地中海中央部に位置するマルタ諸島では，海岸沿いの石灰岩波食棚に塩田がつくられている．夏に高温・乾燥となる典型的な地中海性気候を利用し，古代ローマ時代から現在に至るまで，天日採塩法による製塩が伝統的に行われてきた（Gauci et al., 2017）．この薄黄色の細粒石灰岩層は，グロビゲリナ属有孔虫微化石を多く含み，中新世（約2300～2000万年前）にアフリカプレートの陸棚外縁部で堆積したものである．塩田では石灰岩の柔らかく加工しやすい特徴を活かして，深さや大きさの異なる濃縮池，結晶池，そして乾燥台が造成されている．これらの石灰岩はマルタの巨石神殿群（紀元前3600～2800年頃）や首都バレッタの城塞都市（16世紀）の建築石材としても広く用いられ，イタリアやギリシャ，リビアなどにも輸出されていた．現在では「グロビゲリナ石灰岩」としてIUGS天然石材遺産にも認定されている（Cassar et al., 2017）．

（写真・説明：飯塚 遼　2022年8月16日撮影）

 Seas of clouds (SOCs) attract mountain trekkers/photographers and are an important resource for rural tourism. The recognition of SOCs as a weatherscape in relation to low-level cloud/fog formation is described. Much of the information on the Internet explains SOCs as a low-level cloud/fog formation without considering the geographical conditions of observers. SOCs spots do not always represent meteorologically favorable conditions but are artificially advertised, and cloud/fog types that are the targets of SOCs change depending on the observer's altitude. High visibility is an important condition for the observer, otherwise it can be difficult to evaluate whether the clouds/fogs are in contact with the ground. Fog is also a weather type in which visibility is less than 1 km, so care should be taken not to confuse fog with the concept of SOCs, which require observers to have high visibility. At the foot of Mt. Yatsugatake, the modification of SOCs from midnight radiation fog to early morning low-level stratus and the development of stratocumulus clouds after sunrise and their dissolving with the development of valley winds were observed with an interval camera. Namely, the behavior of SOCs in mountains reflects the process of dry and wet atmospheres mixing at the top of a boundary layer to form a weatherscape. A case study of sunshine hour differences between Ueda and Sugadaira AMeDAS demonstrates important impacts of low-level clouds on the local morning weather in the valley where people live.

 Splashed particles due to raindrop erosion are observed at a radioactively contaminated deciduous broadleaf forest in the Abukuma Mountains, located approximately 35 km northwest of the Fukushima Daiichi Nuclear Power Plant. Morgan Splash Cups, which allow splashed particles to be measured, were installed at three experimental plots with different forest floor cover conditions for one month in October 2016, and from late September to the end of October 2017. Forest floor cover conditions are assessed, and collected data are analyzed to examine correlations among rainfall characteristics, forest floor cover rate, grain size parameters (sorting and skewness), splashed particle weight, and ¹³⁷Cs transport. The results reveal no significant correlations between rainfall intensity or gross precipitation and grain size parameters. Similarly, no significant correlation is found between forest floor cover and grain size parameters. However, when comparing grain size parameters of plots with forest floor cover rates below 60% and those above 90%, it is observed that a plot with a cover rate exceeding 90% exhibited a larger standard deviation in grain size parameters. When normalizing splashed particle weight by gross precipitation, the experimental plot with a forest floor cover rate exceeding 90% showed a tendency for variability to converge, compared to plots with a cover rate below 60%. This indicates that the variation in ¹³⁷Cs transport is smaller at the plot with a cover rate exceeding 90%. These findings suggest that the effects of forest floor cover on raindrop erosion are not a simple correlation. Instead, the protective effects of the forest floor become significantly higher within a specific cover range (60-90%), leading to a shift in the rainsplash behavior of forest floor soil.

 Activities are underway to estimate the overall viscosity structure of the upper mantle using geodetic observational data on postseismic deformation caused by deep earthquakes in subduction zones. Viscoelastic relaxation following a deep earthquake with a magnitude of Mw 7.7 that occurred on August 14, 2012, in the southern Sea of Okhotsk near Japan at a depth of 598.2 km is examined, as well as the extent to which this phenomenon is reflected in GNSS observation data in northern Hokkaido and Sakhalin, using a three-dimensional viscoelastic model. Multiple models with a stratified + slab structure are adopted, each differing in the depth of the low-viscosity layer within the upper mantle. It is found that efficient Maxwell viscoelastic relaxation can result in surface displacements exceeding 1 millimeter. This effect is observed when a low-viscosity layer, encompassing the depth range of the source fault, is present within the mantle transition zone—even when the viscosity of the upper mantle adheres to the conventional standard of 10²⁰ Pascal seconds. It is assumed that three-dimensional heterogeneity (low-viscosity region) in the asthenosphere or beneath the slab does not significantly alter these results, although three-dimensional heterogeneity caused by the presence of the slab plays an important role. However, at present, it is challenging to detect the postseismic deformation signal of the deep earthquake due to the dominance of surface displacement signals that are an order of magnitude larger, such as those from the postseismic deformation of the 2011 Tohoku megathrust earthquake, in observational data from the same period. It will become possible to overcome this challenge with future advances in observational and analytical technologies.

 A large-scale rockslide occurred at the western side of the summit of Mount Manaitayama in the Otari Mountains. Several estimates have been proposed regarding the timing of the rockslide. Two small plant macrofossils were discovered directly below dammed-lake deposits formed by the rockslide, and their radiocarbon (¹⁴C) ages were measured. Using the latest data set and a calibration program, it is found that the two samples died between cal AD 1427 and 1442. Considering a tree-ring wiggle-matched ¹⁴C single date of the tree trunk sample obtained from the same stratigraphic position by a previous study, it can be concluded that this massive slope failure occurred before the first half of the 15th century. On the other hand, it is unlikely that the 1502 Echigo-Nanseibu Earthquake, which is thought to have occurred near Manaitayama based on another study, caused the Manaitayama rockslide. At present, there are no historical records indicating that strong earthquakes occurred in this area in the first half of the 15th century. Thus, it is necessary to continue to investigate potential causes of the Manaitayama rockslide such as torrential rain or rapid snow ablation.

 A detailed analysis is conducted using digital elevation model (DEM) data and aerial photographs of low-relief surfaces and active faults distributed in the western Chugoku Mountains. In particular, geographic information systems (GIS) are used to identify low-relief surfaces and provide a clear, detailed image of their distribution. The analysis suggests that many parts of Surface I may have been flattened by periglacial action from the ridges of mountainous spines with a certain altitudinal difference. Surfaces II-1, II-2, and III-1 may have originated from valley floor plains formed by rivers that crossed the spine mountains in the past. Therefore, in this area, the hypothesis that the difference in height between high- and medium-level low-relief surfaces was caused by crustal deformation accompanied by fault activity can be rejected. Furthermore, preceding rivers probably flowed north to northwest toward the Sea of Japan. Many parts of Surfaces IV-1, IV-2, and IV-3 may have originated from floodplains formed by rivers in the current river system or in the relatively recent past. In this area, the water system has changed significantly due to the uplift of the mountainous spine and various low-relief surfaces have formed. Furthermore, the activity of main faults caused displacements of each low-relief surface, forming a topography of steep cliffs on the northwest sides of spine mountains, whereas a mountainous topography descending in a step-like manner formed on the southeast side.

 In recent years, inexpensive, small, and lightweight measurement instruments compatible with high-precision positioning such as Centimeter-Level Augmentation Service Global Navigation Satellite System (CLAS-GNSS) and hand-held laser scanners have become available. These devices have the potential to enable rapid and efficient surveying of topographic changes immediately after disasters. The 2024 Noto Peninsula earthquake (M_j 7.6) caused a range of topographic changes from coseismic uplift to slump scarps away from the source fault. In this study, we use a CLAS-GNSS instrument and a hand-held laser scanner to investigate the topographic changes caused by the earthquake and discuss their effectiveness. To constrain coseismic uplift, we analyze the difference between elevations obtained from the pre-earthquake high-resolution digital elevation model and the post-earthquake CLAS-GNSS survey. The results show that coseismic uplift occurred over a wide area along the northern coast of the Noto Peninsula, especially in the northwestern part of the peninsula, with a maximum coseismic uplift of 4.5 m. Using the pre-earthquake high-resolution digital elevation model as a reference, we combined CLAS-GNSS and handheld laser scanner measurements to investigate slump scarps in the post-earthquake topography. The results show that scarps more than 2.5 m high occurred, as well as backward flexural deformation. These results are consistent with those obtained from studies of dead marine sessile organisms, satellite image analyses, and structure from motion multi-view stereo. The equipment used in this study should enable fast and efficient on-site investigations of topographic changes that occur during disasters.

 The formation ages of beachrocks have been determined from the radiocarbon ages of fossil coral and shell samples, however, each age measured only indicates an extinction age. Therefore, the ages of fossil coral and shell samples show apparently different ages from the true formation ages of each beachrock. Based on the analyses of nine cemented materials in total collected from Zamami, Aka, and Tokashiki Islands, west of Okinawa Island, it is recommented to determine the formation age of conglomeratic beachrock based on cemented materials. Elemental concentrations are measured with ICP-MS and show high Ca concentrations of between 25.2 and 55.1 wt%, suggesting high CaCO₃ concentrations. These high CaCO₃ concentrations made it possible to form conglomeratic beachrocks. The radiocarbon ages of cemented materials yield an age of between 3764 ± 62 yr BP and 871 ± 60 yr BP, indicating the oldest and the youngest formation ages of beachrocks.

 How to represent place names and geographical features in foreign languages is a complex and nuanced issue. The process that led to the realization that the location referred to in Japanese as Kutsurū Island is actually a reef at the Ngulu Atoll of the Yap Islands is described.