Erosion-driven drawdown of atmospheric carbon dioxide: The organic pathway

Rapidly eroding, coastal mountain belts, where steep rivers and submarine channels connect upland sources to nearby marine sinks are hotspots of organic carbon transfer from life biomass, soil and exhumed bedrock into geological storage. Using observations from the Southern Alps of New Zealand, and Taiwan, we have mapped this organic pathway to geological carbon sequestration, and can evaluate the magnitude and efficiency of transfers between sources and sinks. We demonstrate that POC is harvested by landsliding, but importantly also by common and widespread surface runoff on steep hillslopes. Although terrestrially sourced POC is found in many sedimentary environments associated with mountain belts and frontier basins, it appears to be most abundantly trapped and preserved in marine turbidites. The loss of all forms of POC in onward transport through short, steep routing systems to this repository is limited. This is in marked contrast to larger routing systems, in which only the most resilient forms of POC survive into long-term deposition.     

Correction to: Social determinants in choice of shelter: an evidence-based analysis

Natural Hazards - The article was published with categories “80,000–10,999” and “≥?11,000” of the variable Family monthly income in Table 2 and...     

Impact of rainstorm-triggered landslides on high turbidity in a mountain reservoir

Typhoon-triggered landslides deliver huge amounts of sediment to the upstream channel of the Shihmen Reservoir in northern Taiwan. Observation data regarding landsliding, sediment discharge and water turbidity following five major typhoon events from 1985 to 2006 demonstrated that each time water turbidity in the reservoir area rapidly increased up to ten-fold from the river catchment drainage, and the weight of landslide debris exceeded total sediment discharge five-fold. The fact that huge amounts of landslide debris still remained on upstream slopes and water turbidity suddenly increased in the reservoir area but not in upstream channel implied that the increasing water turbidity in the Shihmen Reservoir was indirectly related to the large landslides occurring in the upstream catchment. The main cause of high turbidity in the reservoir area was that, during a typhoon event, high water discharge flowing into the reservoir scoured the fine fraction sediment at the bottom of the reservoir and formed hyperpycanl flow with high turbidity, which then ascended to contaminate the reservoir surface water.     

Geological factors for hazardous debris flows in Hoser, central Taiwan

By means of an onsite investigation, the largest debris flow in Taiwan's history is analyzed in this paper. A heavy rainfall of 1,748 mm/day occurred during typhoon Herb in the Hoser area at the end of July 1996. Aerial photographic assessment and observations of geological and geomorphological features have contributed to our understanding of this massive destruction. Mechanisms of the hazardous debris flow are explored and discussed. Data revealed that the rock discontinuities were a major factor in the voluminous loose materials in the debris flows. The heavy and rapid rainfall instantly transported massive amounts of debris flow materials into the center, and then quickly funneled them to the lower parts of gullies. The heavy slurry became an effective cutting device to erode the side walls and move large quantities of the debris materials to the end of the gullies.     

Evaluating the susceptibility of landslide landforms in Japan using slope stability analysis: a case study of the 2016 Kumamoto earthquake

This study analyzed 267 landslide landforms (LLs) in the Kumamoto area of Japan from the database of about 0.4 million LLs for the whole of Japan identified from aerial photos by the National Research Institute for Earth Science and Disaster Resilience of Japan (NIED). Each LL in the inventory is composed of a scarp and a moving mass. Since landslides are prone to reactivation, it is important to evaluate the sliding-recurrence susceptibility of LLs. One possible approach to evaluate the susceptibility of LLs is slope stability analysis. A previous study found a good correlation (R ² = 0.99) between the safety factor (F _s ) and slope angle (α) of F _s  = 17.3α ^?0.843. We applied the equation to the analysis of F _s for 267 LLs in the area affected by the 2016 Kumamoto earthquake (M _j  = 7.3). The F _s was calculated for the following three cases of failure: scarps only, moving mass only, and scarps and moving mass together. Verification with the 2016 Kumamoto earthquake event shows that the most appropriate method for the evaluation of LLs is to consider the failure of scarps and moving mass together. In addition, by analyzing the relationship between the factors of slope of entire landslide and slope of scarp for LLs and comparing the results with the Aso-ohashi landslide, the largest landslide caused by the 2016 Kumamoto earthquake, we also found that morphometric analysis of LLs is useful for forecasting the travel distance of future landslides.     

Increase in basin sediment yield from landslides in storms following major seismic disturbance

The landslide area along the Tachia River catchment of central Taiwan was investigated using the remote sensing images of various typhoon and earthquake events taken from 1996 to 2004 and the sediment discharge measured at hydrometric stations. Our findings indicate that 88% of the coseismic landslides triggered by the 1999 Chi-Chi earthquake were first-time occurrences. After the Chi-Chi earthquake, 59% of the landslide area was reactivated during typhoon Toraji and 66% during typhoon Mindulle. The landslides prone to reactivation were on the formations with closely spaced discontinuities. It is suggested that further rock-mass defects in the formations were added or opened by the earthquake, and that the landslide areas continued to extend until the end of 2004. Post-1999 rainstorms delivered large amounts of colluvial sediment into the main channel, leading to a 2-fold increase in post-seismic sediment discharge while the precipitation was only half that of the pre-earthquake rate.     

The relationship between slope gradient and lateritic cobble orientation with respect to shape, northwestern Taiwan

In situ investigations of lateritic cobble slopes have demonstrated that where the grain orientation is more uniform, the anisotropy is more obvious. Grain orientation will also affect the slope gradient and slope surface. The slope forms an escarpment when the intersection between the cobble orientation strike and the slope surface ranges between 90 and 180°. By contrast, there is a dip-slope geometry when the angle of intersection is 0°. The slope gradient increases and has an angle of 50 to 80° when the intersected angle ranges from 0 to 180°. The results indicate a positive relationship between these two factors. The slope grade will increase when the disk and bladed grain shape of the cobbles increase their percentage relative to the material composition. On the other hand, the slope gradient decreases when the proportion of equant and roller grain shapes of cobble increase in the composition.