BC 4,225-3,965) are deformed. This suggests the age of deformation is younger, and probably coincides with the latest event at the Banba S trench. At the Shinmiya trench, the late Pleistocene terrace is divided into two parts by a flexural scarp, probably produced by a blind reverse fault. The scarp is formed prior to 14,000 yrs BP (BC 14,710-13,700). In addition, a younger event is recognized to have occurred between 9,400 and 8,900 yrs BP (BC 8,555-8385 to BC 8,000-7,910). In contrast to those trenches on the west-facing scarps, trench logs at Miyakuri, located on an east-facing scarp, show possibly two events with relatively steep fault planes during the last 32,000 yrs. The latest activity at Miyakuri occurred between 9,500 and 7,400 yrs BP (BC 8,955 to BC 6,365-6,045), but the age of the penultimate event cannot be precisely determined. However, we suggest that the faulting interval at Miyakuri is longer than that of other fault branches. In summary, from this study, we can identify at least three paleoseismic events, namely, I, II, and III, and a possible event IV for the Eastern Marginal Fault of the Tokamachi Basin. Event I is clearly identified at Banba S and N trench. Three faults probably moved simultaneously by Event II. Two other events are only recognized locally. Faulting on the west-facing scarp is more frequent and has a high slip rate, reaching nearly 1 m/ky.
The study investigates the past 1 Ma tephrostratigrapy of the Miyazaki plain in southern Japan. There are over 50 tephra layers, 80% of which originate from Kirishima volcano 25 km west of the plain. Several widely spread marker tephra layers in the layers and fission-track dating are used to establish tephrochronology. The explosive eruptive history of the volcano was reconstructed on the basis of tephrostratigraphy and tephrochronology. The history has two volcano groups: Pre-Kirishima 900-600 ka and Kirishima 600-0 ka. Pre-Kirishima volcanoes are unknown in detail. Kirishima volcano is divided into the Older Kirishima volcano, 600-330 ka, and the Younger Kirishima volcano, 330-0 ka. The Older Kirishima is characterized by calder-forming eruptions and large-scale pyroclastic flows, > 100 km3 in volume. Older Kirishima consists of four stages: O1 (600-530 ka), O2 (530-520 ka), O3 (520-340 ka), and O4 (340-330 ka). The tephra of O1 includes over five crystal-enriched ash fall layers, which indicate that vulcanian and phreatomagmatic eruptions occurred intermittently at that stage. O2 is the first calder-forming stage, in which the Kobayashi-Kasamori pumice fall and pyroclastic flows and Kobayashi caldera were formed. The pumice falls and a co-ignimbrite ash fall of the pyroclastic flow were dispersed over 1000 km east of the source, and covered the western half of the main island of Japan. O3 tephra layers are composed of over ten tephra layers formed by intermittent plinian and phreatomagmatic eruptions. The latter indicates that lakes emerged in the caldera. O4 stage is a large-scale eruption with the Kakuto pyroclasatic flow and Kakuto caldera forming. The Kakuto pyroclastic flow was accompanied by a pumice fall and a scoria fall. They were small-scale scatterings near the source from small-scale eruptions, while the co-ignimbrite ash fall reached Kanto, which is 1000 km east of the source. The Younger Kirishima began with intermittent pumice and scoria falls soon after the O4 stage. The Younger Kirishima forms the main landform in the Kirishima volcano. Most of the Younger Kirishima tephra layers of more than twenty scoria and pumice falls were caused by plinian and sub-plinian eruptions accompanied by lava flows. The activity of the Younger Kirishima volcano is subdivided into four stages: Y1 (330-130 ka), Y2 (130-50 ka), Y3 (50-30 ka), and Y4 (30-0 ka) on the basis of thick soil and erosive horizon, which suggest quiet volcanic activity with no eruptions or only lava flow eruptions. Y1 includes over five tephra layers from sub-plinian eruptions in the western part of Kirishima volcano. There is a long quiet period between 240 ka and 130 ka. Y2 has six scoria falls, which show sub-plinian eruptions in the western part of the volcano. Y3 tephra is composed of Uchiyama pumice fall, Iwaokoshi pumice fall, and Awaokoshi scoria fall. Iwaokoshi from Onaminoike 40 ka old and Awaokoshi from Hinamori-dake 30 ka old, were much larger eruptions than other tephra of the Younger Kirishima volcano. Forming stratovolcano at the source, they reach the Pacific Ocean and Miyazaki plain 50 km east of the source, while most of the Younger Kirishima tephra are distributed near Kirishima volcano. Y4 has more than ten pumice, scoria, and ash falls, which include historically recorded tephra layers. Of them, the Kirishima-Kobayashi pumice fall from Karakuni-dake 16.7 ka spread over the widest area, covering half of the Miyazaki plain and reaching the Pacific Ocean.
The present situation of studies on accretionary wedge formation and related phenomena is briefly summarized from various perspectives, ranging from theories, model experiments, observations on land and submarine, exhumation of high-pressure metamorphic rocks, fluid seepage, stress field, and asperity. Future perspectives are also considered from such recent results with potential areas of study. Gravity acts ubiquitously—everywhere and at all times—on the Earth's materials, so the role of gravity is also accounted for in the wedge development.