Badland landscape response to individual geomorphic events

Landscapes form by the erosion and deposition of sediment, driven by tectonic and climatic forcing. The principal geomorphic processes of badland – landsliding, debris flow and runoff erosion – are similar to those in full scale mountain topography, but operate faster. Here, we show that in the badlands of SW Taiwan, individual rainfall events cause quantifiable landscape change, distinct for the type of rainfall. Typhoon rain reduced hillslope gradients, while lower-intensity precipitation either steepened or flattened the landscape, depending on its initial topography. The steep topography observed in our first survey is inconsistent with the effects of any of the rainfall events. We suggest that it is due to the 2016 Mw 6.4 Meinong earthquake. The observed pattern in the badlands was mirrored in the response of the Taiwan mountain topography to typhoon Morakot in 2009, confirming that badlands offer special opportunities to quantify natural landscape dynamics on observational time scales.

Bird’s eye view on steep topography

<p>In nadir view, normal to topography, landscapes with gentle slopes and those with steep surfaces look similar. This is due to the projection of a 3D structure onto a 2D plane. In orthophotos and digital elevation models (DEMs) topography is represented in this nadir or bird’s eye perspective. Elevation models of the Earth or planetary surfaces are often represented by gridded cells, each cell assigned with a mean elevation. In geomorphic studies, DEMs are widely used to calculate hillslope angles and surface area. Due to the projection, hillslopes at a steeper angle appear shorter and thus are represented by a smaller fraction of grid cells. Consequently, mean or median hillslope angles are distorted towards gentle slopes. This bias becomes even more obvious when comparing the projected 2D surface area versus the 3D surface area. The ratio by which a 3D surface area is underrepresented in 2D is by the cosine of the slope of the plane. Hence, the degree of area under-representation increases towards steeper slopes. At an angle of 60°, theoretically only half of the 3D surface area would be accounted for in a gridded DEM. And a hillslope at 90° is a no-show in the DEM. But already gentle slopes of 20° to 30° would be under-represented by about 10%. In addition to the under-representation of steep slopes due to the projection, DEM’s spatial resolution amplifies this bias where increasing grid size decreases the representation of steep slopes.</p><p>In essence, due to the bird’s eye view, measures of hillslope angle distribution and surface area have a bias disadvantaging steep slopes and skewing our perception towards a (flat) world of gentle slopes. Here we will discuss if and by how much this bias due to the bird’s eye view matters. First, we investigate artificial DEMs of Gaussian hills. We compare slope and surface area values using standard methods of gridded-data analysis to analytical solutions. Second, we investigate the impact of under-representation on a range of natural landscapes. This potential bias favouring gentle landscape elements has several implications for geomorphological interpretation of DEMs, including for example analyses of average erosion rates, landslide distribution or hydrological processes.</p>

Sedimentary breccias formed during extensional tectonics: facies organization and processes

<p>Sedimentary breccias formed during extensional tectonics are spatially associated with large-throw normal faults. They result from the creation of a steep topography that becomes unstable, producing major rockfalls. The studied breccias, in Crete and in the Pyrenees, are up to 300 meters thick and are characterized by poorly sorted polygenic deposits of pebbles to boulders composed of highly angular plurimillimetric to plurimetric carbonate clasts. A lateral evolution is observed, with pebble-size clasts found near the normal fault and boulder-size clasts away from the fault. This evolution is related to the rockfall process as the total kinetic energy acquired by the small clasts during the fall is lower than that acquired by the bigger ones; as a result, the latter are able to travel farther. Interestingly, the fact that the smallest clasts are proximal while the bigger ones are more distal is contrary to the distribution found in alluvial fan systems, making it possible to differentiate from one another. The studied breccias commonly show disorganized layers and/or no noticeable layering across large distances. We interpret this feature as related to the movement on the normal fault, which progressively tilts the breccia layers and favours their gliding along the slope. Gliding is an important internal process to take into account in rockfall systems because it may disorganize the layering, create specific geometries like onlap around olistoliths, and produce deformation inside the breccia layers; the latter feature could be mistakenly interpreted as resulting from post-deposition regional deformation.</p><p>According to our observations, active normal faults with large throws provide the conditions for the formation and preservation of great volumes of sedimentary breccias through the following processes: i) footwall uplift, creating a pronounced topography with steep slopes, giving rise to major rockfalls, ii) hangingwall rapid subsidence, which allows the accumulation and preservation of the breccias without clast reworking by drainage systems. The latter is reinforced by the fact that, during the early stages of extension, the main watersheds point in a direction opposite to the fault slope whereas only small, discontinuously distributed watersheds flow in the direction of the fault slope. Upon ongoing extension, the size of these small watersheds increase. At one point, the sedimentary flow coming from these watersheds becomes more important than rockfall processes. Part of the breccia body is then eroded, reworked, and replaced by conglomerates of an alluvial fan deposited unconformably above the breccias.</p><p>Summing up, sedimentary breccias are readily formed as thick syn-tectonic deposits during early stages of extensional basin development. Thus, they may be considered as a typical lithology, and a marker, of continental extension.</p>

CLIMATE CHANGE VULNERABILITY ASSESSMENT FOR AMERICAN SAMOA: FOCUS ON TRANSPORTATION INFRASTRUCTURE

Essential transportation infrastructure around the globe will be increasingly compromised by interrelated climate change impacts. Due to geographic isolation and limited natural resources, the economy and security of many Pacific territories and nations, including American Samoa, depend heavily on the resilience of these transportation infrastructure systems. Of particular relevance are the coastal impacts of climate changes such as sea level rise and storm surges which will threaten transportation infrastructure including both temporary and long-term flooding of airports, ports and harbors, and roads which are vital lifelines for trans-Pacific, interisland, and intra-island commerce and community services. The majority of the transportation assets in American Samoa are along a narrow coastal plain backed by steep topography, precluding relocation or retreat in response to increased coastal flooding accompanying a changing climate.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/k-qJPMVwvVc

Exploring the Fingerprints of Past Rain-on-Snow Events in a Central Andean Mountain Range Basin Using Satellite Imagery

Rain-on-snow (ROS) events can alter nival regimes and increase snowmelt, peak river flow, and reduce water storage. However, detection of ROS events is challenging and only the most intense and obvious cases are identified. Rain is known to reduce snow cover and decrease near-infrared reflectance due to increased grain size. This study explored the fingerprints of ROS events on mountain snowpack with a simple typology that classifies changes in snow reflectance using fifteen years of MODIS imagery, reanalysis, and surface hydrometeorological data. The Maipo River Basin, with strong nival regime and a steep topography, in the western Andean mountain range was selected as a case study. Statistical analysis showed two distinct and opposite responses in the near infrared reflectance distribution of snow-covered pixels after precipitation, consistent with the typology for rain or snow events. For the probable ROS events, the daily maximum and minimum temperature increased in the days preceding the event and subsequently decreased, in some cases followed by a less consistent response in river flow. Although much remains to be studied, this approach can be used to expand historical records and improve modelling and detection schemes.

Landslide Potential Evaluation Using Fragility Curve Model

The geological environment of Taiwan mainly contains steep topography and geologically fragile ground surface. Therefore, the vulnerable environmental conditions are prone to landslides during torrential rainfalls and typhoons. The rainfall-induced shallow landslide has become more common in Taiwan due to the extreme weathers in recent years. To evaluate the potential of landslide and its impacts, an evaluation method using the historical rainfall data (the hazard factor) and the temporal characteristics of landslide fragility curve (LFC, the vulnerability factor) was developed and described in this chapter. The LFC model was based on the geomorphological and vegetation factors using landslides at the Chen-Yu-Lan watershed in Taiwan, during events of Typhoon Sinlaku (September 2009) and Typhoon Morakot (August 2009). The critical hazard potential (Hc) and critical fragility potential (Fc) were introduced to express the probability of exceeding a damage state of landslides under certain conditions of rainfall intensity and accumulated rainfall. Case studies at Shenmu village in Taiwan were applied to illustrate the proposed method of landslide potential assessment and the landslide warning in practice. Finally, the proposed risk assessment for landslides can be implemented in the disaster response system and be extended to take debris flows into consideration altogether.

Underground Pumped Storage Hydropower Case Studies in Belgium: Perspectives and Challenges

To avoid the geographical and topographical prerequisites of the conventional pumped hydro energy storage, the use of underground cavities as water reservoirs allows countries without steep topography, such as Belgium, to increase the potential of the energy storage capacity. Belgium abounds in disused mines and quarries convertible into water basins. In this article, two Belgian case studies are presented and discussed for their singularity. A slate quarry in Martelange is discussed in technical aspects proposing three operating scenarios. Moreover, a preliminary economic analysis of the underground pumped storage system and a greenhouse gas emission evaluation for the storage system’s lifetime are presented. The analysis for a 100 MW power plant estimates a total initial investment of over 12 million euros and two million of CO2 avoided over its lifetime. This article also proposes the use of the coal mine 500 m deep of Pérronnes-lez-Binche. The mine representation discussed here offers a high energy capacity, but the substantial head drop (from about 500 to 200 m) challenges the selection of the hydraulic turbomachinery. A 1D simulation computed in SIMSEN draws out the behaviour of the unusual hydraulic configuration of turbines in series.

Sistem Alley Cropping: Analisis SWOT dan Strategi Implementasinya di Lahan Kering DAS Hulu

<p><strong>Abstrak</strong>. Ditinjau dari segi luasan, lahan kering di Indonesia merupakan lahan yang cukup potensial, untuk dikembangkan sebagai areal pertanian. Namun usaha pertanian di areal ini dihadapkan pada beberapa kendala, diantaranya karena lahan ini banyak tersebar di daerah pegunungan dengan topografi yang curam sehingga rawan erosi. Untuk itu usahatani konservasi mutlak perlu dilakukan. Teknik konservasi mekanik berupa teras bangku, yang telah banyak dikenal dan diadopsi petani, diyakini dapat menurunkan erosi, namun teknik ini tidak selalu cocok diimplementasikan pada semua kondisi, selain memerlukan biaya yang cukup tinggi. Oleh karena itu, teknik konservasi vegetatif lebih disarankan untuk diapliksikan di areal ini. Sistem pertanaman lorong (alley cropping) merupakan teknik konservasi vegetatif yang telah terbukti efektif mengendalikan erosi dan aliran permukaan (runoff), kehilangan hara, meningkatkan produktivitas tanah dan tanaman, efisien dari segi biaya, serta dapat diadopsi oleh petani berdasarkan hasil-hasil penelitian. Dengan demikian, sistem pertanaman lorong berpeluang untuk dikembangkan di areal lahan kering dengan memperhatikan keunggulan dan kelemahannya. Makalah ini mengemukakan tentang keunggulan dan kelemahan sistem pertanaman lorong serta peluang dan tantangan yang akan dihadapi di dalam implementasinya di lahan kering berdasarkan hasil analisis SWOT (strengths, weeknesses, opportunities, threats). Pengembangan strategi untuk implementasi sistem alley cropping meliputi strategi yang bersifat teknis dan non teknis.</p><p><em><strong>Abstract</strong></em>. In terms of area, upland in Indonesia is a potential land to be developed as an agricultural area. However, this agricultural bussines on this area is faced with several problem, some of them is because the agricultural land is spread in mountainouns area with a steep topography that is easy to erosion, therefore conservation agriculture system is absolutely needed. Mechanical soil conservation techniques such as bench terrace which have been widely known and farmer-friendly are believed to reduce erosion, but this technique is not always suitable to be implemented in all condition other than requiring high cost, therefore vegetative conservation vegetative conservation techniques are more suggested to control erosion in this area. Alley cropping system is a vegetative conservation technique that has been proven effective in controlling erosion and runoff, nutrient loss, increasing land and crop productivity, cost efficient and can be adopted by farmers based on the research results. Thus, the alley cropping system is likely to be developed in upland area with attention to its advantages and disadvantages. This paper presents the advantages and disadvantages of alley cropping system and the opportunities and challenges that will be faced in its implementation in upland based on SWOT (strengths, weeknesses, opportunities, threats) analysis. Development of strategy for implementation of alley cropping system includes technical and non technical strategy.</p><p align="center"><strong> </strong></p>

Probabilistic identification of rockfall source areas: an example from El Hierro island (Canary Island, Spain)

&lt;p&gt;Rockfalls are the most frequent and dangerous instability phenomena in mountainous areas, causing high economic and social damages. Rockfalls are triggered by complex instability mechanisms and the source areas are controlled by environmental factors like geology, the presence of discontinuities and slope angle. Modeling rockfall phenomena is complex and requires diversified input including parameters controlling the boulders trajectories and the source areas identification.&lt;/p&gt;&lt;p&gt;In the Canary Islands, the steep topography and the geological complexity influence the activation of slope dynamics and the occurrence of slope failures. In particular, rockfalls are very common and they represent a major threat to society, costing lives, disrupting infrastructures and destroying livelihoods. In 2011 the volcanic crisis in El Hierro Island triggered numerous rockfalls that affected the road network causing a great social alarm.&lt;/p&gt;&lt;p&gt;After the recent event, we have attempted to identify rockfall source areas using different approaches including probabilistic modeling. The probabilistic approach applies a combination of multiple statistical models and requires a map of the observed source areas as dependent variable and a set of thematic information as independent variables (e.g., morphometric parameters derived from DTM, lithological information that considers the mechanical behavior of the rocks). For the purpose, we have identified various scenarios selecting different training and validation zones and evaluating for each scenario the associated errors. The maps resulting from the models, provide for the whole El Hierro Island, the probability of a pixel being a source area and can be used as input for the rockfall modeling.&lt;/p&gt;