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The Palaeo-Mesozoic geodynamic evolution of the Tangjia–Sumdo accretionary complex belt, which separates the North and South Lhasa Terrane, remains controversial. Moreover, the lack of geological records restricts the understanding of the evolution of the Sumdo Palaeo-Tethys Ocean from the middle Permian until the middle Triassic. Here we present zircon U–Pb geochronology, whole-rock geochemistry and Sr–Nd–Hf isotopic compositions of the Yeqing gabbro. Zircon U–Pb geochronology yields ages from 254 ± 1 to 249 ± 1 Ma. In situ Hf isotopic analyses yield ϵHf(t) values of −0.2 to +6.3. These samples have high TiO2 (3.69 wt %) and P2O5 (0.78 wt %) contents, with typical patterns like ocean island basalt (OIB). Besides, they are classified as high-Nb basalts (HNBs) based on the high content of Nb (45.3–113.5 ppm). Whole-rock Sr–Nd isotopic compositions are similar to OIB, with initial 87Sr/86Sr of 0.7047–0.7054, 143Nd/144Nd of 0.512526–0.512647 and ϵNd(t) of 0.3–2.7. These signatures suggest that the Yeqing gabbro is mainly derived from low-degree melting of the garnet lherzolite mantle. Based on field observations of HNBs intruding into the continental margin and their geochemical characteristics, we infer that the Yeqing gabbro was generated in a subduction environment. Combined with the regional geology of the subduction environment and the evolution of oceanic islands in the Sumdo Palaeo-Tethys Ocean, we propose that the Yeqing gabbro may represent a product of the asthenosphere upwelling through a slab window produced by subduction of seismic ridge in the Sumdo Palaeo-Tethys Ocean, called plume – subduction-zone interaction, during the late Permian to early Triassic.

The late Paleozoic tectonic evolution of the Lhasa terrane and opening of the Sumdo Paleo-Tethys Ocean remain controversial due to limited data and the ambiguous tectonic significance of Paleozoic magmatism in the southern Lhasa subterrane. Here, we explore the petrogenesis of meta-basalt from the Tangjia area and meta-gabbro from the Sumdo area to provide new constraints on the evolution of the Lhasa terrane. The geochemical characteristics of meta-gabbro are similar to those of oceanic island basalt and have positive whole-rock εNd(t) values (+0.08 to +1.03) and zircon εHf(t) values (+3.4 to +4.9), which suggests that they originated from asthenospheric mantle with minor contributions from lithospheric mantle in an intracontinental rift setting. The meta-basalt yields positive whole-rock εNd(t) values (+6.47 to +6.60) and zircon εHf(t) values (+14.2 to +15.2) and has enriched mid-oceanic-ridge−like geochemical characteristics; we suggest that the meta-basalt was sourced from the depleted mantle and interacted with enriched components in an initial oceanic basin setting. Zircon U−Pb geochronology of meta-basalt and meta-gabbro yielded crystallization ages of ca. 338 Ma and ca. 345 Ma, respectively. We suggest that the Sumdo Paleo-Tethys Ocean opened in the early Carboniferous. Negative buoyancy of Paleo-Tethys oceanic slab during subduction toward Eurasia drove the opening of the Sumdo Paleo-Tethys Ocean. Given that the Sumdo Paleo-Tethys Ocean was a limited oceanic basin, the Lhasa terrane was not completely separated from the northern margin of Gondwana before the Permian.

The volcanic rocks hosting the iron deposits in the Aqishan–Yamansu metallogenic belt are sodium-rich. The geochronology, petrography, and geochemistry of minerals and sodium-rich rocks as well as the relationship between these rocks and the iron deposits are studied. Geochemically, the ore-hosting volcanic rocks are sodium-rich (the averages of Na2O and Na2O/K2O are 4.31 ​wt.% and 8.56, respectively) and belong to the calc-alkaline series. They are enriched in LREEs and LILEs (Ba, U, K, and Sr), but depleted in HFSEs (Nb, Ta, and Ti). SHRIMP zircon U–Pb dating of the crystal tuff in the Aqishan Formation and the dacite in the Tugutu Bulak Formation yields ages of 337.5 ​± ​2.3 ​Ma (n ​= ​15, MSWD ​= ​0.85) and 313.0 ​± ​3.3 ​Ma (n ​= ​13, MSWD ​= ​0.74), respectively, indicating that the sodium-rich volcanic rocks formed from the early–late Carboniferous. Electron microprobe data from plagioclases demonstrate that albites and/or oligoclases were formed in the basic–intermediate–acid volcanic rocks. Two stages of albitization are identified, and the latter is likely attributed to the dissolution of iron in the Aqishan–Yamansu belt. The sodium-rich volcanic rocks probably formed by the interaction between volcanic lava and seawater after volcanoes erupted on the seafloor; meanwhile, the albites formed by element substitution in a low-metamorphic environment. The spatiotemporal coupling relationship between sodium-rich volcanic rocks and iron deposits in the Aqishan–Yamansu belt is favorable. Iron dissolved from the dark minerals of basic–intermediate volcanic rocks through sodium metasomatism is one of the material sources for the iron deposits. Keywords: Sodium-rich volcanic rock, Geochronology, Rock geochemistry, Yamansu metallogenic belt, Eastern tianshan orogenic belt

In some steep valleys, flood-induced changes in river bed elevation pose significantly greater risks to infrastructure than floodwaters alone. Over the short term, the river may aggrade or degrade by several meters during a single flood. Whereas floodwaters recede after each event, moreover, riverbed changes add up over successive floods. To quantify the resulting geomorphic risk and its evolution over time, we propose in this paper a new stochastic model of river bed elevation change. The bed is assumed to rise and drop according to a random walk, driven by the composition of two gamma processes that respectively pace the hydrologic forcing and the geomorphic response. The model can therefore incorporate various sources of uncertainty, associated with precipitation and debris flow activity within the contributing watershed. To test the model, we apply it to a highly active montane river, the Laonong River in southwestern Taiwan. Model calibration is achieved from a combination of long and short term data, including radiocarbon-dated deposits and modern river records. The modelled distributions fit the data well, including the likelihood of extreme changes. The model also produces a reasonable hindcast of the geomorphic damage suffered over the last ten years by Highway 20, a vulnerable road link sited along the river, and can be used to forecast future geomorphic risk.

The Hongyuntan magnetite deposit, which is located in the Aqishan–Yamansu belt of Eastern Tianshan, Xinjiang, is hosted within Carboniferous submarine volcanic-sedimentary sequences. The deposit is characterized by five metallogenic stages: Stage I (garnet–diopside), Stage II (magnetite–tremolite–chlorite–pyrite), Stage III (magnetite–quartz–albite–actinolite), Stage IV (pyrite–quartz–epidote) and Stage V (hematite–limonite). Pyrite associated with magnetite formed during the Stage II has a Re-Os isochron age of 324 ± 31 Ma. Four types of fluid inclusions were observed in the mineral assemblages, namely, two-phase liquid and vapor inclusions, multi-phase daughter mineral-bearing inclusions, multi-phase CO2-bearing inclusions, and monophase vapor inclusions. Microthermometry data reveal that the ore-forming fluids evolved from high-temperature (average 532.5 °C) and high-salinity (average 26.9 wt% NaCleqv) fluids to moderate–low-temperature (average 203.6 °C) and low-salinity (5.07 wt% NaCleqv) fluids. Magnetite precipitation may have been greatly assisted by mixing and boiling in Stage II and Stage III, respectively. The hydrogen and oxygen isotopic values of Stage I garnet (δDV-SMOW = −107.9‰ to −76.7‰, δ18Ofluid = 6.4–10.7‰) and Stage III quartz (δDV-SMOW = −85.5‰ to −83.2‰, δ18Ofluid = 3.8–4.7‰) indicate that the ore-forming fluids were dominated by magmatic water, whereas fluid mixing occurred during Stage II (δDV-SMOW = −117.3‰ to −112.6‰, δ18Ofluid = 3.3–5.7‰) and Stage IV (δDV-SMOW = −115.2‰ to −58.5‰, δ18Ofluid = −1.3‰ to 4.5‰). The variable δ34S values of pyrite (−3.8‰ to 4.7‰) and δ18Omgt values of magnetite (−0.6‰ to 4.1‰) suggest that they were not sourced from a single reservoir. The Hongyuntan magnetite deposit is spatially and temporally associated with volcanism and may be genetically related to it. The fluid inclusions and isotopic compositions of this deposit indicate that its ore-forming fluid was derived from the exsolution of deep-seated magmas and that fluid mixing could have effectively triggered the deposition of ore-forming materials. Multiple periods of volcanic activity could have incorporated additional heat and ore metals into the ore-forming system. Based on our data, we conclude that the origin of the Hongyuntan magnetite deposit is related to the volcanism in the Carboniferous period.

Geomorphic studies on the Taiwan orogen have long focused on the rapid erosion and efficient sediment transport in response to active tectonic uplift and frequent earthquakes/heavy rains. Little attention has been paid to the common low-relief surfaces in high mountains that appear to have been geomorphically stable for a long period of time. We undertook a study on a group of such gentle surfaces in Alishan, which consist of poorly drained hummocky slopes averaging 15° and as wide as 2 km. These gentle slopes are underlain by mass-wasting gravels 60–100 m thick, from which 22 radiocarbon dates >50 to 40 ka BP in age were obtained. Below these thick colluvial deposits are ~20° bedrock bedding planes apparently exposed by dip-slope failures. Combining these data reveals alternating hillslope erosion and deposition, along with episodic river downcutting, at a time scale of several 104 yr. We relate this temporal change in geomorphic processes to glacial-interglacial climate change. During the wet inter-/post-glacial periods characterized by frequent heavy rains, landslides/debris flows prevailed and rivers were capable of conveying most sediment eroded from hillslopes. Frequent debris flows combined with sufficient bedload sediments serving as tools for fluvial erosion caused rapid river downcutting. In contrast, the low river erosion/transport capacity during the dry last-glacial period allowed progressive deposition of thick colluvium on the preexisting, gentle bedding surfaces probably eroded during the last interglacial period. This study shows how glacial-interglacial climate change influenced the river/hillslope processes and landscape evolution of the Taiwan orogen.

The cosmogenic meteoric 10Be that is produced in the atmosphere and mainly scavenged by rainfall is a valuable tool for determining dates and rates of Earth surface processes. A key prerequisite for its applications is the knowledge of the long-term 10Be depositional flux to Earth's surface. Previous efforts on obtaining 10Be depositional fluxes include general atmospheric circulation modelling (GCM), empirical fitting of rainfall 10Be records, and determining the inventory of soil profiles of known age. Here, we derive 10Be depositional fluxes from Holocene river terrace 10Be inventories across the Taiwan mountain belt. We measured 10Be and 9Be concentrations from three terrace profiles, with 14C ages ranging between 3.83 and 9.05 cal. kyr BP and sampling depths of up to 6.2 m. Based on 10Be inventories of our river terraces, the calculated long-term 10Be depositional fluxes vary from 0.32 to 0.49 × 106 at/cm2/yr in the Taiwan orogen. We identify partial Be retention, surface erosion, multi-phase sediment deposition, and incomplete sampling depth in these terraces as potential causes of flux underestimation. When accounting for each of these factors and their uncertainties, the resulting flux estimates of each terrace show an overlapping range of 0.66–0.88 × 106 at/cm2/yr. This newly constrained flux range representative over millennial timescales is thus recommended for Earth surface applications in the fast-eroding Taiwan orogen, especially in regions with similar climatic conditions as the studied terraces. When comparing to flux estimates from other approaches, the flux from the rainfall-based fitting equation exceeds our new terrace-derived flux by more than a factor of two. We consider such high flux to be unlikely for the Taiwan orogen, and suggest that the control of precipitation on the 10Be flux here may be overestimated in rainfall data fitting. The GCM-derived flux overestimates the 10Be depositional flux in this setting to a smaller degree (at least 23%), which is in accordance with findings from previous global data compilation of 10Be fluxes.

Fluvial bedrock incision, which creates topographic relief and controls hillslope development, has been considered the key medium linking denudation and tectonic uplift of unglaciated mountains. This article, however, shows a different scenario from the Coastal Range in eastern Taiwan. This range, with the steepness inherited from pre-orogenic volcanoes, has been subject to mass wasting even before its emergence above sea level no earlier than Middle Pleistocene. Numerous terraced alluvial fans/fan deltas record the ancient mass movements of the range, including rock avalanches. Multiple radiocarbon dates 1 km 2 . Alluvial terraces are typically exhibited close to the source ridges of mass movements, and strath terraces along the downstream parts of rivers. Both were created when enormous sediment supply had exceeded or matched the prevailing river transport capacity. This process, along with the protection by giant boulders from mass movement, disturbed the long-term incision trend of rivers in response to tectonic uplift. As a result, the observed Holocene bedrock incision at most sites has not kept pace with the tectonic uplift. The spatial contrast in mass-wasting histories further accounts for the great diversity of the terrace sequences, even in areas with similar tectonic and base-level conditions.

One of most hotly debated topics concerning the Late Mesozoic evolution of Tethyan and the Tibetan Plateau is the timing of the closure of the Meso-Tethys ocean, which is represented by the Bangong–Nujiang suture zone. The Upper Jurassic–Lower Cretaceous Shamuluo Formation, which unconformably overlies the older Mugagangri Group accretionary complex, provides important information on the closure of the Meso-Tethys Ocean. This paper precisely confines the depositional age of the Shamuluo Formation in the western segment of the Bangong–Nujiang suture zone, extending it from the Late Jurassic to the Albian. Combined with the results of previous studies, we suggest that the Shamuluo Formation in the Awengco–Baerqiong region mainly contains a bathyal Berriasian–Hauterivian subunit and a shallow-marine Albian subunit. Provenance analysis indicates that the Berriasian–Hauterivian subunit was mainly derived from the Jurassic southern Qiangtang magmatic arc, while the Albian subunit was derived from the coeval volcanic rocks and the Upper Carboniferous–Upper Permian strata in the southern Qiangtang terrane. Thus, the two subunits of the Shamuluo Formation have significant distinct sedimentary facies and provenances, indicating that they were deposited in different tectonic settings. Based on the regional geological data, we suggest that the bathyal Berriasian–Hauterivian subunit and the shallow-marine Albian subunit of the Shamuluo Formation should be interpreted as a record of the oceanic arc-continent collision and the Lhasa–Qiangtang soft-collision, respectively. Thus, the closure time of the Meso-Tethys Ocean is at least limited to the Albian.

We have discovered in a marine core, located 20 km east of the Coastal Range of Taiwan at the top of a 1200 m deep submarine high, sheltered from rivers discharges and gravitational flows, a 23 cm-thick anomalous sequence topped with broken bivalves and wood fragments. Based on radiocarbon dating, we distinguish five sub-events within ∼ 100 yrs, about 3000 years ago. The oldest four sub-events are interpreted as the record of local submarine landslides, likely triggered by clustered earthquakes that are common in this tectonically active area. The last event including shells and wood has a different origin. Despite the high level of climatic and tectonic recent activity, no comparable event has been observed at the same site since that time, making it unique during the last 3.75 ka. Hydrodynamical modeling stimulated with a set of submarine landslide-triggered tsunami sources and combined with the regional oceanic circulation dominated by the Kuroshio Current, allow us to better constrain the transport paths of the suspended material, the expected run-up at the coast, and ultimately the trigger and source that best fit our observations. The Kuroshio Current appears as a strong constraint that generally prevents cross-shore transport of suspended material even during a major tsunami. Since the largest aerial debris flow observed along the east coast of Taiwan during the last 4 ka was synchronous with the marine deposit, our preferred scenario starts with the occurrence of four distinct large earthquakes within less than a century, triggering both submarine and aerial landslides in the study area. Then, a giant typhoon reworked the nearshore material as well as the slided material stored upstream resulting in a debris flow. It deeply modified the surface current, allowing the wood debris and shells to fastly reach the core site.

The Sumdo Paleo-Tethys Ocean was the southernmost part of the Paleo-Tethys Ocean, located on the Qinghai–Tibet Plateau. However, the evolution of the Sumdo Paleo-Tethys Ocean and the origin of eclogites in the Sumdo area of Tibet are still matters of debate. Here we report newly discovered adakitic granite dikes from the Sumdo area of the central Lhasa terrane. The rocks have high SiO2, Al2O3, and Sr contents, high Sr/Y and La/Yb ratios, enrichment in light rare-earth elements (REEs), and depletion in Y, Yb, Th, and heavy REEs. They are characterized by low 87Sr/86Sr (0.703678–0.704427) and high 143Nd/144Nd (0.512825–0.512904) ratios, and positive eNd(t) (+6.41 to +7.38) and eHf(t) (+13.8 to +15.7) values. Zircon U–Pb dating yielded ages of 269.1 ± 4.1 and 266.4 ± 2.0 Ma for the rocks. Our data indicate that the Sumdo adakitic granite dikes were derived from partial melting of subducted oceanic slab, with the magma being influenced by slab-derived fluids and slight interaction with peridotite in the mantle wedge during ascent. By combining our new geochemical data with results of previous studies, we infer a subduction event involving the Sumdo Paleo-Tethys Ocean during the middle Permian, which led to the formation of the Sumdo adakitic granite dikes and the Sumdo, Jilang, and Xindaduo eclogites.

We used multi-decadal pollen and diatom records from sediment core TFL-1 from Tsuifong Lake to reconstruct the vegetation dynamics and hydroclimate in northeastern Taiwan during the past 3500 cal BP. Coarse grained sediments in association with higher percentages of wetland pollen (Cyperaceae) and upper conifer pollen (Tsuga and Pinus) in the lower part of the core indicate low lake levels and a relatively cold/dry climate between 3500 and 2030 cal BP, reflecting a decline of the East Asian summer monsoon (EASM). Muddy sediments coupled with reduction of wetland pollen represent the rise of lake levels, implying the re-strengthening of the EASM during the past 2000 years. Paleotemperature was inferred from the variation of pollen origin from the upper and lower mountain forest, indicating the global temperature anomalies of the Medieval Warm Period (MWP) and the Little Ice Age (LIA). In comparison to the main climate forces in the North Pacific, we suggest that the long-term climatic trend in Taiwan was controlled by variations in EASM intensity, while increased precipitation over the past 2000 years may also be linked to warmer sea surface temperature (SST) of the western Pacific Warm Pool (WPWP) and increased El Nino-Southern Oscillation (ENSO) events, which increased typhoon intensity. Higher diatom-inferred pH during 2930–2030 cal BP and the LIA suggest strong hydrological disturbances, reflecting more typhoons passing over Taiwan. The frequent typhoon events could be linked by an abrupt shift of typhoon track, due to the reduction of the WPWP and expansion of the Northwestern Pacific High, which move typhoons in a more westerly direction.

The Hongyuntan deposit, which is one of the typical volcanic-hosted Fe deposits in the Aqishan–Yamansu metallogenic belt of the Eastern Tianshan Orogenic Belt, primarily consists of Fe and skarn minerals (especially garnet). Two generations (three types) of garnets were identified in the Hongyuntan deposit based on field and optical characteristics. Hongyuntan garnets are Fe-rich and belong to the grossular–andradite solid solution series (And = 50.99%–100.00%, average: 79.06%). Garnets of the first generation (Grt1) are massive aggregates and are fine-grained with well-developed oscillatory zonings. They have Type I (two-phase liquid and vapor) and Type II (multi-phase daughter mineral-bearing) fluid inclusions and experienced high temperature (540–560 °C) and salinity (9.2–63.2 wt% NaCl eqv) conditions. The Grt1 have high ΣREE, LfREE/HREE, δEu, U, Y, and high field strength element (HFSE: sum of Nb, Ta, Zr, and Hf) contents. Garnets of the second generation (Grt2) are vefin types and are characterized by irregular shapes with irregular zonings. Type A garnets of the second generation (Grt2-A) usually coexist with mafgnetite and have Type I and Type II fluid inclusions with relatively high temperature (480–500 °C) and salinity (9.5–36.6 wt% NaCl eqv) values. Compared to Grt1, Grt2-A have low And, U, and LREE/HREE together with medium ΣREE, δEu, HFSE, and Y contents. Type B garnets of the second generation (Grt2-B) usually coexist with epidote and quartz. They merely have Type I fluid inclusions with medium–low temperature (260–280 °C) and salinity (6.6–12.7 wt% NaCl eqv) values. Grt2-B have high And, δEu, and LREE/HREE contents but very low ΣREE, HFSE, and Y contents. The fluid inclusions and geochemical properties of the garnets indicate that the temperature, salinity, oxygen fugacity (fO2), and pH of the ore-forming fluid fluctuated, indicating Hongyuntan deposit likely experienced superimposed mineralization. Grt1 originated in a magmatic–hydrothermal fluid and formed through diffusive metasomatism under relatively high fO2, neutral pH, and low water/rock (W/R) ratio conditions. The reduced Fe and other siderophile elements in the ore-forming fluid, which formed Grt1, are believed to be the material basis for iron ores in the later main metallogenic stage. Grt2-A demonstrate the characteristics associated with transitional fluid, which most likely originated from the episodic hydrothermal supplies. However, the ore-forming fluid system gradually opened up during the crystallization of Grt2-B, and the decreasing temperatures and depletion of ore-forming materials were ultimately unfavorable for the deposition of magnetite.

By analyzing metallogenic regulation of the deep skarn ore bodies in Laochang ore field,3D metallogenic features model was established with 3D visualization technology. With “the cubic predicting model” method, the major ore-controlling factors in deep include granites, strata, faults and chemical elements abnormal. We delineated prospect area and outlined ten targets through evidence weight method. Calculating the ore-containing probabilities and the quantities of mineral resources ,it realized prediction of mineral resources on quantity, position and probability. It is important for deep mineral exploration of Laochang ore field in Ge jiu.

Although dominated by erosion over long term, the tectonically active mountains of Taiwan commonly contain thick landslide and debris-flow gravels capping hillslopes or forming alluvial terraces. These deposits and their associated landforms serve to study ancient mass-wasting histories and their controls on fluvial processes. This study focuses on the Pa-chang River draining the 50 mm yr− 1) are detected further downstream after the recent gravel mining. The fact that the obtained bedrock incision rates and patterns are decoupled with the tectonic uplift advises caution in using short-term erosion data to interpret the tectonics of the Taiwan's mountains.

After the bridge is damaged by fire, it is necessary to quickly probe the situation of the damaged structure, to take a response as soon as possible to ensure the safe passage of the bridge. A series of related work such as the component surface damage detection, carbonation depth, concrete strength testing and Axial compressive strength tested by core drilling combined with the analysis and calculation after fire had provided a basis for the safety assessment of structures. According to the results of the test and the conclusion of the finite element calculation, it was found that the bridge belongs to the dangerous situation, and the relevant strengthening measures should be taken.

This paper, based on the origin of Karst Area landslide and the geographical conditions of Guizhou, studies the application of WSN technology on monitoring and forecast landslide and other geological disasters in Karst, and then put forward a landslide monitoring plan. We study the data acquisition layer node topology, and construct WSN monitoring system and test it under the stimulated environment. The result has shown that, the constructed monitoring system can meet the need of real time monitoring of landslide stability in Karst Area.

The cold intensity of the last glacial stadials corresponding to marine isotope stage (MIS) 5d (or 5b), MIS 4 and MIS 2 in terrestrial East Asia monsoon area is not discussed much due to the paucity of long continuous pollen records. A palynological study of drilling cores from three closely-linked intramontane basins (Toushe, Sun-moon Lake and Yuchi) in central Taiwan provides a history of shifting altitudinal vegetation zones in surrounding mountains during late Quaternary climate changes. By integrating these records, we found that the alpine conifer forest approached its lowest altitude, about 614 m, during the earliest stadial (≒MIS 5d or 5b), and 745 m during the early stadial (≒MIS 4) based on records of Yuchi Basin and Sun-moon Lake. In addition, the pollen records of Toushe Basin and Sun-moon Lake show more temperate conditions for the late stadial (≒MIS 2) than the early stadial (≒MIS 4). This leads to an interpretation of a decreasing intensity of stadials during the last glaciation, which might follow the regional insolation amplitude. Such a decreasing trend in coldness during the last glacial stadials does not exist in the record for the South China Sea which reflects a different sensitivity and response to climatic forcings between terrestrial and marine.

With cumulative rainfall of 1700 mm, Typhoon Morakot triggered a catastrophic landslide at Hsiao-lin (9 August, 2009), which dammed the river, buried the village and killed > 400 people. We conducted a geomorphic study to understand the origin of this landslide in the context of the long-term evolution of the hillslope. The landslide originated from a broad, poorly drained slope (21°–23°) and ran down along two first-order channels. The erosion, up to 80 m thick, has created a concave-shape slope and exposed mostly loose debris, which implies that the landslide was mainly the reworking of ancient colluviums. The genesis of the concave-shape slope where the source sediments of the landslide resided reflects the weakness of the mudstone/shale bedrock underlying this slope, in contrast to the sandstone-based transport area. The two channels in the transport area also follow old faults or joints. Given that the source area has been subject to erosion during large landslides, the subsequent deposition here was likely achieved by minor colluvial processes. This deposition continued until the catastrophic failure in 2009, which could be controlled by (1) the amount of sediments deposited, which determined the slope angle, and (2) the headward expansion of the channels from the transport area, which enhanced groundwater convergence and later provided routes for the landslide materials to run downslope. Extensive mass-wasting motions had occurred in the area, as shown by the prevalence of > 20 m thick landslide/debris-flow sequences on the lower part of the hillslope, which are dated 21, 14.9, 13.7 and 12.0 ka by the radiocarbon method. These mass-wasting events had hindered the long-term incision of the trunk river in response to the rapid tectonic uplift. At least the 12.0 ka event, which caused extensive mud-flow deposition, had dammed the river. Overall, this study shows how bedrock lithology and structures controlled the shape of a hillslope and caused extremely unsteady mass-wasting transport in the active mountains of Taiwan.

Landslides and debris flows rarely occurred during historical times in the tectonically active Coastal Range of eastern Taiwan. This topographic stability, however, contrasts greatly with the widespread existence of terraced alluvial fans and fan-deltas on the Hua-tung coast which fringes the range. This study focuses on the two largest fan–terrace systems on the Hua-tung coast, both of which consist of alluvial fans (plane-view areas up to 8 km 2 ) larger than their contributing catchments. Stratigraphic data show that both systems were in sandy, wave-dominated settings during de-glacial times. The systems were then disturbed by a catastrophic landslide/debris-flow event (or events), which brought enormous amounts of gravel (Facies Gm) into the systems, deforming previously-deposited marine sands (Facies Sm) and shallowing the seafloor. The combined Gm/Sm complex yields multiple radiocarbon dates ranging from 11.3 to 8.3 ka cal BP, with a cluster around 8.6 ka cal BP. This mass-wasting event has been unique since the emergence of its contributing catchment 0.2–0.3 Ma ago. The low frequency of such an event could reflect the great resistance of rock mass in the source areas to weathering and erosion. The common blockage of valley floors by giant-boulder piles, which limits channel incision and sediment transport, could also increase the apparent stability of the mountain. The trigger of landslides in the Coastal Range has been linked to large earthquakes. Additionally, we propose that the great magnitude and duration of the observed early Holocene event were caused by the contemporaneous prolonged rainfall (and/or high frequency of typhoons) associated with the East Asian summer monsoon maximum.

Development of fan terraces in incision-dominated river settings documents episodic increases of sediment supply from upland catchments. In the non-glaciated, active mountains of Taiwan, such increases in sediment supply result typically from increases in landslide/debris flow activity. Studying fan terraces, therefore, helps understand the history and nature of mass-wasting processes eroding the mountains. This study explores fan-terrace successions developed at tributary mouths of the Chen-yeo-lan and Lao-nung Rivers in central-southern Taiwan. Judging from the spatial variations of sizes, heights, sequences and sedimentation of the fan terraces, the magnitude and frequency of mass-wasting activities appear to vary from tributary catchment to catchment. Two types of tributary catchment are differentiated, which can be located in close proximity to each other. One has been subject to extremely large but infrequent mass-wasting events, as a result of which high and/or large fan terraces with 100–200 m thick debris-flow/fluvial gravels have been formed. Seven examples of this type of fan terrace have yielded radiocarbon dates of >40 ka, ∼18.4 ka, ∼13.9 ka, 8.9–9.5 ka, 3.9–4.8 ka, ∼3.3 ka, and ∼1.4 ka in age. With the availability of multiple dates, this type of fan terrace can be shown to have been created in no more than 1000 years, from the aggradation of thick gravel sequences to subsequent incision. The second type of catchment has been subject to relatively minor but frequent mass-wasting events. Due to repeated incision after each such event, the resultant fan terraces are relatively low and limited in size but have formed over lengthy periods. Although located in the same geological and geomorphic setting, the dated fan-forming mass-wasting events in the Chen-yeo-lan catchment do not appear to have occurred synchronously with those in the Lao-nung catchment. Nor could the succession of these events, or their origins, be clearly linked to known paleo-climate data. These findings highlight the importance of internal factors (e.g., rock-mass strength) in determining the timing, magnitude, and frequency of mass-wasting events in the studied mountains, which are subject to active rock uplift, highly active seismicity, and intense rainfall.

The evidence of coseismic uplift on the dynamic, wave-dominated Hua-tung coast fringing the active Coastal Range (eastern Taiwan) has been equivocal, due to complex controls by wave and terrestrial sediment over morphological and ecological systems of the coast. This study, by applying radiocarbon dating methods, demonstrates coseismic-uplift nature of the coast by finding synchronously killed intertidal organisms (mostly boring shell Jouannetia sp.) stranded at different sites of the coast with distinct physiographic characters. Based on these data, together with evidence from wave-cut notch sequences, two coseismic-uplift systems are recognized. One centers around the northern-middle part of the coast and yields events with uplift amounts of maximal 3–6 m and an average recurrence interval of at least several hundred years. The most recent activity of this system, influencing at least 70 km of coast, occurred at ~ 0.9 ka. The earthquake generating this event also triggered extensive landslides/debris flows in the region. Another system, exemplified by the uplift associated with the 2003 Cheng-kung earthquake, centers on the southern part of the coast and yields uplift of likely

To understand whether soils on the same geomorphic surface have similar properties, this study examines the morphology of soils developed on the 30-kyr-old Taoyuan Terrace, Northwestern Taiwan. Relationships among soil morphology, variations in the groundwater table, and soil forming processes were established based on field investigations and previously published datasets. The soil series in the study area can be grouped into seven types, including three homogeneous groups, two mottled groups, one gley group, and one reworked group. Fifteen hand-core samples collected in the field and borehole data were used to understand spatial variations in soil morphology. The results indicate that soil morphology on the southern Taoyuan Terrace changes systematically from the fore-edge to the back-edge: from red/orange soils to yellow soils, then to mottled soils, and finally to gley soils. The borehole data indicate that the groundwater table is generally parallel to the ground surface but drops significantly near the terrace fore-edge. This pattern matches with the observed soil toposequence, indicating that the pedogenic processes in the study area are mainly controlled by groundwater distribution determined by topography. Although soils on the terrace fore-edge have developed under the well-drained conditions that favor lateritization, at least two distinct soil types (i.e., red and orange) can be observed there, reflecting different geomorphological settings in a paleo-fluvial landscape. This work suggests that geomorphological and hydrological conditions should be examined carefully before using soil morphology for correlating geomorphic surfaces.

The surface rupture of the 1999 Chi-Chi earthquake ( M w 7.6) trendsmore than 100 km in a north–south direction. Surface deformation at the northernend stops abruptly at an area between the Tachia River and the Taan River where abroad pop-up structure with east to northeast strike can be found that has a trenddifferent from the north–south-striking main thrust. We combine the absolute ele-vation data before and after the Chi-Chi earthquake to obtain the regional verticaldisplacement and the magnitude of the pop-up structure. The greatest uplift couldreach as high as 15–16 m. Using deformation magnitude and the area-balancingmethod, we measure the depth of the detachment to show the subsurface geometryof the Chelungpu fault at its northern end. This shows that the geometry of theChelungpu fault controls termination of the surface rupture and the depth of thedetachment controls the amount of deformation.Introduction Perhaps the most unexpected geological feature asso-ciated with the Chi-Chi earthquake (

We used radiometric dates from 19 sites to determine the Holocene uplift rates of the 140-km-long Hua-tung coast in eastern Taiwan. These rates ensure that the formation of major marine terraces on the coast, several tens of meters in height, is related to the deglacial relative sea-level cycle, with which the uplift rates were further constrained by the elevations of the marine-terrace elements. Uplift rates are less than 4 mm/yr in the northernmost 30 km-long coast, and are 4–7 mm/yr in the adjacent 30-km-long coast. The rest of the coast is generally uplifted 7–9 mm/yr, with local troughs ( 700 m) and high (>40 m) mudstone platforms are observed to slope below the sea level. These changes in uplift rate or style are all accommodated on the surface by warping. Most of them are irrelevant to the known bedrock structures, suggesting a change in uplift style, and perhaps also mechanics, of the coast during the Holocene.

About 100 slip vectors were surveyed along the 1999 Chi-Chi earthquake rupture (100 km long), western Taiwan, to understand the coseismic reverse-faulting processes. The surveyed slip azimuths vary locally (over 80°) where the rupture is irregular or associated with flexure. Even where the rupture is straight and has consistent slip azimuths, the fault-scarp heights, horizontal slips and fault dip-angles oscillate in a distance of hundreds of meters along the rupture. Despite these local variations, the net slip (up to 11.5 m), vertical and horizontal slips are significant greater in the north, on which maximum shortening (6 m; by pure thrust) and strike slip (8 m; by left-lateral fault) occur in association with the bend of the rupture. The slip azimuths also progressively rotate from north/northwest in the north to west/southwest in the south. These patterns generally agree with those revealed by GPS surveys, except that the slips by GPS in the south move to the west/northwest and have values unexpectedly smaller than our measurements. Our obtained SW-directed slips resulted in dominantly right-lateral faulting (up to 2.4 m) where the rupture ends to the southeast. This, however, does not correspond to focal mechanisms of any main shocks or aftershocks.

We reconstruct the Holocene river history of the Erhjen River (area: 140 km 2 ) by correlating river terraces aided by 28 radiocarbon dates. Multiple terraces developed in the lower Erhjen River since the middle Holocene; they converge downstream to the Coastal Plain. The rates of channel incision into bedrock calculated from these terraces at Yuehshihchieh are 7–8 mm/year during ca. 5.7–2.5 ka, 5 cm/year during 1.5–1.3 ka, and 1 cm/year since 1 ka; the last is close to the average incision rate since middle Holocene. Meanwhile, only a single but wide middle–late Holocene paleo-floodplain was developed in the upper Erhjen River; it was completely abandoned only after 0.8 ka, likely following an episode of base-level fall starting from the Coastal Plain. Based on the apparent downstream and upstream convergence of these dated terraces, we identify a doming structure or anticline within the basin, which results in a tilt rate of 10 −6 to 10 −7 per year in the lower Erhjen River valley. The major terraces here had different initial long profiles, which implies that a critical (graded) long profile may not be a prerequisite for formation of a wide erosional terrace surface. Instead, we propose that these terraces were initiated by a series of catastrophic rainfall events, probably climatic-related, which brought a large amount of bedload from hillslopes to prevent the channel from incising when valley widening was facilitated by high-discharge runoff. We find that not only terrace-surface formation but also channel incision can be strongly controlled by climatic-driven discharge and bedload conditions, as suggested by the contrast of bedrock incision rates we observe at Yuehshihchieh. Apparently, the climate and its effects on the landscape cannot be regarded as constant during the Holocene even in a humid tropical area like Taiwan. However, such a fluctuation of climate could only be recorded in a setting where rivers have a high tendency to incise so that multiple terraces can be created. The lower Erhjen River that is characterized by active tectonic tilting is an example of this setting.

Based on the palynological study of two alpine lakes of the central mountains and a lake at 460 m elevation in northeastern Taiwan, a warm event which lasted several hundred years from about cal 2 ka, followed a cool-dry interval from about cal 3.7–2.0 ka. Evidence indicates a warmer annual temperature of 1–2°C and relatively higher precipitation during the warm interval compared with the cool-dry interval. Sea level at cal 2–1.5 ka is estimated to have been 130–150 cm higher than at present based on data from the Penghu Islands off western Taiwan (Chen and Liu, Quaternary Research 45, 254–262, 1996). In northern Taiwan, the corresponding sea level rise is recognized by a widening of the estuary in the Taipei Basin (Lin, Development of Taipei City, pp. 159–246, 1981), which is consistent with the distribution of archaeological sites around cal 2 ka. The age of lower river terraces in northern (Lanyang) and southern (Erhjen) Taiwan, are consistently in the range cal. 2.5–1.5 ka. This suggests an island-wide morphological process, probably relating to climate change. This study discusses the inferred climate change and possible morphological responses.

[1] To characterize the present-day vertical displacement field in the active Taiwan orogenic belt, 1843 precise leveling and 199 continuous GPS measurements from 2000 to 2008 are collected and analyzed in this study. Vertical velocities derived from the leveling data are placed in a reference frame of the Chinese continental margin using continuous GPS observations at nearby sites. The leveling and GPS vertical velocities generally reveal a dome-shaped pattern with uplift of ∼0.2–18.5 mm/yr in the interior of the mountain range and subsidence on the flanks of the mountains and coastal plains. Modern uplift rates in the active fold and thrust belt are generally consistent with geologic uplift rates. However, present-day uplift rates in the Central Range are faster than the million-years-averaged exhumation rates. The modern subsidence rates are generally consistent with geologic rates, except for the rates in western coastal areas due to groundwater pumping. Present-day subsidence in the southern Central Range and northern Coastal Range is, however, inconsistent with long-term uplift, which may reflect interseismic elastic strain accumulation across faults. Present-day subsidence in northern Taiwan occurs in a region of postcollisional orogenic collapse. We model the present-day and geologic vertical velocities and published GPS horizontal velocity data across southern Taiwan using a 2-D lithospheric model. The model suggests a combined slip rate of 40 mm/yr on the frontal thrusts and 45 mm/yr on the Longitudinal Valley fault. The model requires an additional source of crustal thickening under the Central Range to match the observed present-day uplift rates.

This paper is concerned with the tectonic trends that can be deduced from the Holocene raised shorelines between Ch'eng-kung and Hsin-she, along a 65-km long coastal sector in the eastern Coastal Range of Taiwan. Sequences of up to eight superimposed shorelines have been identified in a single section. Twelve new radiocarbon dates (six of which were obtained by accelerator mass spectrometry) of in-situ marine samples (up to 40 m in altitude) have confirmed a Holocene age. However, it is difficult to define clearly the upper marine boundary in the highest Holocene coastal terraces, which have been uplifted to 65–70 m, but have been capped by, and often also interfingered with, alluvial deposits. High uplift rates, ranging from 2.5–3.0 to over 8 mm/yr, have been inferred along the coast, providing evidence of differential uplift. In some cases uplift movements appear to have occurred by steps, probably spasmodically. Recurrence periods of fast uplifts seem to be of the order of at most 1000 yr. This means that a new spasmodic movement may be imminent, because the last displacement (4–6 m) has been dated about 1000 yr BP.

[1] We use field observations, laboratory experiments, and mathematical theory to characterize the full life cycle of a tributary-dammed lake. The natural lake formed in August 2007 at the confluence of the Laonong River, southern Taiwan, with a steep tributary. Due to heavy rains from typhoons Wutip and Sepat, the tributary delivered massive amounts of sediment to the confluence. This caused damming of the trunk river, the growth of a lake, and the demise of a bridge upstream of the confluence. The lake lasted until October 2007, gradually decaying due to incision and infill by subsequent stream flow. We reconstruct the episode using hydrological records, ground observations, and surveyed profiles. We then use the event to verify a mathematical theory of river and lake bed evolution. The theory is based on a diffusion description of river morphodynamics, constrained by backwater effects due to lake formation. After validation using laboratory experiments, the theory is applied to the Laonong field event. Good agreement is obtained between calculated and surveyed long profiles. The theory can also reproduce the complex stage hydrograph recorded upstream of the confluence. This suggests a role for simplified, but laboratory-tested mathematical theory in quantitative investigations of fluvial processes in the field.

International audience; Lateral erosion in bedrock rivers is an important control on the shape of channel crosssections, and the coupling of channels and hillslopes. Recent observations link lateral erosionto the variability of flow. We propose two mechanisms to explain this. One is based on changing shear stress distributions within the channel with varying flood level, the other on the competition between cover and tool effects in fluvial bedrock erosion. We assess these processes for the Liwu River, Taiwan, and conclude that cover and tool effects dominate the partitioning of lateral and vertical erosion in this case.

Twenty-nine cores and two outcrops in the Western Coastal Plain, each containing more than one radiocarbon date (5 - 20 ka; totally 74 dates), are used to determine the 11 - 5 ka eustatic sea level in Taiwan. All the dates are obtained from coastal sediments with deposition positions assumed Âą3 m of the sea level. These dates can be used to calculate rock uplift (subsidence) rates for given eustatic sea-level data. The sea level data derived from Penghu (< 5 ka) and the Sunda Shelf (> 11 ka) are applied, and the rock uplift of the study sites is assumed to be steady over time. The 11 - 5 ka sea level is constructed by repetition of changing its shape until the dates in the same cores yield consistent rock-uplift rates. Optimal sea-level curves are found to fit all but seven dates used. These sea-level curves are characterized by: (1) a rapid rise (> 13 m ky-1) around 11 - 10 ka; (2) a rise of 8 - 9 m ky-1 from ~10 ka to 6.5 - 6.6 ka when the sea level approached the modern level, and (3) a much slower rise after 6.5 - 6.6 ka.

International audience; Marine sediments deposited some 14,000 years ago, when the sea level was between 80 and 100 m below the present sea level, have been found exposed at about 17 m in altitude near Tu-lan, on the east coast of Taiwan. This implies a minimum average uplift rate of 7.6$\pm$0.9 mm/yr; similar values of tectonic uplift are not uncommon on the eastern Coastal Range of Taiwan. Such rates of tectonic uplift, among the highest reported in the literature, are of the same order as present-day maximum glacio-isostatic uplift rates.

The Chi-Chi earthquake rupture that mostly follows the mountain front in central Taiwan bends east/northeast into hills in the Tachia River valley. We found no major pre-existing fault systems in this hill area. However, based on river terrace morphology and sequences, the lower Tachia River valley appears to have been uplifted more rapidly than the lower Taan River valley in the past ten thousands of years, which is consistent with the bend of the earthquake rupture. The earthquake rupture (and associated uplift) also coincides with: (I) straight mountain-front escarpment south of the Tachia River valley; (2) two fault/fold-scarps on the Holocene terraces, and abnormal sideward inclination and downstream flattening of these terraces in the Tachia River valley; (3) local development of non-laterized terraces in the Taan River valley; (4) abnormal rise and narrowing of the Taan/Tachia drainage divide. These geomorphic anomalies, however, are either local or diffusive; features (1) to (3) might have been interpreted as of fluvial origin. Also, the link between these features and the movement of the Chelungpu-Sanyi fault, the causative fault of the earthquake, might have been uncertain. We thus argue that the pre-location of this portion of the Chi-Chi earthquake rupture would have been difficult, even though we could have roughly delineated a potential coseismic deformational zone in the region.